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Journal Articles: River Deltas and Ecosystems

Articles  :   Geology  |   Ecosystems  |   Climate Change  |   Sea Level Rise  |   Fauna  |   Birds  |   Fish

Admiraal, W., S. D. Mylius, et al. (1993). "A Model of Phytoplankton Production in the Lower River Rhine Verified by Observed Changes in Silicate Concentration." Journal of Plankton Research 15(6): 659-682.

The production of phytoplankton in the three main branches and sedimentation areas of the River Rhine in the Netherlands was analyzed using a simulation model describing the carbon and silicate metabolism. This model is based on data derived from a sampling programme in which river water was followed during downstream transport. A 'plug-flow model' was developed, including sky irradiance and light attenuation in the water, and integrating photosynthetic rates determined in the laboratory. On the basis of the silicate content of diatom-dominated phytoplankton and silicate regeneration in the river bottom, changes in silicate concentrations were simulated and found to match observed changes in dissolved silicate. Low silicate concentrations were shown to restrict the maximum population density of diatoms. Depth- and time-integrated rates of photosynthesis were shown to permit multiplication of the phytoplankton at a rate of up to one doubling day-1. In the primary production period April-August 1988, values of 0.48-6.33 g C m-2 day-1, close to the few values reported for highly eutrophic rivers and lakes, were observed. Model runs, including phytoplankton production and losses, such as respiration, sedimentation and planktonic grazing, were carried out to simulate the downstream development of phytoplankton biomass. These simulations confirm the view that a substantial part of the phytoplankton biomass and production is grazed or settles in the river delta despite residence times of only 52-97 h.

Bano, N., M. U. Nisa, et al. (1997). "Significance of bacteria in the flux of organic matter in the tidal creeks of the mangrove ecosystem of the Indus River delta, Pakistan." Marine Ecology-Progress Series 157: 1-12.

We studied bacterial biomass and production in 3 tidal creeks (Isaro, Gharo and Phitti Creeks) in the mangrove forests in the Indus River delta, Pakistan, to assess the significance of bacteria-mediated carbon fluxes in the creek ecosystem. Bacterial biomass, bacterial carbon production (BCP) and primary productivity (PP) were measured periodically for over a year during 1991-92. BCP was high, generally 50 to 300 mu g C l(-1) d(-1). Despite such high BCP, bacterial abundance remained between 1 x 10(6) ml(-1) and 4 x 10(6) ml(-1) (20 to 80 mu g C l(-1)) indicating tight coupling between bacterial production and removal. Specific growth rates generally ranged from 1 to 7 d(-1) but the rate reached 24 d(-1) during a phytoplankton bloom, apparently a red tide, and this was an unprecedented growth rate for a natural assemblage. The abundance of attached bacteria exhibited a large variation, ranging from 4 to 92 % (mean 35 +/- 21 %, n = 41) in Isaro Creek and from 14 to 84% (mean 37 +/- 28%, n = 10) in Gharo Creek. Bacterial production due to attached bacteria was 73 to 96 % of the total. Thus, a major fraction of BCP may have been directly available to metazoan grazers. BCP was generally much higher than net PP; the yearly integrated average BCP/PP for all sites was 2.0. Thus, the growth of bacteria, attached and free, probably represented the major pathway of the production of high quality (low C:N) biomass potentially available to the grazers. Average yearly integrated bacterial carbon demand (BCD), estimated conservatively by assuming a 30 % growth efficiency for all sites, was 6.9 times net PP. Thus, the creek water columns were strongly and persistently net heterotrophic. Data integrated over the entire study period show that even if all phytoplankton production was utilized by bacteria it would satisfy only 7 to 20% of the BCD; the remaining 80 to 93% of BCD would be met by reduced carbon from other sources. Phytoplankton production was light Limited due to high turbidity and, apparently, the majority of BCP could be supported by the input of mangrove detritus. Estimates of utilizable dissolved organic carbon (UDOC) in selected samples were 97 to 656 mu g C l(-1), indicating that in order to sustain the measured BCD (643 +/- 671 mu g C l(-1) d(-1)) the UDOC pool would turnover in <1 d to a few days. Limited data suggest that bacterial production was carbon rather than N or P limited, consistent with sustained high levels of inorganic N and P in the surface water. Since mangrove detritus provides most of the energy for bacterial production, which in turn is a significant source of high quality food for grazers, particularly via ingestion of attached bacteria, we predict that the ongoing destruction of mangrove forests in the Indus delta and elsewhere could have a major impact on mangrove ecosystem structure and functioning and the production of economically important fish and shrimp in mangrove creeks.

Baron, J. S., N. L. Poff, et al. (2002). "Meeting ecological and societal needs for freshwater." Ecological Applications 12(5): 1247-1260.

Human society has used freshwater from rivers, lakes, groundwater,, and wetlands for many different urban, agricultural, and industrial activities, but in doing so has overlooked its value in supporting ecosystems. Freshwater is vital to human life and societal well-being, and thus its utilization for consumption, irrigation, and transport has long taken precedence over other commodities and services provided by freshwater ecosystems. However, there is growing recognition that functionally intact and biologically complex aquatic ecosystems provide many economically valuable services and long-term benefits to society. The short-term benefits include ecosystem goods and services, such as food supply, flood control, purification of human and industrial wastes, and habitat for plant and animal life-and these are costly, if, not impossible, to replace. Long-term benefits include the sustained provision of those goods and services, as well as the adaptive capacity of aquatic ecosystems to respond to future environmental alterations, such as climate change. Thus, maintenance of the processes and properties that support freshwater ecosystem integrity should be included in debates over sustainable water resource allocation. The purpose of this report is to explain how the integrity of freshwater ecosystems depends upon adequate quantity, quality, timing, and temporal variability of water flow. Defining these requirements in a comprehensive but general manner provides a better foundation for their inclusion in current and future debates about allocation of water resources. In this way the needs of freshwater ecosystems can be legitimately recognized and addressed. We also recommend ways in which freshwater ecosystems can be protected, maintained, and restored. Freshwater ecosystem structure and function are tightly linked to the watershed or catchment of which they are a part. Because riverine networks, lakes, wetlands, and their connecting groundwaters, are literally the "sinks" into 'Which landscapes drain, they are greatly influenced by terrestrial processes, including many human uses or modifications of land and water. Freshwater ecosystems, whether lakes, wetlands, or rivers, have specific requirements in terms of quantity, quality, and seasonality of their water supplies. Sustainability normally requires these systems to fluctuate within a natural range of variation. Flow regime, sediment and organic matter inputs, thermal and light characteristics, chemical and nutrient characteristics, and biotic assemblages are fundamental defining attributes of freshwater ecosystems. These attributes impart relatively unique characteristics of productivity and biodiversity to each ecosystem. The natural range of variation in each of these attributes is critical to maintaining the integrity and dynamic potential of aquatic ecosystems; therefore, management should allow for dynamic change. Piecemeal approaches cannot solve the problems confronting freshwater ecosystems. Scientific definitions of the requirements to protect and maintain aquatic ecosystems are necessary but insufficient for establishing the appropriate distribution between societal and ecosystem water needs. For scientific knowledge to be implemented science must be connected to a political agenda for sustainable development. We offer these recommendations as. a beginning to redress how water is viewed and managed in the United States: (1) Frame national and regional water management policies to explicitly incorporate freshwater ecosystem needs, particularly those related to naturally variable flow regimes and to the linking of water quality with water quantity; (2) Define water resources to include watersheds, so that freshwaters are viewed within a landscape, or systems context; (3) Increase communication and education across disciplines, especially among engineers, hydrologists, economists, and ecologists to facilitate an integrated view of freshwater resources; (4) Increase restoration efforts, using well-grounded ecological principles as guidelines; (5) Maintain and protect the remaining freshwater ecosystems that have high integrity; and (6) Recognize the dependence of human society on naturally functioning ecosystems.

Belausteguigoitia, J. C. (2004). "Causal chain analysis and root causes: The GIWA approach." Ambio 33(1-2): 7-12.

The Global International Waters Assessment (GIWA) was created to help develop a priority setting mechanism for actions in international waters. Apart from assessing the severity of environmental problems in ecosystems, the GIWA's task is to analyze potential policy actions that could solve or mitigate these problems. Given the complex nature of the problems, understanding their root causes is essential to develop effective solutions. The GIWA provides a framework to analyze these causes, which is based on identifying the factors that shape human behavior in relation to the use (direct or indirect) of aquatic resources. Two sets of factors are analyzed. The first one consists of social coordination mechanisms (institutions). Faults in these mechanisms lead to wasteful use of resources. The second consists of factors that do not cause wasteful use of resources per se (poverty, trade, demographic growth, technology), but expose and magnify the faults of the first group of factors. The picture that comes out is that diagnosing simple generic causes, e.g. poverty or trade, without analyzing the case specific ways in which the root causes act and interact to degrade the environment, will likely ignore important links that may put the effectiveness of the recommended policies at risk. A summary of the causal chain analysis for the Colorado River Delta is provided as an example.

Bertoli, G. C. (1996). "Aquatic vegetation of the Orinoco River Delta (Venezuela). An overview." Hydrobiologia 340(1-3): 109-113.

The Orinoco River Delta is a complex of relatively unknown ecosystems made up of aquatic and semiaquatic habitats. The region includes a Mariusa National Park and the Orinoco Delta River Biosphere Reserve. The 23 sites studied included lentic habitats (lagoons and creeks) and lotic habitats (streams of variable breadth and current) which varied range from black to white waters. A collection of aquatic vascular plants was made and the physical and chemical variables were measured. A total of 100 species were identified, 48% of which are new records for the Delta territory. A Canonical Correspondence Analysis divided the species and communities into two groups: The lentic habitats of lakes and lagoons, which show a greater species richness and the lotic habitats of the main river courses. This study forms part of an ongoing research project on the floristic and abiotic characteristics of the aquatic communities in the Orinoco River Delta.

Bianchi, C. N. and C. Morri (1996). "Ficopomatus 'reefs' in the Po River Delta (Northern Adriatic): Their constructional dynamics, biology, and influences on the brackish-water biota." Marine Ecology-Pubblicazioni Della Stazione Zoologica Di Napoli I 17(1-3): 51-66.

The serpulid polychaete Ficopomatus enigmaticus (FAUVEL, 1923) builds huge aggregates in the ''Sacca del Canarin'', a brackish inlet of the Po River Delta (Italy). Distribution, structure and development of these 'reefs', together with their associated biota, were studied by field observations and settlement panels from 1977 to 1979. Some aspects of the serpulid biology (settlement periods, tube growth, life strategy) were also taken into account. Ficopomatus reefs influence in many ways the brackish-water ecosystem: they form the main hard substrate; are major sediment source; help in regulating the trophic status of the lagoon; and act as refuge for many invertebrate species.

Boggs, K. and M. Shephard (1999). "Response of marine deltaic surfaces to major earthquake uplifts in southcentral Alaska." Wetlands 19(1): 13-27.

Major earthquake uplifts in south-central Alaska of marine deltaic surfaces to an inter-tidal or supra-tidal status cause drastic shifts in processes and vegetation. To assess long-term ecosystem changes as a deltaic landscape converted from a tidal marsh to a supra-tidal wetland, we studied a four-stage chronosequence of deltaic surfaces (30-yr-old inter-tidal surface, 352-yr-old inter-tidal surface, 30-yr-old supra-tidal surface, and 280-yr-old supra-tidal surface). Plots were used to gather landform, soils, and vegetation information, and landform schematics and aerial photo interpretation were used to determine their spatial distribution. Succession progressed on inter-tidal surfaces from pioneer species (principally Carer lyngbyaei) on newly uplifted mud flats, to a mature tidal marsh with channels, levees, and basins dominated by Carer lyngbyaei with thick root mats. Uplift of the mature tidal surface to a supra-tidal status allowed freshwater tolerant species (Equisetum fluviatile, Sphagnum spp.) to invade the basins, and trees and shrubs displaced herbaceous vegetation on levees. On the oldest supra-tidal surface, basins developed peatlands (Andromeda polifolia, Sphagnum spp.), and pH decreased. Levees supported trees or shrubs on mineral or peat soils. Vegetation zonation within a basin-levee complex was evident and repeated, with some variation, across the surfaces. At the landscape scale moving inland, gradients in vegetation occurred on all surface ages.

Bondavalli, C. (2003). "Effect of eutrophication upon radionuclide dynamics in the Sacca di Goro lagoon (Po River Delta, Italy): a combined field, experimental and modeling study." Environmental Pollution 125(3): 433-446.

The focus of this paper is on the relationship between eutrophication and radionuclide circulation at the whole ecosystem scale in the shallow estuarine environment of the Sacca di Goro (Po River Delta, Italy). This lagoon is frequently affected by dystrophic crises, due to decomposition of huge amounts of macroalgae (mainly Ova rigida), and critical conditions created at the interface between sediment and water are such that Cs-137 accumulated in the sediment can be mobilized and made available in the water column. The release of cesium from sediment in this ecosystem has been evaluated through a field experiment in which chemical conditions typical of anoxic crises were artificially created in enclosures. Also a lab experiment was carried out to shed light on possible cesium release by decomposing macroalgae. The two experiments allowed drawing conclusions on crucial factors controlling cesium release in the Sacca di Goro, the first objective of this research. The second objective was understanding the fate of radiocesium once transported in the water column. To this end ecological information gathered during the experiments and a yearly sampling campaign, has been converted into whole-system seasonal networks describing ecosystem flow structure for the Sacca di Goro. Analyzed by network analysis this model has provided clues about the dynamics of Cs-137 in terms of preferential pathways, sinks, sources, and cycling activity. Sediment, together with seston and dissolved cesium, appear to be the most significant components in the circulation of Cs-137; while macroalgal biomasses play a crucial role as an indirect causal factor. (C) 2003 Elsevier Science Ltd. All rights reserved.

Camacho-Ibar, V. F., L. Aveytua-Alcazar, et al. (2003). "Fatty acid reactivities in sediment cores from the northern Gulf of California." Organic Geochemistry 34(3): 425-439.

Fatty acids were determined in three sediment cores from Delfin Basin, Northern,Gulf of California (NGC), Mexico. Steady-state apparent degradation rate constants (P) were determined to assess the reactivity of the total organic carbon (TOC) pool, the total fatty acids (TFA) and selected individual fatty acids. k' values for TFA were higher than those for TOC, indicating that fatty acids are at least 5 times more labile than the organic carbon pool. A comparison of k' values for selected fatty acids indicates that the long-chain terrigenous fatty acids are less labile than the shorter chained fatty acids from autochthonous sources. The general order of reactivity by source was plankton > bacteria > terrestrial. There are at present essentially no inputs of terrigenous material from the Colorado River. Therefore, the lower reactivity of the terrigenous fatty acids in the Delfin Basin probably suggests that the contemporary source of terrestrial organic matter to the NGC is the eroding Colorado River Delta, which contains already degraded organic carbon. In spite of the high primary productivity in the region, k' values for fatty acids from the NGC were low when compared with those from other marine ecosystems. These results suggest that fatty acid diagenesis during particle settling through the water column in the NGC is intense, allowing only for the deposition of relatively refractory organic matter. (C) 2002 Elsevier Science Ltd. All rights reserved.

Cardoch, L., J. W. Day, et al. (2002). "Net primary productivity as an indicator of sustainability in the Ebro and Mississippi deltas." Ecological Applications 12(4): 1044-1055.

This paper focuses on the use of net primary productivity (NPP) as a measure of sustainable management in the Mississippi and Ebro deltas. Temporal changes in NPP were quantified for these two deltas based on the aerial coverage of different habitat types, Human appropriation of net primary productivity (HANPP) Was used as a measure of direct human use of deltaic productivity. In both deltas, NPP has declined since 1900 due to a high level of HANPP in the Ebro and wetland loss in the Mississippi. In the Mississippi, NPP declined from 2500 g.m(-2).yr(-1) in 1900 to 2000 g.m 2-yr(-1) in 1990, with a decline to 1750 g.m(-2)-yr(-1) predicted by 2050. In the Ebro, total system NPP has increased from 700 to 1000 g.m(-2).yr(-1) due to subsidized agricultural production, mostly of rice. High HANPP of 35% reduces remaining NPP to 600 g.m (2).yr(-1). The natural energies and anthropogenic subsidies that maintain natural and human-modified deltaic ecosystems are analyzed, Elimination or reduction of important pulsing cycles has,, led to environmental deterioration and higher economic costs and necessitates high levels of Subsidies,, Incorporating natural energies is the best way to manage deltas sustainably, The use of wetlands for wastewater treatment and river diversions are presented as examples.

Castellanos, D. L. and L. P. Rozas (2001). "Nekton use of submerged aquatic vegetation, marsh, and shallow unvegetated bottom in the Atchafalaya River Delta, a Louisiana tidal freshwater ecosystem." Estuaries 24(2): 184-197.

We sampled nekton (fishes and decapod crustaceans) in submerged aquatic vegetation (SAV) (Potamogeton nodosus, Najas guadalupensis), in emergent marsh vegetation (Sagittaria spp. and Scirpus americanus), and over unvegetated bottom associated with three islands in the Atchafalaya River Delta, Louisiana. The purpose of our study was to quantify nekton densities in these major aquatic habitat types and to document the relative importance of these areas to numerically dominant aquatic organisms. We collected a total of 33 species of fishes and 7 species of crustaceans in 298 1-m(2) throw trap samples taken over three seasons: summer (July and August 1994), fall (September and October 1994), and spring (May and June 1995). Fishes numerically accounted for > 65% of the total organisms collected. Vegetated areas generally supported much higher nekton densities than unvegetated sites, although bay anchovies Anchoa mitchilli were more abundant over unvegetated bottom than in most vegetated habitat types. Among vegetation types, most species showed no apparent preference between SAV and marsh. However, inland silversides Menidia beryllina and freshwater gobies Gobionellus shufeldti were most abundant in Scirpus marsh in summer, and blue crabs Callinectes sapidus were most abundant in SAV (Potamogeton) in spring. Several species (sheepshead minnow Cyprinodon variegatus, rainwater killifish Lucania parva, and blue crab) apparently selected the vegetated backmarsh of islands (opposite of riverside) over streamside Scirpus marsh. Freshwater gobies, in contrast, were most abundant in streamside Scirpus marsh. Densities of juvenile blue crabs were high (up to 17 m(-2)) in vegetated delta habitat types and comparable to values reported from more saline regions of Gulf Coast estuaries. Shallow vegetated habitat types of the Atchafalaya River Delta and other tidal freshwater systems of the Gulf Coast may be: important nursery areas for blue crabs and other estuarine species.

Ceccherelli, V. U., I. Ferrari, et al. (1994). "Ecological Research on the Animal Communities of the Po River Delta Lagoons." Bollettino Di Zoologia 61(4): 425-436.

The main results of research on invertebrate biology and ecology in the lagoons of the Po River Delta (Sacca del Canarin, Sacca di Scardovari, Sacca di Goro) are presented and related to the more significant approaches followed in ecological research during the last two decades. The lagoons, which are intrinsically eutrophic water bodies, have recently undergone intense eutrophication due to the dramatic increase in the Po river nutrient loading. A shift towards a dystrophic state was indicated by the appearance of large Ulva rigida beds in spring and by extensive anoxia during the summer due to the decomposition of the huge macroalgal biomass. Particularly severe dystrophic crises occurred in the Sacca di Goro. Zooplankton and zoobenthos changes were analyzed according to the variations in hydrographic features as well as those in the trophic state of the water. The significance of population dynamics studies in evaluating biological responses to environmental stresses is emphasized. Investigations on animal populations and communities may be advantaged by maintaining the ecosystem approach as a stimulating frame of reference, but, at the same time, by developing specialized and problem-oriented research. The expansion of knowledge on nutrient cycling and related microbial processes in the lagoons could significantly improve the analysis of the ecological role of animal communities. A trend towards using experiments both in the laboratory and in the field must be encouraged. Finally the need for long-term studies is stressed. Pluriannual series of density data of both plankton and benthos communities have been collected in Sacca del Canarin and Sacca di Goro.

Christian, R. R., E. Fores, et al. (1996). "Nitrogen cycling networks of coastal ecosystems: Influence of trophic status and primary producer form." Ecological Modelling 87(1-3): 111-129.

We have used ecological network analysis to compare nitrogen cycles from five well-researched coastal ecosystems. These included a representative ricefield and two lagoons (Tancada and Encanysada lagoons) in the Ebro River delta, Spain; a region of the Sacca di Gore, a lagoon at the mouth of the Po River, Italy; and a drowned river estuary in North Carolina, USA, the Neuse River estuary. We constructed networks for the various systems and ranked them by trophic status (i.e., degree of eutrophication) using four indices. We then considered the importance of (1) trophic status, (2) growth form of dominant primary producer and (3) water residence time to the intensity and pattern of recycling and to the manner in which the systems can ''filter'' N. Three indices of flux (rate of import, primary productivity and total systems throughput) gave similar rankings of trophic status among ecosystems with the Italian and U.S. systems being most eutrophic, ricefields next, and then the two Spanish lagoons. Patterns of N export and of cycling within the systems were most closely related to the growth form of dominant primary producers. Phytoplankton, with their rapid turnover rate, foster rapid recycling within the water column and continuous transfer to sediments and export. Submersed and emergent aquatic vegetation and macroalgae create lags and pulses within systems by sequestering N during growth and releasing it during senescence, death and decomposition. Trends in cycling among systems relative to trophic status or water residence appear largely secondary to primary producer growth form.

Cooper, L. W., J. M. Grebmeier, et al. (1995). "Evidence for Re-Distribution of Cs-137 Alaskan Tundra, Lake, and Marine-Sediments." Science of the Total Environment 161: 295-306.

Tundra sampling conducted during 1989-1990 at Imnavait Creek, Alaska (68 degrees 37'N, 149 degrees 17'W) indicated that inventories of Cs-137 were close to expectations, based upon measured atmospheric deposition for this latitude band. Typically observed at a depth of 4-10 cm, peak accumulations of Cs-137 were associated with organic materials, above any mineral soil. Accumulated inventories of Cs-137 in tundra decreased by up to 50% along a transect to Prudhoe Bay (70 degrees 13'N, 148 degrees 30'W). Atmospheric deposition of Cs-137 decreased with latitude in the Arctic, but declines in deposition would have been relatively small over this distance (200 km). This finding suggests a recent loss of Cs-137 from tundra over the northern parts of the transect between Imnavait Creek and Prudhoe Bay. This hypothesis is supported by observations of maximum Cs-137 accumulations occurring in surface layers of the more northern tundra rather than at depth (as at Imnavait Creek), as well as by indications of higher Cs-137 accumulations in a lake inlet. On the other hand, marine sediments collected in the Bering Sea and Chukchi Seas, including the Yukon River delta region, show apparently lower inventories compared to tundra or lake sediments, although complete inventories are unavailable due to radiocesium buried to depths (> 20 cm) beyond the sampling capabilities used.

Coppin, P., I. Jonckheere, et al. (2004). "Digital change detection methods in ecosystem monitoring: a review." International Journal of Remote Sensing 25(9): 1565-1596.

Techniques based on multi-temporal, multi-spectral, satellite-sensor-acquired data have demonstrated potential as a means to detect, identify, map and monitor ecosystem changes, irrespective of their causal agents. This review paper, which summarizes the methods and the results of digital change detection in the optical/infrared domain, has as its primary objective a synthesis of the state of the art today. It approaches digital change detection from three angles. First, the different perspectives from which the variability in ecosystems and the change events have been dealt with are summarized. Change detection between pairs of images (bi-temporal) as well as between time profiles of imagery derived indicators (temporal trajectories), and, where relevant, the appropriate choices for digital imagery acquisition timing and change interval length definition, are discussed. Second, pre-processing routines either to establish a more direct linkage between remote sensing data and biophysical phenomena, or to temporally mosaic imagery and extract time profiles, are reviewed. Third, the actual change detection methods themselves are categorized in an analytical framework and critically evaluated. Ultimately, the paper highlights how some of these methodological aspects are being fine-tuned as this review is being written, and we summarize the new developments that can be expected in the near future. The review highlights the high complementarity between different change detection methods.

Corsi, I., M. Mariottini, et al. (2003). "Fish as bioindicators of brackish ecosystem health: integrating biomarker responses and target pollutant concentrations." Oceanologica Acta 26(1): 129-138.

Biological responses and contaminant levels in biological tissues were investigated in fish specimens of grass goby (Zosterisessor ophiocephalus) collected in spring 2000 in a moderately polluted brackish ecosystem, the Orbetello lagoon (southern coast of Tuscany, Italy). The complexity of harmful effects that contaminants may cause in fish over time was assessed. General condition indices (somatic liver index, and gonadal somatic index), cytochrome P450 enzymes, acetylcholinesterase activity and ovarian morphology were integrated with the content of organochlorines (OCs-hexachlorobenzene, DDTs and polychlorinated biphenyls) in liver and ovaries and p-nonylphenol (NP) and lower ethoxylate (NPE1-2) content in muscle and ovaries as well. Samples collected from the western basin of the lagoon near the Orbetello sewage treatment plant had somatic liver index values and two P450 activities significantly higher than those collected from the same basin at the Albegna river delta and in the Ansedonia canal in the eastern basin (P < 0.05). On the other hand, while muscle content of p-NP and NPE1-2 was significantly higher in samples from the Orbetello and Albegna river sites than in samples from the Ansedonia canal site, OC levels in liver (DDTs > PCBs > HCB) were particularly lower in samples from STP compared to levels detected in sites AC and AR. Light microscopy of ovaries revealed that although the gonads were sexually mature, the diameter of the oocytes and eggs was smaller than that commonly reported. High levels of M and NPs were, in fact, observed in grass goby ovaries, and the differences observed between acetylcholinesterase activities among investigated sites suggest exposure to insecticides as well. The integration of biological responses and contaminant tissue content reveals that certain areas of the lagoon are selectively impacted by various human activities and helps in distinguishing relationships between biological responses and contaminant load in the lagoon environment. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.

Darnaude, A. M., C. Salen-Picard, et al. (2004). "Depth variation in terrestrial particulate organic matter exploitation by marine coastal benthic communities off the Rhone River delta (NW Mediterranean)." Marine Ecology-Progress Series 275: 47-57.

Carbon and nitrogen stable isotopes were used to study depth variation in terrestrial particulate organic matter (POM) sedimentation off the mouth of the Rhone River delta, and its use by the main benthic invertebrates (polychaetes, crustaceans, molluscs and echinoderms) and flatfishes (Arnoglossus laterna, Buglossidium luteum and Solea solea). Coastal water POM and surface sediment exhibited low delta(13)C values, denoting dominance of terrestrial material in their carbon pools (25 to 80% and >50%, respectively), but the importance of river input differed as a function of depth. Terrestrial organic matter contribution to the total POM was greatest at 30-50 m (72 to 99%), and least at 70-100 in depth (25 to 77%). Most of the invertebrate groups studied (delta(13)C = -24.5 to -17.5parts per thousand; delta(15)N = 4.3 to 9.7parts per thousand) mainly relied on marine primary production irrespective of depth. However, deposit-feeding polychaetes mainly exploited terrestrial POM, and carnivorous and suspension-feeding polychaetes, bivalves, brachyurans and shrimps (Caridea) showed a partial uptake of terrestrial POM, depending on its availability. Incorporation of terrestrial POM by flatfishes (delta(13)C = -22.4 to -16.8parts per thousand; delta(15)N = 9.7 to 11.2parts per thousand.) was species- and depth-dependent. It was related not only to the fishes' diets but also to the trophic adaptability of their prey. S. solea, the main consumer of deposit-feeding polychaetes, showed the lowest VC irrespective of depth, but flatfish exploitation of terrestrial POM peaked at 30-50 m, where both polychaete consumption by fishes and terrestrial POM use by the benthos were maximal. Unlike most estuarine systems, terrestrial inputs in deltaic areas can therefore peak at intermediate depths, where some of the marine macrobenthos, including flatfishes, efficiently exploit them. These results allow better assessment of the role of river input to marine coastal zones in increasing fish abundance, and will therefore be of major interest for demersal fisheries management off deltaic areas.

Fores, E., R. R. Christian, et al. (1994). "Network Analysis on Nitrogen Cycling in a Coastal Lagoon." Marine Ecology-Progress Series 106(3): 283-290.

Network analysis was applied to nitrogen cycling data from 6 ecosystem components (phytoplankton, Potamogeton pectinatus, Ruppia cirrhosa, detritus plus heterotrophs, sediment, and dissolved inorganic nitrogen) in Tancada Lagoon (Ebro River delta, NE Spain) to ascertain (1) the relative importance of internal recycling versus external exchanges, (2) the main biogeochemical processes and (3) the fate of nitrogen imported to the lagoon. We compared cycling from 2 periods of the year: May-October, dominated by freshwater inputs, and November-April, dominated by seawater. Nitrogen recycling in the lagoon is equal to or more important than exchanges with other ecosystems, as indicated by the Finn Cycling Index (FCI). FCI values are the percentage of total flow in the network which is associated with internal cycles and not with imports or exports. These internal cycles involve flows from a compartment that can be traced through 1 or more other compartments and back to the original. FCI values were 62% during the freshwater period and 52% during the seawater period. Nitrogen input to the lagoons was mainly as detritus plus heterotroph nitrogen (0.81 and 0.51 mmol N m-2 d-1 during the fresh- and seawater periods respectively). Most nitrogen export was as phytoplankton (0.2 mmol N m-2 d-1 during both periods). Denitrification rates were comparable to other exports (0.17 and 0.09 mmol m-2 d-1 during the fresh- and seawater periods respectively). Sediment played a key role in the internal recycling of nitrogen. A total of 80% of the phytoplankton nitrogen flow came indirectly from ammonium fluxes between sediment and water during the freshwater period, and 60% during the seawater period. Thus several differences were noted in the N cycles between these 2 periods involving both the amount of recycling and the relative importance of different processes to the fate of nitrogen.

Glenn, E., R. Tanner, et al. (1998). "Growth rates, salt tolerance and water use characteristics of native and invasive riparian plants from the delta of the Colorado River, Mexico." Journal of Arid Environments 40(3): 281-294.

Six riparian plant species representing native and invasive species from the Colorado River delta in the Sonoran Desert of Mexico were tested for salt tolerance and water use characteristics in a greenhouse study in Tucson, Arizona. Negative linear regression equations relating relative growth rates (RGR, g g(-1) day(-1)) of each species to mean root zone salinity had high coefficients of determination (r(2) = 0.73-0.86, P < 0.001). Salt tolerance levels, expressed as % reduction in RGR per g l(-1) NaCl in soil solution, varied widely among species: Allenrolfea occidentalis, 0% reduction; Tamarix ramosissima, 1.8% reduction; Pluchea sericea, 3.5% reduction; and Baccharis salicifolia, Salix gooddingii and Populus fremontii, 7-9% reduction (p < 0.05). Transpiration was proportional to RGR for all species. Contrary to some previous reports, Tamarix did not have unusually high water use compared to the other species. Differences in salt tolerance among species determined in this study support field observations that soil salinity, which can reach high values along channelized and flow-regulated stretches of south-western United States rivers due to lack of overbank flooding, is a major factor in the replacement of native riparian species by invasive species. (C) 1998 Academic Press.

Harrison, P. J., N. Khan, et al. (1997). "Nutrient and phytoplankton dynamics in two mangrove tidal creeks of the Indus River delta, Pakistan." Marine Ecology-Progress Series 157: 13-19.

We report the results of a 3 yr study on 2 tidal creeks in the northwest corner of the Indus River delta (Pakistan) mangrove ecosystem. We measured Light (extinction coefficients), nutrients (nitrate, nitrite, phosphate, silicate and ammonium), chlorophyll a (chi a), suspended load, primary productivity (C-14 uptake) and phytoplankton species in Isaro and Gharo Creeks. There was no clear seasonal cycle in any of the 5 nutrients in either of the 2 tidal creeks. NO3 ranged from 1 to 8 mu M, NH4 from 2 to 15 mu M, SiO4 from 3 to 20 mu M, and PO4 from 0.2 to 2 mu M (except when it was undetectable during a bloom in Isaro Creek in June). Hence, nitrogen and silicate do not Limit primary productivity, but during a large bloom phosphate may become limiting. When phosphate samples were reanalyzed without removing the sediment (no filtration), phosphate concentrations were about 25 % higher. This suggests that phosphate is adsorbed to sediment particles and could potentially be biologically available. There was a high suspended load (100 to 180 mg l(-1)) because the sediments were fine (silt and clay) and they were kept suspended by high tidal currents (0.5 to 1.5 m s(-1)) caused by tidal ranges of up to 4 m during spring tides in these shallow (3 to 9 m deep) creeks. Hence, extinction coefficients were very high (1 to 2 m(-1)) and the 1% light depth ranged from <1 m in August (the rainy season) to about 4 m in January and February. Consequently, primary productivity appeared to be light-limited throughout the year. Chi a ranged from 1 to 4 mu g l(-1) with occasional blooms up to 40 mu g l(-1). Primary productivity ranged from 0.2 to over 1 g C m(-2) d(-1) in Isaro Creek. There was no apparent seasonal cycle in chi a or primary productivity. Phytoplankton species were predominantly large centric diatoms which were presumably kept in suspension by tidal currents. Since nutrients are rarely limiting, there is an export of nutrients from the creeks to the coastal area which may stimulate phytoplankton productivity.

Heilman, J. L., D. R. Cobos, et al. (1999). "Tower-based conditional sampling for measuring ecosystem-scale carbon dioxide exchange in coastal wetlands." Estuaries 22(3A): 584-591.

Long-term measurements of CO2 exchange between coastal wetlands and the atmosphere are necessary to improve our understanding of the role these ecosystems play in the global carbon cycle, and the response of these systems to environmental change. We conducted research to adapt and evaluate tower-based conditional sampling as a method for measuring net CO2 exchange (NCE) at the ecosystem scale on a continuous basis. With conditional sampling, NCE is determined from the product of the standard deviation of vertical wind velocity, the difference in CO2 concentration between updrafts and downdrafts in the constant flux portion of the boundary layer above the surface, and an empirical coefficient. We constructed a system that used a sonic anemometer to measure vertical wind velocity (w) and control a high-speed three-way valve that diverted air from updrafts and down,drafts into separate sample lines, depending on the direction of w. An infrared gas analyzer was used to measure the concentration difference. The conditional sampling system was installed and tested in a marsh in the Nueces River Delta near Corpus Christi, Texas, as part of a long-term study of effects of freshwater inflow on CO2 flux. System accuracy was evaluated by comparing conditional sampling measurements of water vapor flux with independent estimates obtained with the Bowen ratio method. Average daily flux estimates for the two methods agreed to within 13%. Measurements showed that freshwater inflow due to flooding of the Nueces River increased NCE by increasing CO2 assimilation and decreasing CO2 efflux. Over a 65-d period, daily NCE varied from a maximum gain of 0.16 mol CO2 m(-2) d(-1) during flooding to a maximum loss of -0.14 mol CO2 m(-2) d(-1) when the marsh dried. Our study showed that conditional sampling was well suited for quantifying CO2 exchange in coastal wetlands on a diel, daily, and seasonal basis.

Heilman, J. L., F. A. Heinsch, et al. (2000). "(E)nergy balance of a high marsh on the Texas Gulf Coast: Effect of water availability." Journal of Geophysical Research-Atmospheres 105(D17): 22371-22377.

The supply of water to the Nueces River Delta near Corpus Christi, Texas, and its estuarine marshes is limited by low tidal ranges in the Gulf of Mexico and by channelization of the Nueces River which restricts freshwater inflow. Micrometeorological measurements were made at the upper end thigh marsh) of the delta to determine how daily and seasonal changes in the surface energy balance were affected by availability of water. The marsh consists of shallow ponds interconnected by narrow channels, and elevated areas containing emergent vegetation. During the spring and fall when ponds were flooded, latent and sensible heat flux averaged 67% and 30%, respectively, of net radiation. In the summer when ponds dried, energy partitioning was reversed with sensible heat flux accounting for 65% of net radiation and latent heat accounting for 27%. When ponds were flooded, heat storage in the water column was the major component of storage heat flux. When ponds dried, storage heat flux was controlled by sediment water content, largely through its effect on thermal diffusivity. The ratio of actual to equilibrium evaporation averaged 0.7 in the spring and fall, and 0.3 in the summer, indicating that the marsh behaved more like a dryland ecosystem than a wetland.

Heinsch, F. A., J. L. Heilman, et al. (2004). "Carbon dioxide exchange in a high marsh on the Texas Gulf Coast: effects of freshwater availability." Agricultural and Forest Meteorology 125(1-2): 159-172.

The supply of water to the Nueces River Delta near Corpus Christi, Texas is limited by dams and channelization of the river which restrict freshwater inflow. The upper end (high marsh) of the delta frequently dries up during the summer. The marsh consists of slightly elevated islands containing emergent halophytes, and shallow ponds interconnected by narrow channels. Carbon dioxide exchange in the marsh was measured by relaxed eddy accumulation (REA) during two periods, one in 1997 that included two floods from the river followed by an extended period of drying and disappearance of standing water, and the other in 1998 that was in the midst of a drought with no standing water present. The marsh was a net CO2 sink during periods of high water availability and low sediment salinity, and a net source when water availability was low and salinity was high. During the 1997 period, net ecosystem exchange (NEE) and gross ecosystem production (GEP) ranged from -7.3 g CO2 m(-2) per day (net gain of CO2) and 12.3 g CO2 m(-2) per day, respectively, after flooding to +8.7 g CO2 m(-2) per day (net loss of CO2) and 0.4 g CO2 m(-2) per day, respectively, when sediments were dry. NEE and GEP averaged 0.5 and 7.7 g CO2 m(-2) per day, respectively, during this period. Standing water, and water in pores restricted gas exchange between sediment and the atmosphere so that ecosystem respiration (R) increased as the marsh dried, with R ranging from 1.2 to 15.6 g CO2 m(-2) per day and averaging 8.2 g CO2 m(-2) per day. During the 1998 drought, NEE, GEP, and R averaged 5.8, 3.3, and 9.19 CO2 m(-2) per day, respectively. A 27 turn rain during this period produced a 14-fold increase in GEP and a 75% reduction in R that lasted for 2 days. In 1997, NEE and its components were all significantly correlated at the 0.05 level with water availability as estimated by the cumulative difference between rainfall and evaporation, while in 1998, only NEE and GEP were significantly correlated with water availability. Results of this study indicate that the marsh NEE behaved more like that of a dryland ecosystem than a wetland because of limited freshwater inflow. (C) 2004 Elsevier B.V. All rights reserved.

Hinojosa-Huerta, O., S. DeStefano, et al. (2001). "Distribution and abundance of the Yuma clapper rail (Rallus longirostris yumanensis) in the Colorado River delta, Mexico." Journal of Arid Environments 49(1): 171-182.

We estimated the abundance of Yuma clapper rails in the Cienega de Santa Clara and determined the distribution of the subspecies in the Colorado River delta region in Mexico, The maximum estimate of abundance was 6629 individuals (95% C.I. 4859-8399), assuming a response rate by rails to taped calls of 60%. Rails were widely distributed in the delta, occupying almost all marshlands dominated by cattail. As this is an endangered subspecies shared by Mexico and the U.S., the conservation of the delta ecosystem should be the interest of both countries, especially when water management decisions upstream in the U.S. have an impact over natural areas downstream in Mexico. (C) 2001 Academic Press.

Ip, C. C. M., X. D. Li, et al. (2004). "Over one hundred years of trace metal fluxes in the sediments of the Pearl River Estuary, South China." Environmental Pollution 132(1): 157-172.

The rapid economic development in the Pearl River Delta (PRD) region in South China in the last three decades has had a significant impact on the local environment. Estuarine sediment is a major sink for contaminants and nutrients in the surrounding ecosystem. The accumulation of trace metals in sediments may cause serious environmental problems in the aquatic system. Thirty sediment cores were collected in the Pearl River Estuary (PRE) in 2000 for a study on trace metal pollution in this region. Heavy metal concentrations and Pb isotopic compositions in the four Pb-210-dated sediment cores were determined to assess the fluxes in metal deposits over the last one hundred years. The concentrations of Cu, Pb and Zn in the surface sediment layers were generally elevated when compared with the sub-surface layers. There has been a significant increase in inputs of Cu, Pb and Zn in the PRE since the 1970s. The results also showed that different sampling locations in the estuary received slightly different types of inputs. Pb isotopic composition data indicated that the increased Pb in the recent sediments was of anthropogenic origin. The results of trace metal influxes showed that about 30% of total Pb and 15% of total Zn in the sediments in the 1990s were from anthropogenic sources. The combination of trace metal analysis, Pb isotopic composition and Pb-210 dating in an estuary can provide vital information on the long-term accumulation of metals in sediments. (C) 2004 Elsevier Ltd. All rights reserved.

Jassby, A. D. and J. E. Cloern (2000). "Organic matter sources and rehabilitation of the Sacramento-San Joaquin Delta (California, USA)." Aquatic Conservation-Marine and Freshwater Ecosystems 10(5): 323-352.

1. The Sacramento-San Joaquin River Delta, a complex mosaic of tidal Freshwater habitats in California. is the focus of a major ecosystem rehabilitation effort because of significant long-term changes in critical ecosystem functions. One of these functions is the production, transport and transformation of organic matter that constitutes the primary food supply, which may be sub-optimal at trophic levels supporting fish recruitment. A long historical data set is used to define the most important organic matter sources, the factors underlying their variability, and the implications of ecosystem rehabilitation actions for these sources. 2. Tributary-borne loading is the largest organic carbon source on an average annual Delta-wide basis; phytoplankton production and agricultural drainage are secondary; wastewater treatment plant discharge, tidal marsh drainage and possibly aquatic macrophyte production are tertiary; and benthic microalgal production, urban run-off and other sources are negligible. 3. Allochthonous dissolved organic carbon must be converted to particulate form-with losses due to hydraulic flushing and to heterotroph growth inefficiency-before it becomes available to the metazoan food web. When these losses are accounted for, phytoplankton production plays a much larger role than is evident from a simple accounting of bulk organic carbon sources, especially in seasons critical for larval development and recruitment success. Phytoplankton-derived organic matter is also an important component of particulate loading to the Delta. 4. The Delta is a net producer of organic matter in critically dry years but, because of water diversion from the Delta, transport of organic matter from the Delta to important, downstream nursery areas in San Francisco Bay is always less than transport into the Delta from upstream sources. 5. Of proposed rehabilitation measures, increased use of floodplains probably offers the biggest increase in organic matter sources. 6. An isolated diversion facility-channelling water from the Sacramento River around the Delta to the water projects-would result in substantial loading increases during winter and autumn, but little change in spring and summer when food availability probably matters most to developing organisms. 7. Flow and fish barriers in the channel could have significant effects, especially on phytoplankton sources and in dry years, by eliminating 'short-circuits' in the transport of organic matter to diversion points. 8. Finally, productivity of intentionally flooded islands probably would exceed that of adjacent channels because of lower turbidity and shallower mean depth, although vascular plants rather than phytoplankton could dominate if depths were too shallow. Copyright (C) 2000 John Wiley & Sons, Ltd.

Jassby, A. D., J. E. Cloern, et al. (2002). "Annual primary production: Patterns and mechanisms of change in a nutrient-rich tidal ecosystem." Limnology and Oceanography 47(3): 698-712.

Although nutrient supply often underlies long-term changes in aquatic primary production, other regulator processes can he important. The Sacramento-San Joaquin River Delta, a complex of tidal waterways forming the landward portion of the San Francisco Estuary, has ample nutrient supplies, enabling us to examine alternate regulatory mechanisms over a 21-yr period. Delta-wide primary productivity was reconstructed from historical water quality data for 1975-1995. Annual primary production averaged 70 C m(-2), but it varied by over a factor of five among years. At least four processes contributed to this variability: (1) invasion of the clam Potamocorbula amurensis led to a persistent decrease in phytoplankton biomass (chlorophyll a) after 1986: (2) a long-term decline in total suspended solids-probably at least partly because of upstream dam construction-increased water transparency and phytoplankton growth rate: (3) river inflow, reflecting climate variability, affected biomass through fluctuations in flushing and growth rates through fluctuations in total Suspended solids: and (4) an additional pathway manifesting as a long-term decline in winter phytoplankton biomass has been identified, but its genesis is uncertain. Overall, the Delta lost 43% in annual primary production during the period. Given the evidence for food limitation of primary Consumers, these findings provide a partial explanation for widespread Delta species declines over the past few decades. Turbid nutrient-rich systems Such as the Delta may he inherently more variable than other tidal systems because certain compensatory processes are absent. Comparisons among systems, however can be tenuous because conclusions about the magnitude and mechanisms of variability are dependent on length of data record.

Khush, G. S. (1997). "Origin, dispersal, cultivation and variation of rice." Plant Molecular Biology 35(1-2): 25-34.

There are two cultivated and twenty-one wild species of genus Oryza O. sativa, the Asian cultivated rice is grown ail over the world. The African cultivated rice, O. glaberrima is grown on a small scale in West Africa. The genus Oryza probably originated about 130 million years ago in Gondwanaland and different species got distributed into different continents with the breakup of Gondwanaland. The cultivated species originated from a common ancestor with AA genome. Perennial and annual ancestors of O. sativa are O. rufipogon and O. nivara and those of O. glaberrima are O. longistaminata, O. breviligulata and O. glaberrima probably domesticated in Niger river delta. Varieties of O. sativa are classified into six groups on the basis of genetic affinity. Widely known indica rices correspond to group I and japonicas to group VI. The so called javanica rices also belong to group VI and are designated as tropical japonicas in contrast to temperate japonicas grown in temperate climate. Indica and japonica rices had a polyphyletic origin. Indicas were probably domesticated in the foothills of Himalayas in Eastern India and japonicas somewhere in South China. The indica rices dispersed throughout the tropics and subtropics from India. The japonica rices moved northward from South China and became the temperate ecotype. They also moved southward to Southeast Asia and from there to West Africa and Brazil and became tropical ecotype. Rice is now grown between 55 degrees N and 36 degrees S latitudes. It is grown under diverse growing conditions such as irrigated, rainfed lowland, rainfed upland and floodprone ecosystems. Human selection and adaptation to diverse environments has resulted in numerous cultivars. It is estimated that about 120000 varieties of rice exist in the world. After the establishment of International Rice Research Institute in 1960, rice varietal improvement was intensified and high yielding Varieties were developed. These varieties are now planted to 70% of world's riceland. Rice production doubled between 1966 and 1990 due to large scale adoption of these improved varieties. Rice production must increase by 60% by 2025 to feed the additional rice consumers. New tools of molecular and cellular biology such as anther culture, molecular marker aided selection and genetic engineering will play increasing role in rice improvement.

Laxton, N. F., C. R. Burn, et al. (1996). "Productivity of Loessal grasslands in the Kluane lake region, Yukon territory, and the Beringian ''production paradox''." Arctic 49(2): 129-140.

The Beringian ''Production Paradox'' is posed by abundant evidence that large ungulates populated unglaciated portions of northwestern North America and adjacent northeast Asia during the late Pleistocene, while botanical data from the same period suggest a poorly productive tundra environment. It is not clear how the large animals sustained themselves, but portions of Beringia, locally in receipt of loess, may have harbored sufficient forage-producing plants to nourish these animals. Loessal soils in the region today are warm and dry in summer, and are often used as rangelands. The loessal hypothesis was examined on grasslands in the Kluane Lake area, southwest Yukon Territory, at sites which have recently received loess blown from the Slims River delta. The biomass and species diversity of grasslands around the lake increase with the quantity of silt in the soil. Likewise, soil fertility indices, including total nitrogen, available nitrogen (NH4), and total carbon, increase with silt content, particularly at sites where the soil surface has been stable for some time, and a ''humified'' loess (Ahk) horizon has developed. These results support the hypothesis that sites in receipt of loess may have played a significant role in the vegetative productivity of the Beringian ecosystem.

Leconte, R., A. Pietroniro, et al. (2001). "Effects of flow regulation on hydrologic patterns of a large, inland delta." Regulated Rivers-Research & Management 17(1): 51-65.

The Peace-Athabasca River Delta (PAD) is one of the largest freshwater deltas and most biologically productive in the world. Because regional evaporation is greater than precipitation, the thousands of lakes and wetlands dotting this area rely on periodic flooding from the Peace and Athabasca rivers to be replenished. Flood frequency significantly declined beginning in the mid-1970s, several years after the initiation of flow regulation of the Peace River. However, the drying trend was interrupted in 1996 when the PAD experienced extensive inland inundation on two separate occasions, one in the spring and one in the summer. A one-dimensional numerical hydrodynamic model was used to evaluate the role of flow regulation and hydroclimatic conditions on the water levels of major lakes found in the PAD. Three Peace River flow scenarios were analysed: the observed flows, the flow regime without the 'precautionary drawdown' spill which was required because of the discovery of a sinkhole at the crest of the dam, and the naturalized flow regime, which assumed no dam regulation. Modelling results indicated that the effect of the spill on the flow regime within the PAD was approximately equivalent in magnitude, although different in timing, to what would have resulted from the prevailing hydroclimatic conditions in an unregulated system. Furthermore, even in the absence of the precautionary drawdown spill, the lake levels would have risen well above the maximum daily average, suggesting that 1996 was one of the wettest years on record. Finally, the hydrodynamic regime observed at the end of the summer 1996 was very similar to that modelled under unregulated flow conditions, suggesting that flow regulation could be used to alter the hydrodynamic regime of a large delta to at least partially restore natural conditions and potentially improve ecosystem health. Copyright (C) 2001 John Wiley & Sons, Ltd.

Lohrenz, S. E., G. L. Fahnenstiel, et al. (1997). "Variations in primary production of northern Gulf of Mexico continental shelf waters linked to nutrient inputs from the Mississippi River." Marine Ecology-Progress Series 155: 45-54.

Increases in nutrient concentrations in the Mississippi River over the past 35 yr have led to speculation that primary production of organic carbon has been elevated as a result of increased nutrient fluxes that have occurred in the northern Gulf of Mexico coastal ecosystem. However, studies thus far have not provided direct demonstration of temporal relationships between measured primary production in continental shelf waters and river-borne nutrient fluxes. This investigation compared temporal variations in primary production with associated annual and interannual changes in river-borne nutrient inputs. Primary production in shelf waters near the river delta were found to be significantly correlated with nitrate (NO3-) + nitrite (NO2-) concentrations and fluxes over a 6 yr period from 1988 to 1994. Although light limitation was probably an important factor during winter months, a positive correlation was demonstrated between river inputs of NO3-+NO2- and primary production for data collected from other times of the year. Peak nutrient inputs generally occurred in the spring. The magnitude of the riverborne NO3-+NO2- inputs averaged 106% of estimated nitrogen requirements for phytoplankton in the river-impacted region, considerably greater than in Amazon shelf waters, which have been less subject to anthropogenic nutrient increases. The possibility exists that further increases in anthropogenic nutrients in the Mississippi River could lead to higher and more widespread primary production, and this may intensify and extend the depletion of oxygen that has already been observed in the Louisiana shelf ecosystem. However, such a prediction is difficult because relationships between increasing nutrient inputs and primary production are unlikely to be Linear, and a complete understanding of processes intermediate between primary production of organic matter and oxygen depletion in bottom waters on the Louisiana shelf is still lacking.

Lovvorn, J. R. and J. R. Baldwin (1996). "Intertidal and farmland habitats of ducks in the Puget Sound region: A landscape perspective." Biological Conservation 77(1): 97-114.

In managing coastal ecosystems, adjacent uplands have been considered mainly as sources of materials affecting littoral environments, and not as parts of an integrated system of habitats directly used by semiaquatic fauna. Agriculture is often viewed as detrimental to coastal habitats, but many waterbirds use both marine and farmland habitats on a daily and seasonal basis. We investigated the importance to dabbling ducks (Anatini) of the juxtaposition of farmland and intertidal habitats in the Puget Sound region of USA and Canada. When feeding in intertidal areas of the Fraser River Delta in British Columbia, wintering dabbling ducks ate mainly the exotic eelgrass Zostera japonica and appeared to avoid the native Zostera marina. Biomass of Z. japonica leaves was insufficient to support herbivorous American wigeon Anas americana throughout winter. Intertidal invertebrates might be adequate to support omnivorous northern pintail A. acutus, mallard A. platyrhynchos and green-winged teal A. crecca, but invertebrate biomass declined substantially in winter. A switch by these ducks from feeding in intertidal areas in autumn to farmland in winter might have resulted from inadequate or much reduced food resources in intertidal areas. Throughout the Puget Sound region, intertidal habitats with adjacent farmland supported about 75% of wigeon, 94% of pintail, 93% of mallard and 92% of teal, and few sites that lacked farmland supported substantial numbers of these species throughout winter. Radio-tagged wigeon and pintail moved among coastal sites even in a mild winter, and temperature patterns over 60 years suggest that ice cover on marine bays and flooded farmland forces dabbling ducks to leave the Fraser Delta in about 13% of all winters to seek alternative sites. For dabbling ducks in this region, it appears that farmland adjacent to intertidal areas is an important component of coastal habitat complexes, and a system of alternative sites should be included in regional landscape plans. Copyright (C) 1996 Published by Elsevier Science Ltd

Lucas, L. V., J. E. Cloern, et al. (2002). "Functional variability of habitats within the Sacramento-San Joaquin Delta: Restoration implications." Ecological Applications 12(5): 1528-1547.

We have now entered an era of large-scale attempts to restore ecological functions and biological communities in impaired ecosystems. Our knowledge base of complex ecosystems and interrelated functions is limited, so the outcomes of specific restoration actions are highly uncertain. One approach for exploring that uncertainty and anticipating the range of possible restoration outcomes is comparative study of existing habitats similar to future habitats slated for construction. Here we compare two examples of one habitat type targeted for restoration in the Sacramento-San Joaquin River Delta. We compare one critical ecological function provided by these shallow tidal habitats-production and distribution of phytoplankton biomass as the food supply to pelagic consumers. We measured spatial and short-term temporal variability of phytoplankton biomass and growth rate and quantified the hydrodynamic and biological processes governing that variability. Results show that the production and distribution of phytoplankton biomass can be highly variable within and between nearby habitats of the same type, due to variations in phytoplankton sources, sinks, and transport. Therefore, superficially similar, geographically proximate habitats can function very differently, and that functional variability introduces large uncertainties into the restoration process. Comparative study of existing habitats is one way ecosystem science can elucidate and potentially minimize restoration uncertainties, by identifying processes shaping habitat functionality, including those that can be controlled in the restoration design.

Maccracken, J. G., V. Vanballenberghe, et al. (1993). "Use of Aquatic Plants by Moose - Sodium Hunger or Foraging Efficiency." Canadian Journal of Zoology-Revue Canadienne De Zoologie 71(12): 2345-2351.

Use of submergent aquatic plants by North American moose (Alces alces) has been linked to sodium hunger. Habitat preferences, seasonal diets, forage abundance and quality, and population surveys indicated that emergent plants in small shallow ponds were important to moose on the Copper River Delta, Alaska. However, sodium was abundant in terrestrial browse. We propose that foraging in aquatic habitats, particularly on emergent species, may be highly efficient based on the following habitat attributes and behavioral observations: (i) ponds dominated by either emergent or submergent species produced about 4 times more forage than terrestrial habitats, (ii) emergent and submergent plants were more digestible and had higher concentrations of minerals than browse, (iii) use of aquatic habitats followed trends in forage production over the growing season, (iv) indirect evidence suggested that forage intake rates were greater in aquatic habitats, and (v) use of aquatic habitats by male and female moose was in proportion to the sex structure of the population. These data provide consistent circumstantial evidence that use of emergent species, and possibly submergents, may maximize the intake of nutrients and also reduce conflicts between cropping forage and vigilance during a foraging bout.

Manariotis, I. D. and P. C. Yannopoulos (2004). "Adverse effects on Alfeios River Basin and an integrated management framework based on sustainability." Environmental Management 34(2): 261-269.

The Alfeios River, the longest and highest flow-rate river in Peloponnisos, constitutes an important water resource and ecosystem in Greece. In the present study, human activities in the Alfeios River Basin are described, and their impacts on water quality and the ecosystem are analyzed; effects resulting from interventions on river geomorphology between Flokas Dam and the river delta are determined. These actions have caused significant adverse impacts on the infrastructure (the dam, railroad, and road bridges), the level of aquifer water table and area water uses, and the aquatic and riparian ecosystem. A general integrated management strategy is formulated and a master management plan is proposed for resolving management problems in river basins. The plan considers local conditions and national requirements and complies with the European Communities legislation; it would help prevent further basin deterioration, improve water quality, and protect water resources and ecosystems in the area in accordance to sustainable development. The Alfeios River Basin serves as a case study in the development of the plan.

Marchini, A., K. Gauzer, et al. (2004). "Spatial and temporal variability of hard-bottom macrofauna in a disturbed coastal lagoon (Sacca di Goro, Po River Delta, Northwestern Adriatic Sea)." Marine Pollution Bulletin 48(11-12): 1084-1095.

The sessile and mobile macrobenthos on artificial hard bottoms was studied in 12 stations of the Sacca di Goro lagoon, a brackish, highly stressed water basin in the delta of the river Po, open to the Northwestern Adriatic Sea. Three sampling surveys were carried out in June and September 2000 and June 2001 in order to make three types of temporal comparisons: (i) on a seasonal scale, before and after a summer dystrophic event; (ii) on an annual basis, before and after the works of excavation of a canal through the outer sand bank; (iii) on a multiannual scale, comparing the data with those of a survey carried out in 1988. The biocoenoses did not show large fluctuations after a moderately severe summer dystrophic crisis, while the digging of the canal caused clear changes in the macrobenthos community structure after one year. The long-term comparison showed a shift in the community patterns after a decade. (C) 2003 Elsevier Ltd. All rights reserved.

Martin, J. F., M. L. White, et al. (2000). "Evaluation of coastal management plans with a spatial model: Mississippi delta, Louisiana, USA." Environmental Management 26(2): 117-129.

A landscape spatial model that operates with a cellular grid was utilized to evaluate proposed management plans in the Barataria and Terrebonne basins of the Mississippi River delta. By explicitly incorporating system processes and relationships, models of this type can identify both short- and long-term impacts of proposed plans across space and offer a solution to the spatial and temporal isolation that plagues many environmental management decisions. Four management proposals, which included a river diversion, levee plans, and a hydraulic retention scenario, were analyzed with regard to reducing land loss, a pervasive problem in many of the world's deltas. The model simulated 30 years of habitat change for each plan and "no action plans" in each basin were used as a baseline of comparison for the management plans. By restoring natural deltaic functions and increasing wetland elevations, the river diversion proved to be an effective method to reduce land loss in these environments. Habitat changes during the hydraulic retention scenario highlighted the use of the model in recognizing distant spatial impacts of management plans. Simulations of levee plans illustrated limitations of the model and produced ambiguous results, suggesting areas for future model refinement. The river diversion and hydraulic retention scenarios demonstrate that spatial landscape models are tools capable of predicting landscape responses to regional management plans.

Martin, J. F., E. Reyes, et al. (2002). "Landscape modeling of the Mississippi delta." Bioscience 52(4): 357-365.

Martin, J. F. (2002). "Emergy valuation of diversions of river water to marshes in the Mississippi River Delta." Ecological Engineering 18(3): 265-286.

River diversions within the Mississippi Delta deliver river water and associated sediments and nutrients to interior marshes that were previously isolated from river inputs by elevated levees. When isolated from river inputs. the marshes subside and deteriorate to open water, resulting in ecological and economic losses, River diversions are an ecological engineering method to reverse this trend by restoring controlled flows of river water through modified levees. This study compares the cost of constructing and operating the diversions with potential benefits to determine whether the diversions yield a net public benefit. The Caernarvon and Davis Pond river diversions were evaluated using emergy analysis to provide a common basis to quantify and compare economic and ecological costs and benefits. The analysis quantified high concentrations of natural resources inherent to deltas and demonstrated benefits produced by investing economic resources in river diversions to capture and utilize renewable resources. The diversions resulted in large net emergy yield ratios (33.2 and 9.36) that varied depending on the rate of marsh gain produced by the diversions. (C) 2002 Elsevier Science B.V. All rights reserved.

Millan-Nunez, R., E. Santamaria-del-Angel, et al. (1999). "The Colorado River Delta: A high primary productivity ecosystem." Ciencias Marinas 25(4): 509-524.

The construction of major dams in the Colorado River has produced a drastic effect on the amount of fresh water entering the Colorado River Delta. After 1935 there was a dramatic decrease in fresh-water input, causing ecological impacts and a decrease of organisms in the natural habitat. We carried out six spatial samplings during a period elf no fresh-water inflow to the delta, in June, August and November 1989, and February, April and June 1990; during each sampling, a 24-hour time series was conducted at one station and seawater samples were taken every two hours. Also, in May 1991 we carried out an eight-day time series, taking samples of seawater at 08:00, 12:00 and 16:00 hours. The objective was to estimate phytoplankton abundance, chlorophyll concentration and primary productivity during a period of no fresh-water input. In the spatial distribution, the chlorophyll a concentrations and phytoplankton abundance were higher on the Baja California side than on the Sonora side, with concentrations of 2.6-18.2 mg m(-3) and 1.8-12.7 mg m(-3) and of 274 and 166 cells mL(-1), respectively. In the time series, the dinoflagellates were more abundant than the diatoms. The primary production showed a tendency to decrease from August 1989 to June 1990, with values of 15.0 to 0.5 mgC m(-3) h(-1). The primary productivity values in the time series presented a tendency to increase during the tide transition, reaching values of 76 mgC m(-3) h(-1). The variations of chlorophyll concentration, phytoplankton abundance and primary productivity were strongly influenced, by the effects caused by the tidal currents.

Mistri, M., R. Rossi, et al. (2001). "Structure and secondary production of a soft bottom macrobenthic community in a brackish lagoon (Sacca di Goro, north-eastern Italy)." Estuarine Coastal and Shelf Science 52(5): 605-616.

The composition and distribution of the macrobenthic community in a lagoon in the Po River delta was investigated by taking monthly samples at three sites during 1994. A total of 38 macroinvertebrate taxa, representing five phyla, were identified. Gastropods, amphipods, and chironomid larvae dominated the macrofauna in term of abundance, while in terms of biomass bivalves were the dominant taxon. Monthly total invertebrate abundance showed considerable fluctuations, depending on the season and on the presence of the red macroalgae Gracilaria verrucosa. In the central area of the lagoon, a significant relationship was demonstrated between macrobenthic community parameters and amount of macroalgal cover. Taking the most important species, i.e. those that contributed most to similarity within sites, only Cerastoderma glaucum was found to be negatively related to the amount of macroalgal biomass. Mean annual secondary production varied between 50 and 75 g AFDW m(-2) yr(-1) depending on the site, yielding P/B ratios between 1.02 and 1.08. Confinement and moderate disturbance due to the presence of algal cover are hypothesized to determine structure, composition, and production of the macrobenthic community in the Sacca di Goro. (C) 2001 Academic Press.

Mistri, M. (2002). "Ecological characteristics of the invasive Asian date mussel, Musculista senhousia, in the Sacca di Goro (Adriatic Sea, Italy)." Estuaries 25(3): 431-440.

A population of the invasive mussel Musculista senhousia was monitored bimonthly from May 1999 through April 2000 in the Sacca di Goro, a brackish lagoon of the Po River Delta, Northern Adriatic Sea, in order to give information on the gametogenic cycle, population dynamics, and secondary production of this successful invader. The gonad underwent 4 different stages: spent (December to February), developing (March to May), ripe (June to August), and spawning (September to November). The population was numerically dominated by a single cohort of individuals for most of the year. The mean size of this cohort rapidly increased to 24-25 mm shell length, after which growth slowed and mussels rarely grew larger than 30-32 mm. Summer anoxia may have greatly reduced mussel abundance; annual cohort mortality was 95%. No recruitment was registered on the bed until February 2000, and there was a large pulse of new recruits in April when two cohorts were clearly recognizable. The established bed was the primary site for new recruitment. Secondary production, calculated with two different methods, gave comparable estimates; P:B ratios were 1.5 and 1.7. M. senhousia beds; seemed to facilitate the presence of other macrofaunal taxa: abundance of some species (a small gastropod, amphipods, and tube-building polychaetes) were significantly higher within mussel mats at two sites sampled in May 2000 than they were in soft-sediments similar to100 m away.

Mistri, M., R. Rossi, et al. (2004). "The spread of an alien bivalve (Musculista senhousia) in the Sacca di Goro Lagoon (Adriatic Sea, Italy)." Journal of Molluscan Studies 70: 257-261.

The Asian date mussel, Musculista senhousia (Mytilidae), which is endemic in the western Pacific, appeared and became abundant in the Sacca di Goro, a brackish lagoon in the Po River Delta (northern Adriatic Sea, Italy) in the early 1990s. The course of the invasion was documented through a macrobenthic monitoring programme at three sites in the Sacca. From 1994, when the new mussel was first collected, M. senhousia spread throughout the lagoon and, within a few years, reached densities exceeding 10,000 individuals m(-2). Mussel effects on biodiversity were assessed by comparing macrobenthic community structure and composition: over a 5-year period some changes in the macrobenthic community seem to be apparent, suggesting a positive effect of the mussel on the number of species and benthic richness. Considering trophic guilds, significant positive correlations were found between M. senhousia and detritivores and herbivores, while suspension feeders probably suffered competition from the mussel. Musculista senhousia was initially successful because it exploited a naturally disturbed, sparsely occupied environment. The well-dated documentation of the first collections, increasing abundance and spread of M. senhousia at our study sites provided an opportunity to observe a biological invasion of a habitat in progress.

Nagler, P. L., E. P. Glenn, et al. (2001). "Assessment of spectral vegetation indices for riparian vegetation in the Colorado River delta, Mexico." Journal of Arid Environments 49(1): 91-110.

This study tested the relationship between three, commonly-used vegetation indices (VIs), percent vegetation cover (% cover) and leaf area index (LAI) over a complex riparian landscape in the Colorado River delta, Mexico. Our objective was to correlate vegetation and soil features with VIs using low-level aerial photography, in preparation for scaling up to analysis of vegetation features using satellite imagery, We used a three-band digital imaging camera (Dycam) to collect data from an aircraft flying at 150 m. A series of 84 images (67 x 100 m) were analysed. Nine of these sites were ground-truthed; the species, % cover, and LAI were determined. Measured LAI (nine sites) from tree, shrub, and groundcover categories were used to determine a global (GLAI) value for 63 images. We conducted both VIs: % cover and VIs: GLAI regression analyses. The normalized difference vegetation index (NDVI) was the VI that best predicted % cover (r(2) = 0.837), but the soil adjusted vegetation index (SAVI) and enhanced vegetation index (EVI) gave nearly equal results (r(2) = 0.807 and 0.796, respectively). Normalized difference vegetation index, SAVI and EVI were less useful in predicting GLAI (r(2) = 0.73, 0.65, 0.64, respectively). Variability in GLAI was due mainly to differences in % cover among images rather than differences in LAI among vegetation types. We also measured reflectance values of the major plant types between 450 and 900 nm, and found small but significant (p < 0.05) differences among some of the species. The results support the conclusion that vegetation indices are most simply related to % vegetation cover, rather than species differences in LAI or VIs, even in this mixed riparian biome. There was also a near 1:1 correspondence between the Dycam and Thematic Mapper (TM) NDVI values over a wide range of landcover types (water, bare soil, partial and complete vegetation cover), which indicate that reflectance-based NDVI values can be scaled from low-level aerial Dycam images to satellite images for this ecosystem. (C) 2001 Academic Press.

Pitt, J. (2001). "Can we restore the Colorado River delta?" Journal of Arid Environments 49(1): 211-220.

The Colorado River delta in Mexico merits conservation due to the value of its habitat and wildlife resources. Colorado River water sustains the delta's current extent of 60,000 ha but the instream flow is not protected. Analysis of Colorado River water use by different sectors of the United States and Mexican economies demonstrates that agriculture uses most of the river's water but contributes only a small portion of the regional economy. Despite increasing consumptive demands on the river, it may be possible to purchase or dedicate water for the delta ecosystem if government commitments to ecosystem restoration and species preservation can be implemented. (C) 2001 Academic Press.

Postel, S. L., J. I. Morrison, et al. (1998). "Allocating fresh water to aquatic ecosystems: The case of the Colorado River delta." Water International 23(3): 119-125.

A major challenge for 21st-century water management is to satisfy growing human demands for water while protecting the aquatic ecosystems upon which regional economies and life itself depend. In arid regions with rapidly growing populations and economies, rite task can appear daunting. In this article, we attempt to demonstrate that the unique biological assets of the Colorado River delta-estuary, along with the potential economic benefits of a revitalized and protected delta ecosystem, justify efforts to determine and satisfy the water needs of this threatened aquatic environment. We discuss priorities for delta restoration and demonstrate how a met of policy and legal reforms, economic incentives, and efficiency investments could help generate water supplies to rejuvenate and maintain a healthier delta ecosystem.

Postel, S. L. (2000). "Entering an era of water scarcity: The challenges ahead." Ecological Applications 10(4): 941-948.

Fresh water is a renewable resource, but it is also finite. Around the world, there are now numerous signs that human water use exceeds sustainable levels. Groundwater depletion, low or nonexistent river flows, and worsening pollution levels are among the more obvious indicators of water stress. In many areas, extracting more water for human uses jeopardizes the health of vital aquatic ecosystems. Satisfying the increased demands for food, water, and material goods of a growing global population while at the same time protecting the ecological services provided by natural water ecosystems requires new approaches to using and managing fresh water. In this article, I propose a global effort (1) to ensure that freshwater ecosystems receive the quantity, quality, and timing of flows needed for them to perform their ecological functions and (2) to work toward a goal of doubling water productivity. Meeting these challenges will require policies that promote rather than discourage water efficiency, as well as new partnerships that cross disciplinary and professional boundaries.

Prowse, T. D. and V. Lalonde (1996). "Open-water and ice-jam flooding of a northern Delta." Nordic Hydrology 27(1-2): 85-100.

Flooding is critical to the ecosystem health of many river-delta environments, particularly to perched-ponds and lakes that are vertically separated from the open-water flow system. This is the case for the Peace-Athabasca Delta in northern Canada, one of the world's largest, freshwater deltas. Unfortunately, this delta has not experienced a major flood since 1974. As a result, significant drying has occurred in the higher-elevation portions of the Delta landscape. This has led to significant changes in, for example, the vegetation regime and the related small-mammal habitat. For almost two decades, popular belief was that drying of the Delta was due to a reduction in the size of open-water floods resulting from upstream flow regulation and/or changes in climate. Following a historically high flood in 1990, however, it was realized that open-water floods were relatively ineffective in flooding the perched bases. A historical analysis of hydrometric records revealed that the major peak-water levels have been produced at the time of break-up. The spring flow driving such events are more related to downstream tributary runoff than flow produced within the headwaters, above the point of regulation. Other ice factors, however, such as thickness, strength, and winter levels, may also have been important in controlling break-up severity.

Prowse, T. D., F. M. Conly, et al. (2002). "A review of hydroecological results of the Northern River Basins Study, Canada. Part 1. Peace and Slave rivers." River Research and Applications 18(5): 429-446.

During the early 1990s a multi-component research programme was initiated by the Northern River Basins Study (NRBS) in Canada to answer the question: How does and how could flow regulation affect the aquatic ecosystem? Research focused on the major headwaters of the Mackenzie River, the Peace and Slave rivers, which became regulated in 1968 by the W.A.C. Bennett Dam in the Rocky Mountains. The lack of knowledge about the hydroccology of large northern rivers as well as a paucity of data for this relatively isolated basin required that studies be undertaken to assess how flow regulation had modified the physical template of this system. Research focused on quantifying the regulation effects on the flow regime, ice conditions, fluvial geomorphology and riparian vegetation of the Peace and Slave rivers and the Slave River Delta. Results of the NRBS studies indicate that regulation of the Peace River has shifted the pattern of seasonal flows and damped flow extremes creating a less variable annual regime. Increased winter releases from the reservoir have virtually eliminated the formation of a complete winter ice cover for a significant distance below the dam and delayed ice-cover formation farther downstream. Higher ice levels that accompany increased winter flows are thought to affect the frequency and magnitude of ecologically important ice-induced floods that occur during the spring. Although more difficult to link solely to the effects of flow regulation, pronounced morphologic and vegetation changes have been observed along the Peace River, including channel narrowing via the abandonment of secondarylbackwater channels and in-channel shoaling along the lower reaches. Vegetation succession has been especially evident on abandoned bar surfaces. Morphological changes were also observed in the Slave River Delta, particularly along the ecologically sensitive outer margin of the delta. Copyright (C) 2002 Environment Canada. Published by John Wiley Sons, Ltd.

Reyes, E., M. L. White, et al. (2000). "Landscape modeling of coastal habitat change in the Mississippi delta." Ecology 81(8): 2331-2349.

A landscape model was developed to investigate and predict the environmental factors affecting wetland habitat change within the Barataria and Terrebonne basins of coastal Louisiana, USA. The model linked an overland-flooding hydrodynamic module, using cells of 100 km(2) in size and operating at a 1-h time step, and a spatially articulated ecosystem module, resolving habitat type and change for 1-km(2) cells in daily time steps. Integration across different temporal and spatial scales was accomplished with interpolation routines and averaging algorithms. Forcing functions included dominant regional processes, such as subsidence, sedimentation, and sea-level rise. Hydrologic functions were calibrated against existing climate and hydrologic time series, while habitat information was compared to maps prepared by the United States Fish and Wildlife Service (USFWS) for 1978 and 1988. Spatial calibration was done by initializing the landscape pattern of the model to a 1978 USFWS habitat map. After a 10-yr simulation, the results were compared against a 1988 USFWS habitat map. Simulated maps had an accuracy of 85-90 (out of a maximum of 100), based on a multiple resolution fit algorithm. For validation the model was initialized with a 1956 USFWS habitat map, and the results from a 32-yr simulation were compared to the 1988 USFWS habitat map. The landscape model produced reasonable regional agreement, despite the fact that small-scale processes and features were not included. The validation runs produced land-loss rates that matched historical trends with an accuracy fit above 75. The model simulated 30 years into the future, starting in 1988, testing for long-term climate variability under diverse scenarios. Results indicated that weather variability impacts land-loss rates more than replication of extreme weather years. Even when extreme dry and wet years were repeated, the model predicted lower land loss when compared to historical records. This is indicative of the ability of the simulated plant communities to adapt to repetitive climatic forcing functions.

Risnoveanu, G. and A. Vadineanu (2003). "Long term functional changes within the Oligochaeta communities within the Danube river delta, Romania." Hydrobiologia 506(1-3): 399-405.

Within the Danube River delta's lakes the Oligochaeta communities comprise between 7.9% and 36.2% of the total biomass of benthic fauna. Their importance in energy flow at the ecosystem level changed in relation to fast trophic transition of all shallow lakes to the hypertrophic state. The parameters of the energy budget of the dominant populations and the potential production of benthivorous fish species assessed during 1976-1994 interval support this conclusion. P/B ratio, K-1 and K-2 coefficients assessed for both the 1976-1980 and 1991-1994 intervals revealed different functional patterns of response of Potamothrix hammoniensis (Michaelsen, 1901) and Limnodrilus hoffmeisteri (Claparede, 1862) to varying trophic conditions. Changes in communities structure, size of the constituent populations and their age distribution, as well as the quantity and quality of food supply and level of hypoxia at the sediment/water interface were the main factors that affected the role of these populations as energy carrier from the huge energy pool represented by sedimented organic carbon to benthivorous fish species.

Ronnback, P., M. Troell, et al. (2003). "Mangrove dependence and socio-economic concerns in shrimp hatcheries of Andhra Pradesh, India." Environmental Conservation 30(4): 344-352.

There are many environmental and socio-economic concerns about the shrimp aquaculture industry. This study, based on interviews, direct observations and literature reviews, shows that the Indian hatchery industry is heavily dependent upon the continuous support of natural resources and ecosystem services generated by marine, freshwater and terrestrial ecosystems. The mangrove ecosystem support area ('ecological footprint') needed to supply the hatcheries with Penaeus monodon shrimp broodstock, and the aquaculture grow-out ponds with postlarvae, exemplify the dependence on external ecosystems. Each hectare of mangrove in the Godavari River delta generated an annual fisheries catch of 0.8-1.5 P. monodon spawners (gravid females), valued at US$ 92-184. The entire Godavari mangrove delta had a partial gross economic value of US$ 3.0-6.0 million per year for the provision of shrimp spawners alone. The average hatchery, producing 75 million postlarvae annually, had an ecological footprint of 534 ha mangrove for the life-support input of shrimp spawners. The ecological footprint of intensive shrimp ponds was up to 11 times the pond area for postlarval input alone. The shrimp ponds in the State of Andhra Pradesh needed 35000-138000 ha of mangroves to satisfy the spawner requirement to hatcheries, and this implied a need to appropriate mangroves in other regions. Hatcheries were prepared to pay up to US$ 2000 for a single shrimp spawner, which also illustrated that the mangrove support areas regionally available were too small. Other concerns about the industry are the net loss of employment if hatcheries replace wild postlarvae collection, the extensive use of groundwater creating direct resource-use conflicts, by-catch problems in broodstock fisheries, and pollution by effluents. The risk of hatcheries introducing, amplifying and propagating disease affecting both cultured organisms and wild biota is another concern that can, and should, be addressed.

Ruess, R. W., D. D. Uliassi, et al. (1997). "Growth responses of Carex ramenskii to defoliation, salinity, and nitrogen availability: Implications for geese-ecosystem dynamics in western Alaska." Ecoscience 4(2): 170-178.

The Yukon-Kuskokwim River Delta in western Alaska is the principal nesting area for several species of geese, including Pacific black brant. Grazing by geese on Carex ramenskii, one of the most abundant plant species throughout much of this region, appears to have increased in recent years. The purpose of this study was (i) to evaluate the effects of early-season defoliation and fertilization on plant growth and nutrient cycling processes within field plots of C. ramenskii over a 3-year period, and (ii) to study the interactive effects of defoliation, N availability, and salinity stress on growth, and biomass and N allocation in C. ramenskii under controlled, greenhouse conditions. Relative to control plots, clipped-fertilized plots showed significant increases in aboveground net primary production (AGNPP) and leaf N concentration, resulting in significant increases in offtake biomass and offtake N during both 1991 and 1992. In the greenhouse, total production of clipped and unclipped plants did not differ, but clipped plants had significantly higher offtake biomass, and biomass and N allocation to offtake compared to unclipped plants. Both field and laboratory experiments found that rapid regrowth following defoliation was dependent on soil nutrient availability. Fertilization increased soil respiration rates each year, but tended to decrease rates of net N mineralization, indicating that the soil microbial biomass is a strong nutrient sink in this ecosystem. In addition to the direct positive effects that goose feces have on plant growth, nitrogen recycled through feces may be an important source of nitrogen contributing to salinity tolerance in C. ramenskii. Our results also suggest that the observed increase in grazing pressure on patches of C. ramenskii early in the growing season may increase forage quality and quantity within these swards, and have important implications for geese-ecosystem interactions at a time of rapid goose population increase.

Sanchez-Cabeza, J. A., P. Masque, et al. (1999). "Pb-210 atmospheric flux and growth rates of a microbial mat from the northwestern Mediterranean Sea (Ebro River Delta)." Environmental Science & Technology 33(21): 3711-3715.

Environmental archives are needed to study the variability of natural systems and the impact of man on them. Microbial mats, modern homologues of stromatolites, can be found in extreme environments such as the Ebro River Delta and were studied as potential environmental archives of atmospheric deposition. Pb-210, a radiotracer widely used in geochronology studies, was used both to determine the growth rates of a microbial mat from this environment and to estimate the Pb-210 atmospheric flux in the northwestern Mediterranean Sea. The Pb-210 profile showed the presence of three distinct peaks related to low growth-rate periods. This variability indicated the sensitivity of the system to external forcing. The annual atmospheric flux of Pb-210 was 81.2 +/- 1.4 Bq m(-2) yr(-1), which is similar to other Values found in the literature. The age profile showed two layers of differing growth rates, being 0.99 +/- 0.10 mm yr(-1) from the surface down to 10 mm depth. The accumulated mass profile showed a change at about 9 mm depth, corresponding to year 1983 +/- 1. It is noteworthy that this is coincident with a strong El Nino Southern Oscillation event during 1982-1983, which has been shown to affect other ecosystems, including some in the Mediterranean area.

Schone, B. R., K. W. Flessa, et al. (2003). "Upstream dams and downstream clams: growth rates of bivalve mollusks unveil impact of river management on estuarine ecosystems (Colorado River Delta, Mexico)." Estuarine Coastal and Shelf Science 58(4): 715-726.

We studied how the extensive diversion of Colorado River water, induced by dams and agricultural activities of the last 70 years, affected the growth rates of two abundant bivalve mollusk species (Chione cortezi and Chione fluctifraga) in the northern Gulf of California. Shells alive on the delta today ('Post-dam' shells) grow 5.8-27.9% faster than shells alive prior to the construction of dams ('Pre-dam' shells). This increase in annual shell production is linked to the currently sharply reduced freshwater influx to the Colorado River estuary. Before the upstream river management, lower salinity retarded growth rates in these bivalves. Intra-annual growth rates were 50% lower during spring and early summer, when river flow was at its maximum. Growth rates in Chione today are largely controlled by temperature and nutrients; prior to the construction of dams and the diversion of the Colorado River flow, seasonal changes in salinity played an important role in regulating calcification rates. Our study employs sclerochronological (growth increment analysis) and geochemical techniques to assess the impact of reduced freshwater influx on bivalve growth rates in the Colorado River estuary. A combination of both techniques provides an excellent tool to evaluate the impact of river management in areas where no pre-impact studies were made. (C) 2003 Elsevier Ltd. All rights reserved.

Sobczak, W. V., J. E. Cloern, et al. (2002). "Bioavailability of organic matter in a highly disturbed estuary: The role of detrital and algal resources." Proceedings of the National Academy of Sciences of the United States of America 99(12): 8101-8105.

The importance of algal and detrital food supplies to the planktonic food web of a highly disturbed, estuarine ecosystem was evaluated in response to declining zooplankton and fish populations. We assessed organic matter bioavailability among a diversity of habitats and hydrologic inputs over 2 years in San Francisco Estuary's Sacramento-San Joaquin River Delta. Results show that bioavailable dissolved organic carbon from external riverine sources supports a large component of ecosystem metabolism. However, bioavailable particulate organic carbon derived primarily from internal phytoplankton production is the dominant food supply to the planktonic food web. The relative importance of phytoplankton as a food source is surprising because phytoplankton production is a small component of the ecosystem's organic-matter mass balance. Our results indicate that management plans aimed at modifying the supply of organic matter to riverine, estuarine, and coastal food webs need to incorporate the potentially wide nutritional range represented by different organic matter sources.

Sorokin, Y. I., P. Y. Sorokin, et al. (1999). "Analysis of lagoonal ecosystems in the Po River delta associated with intensive aquaculture." Estuarine Coastal and Shelf Science 48(3): 325-341.

Observations on structure and functioning of coastal lagoon ecosystems experiencing a high level of eutrophication impact were accomplished in three lagoons of Ca'Pisani integrated within an experimental aquaculture enterprise variously fertilized by waste effluents discharged from and intensive fish culture plant. During August and early September an extremely dense bloom of dinoflagellate Alexandrium tamarense was recorded in these lagoons with the density of phytoplankton up to 190 g m(-3) of wet biomass, and primary production 2 to 6 mg Cl-1 day(-1). The diel dissolved oxygen fluctuations in water column during the bloom reached 15-20 mg O-2 l(-1). The wet biomass of bacterioplankton in the lagoons attained 5-9 g m(-3). The microzooplankton was dominated by ciliates with biomass 1 to 19 g m(-3). The daytime mesozooplankton was dominated by calanoid copepods with a biomass 0.05-0.25 g m(-3), while the biomass of the demersal zooplankton at night attained 2 to 14 gm(-3). In the lagoon of Ocaro, the phototrophic plankton was dominated by the symbiotic ciliate Mesodinium. The labile sulphides content in the upper layer of the bottom attained over 190 g dm(-3) of wet silt. The rate of microbial sulphate reduction was 5-10 mg S dm(-3) day(-1). The data are generalized within the energy balance in these specific anthropogenically transformed pelagic communities. (C) 1999 Academic Press.

Stromberg, J. C. (2001). "Restoration of riparian vegetation in the south-western United States: importance of flow regimes and fluvial dynamism." Journal of Arid Environments 49(1): 17-34.

Riparian ecosystems in the south-western United States have undergone extensive physical and biological changes, due, in part, to alteration of natural flow regimes and suppression of fluvial processes. Many riparian ecosystem restoration projects are achieving success because they recognize the importance of restoring the hydrologic regime. In other words, these projects are restoring flows of water and sediment in sufficient quantities and with appropriate temporal and spatial patterns. Other projects have proceeded without recognition of the need to incorporate environmental stream flow requirements into management plans. To increase success rate of riparian ecosystem restoration, this paper describes some changes that have occurred within riparian ecosystems of the southwestern United States, reviews the role of stream flow regimes in structuring riparian plant communities, and assesses various ways in which riparian plant communities can be restored by naturalizing ecological processes. (C) 2001 Academic Press.

Timchenko, V., O. Oksiyuk, et al. (2000). "A model for ecosystem state and water quality management in the Dnieper River delta." Ecological Engineering 16(1): 119-125.

An ecologically sound management methodology for maintaining ecosystem state and water quality in regulated rivers downstream of hydropower stations is presented. The main components of this methodology are applied to the Dnieper River mouth zone as an example. The relationship between production-destruction (respiration) balance and releases through the Kakhovka hydropower dam has been determined for the channel network, floodplain lakes, the floodplain proper, and the Dnieper River mouth zone combined. Production-destruction processes are predicted as the change in organic matter content, as measured by BODtot. We have developed calculation methods for ecosystem functioning and water quality management in the Dnieper River mouth zone channel network as a result of releases through the Kakhovka dam. The concept of ecosystem, ecological and extremal (target) releases and sanitary addition to ecosystem release for liquidation of anthropogenic pollution was formulated and the volumes of all these releases for the Dnieper River mouth zone were estimated. This methodology and calculation methods can be used for ecosystem state and water quality management in regulated rivers. (C) 2000 Elsevier Science B.V. All rights reserved.

Turner, R. E., N. Qureshi, et al. (1998). "Fluctuating silicate  :  nitrate ratios and coastal plankton food webs." Proceedings of the National Academy of Sciences of the United States of America 95(22): 13048-13051.

Marine diatoms require dissolved silicate to form an external shell. and their growth becomes Si-limited when the atomic ratio of silicate to dissolved inorganic nitrogen (SI:DIN) approaches 1:1, also known as the "Redfield ratio." Fundamental changes in the diatom-to-zooplankton-to-higher trophic level food web should occur when this ratio falls below 1:1. and the proportion of diatoms in the phytoplankton community is reduced. We quantitatively substantiate these predictions by using a variety of data from the Mississippi River continental shelf, a system in which the SI:DIN loading ratio has declined from around 3:1 to 1:1 during this century because of land-use practices in the watershed, We suggest that, on this shelf, when the Si:DIN ratio in the river decreases to less than 1:1, then (i) copepod abundance changes from >75% to <30% of the total mesozooplankton, (ii) zooplankton fecal pellets become a minor component of the in situ primary production consumed, and (iii) bottom-water oxygen consumption rates become less dependent on relatively fast-sinking (diatom-rich) organic matter packaged mostly as zooplankton fecal pellets. This coastal ecosystem appears to be a pelagic food web dynamically poised to be either a food web composed of diatoms and copepods or one with potentially disruptive harmful algal blooms. The system is directed between these two ecosystem states by Mississippi River water quality, which is determined by land-use practices far inland.

Weng, Q. H. and S. H. Yang (2003). "An approach to evaluation of sustainability for Guangzhou's urban ecosystem." International Journal of Sustainable Development and World Ecology 10(1): 69-81.

Guangzhou has ambitions to build itself into a world class metropolis by 2010. Sustainable development is the only way to achieve this magnificent goal. Based on the ecological perspective of sustainable development and the principles of ecosystem integrity, this paper develops an approach for evaluation of sustainable development in Guangzhou between 1986 and 1995. A hierarchical evaluation system of four tiers of sustainability indicators was established. Using the method of fuzzy multistage synthetic evaluation, sustainability development level index, QIx, was calculated for the indicators at the B, C, D, and E tiers. Development stages were identified based on these index values. The coordination degree among the economic, social, and natural subsystems was also computed. Further, an overall sustainability index for each year was computed by combining the development level index and the coordination degree. It was found that the urban ecosystem in Guangzhou had generally become more sustainable, in spite of fluctuations in coordination degree. The development level index of the economic subsystem has surpassed that of social and natural subsystems since 1995. Appropriate measures must be taken to ensure coordinated development among the subsystems for the purpose of sustainable development.

Wilson, R., S. Allengil, et al. (1995). "Organochlorine Contaminants in Fish from an Arctic Lake in Alaska, USA." Science of the Total Environment 161: 511-519.

A wide range of organochlorine pesticides and polychlorinated biphenyls (PCBs) were measured in muscle tissue and livers of lake trout (Salvelinus namaycush) and Arctic grayling (Thymallus arcticus) from Schrader Lake in Arctic Alaska. Results confirm the long-range transport of these contaminants to a US Arctic freshwater system. The most abundant group of compounds in all tissues was composed of PCBs. Mean concentrations of the sum of a selected group of PCB congeners ranged from 3.2 ng/g in grayling liver to 22.8 ng/g in trout liver and from 1.3 ng/g in grayling muscle to 6.6 ng/g in trout muscle (wet wt.). The second most abundant group was composed of chlordane-related compounds. No significant correlations of organochlorine concentrations with fish weight or length were observed for the data set as a whole. There were marked differences in Sigma PCB, Sigma chlordane and p,p'-DDE concentrations between species. The biomagnification factors for these compounds are similar to ratios reported for other aquatic systems. Comparisons showed that contaminant concentrations in lake trout from Schrader Lake were similar to levels found in burbot and slightly higher than levels in whitefish reported in Canadian studies from the Mackenzie River Delta.

Xu, X. G., H. P. Lin, et al. (2004). "Probe into the method of regional ecological risk assessment - a case study of wetland in the Yellow River Delta in China." Journal of Environmental Management 70(3): 253-262.

Ecological risk assessment (ERA) is a new field of study for evaluating the risks associated with a possible eco-environmental hazard under uncertainty. Regional ERA is more complex than general ERA, as it requires that risk receptors, risk sources, risk exposure, uncertainty and especially spatial heterogeneity all be taken into account. In this paper, a five-step process of regional ERA is developed and tested through a wetland case study in the Yellow River Delta in China. First, indices and formulas are established for measuring degrees of ecological risk and damage to ecosystems. Using a combination of remote sensing data, historical records and survey data, and with the assistance of GIS techniques, the indices and formulas are then applied to the wetland in the study area. On the basis of the assessment results, we propose a number of countermeasures for the various risk zones in the Yellow River Delta. (C) 2003 Elsevier Ltd. All rights reserved.

Yue, T. X., J. Y. Liu, et al. (2003). "Landscape change detection of the newly created wetland in Yellow River Delta." Ecological Modelling 164(1): 21-31.

Four models are employed in the landscape change detection of the newly created wetland. The models include ones for patch connectivity. ecological diversity, human impact intensity and mean center of land cover. The landscape data of the newly created wetland in Yellow River Delta in 1984, 1991, and 1996 are produced from the unsupervised classification and the supervised classification on the basis of integrating Landsat TM images of the newly created wetland in the four seasons of the each year. The result from operating the models into the data shows that the newly created wetland landscape in Yellow River Delta had a great chance. The driving focus of the change are mainly from natural evolution of the newly created wetland and rapid population growth, especially non-peasant population growth in Yellow River Delta because a considerable amount of oil and gas fields have been found in the Yellow River Delta. For preventing the newly created wetland from more destruction and conserving benign Succession of the ecosystems in the newly created wetland, six measures are suggested on the basis of research results. (C) 2003 Elsevier Science B.V. All rights reserved.

Zalidis, G. (1998). "Management of river water for irrigation to mitigate soil salinization on a coastal wetland." Journal of Environmental Management 54(2): 161-167.

The change in water chemistry in the Aries River delta wetland is due to the interruption of river discharge in this area during the irrigation period. The impact, which Visibly affects the wetland's flora, was verified by measuring water salinity in the delta area during the peak irrigation period. Given that additional water supplies are not available, the only way to remedy this problem is to use the available irrigation water wisely. Most irrigation wafer losses are attributed to the fact that the constant water delivery rate does not respond to water demand of the irrigation networks. To cope with this problem, a water resources management system, based on the assessment of wafer requirements, was developed. The system can schedule water supply to the irrigation networks, thus saving enough water to maintain discharges at the delta and to keep water salinity within to acceptable levels. The water resource management system, which was based on fully distributed real time inputs (climate data), was developed using a Geographic information System (GIS). This system adjusts network irrigation supply through a feedback mechanism. This mechanism responds to the changes that might occur in the exogenous system inputs: effective rainfall (R-e) and actual evapotranspiration (ETr), and to the difference between the system's target and calculated e(p) values. In this way irrigation water is used efficiently, thus minimizing the degradation of natural resources. Using the proposed method if was found possible to remedy the environmental impact of agriculture by saving enough fresh wafer to maintain the biotic and abiotic parameters of the natural ecosystem. (C) 1998 Academic Press.

Zanella, L., C. Tessarin, et al. (2000). "Seasonal fluctuations of the organic load of sediments in two ponds of a brackish-water fish farm ("valle") located in the Po River Delta (Italian North Adriatic)." Ophelia 53(2): 79-90.

Seasonal fluctuations of sedimentary Total Organic Carbon (TOC) and Total Kjeldahl Nitrogen (TKN) were investigated in two earthen ponds of a brackishwater extensive fish farm. One was subjected to periodic sediment "ploughing" (hydrocultivation), a practice performed by fishfarmers to oxidise sediments and fertilise the water column. Nutrients and chlorophyll-a were monitored for controlling the impact of hydrocultivation on water overlying treated sediments. The considered variables revealed a dystrophic event occurring in summer, when a dense biomass of macroalgae (7-10 kg m(-2)) died because of a rise in temperature (30 degreesC and over). From July to August a large amount of labile organic matter settled to sediments increasing TOC and TKN from 600 gC m(-2) and 38.5 gN m(-2) to 1500-1800 gC m(-2) and 50-68 gN m(-2), respectively. A phytoplankton bloom occurred, increasing living organic matter in the water column, as pointed out by high values of total-N, total-P and chlorophyll-a. Low levels of dissolved oxygen recorded in August attest to the danger represented by high macroalgae biomasses for the considered ecosystem, mainly because of the high oxygen demand induced by rapid decomposition of macroalgae tissues. In mid-October TOC dropped to 870-890 gC m(-2), and TKN to 42-43 gN m-2. In the two ponds no important difference in variable trends has been pointed out, despite the periodic "ploughing" interventions, probably because hydrocultivation cannot affect dystrophic environments dth such a heavy organic matter recycle.