Aquatic Ecosystem

Studies of cyanobacterial nostocacean taxa are important to the global scientific community, mainly because a significant number of beneficial strains that belong to the order Nostocales fix atmospheric nitrogen, thus contributing to the fertility of agricultural soils worldwide, while others behave as nuisance microorganisms in aquatic ecosystems due to their involvement in toxic bloom events. However, in spite of their ecological importance and environmental concerns, their identification and taxonomy are still problematic and doubtful, often being based on current morphological and physiological studies, which generate confusing classification systems and usually vary under different conditions. Therefore, the present research aimed to investigate through a polyphasic approach differences in morphological, biochemical and genotypic features of three nostocacean cyanobacterial strains isolated from central-western Portuguese shallow freshwater bodies. Morphometric, genetic (16S rRNA, nifH and hetR fragments) and biochemical (fatty acid methyl ester; FAME profiles) data were used to characterize the strains. Morphological analysis and sequencing of 16S rRNA fragments showed that the strains belonged to Anabaena cylindrica (UTAD_A212), Aphanizomenon gracile (UADFA16) and Nostoc muscorum (UTAD_N213) species. These strains showed clear distinct morphological and genetic features, allowing easy allocation to their respective genera. The same happened by using partial sequences of hetR and nifH genes, in spite of the scarcity of deposited sequences. Biochemical characterization showed that the FAME profiles obtained were consistent with both morphological and molecular analyses. It was suggested that the ratio of monounsaturated to polyunsaturated FAMEs, together with the unsaturation index, could be used as genus-specific chemotaxonomic biomarkers.

In order to assess the condition of heavy metal pollution in the Yellow River, Lanzhou section, China, and to quantify heavy metal (copper, lead, zinc, and cadmium) contents in tissues (liver, kidney, gills, and muscles) of two fish species (Triplophysa pappenheimi and Gobio hwanghensis), levels of these four metals in the water body, sediment, and tissues of the two fish were measured using inductively coupled plasmaatomic emission spectrometry. The metal levels from this study were compared with the threshold values in the guidelines of water, sediment, and food given by the National Environmental Protection Agency of China, the National Oceanic and Atmospheric Administration of America, and the National Standards Management Department of China. We found the mean concentrations of Cu, Pb, Zn, and Cd in THE water body, sediment, and muscles of two fish species were far below the values in guidelines. We also found that the type of metals present and their concentrations varied in different tissues and species. The results suggested that (1) Cu, Pb, Zn, and Cd did not contaminate the aquatic ecosystem severely and did not threaten the safety of human consumption in the Yellow River, Lanzhou section, and (2) organs that are sensitive to accumulating heavy metals may be useful to develop bioindicators for monitoring metal contamination. Considering environmental variables, further study is necessary before deciding which fish species or tissue could be the ideal bioindicators for aquatic pollution.

The Tonle Sap Lake and floodplains in the heart of Cambodia contain the largest continuous areas of natural wetlands habitats remaining in the Mekong system, while being the largest permanent freshwater body in Southeast Asia. Tonle Sap is a crucially important source for food and living in Cambodia. More than one million people live in the immediate surroundings of the Tonle Sap Lake and wetlands, being the poorest ones in Cambodia, and highly dependent on agriculture and fisheries. An important phosphorus source of the mainly phosphorus limited aquatic ecosystem is the sediment carried by the flood. Mekong Upstream developments, like construction of dams may lead, and has already led, to significant trapping of sediments and nutrients. This would dramatically reduce the productivity of the Tonle Sap system. The 3D mathematical model has been set up for Tonle Sap Lake for simulating water levels and currents, inundation of the floodplain, suspended sediment transport and sedimentation, dissolved oxygen as well as nutrients and algal growth (chlorophyll-a) to understand the ecosystem processes and the possible changes in it due to the upstream development.

Treated sewage effluent is one of the most common types of pollution found in urban rivers. Both the quality and quantity of effluent result in various impacts on the receiving freshwater as well as marine environment. This paper outlines these impacts from an ecological, social and economic perspective, and provides some suggestions on the way forward with regards prioritising wastewater

Alligatorweed, (Alternanthera philoxeroides (Mart.) Griseb.), an aquatic and wetland plant native to South America, is an aggressive weed in many parts of the world. Its ability to compete with other native plants and to impede waterways has made it a serious threat to aquatic ecosystems. Although biological control with insects has been fairly successful in aquatic habitats, there is a need for additional agents to manage the weed in upland sites. Accordingly, in a survey in Brazil in 1997 a fungus, Nimbya (=Alternaria) alternantherae (Holcomb and Antonopoulus) Simmons and Alcorn, was discovered and confirmed to be highly damaging to alligatorweed. Studies were conducted to determine the potential of this fungus for controlling this weed. Several isolates from Brazil, USA, and Puerto Rico were compared and no differences in virulence were observed, although a lower dew requirement was demonstrated for the Brazilian isolates. Conidia were more effective than mycelial suspension, and inoculum concentrations of 1 • 10 5 and 1 • 10 6 conidia per ml provided significant levels of control of the weed in greenhouse and field experiments, respectively. In a host-range study, N. alternantherae infected 6 plant species from a total of 42 species belonging to 23 families. N. alternantherae has the potential to be an effective mycoherbicide for alligatorweed.

Spatio-temporal variations in the water quality of the Chao Phraya River, Thailand, were examined, on average-yearly basis, between 1999 and 2008, from 32 surface water stations from the river origin to the delta. Five water quality parameters viz., DO, BOD, TCB, FCB, NH3-N and water temperature were used in the analysis. Analysis was performed by using the Self Organizing Maps. Four distinct spatially approached clusters were classified, according to the similarity of water quality parameters, while temporal variations of most of the surface water stations were not obviously observed. The worst water quality condition was at the stations near the river delta and highly related to anthropogenic stresses. Result from the correspondence analysis showed that, except for the cluster of the worst water quality, the stations of the remaining three clusters were overlapped. There was no statistical difference in water temperature among clusters but the expected effects from climate change should be a precautionary focus since the will eventually affect the water quality.

This paper sets out a conceptual framework for modelling events in aquatic ecosystems as coupled processes in catchments, water columns and sediments. This theoretical framework is developed using ideas from the behaviour of complex adaptive systems. I show that it is possible to use similar models for each subsystem and that there are analogous processes in each, differing only in scale. In this framework the phytoplankton appear as 'system canaries'. Nuisance algal blooms appear as a result of perturbations to the system biogeochemistry at a range of scales. Macrophytes are identified as important components of the coupled catchment, water, sediment system.

Numerous studies have indicated that aquatic pollution affects parasite populations and communities. However, the responses of individual taxa and functional groups to specific contaminants, and their effect sizes, have yet to be assessed quantitatively. We began by summarizing general trends in the literature, and found that reports of significant changes in parasitism were most commonly observed in response to eutrophication and metal contamination. Among parasite taxa, significant changes were most commonly reported for acanthocephalans, digeneans and microparasites. We then conducted a quantitative metaanalysis of the effects of pollution on parasitism in aquatic animals. We calculated signed standardized effect sizes (as Cohen's d) for all published studies that provided the necessary descriptive statistics, and compared them among major contaminant types (pesticides, hydrocarbons, polychlorinated biphenyls, pulp mill effluent, metals, sewage, eutrophication, and acidification) and parasite taxa (Acanthocephala, Cestoda, Digenea, Monogenea, Nematoda and microparasites). Effect sizes were not significantly different from zero for many parasite/contaminant interactions, and tended to be highly variable within individual taxa. However, consistently strong, significant negative effects were noted in Digenea and Monogenea, especially in response to metal pollution. Significant effect sizes were typically negative, indicating that pollutants have negative effects on parasite populations. Contaminants also had a slightly negative effect on community richness. When parasites were grouped into heteroxenous (with >1 obligatory host in life cycle) vs. monoxenous (1 obligatory host in life cycle) taxa, the latter were more susceptible to a wide range of pollutants. Similarly, directly exposed (external parasites and the free-living transmission stages of internal parasites) and freshwater taxa were more susceptible to a wider range of pollutants than indirectly exposed (internal parasites) and marine taxa. This meta-analysis represented a first attempt to consider the size of the effect of pollution on parasites, and highlighted the potential of susceptible parasite taxa, communities, and functional groups for use in the biological assessment of pollution. For instance, our results indicate that freshwater monogeneans and digeneans are good candidates as potential biological indicators of pollution in aquatic ecosystems.

A number of authors have demonstrated that heavy metal concentrations in intestinal Helminths are higher than those found in the tissues of their final hosts. In this work, Pb and Cr concentrations in the Acanthocephalan Acanthocephalus anguillae were measured by means of electrothermal atomic absorption spectrometry. The metal concentrations measured in the whole body of Acanthocephalans were compared to those in the liver of their fish hosts (LeuciscTts cephalus) sampled in the Lambro river (Northern Italy). The results show higher concentrations of Pb and Cr in the parasites, respectively-200 times and-60 times higher than that of the host liver. These results corroborate the usefulness of parasites in the monitoring of biologically available metal concentrations in aquatic ecosystems that are non severely polluted.

ÐA study was conducted to evaluate the distribution of bioresmethrin, cypermethrin, deltamethin, permethrin, fenvalerate and Nurelle DX 550 EC (cypermethrin and chlorpyriphos) in an aquatic ecosystem model. The investigations were carried out at a temperature of 15±198C in two dierent concentrations of each of the tested toxic substances in two parallel series. Cumulative eects and the in¯uence of adaptation capabilities of micro¯ora on their distribution were also studied. The degradation processes developed in accordance with the ®rst kinetic order and depended on a group of determined compounds and initial concentrations. The pyrethroid half-live times at a temperature of 15± 198C fell within the range of 0.5±30.8 days. Chlorpyriphos, a component of Nurelle D 550EC, decomposed faster than most pyrethroids, its relevant half-live times were 5.0±7.1 days. In the case of sediments and organisms of the ecosystem, no accumulation eect of the pyrethroids was observed. However, a negative in¯uence on the aquatic biocenosis was noted.

The 1988 Yellowstone fires were among the first in what has proven to be an upsurge in large severe fires in the western USA during the past 20 years. At the time of the fires, little was known about the impacts of such a large severe disturbance because scientists had had few previous opportunities to study such an event. Ecologists predicted shortand long-term effects of the 1988 fires on vegetation, biogeochemistry, primary productivity, wildlife, and aquatic ecosystems based on scientific understanding of the time. Twenty-plus years of subsequent study allow these early predictions to be evaluated. Most of the original predictions were at least partially supported, but some predictions were refuted, others nuanced, and a few postfire phenomena were entirely unexpected. Post-1988 Yellowstone studies catalyzed advances in ecology focused on the importance of spatial and temporal heterogeneity, contingent influences, and multiple interacting drivers. Post-1988 research in Yellowstone also has changed public perceptions of fire as an ecological process and attitudes towards fire management. Looking ahead to projected climate change and more frequent large fires, the welldocumented ecological responses to the 1988 Yellowstone fires provide a foundation for detecting and evaluating potential changes in fire regimes of temperate mountainous regions.

This paper introduces a new approach for setting streamflow-based river ecosystem management targets and this method is called the 'Range of Variability Approach' (RVA). The proposed approach derives from aquatic ecology theory concerning the critical role of hydrological variability, and associated characteristics of timing, frequency, duration, and rates of change, in sustaining aquatic ecosystems. The method is intended for application on rivers wherein the conservation of native aquatic biodiversity and protection of natural ecosystem functions are primary river management objectives. 2. The RVA uses as its starting point either measured or synthesized daily streamflow values from a period during which human perturbations to the hydrological regime were negligible. This streamflow record is then characterized using thirty-two different hydrological parameters, using methods defined in Richter et al. (1996). Using the RVA, a range of variation in each of the thirty-two parameters, e.g. the values at Ϯ 1 standard deviation from the mean or the twenty-fifth to seventy-fifth percentile range, are selected as initial flow management targets. 3. The RVA targets are intended to guide the design of river management strategies (e.g. reservoir operations rules, catchment restoration) that will lead to attainment of these targets on an annual basis. The RVA will enable river managers to define and adopt readily interim management targets before conclusive, long-term ecosystem research results are available. The RVA targets and management strategies should be adaptively refined as suggested by research results and as needed to sustain native aquatic ecosystem biodiversity and integrity.

1. Viruses have become widely recognized as the most abundant biological entities and important players in aquatic environments, and this realization has profoundly changed our conceptual understanding of the functioning and regulation of aquatic ecosystems in the last two decades. However, most of this research has focussed on marine viruses, especially in pelagic environments. 2. Here we introduce a special issue of Freshwater Biology dealing with viruses in freshwater ecosystems. It represents the first attempt to summarize progress in freshwater viral ecology made by diverse research groups and to direct attention of viral ecologists towards fresh waters. 3. Six review-type articles and ten original research papers cover a wide range of aspects of freshwater viral ecology. This includes reports on the distribution of freshwater viral communities in contrasting habitats (e.g. sediments, wetlands, littoral zone, open waters), on different roles of viruses in freshwater ecosystems (e.g. mortality rates of bacteria and phytoplankton, transduction, influence on bacterial diversity and organic matter), and on different types of viruses (bacteriophages, cyanophages, algal viruses, and a fishpathogenic virus). 4. Collectively the series of papers presented in this special issue indicates that freshwater environments cover great habitat diversity and that the significance of some of the mechanisms controlling viral dynamics and impacts may differ between freshwater and marine habitats.

The Great Plains landscape is less topographically complex than most other regions within North America, but diverse aquatic ecosystems, such as playas, pothole lakes, ox-bow lakes, springs, groundwater aquifers, intermittent and ephemeral streams, as well as large rivers and wetlands, are highly dynamic and responsive to extreme climatic uctuations. We review the evidence for climatic change that demonstrates the historical importance of extremes in north±south dierences in summer temperatures and east±west dierences in aridity across four large subregions. These physical driving forces alter density strati®cation, deoxygenation, decomposition and salinity. Biotic community composition and associated ecosystem processes of productivity and nutrient cycling respond rapidly to these climatically driven dynamics. Ecosystem processes also respond to cultural eects such as dams and diversions of water for irrigation, waste dilution and urban demands for drinking water and industrial uses. Distinguishing climatic from cultural eects in future models of aquatic ecosystem functioning will require more re®nement in both climatic and economic forecasting. There is a need, for example, to predict how long-term climatic forecasts (based on both ENSO and global warming simulations) relate to the permanence and productivity of shallow water ecosystems. Aquatic ecologists, hydrologists, climatologists and geographers have much to discuss regarding the synthesis of available data and the design of future interdisciplinary research.

Previous studies have provided prima facie evidence that runoff from the MI motorway, UK, affects both the quality of the receiving water and the biota living there, in sites short distances from point sources-i.e., possible worst-case situations. Because discharges contain a wide variety of contaminants, both the identification of toxicants and the establishment of causal relationships between observed changes in waterhediment quality and biology are often difficult. In this particular case, the problem was addressed by conducting a series of toxicity tests using the benthic amphipod Gummnruspulex. The abundance of this species was greatly reduced downstream of the point where motorway runoff entered the stream. Stream water contaminated with motorway runoff was not toxic to G. pulex. However, exposure to contaminated sediments resulted in a slight reduction in survival over 14 d, and sediment manipulation experiments identified hydrocarbons, copper, and zinc as potential toxicants. Spiking experiments confirmed the importance of hydrocarbons, and fractionation studies indicated that most of the observed toxicity was due to the fraction containing polycyclic aromatic hydrocarbons. Animals exposed to contaminated sediments and water spiked with sediment extract accumulated aromatic hydrocarbons in direct proportion to exposure concentrations.

Elevated ultraviolet irradiance (UVR, 280-400 nm) damages DNA and induces reorganisation within biological communities at the Earth's surface. Southern high latitude aquatic ecosystems may be particularly susceptible because of low stratospheric ozone levels and extremely low contents of photoprotective dissolved organic matter (DOM). Surveys of shallow lakes and ponds in eastern Antarctica show that cyanobacteria survive elevated UVR exposure by increasing extra-cellular concentrations of photoprotective compounds, which are preserved in sediments together with photosynthetic pigments. Thus, reconstruction of long-term changes in biological UVR receipt, to provide a context for evaluating the long-term significance of recent changes in ozone column depth, is feasible in Antarctic settings. The sediment in Lake Reid (698 23V S, 768 53V E), Antarctica, spans the late-Pleistocene and contains UVR-absorbing pigments from benthic cyanobacteria. Here we show that mean exposure of these benthic cyanobacteria to UVR during the last glacial was more than three times higher than during the Holocene, likely due to short periods of photosynthetic activity coinciding with relatively high UVR fluxes, or due to increased UVR transmission to the Earth's surface resulting from changes in external factors such as stratospheric ozone levels, cloud cover and surface albedo. D

There is concern about environmental impacts of cropping in catchments of Australia's Great Barrier Reef, especially losses of nitrogen (N) from cropping systems. Sugarcane production in the Burdekin region in the dry tropics stands out from other crops/regions because it is grown with the highest applications of irrigation water and N fertiliser rates of any sugarcane producing region in Australia, attributes which may enhance losses of N. Little is known about N losses from sugarcane production systems, especially irrigated systems. We measured parts of the water and N balance over three sugarcane crops at three contrasting sites in different parts of the Burdekin region, covering a range of soil types/textures and irrigation managements. The experimental data were used to parameterise the APSIM-Sugarcane cropping systems model, and the model then used to 'infill' missing data and develop more complete water and N balances for each of the crops at the three sites. The model was also used to simulate long-term yields and N losses through runoff and leaching below the root zone at the sites under a range of N fertiliser and irrigation management practices. Unlike the experience in other cropping systems, N losses through runoff and leaching below the root zone were not higher at our sites than measured in rainfed sugarcane production systems. The long-term simulations showed there were clear opportunities for reducing N losses while maintaining yields through reducing N fertiliser application rates. Simulations results suggested that long-term N surpluses of 50 kg ha −1 yr −1 , considerably less than those during the experiment or common in the study region, were sufficient to maintain yields but reduce N losses by 50-57%. So, N fertiliser management should aim to keep surpluses to that level. Improved irrigation management could also help reduce N losses but generally to a much lesser extent than reduced N fertiliser applications. Research is required to confirm these predicted benefits, and investigate potential interaction between N fertiliser and irrigation management practices, and impacts of other management practices.

Changes in lake water temperature and trophic states were inferred using chironomid fossil assemblages from Lac Long Inférieur (Southern Alps, France). In the Late Glacial, a colder period, possibly analogous to the Younger Dryas, is characterised by a peak in Micropsectra, a cold stenothermic taxon. The increase in temperatures during the Late Glacial interstadial is indicated by a decrease in the percentages of cold stenothermic taxa (Tanytarsus lugens/Corynocera oliveri grp.) and by an increase in taxa linked to the development of vegetation in the littoral zone. The beginning of the Holocene is marked by the presence of taxa adapted to warmer and more eutrophic waters. During the Holocene, the progressive warming of the climate and increase in lake trophic status were indicated by the increase of eutrophic and warmer water indicators. An increase in tributary inflow into Lac Long Inférieur was also inferred by the increase in rheophilous taxa, reflecting increased snowmelt. During the Subatlantic, the composition of the chironomid spectra suggests a re-cooling of the climate and/or a decrease in lake trophic status.

Nitrogen (N) inputs to the world's aquatic ecosystems have increased over the past 100 years. Riparian zones and other wetlands are known to remove N from ground and surface waters before they enter lakes and streams. However, the effect of riparian wetlands on water quality has been shown to differ dramatically among sites. Sources of landscape variation in riparian N dynamics have been poorly documented and rarely quantified. Within the Lake Tahoe Basin (LTB), we hypothesized that differences in riparian N dynamics correlate to differences in ecosystem type. To test this hypothesis, we randomly selected 20 plots, four each of five ecosystem types, along a tributary to Lake Tahoe. Throughout the snow-free season, we measured soil N transformations and groundwater chemistry in each plot. We found significant differences in denitrification potential, net mineralization, net nitrification and groundwater nutrient flux among different ecosystem types. These results suggest that classification of riparian zones into ecosystem types might be useful in predicting landscape differences in riparian water quality effects.

After the definitive ban on tin-based antifouling substances, new organic compounds have recently been introduced in antifouling paint formulations, as either principal or booster biocides. In most cases, previous risk assessment of these biocides has been inadequate so that their possible effects on aquatic ecosystems is a matter of great concern. We studied the effects of two new organic biocides often associated in paint formulations, Sea-Nine 211 TM (4,5 dichloro-2-n-octyl-4-isothiazoline-3-one) and chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile), on haemocytes of the compound ascidian Botryllus schlosseri exposed for 60 min to various concentrations (from 0.1 to 10 M) of the xenobiotics. This species had previously proved to be a good bioindicator of organotin compounds. Both compounds, at concentrations of 1 and 10 M, altered the morphology of phagocytes, and these changes were closely related to disrupting effects on cytoskeletal components. At the same concentrations, phagocytosis, which requires cytoskeletal modifications for pseudopod formation, was severely hindered. Both compounds were able to induce apoptosis of Botryllus blood cells, probably as a consequence of severe oxidative stress related to the reported decrease of intracellular reduced glutathione (GSH) content. In the case of Sea-Nine 211 TM , a substantial increase in intracellular Ca 2+ and a negative effect on Ca 2+-ATPase activity may also be involved in the activation of the cell death machinery. Cytochrome-c-oxidase was also significantly inhibited by the two biocides, indicating perturbation of the mitochondrial respiratory chain. Isodynamic mixtures of Sea-Nine 211 TM and chlorothalonil were used to evaluate the occurrence of interactions between the two compounds. Results suggest the combined action of partial additivity when cell-spreading and cytochrome-c-oxidase activity were considered, and were indicative of antagonism in the case of the GSH depletion. On the whole, our results indicate that short-term in vitro exposure of haemocytes to high concentrations of Sea-Nine 211 TM and chlorothalonil provokes a marked reduction in haemocyte functionality, higher than or comparable to that of TBT. These assays of acute toxicity stress the immunosuppressive potential of these compounds, which, although counterbalanced by their short half-life in the marine environment, can lead to biocoenosis dismantling through rapid bioaccumulation by filter-feeding non-target benthic organisms.

Many streams and rivers throughout North America have been extensively straightened, widened, and hardened since the middle 1800s, but related effects on aquatic ecosystems have seldom been monitored, described, or published. Beginning in the early 1990s, reach-level restoration efforts began to base projects on natural channel design (NCD) techniques and Rosgen's (1994b, 1996) river classification system in an effort to duplicate or mimic stable reference reach geomorphology. Four reaches in three streams of the Catskill Mountains, New York, were restored from 2000 to 2002 using NCD techniques to decrease bed and bank erosion rates, decrease sediment loads, and improve water quality. The effects of restoration on the health of fish assemblages were assessed through a before-after, control-impact (BACI) study design to quantify the net changes in population and community indices at treatment reaches relative to index changes at unaltered reference reaches from 1999 to 2004. After restoration, community richness and biomass at treatment reaches increased by more than one-third. Changes in fish communities were caused mainly by shifts in dominant species populations; fish community biomass and total fish abundance were generally dominated by daces or daces and sculpins before restoration and by one or more salmonid species after restoration. Density and biomass of eastern blacknose dace Rhinichthys atratulus, longnose dace R. cataractae, and slimy sculpin Cottus cognatus did not change appreciably, whereas net salmonid density and biomass increased substantially after restoration. These changes were driven primarily by large increases in populations of brown trout Salmo trutta. The findings demonstrate that the structure, function, and ultimately the health of resident fish populations and communities can be improved, at least over the short term, through NCD restoration in perturbed streams of the Catskill Mountains.

Specifically radiolabeled [14C-lignin]lignocelluloses and [14C-polysaccharide]lignocelluloses were prepared from a variety of marine and freshwater wetland plants including a grass, a sedge, a rush, and a hardwood. These [14C]lignocellulose preparations and synthetic [14C]lignin were incubated anaerobically with anoxic sediments collected from a salt marsh, a freshwater marsh, and a mangrove swamp. During long-term incubations lasting up to 300 days, the lignin and polysaccharide components of the lignocelluloses were slowly degraded anaerobically to 14CO2 and 14CH4. Lignocelluloses derived from herbaceous plants were degraded more rapidly than lignocellulose derived from the hardwood. After 294 days, 16.9% of the lignin component and 30.0% of the polysaccharide component of lignocellulose derived from the grass used (Spartina alterniflora) were degraded to gaseous end products. In contrast, after 246 days, only 1.5% of the lignin component and 4.1% of the polysaccharide component of lignocellulose derived from the hardwood used (Rhizophora mangle) were degraded to gaseous end products. Synthetic [14C]lignin was

Previous studies have provided prima facie evidence that runoff from the MI motorway, UK, affects both the quality of the receiving water and the biota living there, in sites short distances from point sources-i.e., possible worst-case situations. Because discharges contain a wide variety of contaminants, both the identification of toxicants and the establishment of causal relationships between observed changes in waterhediment quality and biology are often difficult. In this particular case, the problem was addressed by conducting a series of toxicity tests using the benthic amphipod Gummnruspulex. The abundance of this species was greatly reduced downstream of the point where motorway runoff entered the stream. Stream water contaminated with motorway runoff was not toxic to G. pulex. However, exposure to contaminated sediments resulted in a slight reduction in survival over 14 d, and sediment manipulation experiments identified hydrocarbons, copper, and zinc as potential toxicants. Spiking experiments confirmed the importance of hydrocarbons, and fractionation studies indicated that most of the observed toxicity was due to the fraction containing polycyclic aromatic hydrocarbons. Animals exposed to contaminated sediments and water spiked with sediment extract accumulated aromatic hydrocarbons in direct proportion to exposure concentrations.

Along with the sequent completion of Manwan and Dachaoshan Dam, the river continuum of the middle and lower reaches of the Lancang River was separated into three types of segments: reservoir, below-dam segment and downstream flowing segment. The long-term series of water quality and river flow data over 20 years were analyzed in order to study the impact of dam construction and operation on water quality and water self-purification capacity of these different river segments. From pre-dam period to the first 7 years after Manwan Dam had been accomplished, the water quality of Manwan Reservoir became worse due to the accumulation of pollutants, and then to the next 5 years the water quality became better in virtue of the water self-purification of the reservoir. The cooperative operation of Manwan and Dachaoshan Dam had cumulatively positive impacts on water quality of their below-dam segment but no impacts on that of downstream flowing segment. From pre-dam period to the first 7 years after the closure of Manwan Dam, the water self-purification capacity of Xiaowan–Manwan segment for BOD5, CODMn and NH3–N decreased. Also, the water self-purification capacity of Manwan–Dachaoshan segment for BOD5 and CODMn decreased but for NH3–N increased. However, the water self-purification capacity of Jinghong–Ganlanba segment changed contrary to Manwan–Dachaoshan segment. In general, the construction of Manwan Dam negatively affected the water self-purification capacity of reservoir and below-dam segment but impose little impact on that of downstream flowing segment. This study suggested that it is necessary to pay attention to the effect of complicated temporal and spatial characteristics of dam on aquatic ecosystem.

The Hierarchical Mosaic of Aquatic Ecosystems (HMAE ® ) was originally developed in Belgium by applying the ecological adaptations of hydrophyte plants to flooded and polluted conditions. The system consisted of a stabilization pond (stage I) followed by a semi-aquatic ecosystem planted with helophytes (stage II) and by a terrestrial ecosystem (stage III) where ligneous species are planted. An HMAE ® experimental system net treatment area of 9.4 m 2 per one equivalent inhabitant (e.i.) showed a high average performance for SS (66.5%); COD (89%); BOD 5 (87.5%) and fecal bacteria (99.997%). The decrease of the treatment area of 2.8 m 2 /e.i. showed a average high performance for SS (75%); COD (80%); BOD 5 (82%) and fecal bacteria (99.9%). An HMAE ® system was built in Bustillo de Cea (Leon, northwest of Spain) and their removal efficiency was studied. Organic matter, nutrients and fecal bacteria were fortnightly analyzed. The whole system showed removal efficiencies in start-up as high as 98% for solids, 95% for BOD 5 and up to 99.99% for fecal bacteria.

Conservation organizations have most often focused on land-use change, climate change, and invasive species as prime threats to biodiversity conservation. Although air pollution is an acknowledged widespread problem, it is rarely considered in conservation planning or management. In this synthesis, the state of scientific knowledge on the effects of air pollution on plants and animals in the Northeastern and Mid-Atlantic regions of the United States is summarized. Four air pollutants (sulfur, nitrogen, ozone, and mercury) and eight ecosystem types ranging from estuaries to alpine tundra are considered. Effects of air pollution were identified, with varying levels of certainty, in all the ecosystem types examined. None of these ecosystem types is free of the impacts of air pollution, and most are affected by multiple pollutants. In aquatic ecosystems, effects of acidity, nitrogen, and mercury on organisms and biogeochemical processes are well documented. Air pollution causes or contributes to acidification of lakes, eutrophication of estuaries and coastal waters, and mercury bioaccumulation in aquatic food webs. In terrestrial ecosystems, the effects of air pollution on biogeochemical cycling are also very well documented, but the effects on most organisms and the interaction of air pollution with other stressors are less well understood. Nevertheless, there is strong evidence for effects of nitrogen deposition on plants in grasslands, alpine areas, and bogs, and for nitrogen effects on forest mycorrhizae. Soil acidification is widespread in forest ecosystems across the eastern United States and is likely to affect the composition and function of forests in acid-sensitive areas over the long term. Ozone is known to cause reductions in photosynthesis in many terrestrial plant species. For the most part, the effects of these pollutants are chronic, not acute, at the exposure levels common in the eastern United States. Mortality is often observed only at experimentally elevated exposure levels or in combination with other stresses such as drought, freezing, or pathogens. The notable exceptions are the acid/aluminum effects on aquatic organisms, which can be lethal at levels of acidity observed in many surface waters in the region. Although the effects are often subtle, they are important to biological conservation. Changes in species composition caused by terrestrial or aquatic acidification or eutrophication can propagate throughout the food webs to affect many organisms beyond those that are directly sensitive to the pollution. Likewise, sublethal Annals of the New York Academy of Sciences doses of toxic pollutants may reduce the reproductive success of the affected organisms or make them more susceptible to potentially lethal pathogens. Many serious gaps in knowledge that warrant further research were identified. Among those gaps are the effects of acidification, ozone, and mercury on alpine systems, effects of nitrogen on species composition of forests, effects of mercury in terrestrial food webs, interactive effects of multiple pollutants, and interactions among air pollution and other environmental changes such as climate change and invasive species. These gaps in knowledge, coupled with the strong likelihood of impacts on ecosystems that have not been studied in the region, suggests that current knowledge underestimates the actual impact of air pollutants on biodiversity. Nonetheless, because known or likely impacts of air pollution on the biodiversity and function of natural ecosystems are widespread in the Northeast and Mid-Atlantic regions, the effects of air pollution should be considered in any long-term conservation strategy. It is recommended that ecologically relevant standards, such as "critical loads," be adopted for air pollutants and the importance of long-term monitoring of air pollution and its effects is emphasized.

Denitrification is a critical process regulating the removal of bioavailable nitrogen (N) from natural and human-altered systems. While it has been extensively studied in terrestrial, freshwater, and marine systems, there has been limited communication among denitrification scientists working in these individual systems. Here, we compare rates of denitrification and controlling factors across a range of ecosystem types. We suggest that terrestrial, freshwater, and marine systems in which denitrification occurs can be organized along a continuum ranging from (1) those in which nitrification and denitrification are tightly coupled in space and time to (2) those in which nitrate production and denitrification are relatively decoupled.

It is widely known that watershed hydrology is dependent on many factors, including land use, climate, and soil conditions. But the relative impacts of different types of land use on the surface water are yet to be ascertained and quanti®ed. This research attempted to use a comprehensive approach to examine the hydrologic effects of land use at both a regional and a local scale. Statistical and spatial analyses were employed to examine the statistical and spatial relationships of land use and the¯ow and water quality in receiving waters on a regional scale in the State of Ohio. Besides, a widely accepted watershed-based water quality assessment tool, the Better Assessment Science Integrating Point and Nonpoint Sources (BASINS), was adopted to model the plausible effects of land use on water quality in a local watershed in the East Fork Little Miami River Basin. The results from the statistical analyses revealed that there was a signi®cant relationship between land use and in-stream water quality, especially for nitrogen, phosphorus and Fecal coliform. The geographic information systems (GIS) spatial analyses identi®ed the watersheds that have high levels of contaminants and percentages of agricultural and urban lands. Furthermore, the hydrologic and water quality modeling showed that agricultural and impervious urban lands produced a much higher level of nitrogen and phosphorus than other land surfaces. From this research, it seems that the approach adopted in this study is comprehensive, covering both the regional and local scales. It also reveals that BASINS is a very useful and reliable tool, capable of characterizing the¯ow and water quality conditions for the study area under different watershed scales. With little modi®cation, these models should be able to adapt to other watersheds or to simulate other contaminants. They also can be used to study the plausible impacts of global environmental change. In addition, the information on the hydrologic effects of land use is very useful. It can provide guidelines not only for resource managers in restoring our aquatic ecosystems, but also for local planners in devising viable and ecologically-sound watershed development plans, as well as for policy makers in evaluating alternate land management decisions.

The polycyclic musk fragrances, mainly 1, 3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta(g)-2-benzopyrane (HHCB) and 7-acetyl-1,1,3,4,4,6-hexamethyltetrahydronaphthalene (AHTN) are synthetic musk fragrances which are used in almost all scented consumer products, such as perfumes, cosmetics and laundry detergents. Concerning their chemical structures the polycyclic musks are indane and tetraline derivatives highly substituted mainly by methyl groups. Their production has been increased continuously during the last years with a world-wide production volume today of about 6000 t/year. After their application in private households they are dumped via the sewage treatment plants into the aquatic environment. In this review the analysis of polycyclic musk compounds in environmental samples is shortly presented and all published data of polycyclic musk compounds in water, sediment, suspended particulate matter (SPM), sewage sludge, and biota are summarized and discussed. The highest HHCB and AHTN concentrations were analysed in water (maximum concentrations: 6 mg HHCB/l, 4.4 mg AHTN/l) and sludge (maximum concentrations: 63 mg HHCB/kg dry matter, 34 mg AHTN/kg dry matter) from sewage plants, and in fish (maximum concentrations: 159 mg HHCB/kg lipid, 58 mg AHTN/kg lipid) from sewage ponds. In all other samples from different aquatic ecosystems these chemicals were unequivocally detected in varying concentrations dependent on the distance to sewage treatment plants. Even in marine water samples from the German Bight HHCB and AHTN could be quantified at the lower ng/l level. Very often HHCB and AHTN formed the major organic contaminants, in all samples their concentrations exceeded those of musk xylene and musk ketone. Also several by-products and impurities of the commercial polycyclic musks were analysed in river and waste water samples in not negligible amounts. The apparently ubiquitous distribution of polycyclic musks in the aquatic environment demonstrates the persistence and lipophilicity of these pollutants. The high log K ow values of HHCB and AHTN (5.7 -5.9) do not directly correlate with their relatively low bioconcentration factors (BCFs) derived from fish experiments, this discrepancy may be explained by a particular metabolism in fish. There are indications of a possible species dependent metabolisation. For a general risk assessment of this new group of environmental pollutants besides the missing toxicological data, further studies on the distribution of the polycyclic musk fragrances including their by-products in the aquatic environment, on possible degradation processes in sediment/sludge as well as on the metabolism in fish are urgently needed.

Pharmaceuticals and other micropollutants in wastewater pose a new challenge to wastewater professionals as well as to the pharmaceutical industry. Although there is a great deal of uncertainty concerning the possible detrimental effects on the aquatic ecosystems, the precautionary principle -or possibly new scientific evidence -may give rise to more stringent demands on wastewater treatment in the future. In conventional wastewater treatment plants, a combination of biological treatment with high sludge residence times and ozonation of the effluent seems to be the most promising technology. Ozonation, however, is an energy-intensive technology. Moreover, in conventional end-of-pipe systems a large part of the pollutants will always be lost to the environment due to leaking, primarily during rain. In the long term, source separation offers the more sustainable solution to the entire wastewater problem, including organic micropollutants. Urine source separation is an elegant solution to the problems of nutrients and pharmaceuticals alike and losses of untreated pollutants to the environment can be minimized. Although few technologies for the separate treatment of urine have been developed to date, the 100-500 times higher concentrations of micropollutants promise more efficient conditions for all removal technologies known from conventional wastewater treatment.

Potassium permanganate is a chemical compound widely used in aquaculture for the control and removal of parasites, and in the prevention of diseases caused by bacteria and fungi. However, this compound can be toxic to fish, being a strong oxidant. Moreover, there is no consistent information in the literature about its toxicity to non-target organisms. The purpose of this study was to evaluate the acute toxicity (LC50;96h) of potassium permanganate for tilapia, Oreochromis niloticus, and to determine its toxic effects on nontarget organisms using ecotoxicological assays performed with the microcrustacean Ceriodaphnia dubia and with the green microalgae Pseudokirchneriella subcapitata. The results showed that the concentration of 1.81 mg L − 1 of potassium permanganate caused acute toxic effect in tilapia fingerlings. The ecotoxicological assays demonstrated that concentrations above 0.12 mg L − 1 can cause chronic toxic effects on non-target organisms, indicating possible deleterious effects on the food chain of the aquatic ecosystem that may receive the discharge of effluents released by fish cultures treated with this chemotherapy. All toxic concentrations determined in this study were below those recommended in the literature for the use of this chemotherapy in fish cultures, demonstrating that this type of therapy should be more carefully considered in order to avoid damage to the treated fish and to the environment.

Where there is water scarcity, the situation is dramatic for aquatic ecosystems. In many Mediterranean basins the exploitation of water resources has gone clearly beyond renewable level and affects aquatic ecosystems. Thus, they may benefit from the recycling of high-quality effluents that can be used to cope with environmental water demands instead of being discharged. Their reclamation with natural technologies produces an improvement in quality based on the development of trophic webs built upon nutrients still dissolved in the reclaimed water. The main project in the Costa Brava area is that of the Empuriabrava constructed wetland system, where nitrified effluent is further treated to reduce the concentration of nutrients in the water and is reused for environmental enhancement. This facility is also an interesting site for bird-watching. Other projects where water recycling produces indirect benefits on the aquatic ecosystems are those in Tossa de Mar, affecting the "temporary" Tossa Creek (a watercourse which flows on temporary basis according to rainfall patterns), and in the Aro Valley, affecting the also "temporary", but slightly bigger, Ridaura River. This document summarizes these projects and proposes practical recommendations for the use of treated effluents in the recreation and restoration of aquatic ecosystems.

Although oil activities generate numerous forms of environmental impact on biological communities, studies of these impacts on Brazilian coastal ecosystems are rare. Results of tests for the content of oil in sediments and organisms indicate a substantially high rate of degradation. Results for uptake of polycyclic aromatic hydrocarbons in bivalves suggested the recent occurrence of oil spills and that these organisms differed in their capabilities to bioconcentrate oil. The mangrove community has suffered constant inputs of oil and has responded with increased numbers of aerial roots, generation of malformed leaves and fruits by plants, and a decrease in litter production. Studies of the impact of oil on rocky shore communities and the toxicity of oil and its by-products to marine organisms have confirmed the results reported in the literature. Presently most of the available studies deal with the macroscopic effects of oil on organisms and have indicated that the nature of oil, climate characteristics, the physical environment, and the structure of the community influence the symptoms of oil contamination in organisms of coastal waters. Longterm studies should be carried out to assess changes in community structure, sublethal effects in populations, and the resilience of contaminated ecosystems.

In the Seine estuary, nitrification is a major process involved in the oxygen budget, together with photosynthesis, heterotrophic bacterial degradation and reaeration. Within the framework of the Seine-Aval programme, we attempted to further understand the process using a molecular approach that was expected to detect nitrifying bacteria, and also to quantify them. On the basis of the PCR approach using specific primers of the genus Nitrobacter, we coupled a competitive PCR method in order to quantify these Nitrobacter, a genus widely distributed in freshwater aquatic ecosystems. This molecular approach was conducted in parallel with a measurement of potential nitrifying with a 14C radiotracing method. We showed that Nitrobacter represent less than 0.1% of the total bacterial community, as determined by epifluorescence microscopy, and that potential nitrifying activity increased with Nitrobacter numbers. Following that methodological step demonstrating a real feasibility, a possible relationship between these two measurements is expected on the basis of five longitudinal field studies already realised. 0 Academic des Sciences / Elsevier, Paris Seine estuary / nitrification / nitrifying bacteria / competiiie PCR R&wni: -La nitrification represente dans l'estuaire de la Seine un processus majeur dans le bilan d'oxygenation, avec la photosynthese, l'activite bacterienne heterotrophe et la reaeration. Dans le cadre du programme Seine-Aval, nous avons pousse l'etude ecologique de ce processus avec une approche molitculaire qui nous permettrait non seulement de detecter ces batteries mais aussi de les quantifier. A la technique d'amplification par PCR avec des amorces specifiques de Nitrobacter, nous avons couple une methode de PCR competitive afin de quantifier ce genre des nitratantes, le plus repandu en milieux aquatiques continentaux. Cette determination a Cte realisee parallelement a une mesure de l'activite nitrifiante potentielle, basee sur le tracage radioactif au 14C. Nous avons montre que les Nitrobacter representent environ 0,l % de la communaute bacterienne totale, estimee en microscopic par epifluorescence et que l'activite potentielle augmente avec le nombre des Nitrobucter. Apres cette &ape de mise au point mitthodologique montrant la faisabilite de l'approche, nous exploiterons * Correspondance et tires a part : [email protected] C. R. Acad. Sci. Paris, Sciences de la vie / Life Sciences 1%9,322,517-526 517 '-T. Berthe et al. les cinq campagnes rkalisees en cherchant 2 dhterminer une relation statistique entre ces deux grandeurs. 0 Acadkmie des Sciences / Elsevier, Paris estuaire de la Seine / nitrifwation / bacth-ies nitrifnntes / PCR comp&itive

ABSTRACT: Channel instability and aquatic ecosystem degradation have been linked to watershed imperviousness in humid regions of the U.S. In an effort to provide a more process-based linkage between observed thresholds of aquatic ecosystem degradation and urbanization, standard single event approaches (U.S. Geological Survey Flood Regression Equations and rational) and continuous hydrologic models (HSPF and CASC2D) were used to examine potential changes in flow regime associated with varying levels of watershed imperviousness. The predicted changes in flow parameters were then interpreted in concert with risk-based models of channel form and instability. Although low levels of imperviousness (10 to 20 percent) clearly have the potential to destabilize streams, changes in discharge, and thus stream power, associated with increased impervious area are highly variable and dependent upon watershed-specific conditions. In addition to the storage characteristics of the pre-development watershed, the magnitude of change is sensitive to the connectivity and conveyance of impervious areas as well as the specific characteristics of the receiving channels. Different stream types are likely to exhibit varying degrees and types of instability, depending on entrenchment, relative erodibility of bed and banks, riparian condition, mode of sediment transport (bedload versus suspended load), and proximity to geomorphic thresholds. Nonetheless, simple risk-based analyses of the potential impacts of land use change on aquatic ecosystems have the potential to redirect and improve the effectiveness of watershed management strategies by facilitating the identification of channels that may be most sensitive to changes in stream power.

Low-cost and simple technologies are needed to reduce watershed export of excess nitrogen to sensitive aquatic ecosystems. Denitrifying bioreactors are an approach where solid carbon substrates are added into the flow path of contaminated water. These carbon (C) substrates (often fragmented wood-products) act as a C and energy source to support denitrification; the conversion of nitrate (NO 3 − ) to nitrogen gases. Here, we summarize the different designs of denitrifying bioreactors that use a solid C substrate, their hydrological connections, effectiveness, and factors that limit their performance. The main denitrifying bioreactors are: denitrification walls (intercepting shallow groundwater), denitrifying beds (intercepting concentrated discharges) and denitrifying layers (intercepting soil leachate). Both denitrifcation walls and beds have proven successful in appropriate field settings with NO 3 − removal rates generally ranging from 0.01 to 3.6 g N m −3 day −1 for walls and 2-22 g N m −3 day −1 for beds, with the lower rates often associated with nitrate-limitations. Nitrate removal is also limited by the rate of C supply from degrading substrate and removal is operationally zero-order with respect to NO 3 − concentration primarily because the inputs of NO 3 − into studied bioreactors have been generally high. In bioreactors where NO 3 − is not fully depleted, removal rates generally increase with increasing temperature. Nitrate removal has been supported for up to 15 years without further maintenance or C supplementation because wood chips degrade sufficiently slowly under anoxic conditions. There have been few field-based comparisons of alternative C substrates to increase NO 3 − removal rates but laboratory trials suggest that some alternatives could support greater rates of NO 3 − removal (e.g., corn cobs and wheat straw). Denitrifying bioreactors may have a number of adverse effects, such as production of nitrous oxide and leaching of dissolved organic matter (usually only for the first few months after construction and start-up). The relatively small amount of field data suggests that these problems can be adequately managed or minimized. An initial cost/benefit analysis demonstrates that denitrifying bioreactors are cost effective and complementary to other agricultural management practices aimed at decreasing nitrogen loads to surface waters. We conclude with recommendations for further research to enhance performance of denitrifying bioreactors. (L.A. Schipper). trated discharges in agricultural systems occur through under-field tile drainage and ditches while diffuse sources are typically through the discharge of shallow groundwater to surface waters. Nitrogen that is captured in biomass passes through the food chain and ends up in wastewater streams, which are ultimately discharged to surface waters.

The CASSARINA Project is a coordinated joint study of recent environmental change in North African wetland lakes. Nine primary sites were selected for detailed study comprising three sites in each of Morocco, Tunisia and Egypt. Multidisciplinary studies were undertaken by scientists from each of these countries working in cooperation with colleagues in the UK and Norway. The detailed results are presented in a consecutive suite of papers that describe both modern ecosystem attributes and the recent environmental histories of each site. This paper presents an overview of the aims, structure and initial results of the project. Modern site attributes measured were water quality and phytoplankton (Fathi et al., 2001), zooplankton (Ramdani et al., 2001b), fish (Kraïem et al., 2001) and littoral vegetation (Ramdani et al., 2001a). Baseline water quality data showed that one site (Megene Chitane) was acid with low salinity but the others had high alkalinities with varying degrees of brackishness. All the sites tended to be eutrophic and the phytoplankton was mainly dominated by green or blue-green algae. Where fish were present, growth rates were high with marginally highest rates in the Egyptian Delta lakes (Kraïem et al., 2001). Marginal vegetation surveys showed that emergent macrophytes were still extensive only in the Delta lakes (Ramdani et al., 2001a) where they form important refuges and restrict water pollution. In 1998, one Moroccan wetland lake (Merja Bokka) was drained completely for cultivation. Site specific environmental change records for the 20th century period were obtained using palaeolimnological techniques. Sediment core chronologies (Appleby et al., 2001) were based mainly on radio-isotopes (210 Pb and 137 Cs). Sedimentary remains of aquatic biota, diatoms, zooplankton, higher plants and benthic animals (Flower et al., 2001; Ramdani et al., 2001c; Birks et al., 2001a) and pollen (Peglar et al., 2001) were investigated (Birks et al., 2001b). Major differences in past species abundances were found and were interpreted in terms relevant to biodiversity and water quality/availability change. Metals and pesticide residues in sediment cores indicated that lake contamination was generally lower than in some European sites but some DDE profiles showed a close correspondence with known usage histories (Peters et al., 2001). Hydrological changes affecting water quality and availability mainly arose from land-use intensification during the 20th century and are shown to be the main driver of biodiversity disturbance at all nine CASSARINA sites. Summarizing floristic and faunistic changes using species richness values indicated that freshening of the Delta lakes during this century generally increased aquatic diversity. Species richness also increased during the final drainage of Bokka but tended to decline in acid Chitane. Modern sampling showed that phytoplankton and epiphytic diatom diversity was higher in the Delta lakes but this was not so for zooplankton. Each biological group reacted differently to environmental disturbance and this lack of concordance makes overall diversity changes difficult to predict. Implications of the combined study are that water quality and availability changes through landuse intensification remain the greatest imminent threat to the ecological integrity of remaining North African wetland lakes. For most sites, recent changes in freshwater supply have occurred causing sometimes catastrophic changes in lake biota (Bokka). The acid lake (Chitane) supports an acidophilous biota that is unique in Tunisia but habitat quality is currently diminishing due to both enrichment and inflow water abstraction. However, sediment records indicate that earlier in the 20th century many of the CASSARINA sites experienced temporarily enhanced freshwater supply from land irrigation and drainage improvements. This was especially marked for the Delta lakes and these remain the most biodiverse sites today. Intensified time-space multidisciplinary environmental monitoring of aquatic ecosystems is identified as a key activity for effective wetland lake management and for validating future environmental change scenarios in North Africa.

The European Water Framework Directive (WFD) establishes a well differentiated typology of water bodies on the basis of scientific and biological criteria. For coastal waters, such criteria have long been established, while for transitional waters they are still under discussion. One of the difficulties when applying the WFD to coastal lagoons is to include them in only one of these categories, and while there is no doubt about the nature of estuaries as transitional waters, there is some controversy concerning lagoons. To what extent, reference conditions may be similar for estuaries and lagoons, or whether features common to all coastal lagoons are more important for differentiating them from other water bodies than the fact that there is (or is not) any fresh water influence, is something that remains unclear and is discussed in this work. Coastal lagoons and estuaries form part of a continuum between continental and marine aquatic ecosystems. Shelter, strong boundaries or gradients with adjacent ecosystems, anomalies in salinity regarding freshwater or marine ecosystems, shallowness, etc. all contribute to the high biological productivity of estuaries and lagoons and determine common ecological guilds in the species inhabiting them. On the other hand, fresh water influence, the spatial organization of gradients and environmental variability (longitudinal onedimensional gradients in estuaries versus complex patterns and three-dimensional heterogeneity in lagoons) constitute the main differences, since these factors affect both the species composition and the dominance of certain ecological guilds and, probably, the system's complexity and homeostatic capability. In the context of the WFD, coastal lagoons and estuaries are closer to each other than they are to continental or marine waters, and, on the basis of the shared features, they could be intercalibrated and managed together. However, coastal lagoons cannot be considered transitional waters according to the present definition. To assume that fresh water influence is an inherent characteristic to these ecosystems could lead to important changes in the ecological organization and functioning of coastal lagoons where natural fresh water input is low or null. In our opinion, the present day definition of transitional waters should be changed substituting the criterion of fresh water influence by another based on common features, such as relative isolation and anomalies in salinity in water bodies with marine influence. Otherwise, coastal lagoons should be considered a particularly characteristic type of water mass for establishing reference conditions of ecological status.