Showing papers in "Aquatic Sciences in 2006"

Biodiversity and its conservation in the Pantanal of Mato Grosso, Brazil

Abstract: The Pantanal of Mato Grosso, Brazil, is famous for its luxurious plant and animal life. We combine a literature review with recent work and show that species diversity is large but that most major plant and animal groups contain a large number of not wetland-specific species that depend on permanently terrestrial habitats within the Pantanal, or are restricted to dry areas during the low water period. These species occur also in the neighbouring biomes of Cerrado, Amazon Forest or Chaco. Until now, very few endemic species have been described, however, there are large populations of species in the Pantanal that are considered rare or endangered in South America. The number of trees adapted to long term flooding is low in comparison with the Amazon River floodplain. We hypothesize that the reason for the lack of local endemisms and the occurrence of a large number of species with a large ecological amplitude is the climatic instability of the region of the Pantanal, which suffered severe drought during glacial periods. The instability of the actual climate, which is characterized by multi-annual wet and dry periods, has a strong impact on distribution, community structure and population size of many plant and animal species and hinders spatial segregation of populations. The dependence of the system on the flood pulse makes the Pantanal very vulnerable to human induced changes in hydrology and the predicted changes in global climate.

Biodiversity and its conservation in the Sundarban Mangrove Ecosystem

Abstract: The Sundarban, covering about one million ha in the delta of the rivers Ganga, Brahmaputra and Meghna is shared between Bangladesh (~60%) and India (~40%), and is the world’s largest coastal wetland. The area experiences a subtropical monsoonal climate with an annual rainfall of 1,600–1,800 mm and severe cyclonic storms. Enormous amounts of sediments carried by the rivers contribute to its expansion and dynamics. Salinity gradients change over a wide range of spatial and temporal scales. The biodiversity includes about 350 species of vascular plants, 250 fishes and 300 birds, besides numerous species of phytoplankton, fungi, bacteria, zooplankton, benthic invertebrates, molluscs, reptiles, amphibians and mammals. Species composition and community structure vary east to west, and along the hydrological and salinity gradients. Sundarban is the habitat of many rare and endangered animals (Batagur baska, Pelochelys bibroni, Chelonia mydas), especially the Royal Bengal tiger (Panthera tigris). Javan rhino, wild buffalo, hog deer, and barking deer are now extinct from the area. Large areas of the Sundarban mangroves have been converted into paddy fields over the past two centuries, and more recently into shrimp farms. The Sundarban has been extensively exploited for timber, fish, prawns and fodder. The regulation of river flows by a series of dams, barrages and embankments for diverting water upstream for various human needs and for flood control has caused large reduction in freshwater inflow and seriously affected the biodiversity because of an increase in salinity and changes in sedimentation. Heritiera fomes (locally called Sundari, from which Sundarban derives its name), Nypa fruticans and Phoenix paludosa are declining rapidly. During the past three decades, large parts of the remaining Sundarban have been protected for wildlife, particularly tiger, through the creation of several sanctuaries and a biosphere reserve. Parts of the Sundarban in both India and Bangladesh have been declared World Heritage sites. However, its biodiversity continues to be threatened by a growing human population that not only places pressure on its biological resources, but also impacts on the freshwater inflows from upstream areas. Oil exploration in coastal areas is also emerging as a new threat. Further threats arise from global climate change, especially sea level rise. The future of the Sundarban will depend upon the management of freshwater resources as much as on the conservation of its biological resources.

Ecosystem engineering: the impact of bioturbation on biogeochemical processes in marine and freshwater benthic habitats

Abstract: In aquatic ecosystems, invertebrate bioturbation significantly influences microbial activities and biogeochemical processes in sediments by modifying water and sediment fluxes at the water-sediment interface. We apply the concept of ecosystem engineering to develop a qualitative general understanding of the role of bioturbation on microbial processes in different benthic environments. We hypothesized that the effects of the bioturbation mode (sediment reworking, biogenic structure building, bioirrigation) on microbial processes vary between diffusion- and advection-dominated benthic environments because bioturbation does not have the same influences on hydrological exchanges (and the flux of resources for micro-organisms living in sediments) at the water-sediment interface of the two systems. To test this hypothesis, we experimentally compared the influence of three bioturbation modes (fine-sediment reworking, U-shaped structure burrowing, and gallery-network burrowing) in a diffusion-dominated system (fine sediments/low interstitial flow rates) and an advectiondominated system (coarse sediments/advection of water in sediments). Our analysis demonstrated that bioturbation modes in the two systems had different impacts on microbial activities. For instance, U-shaped tube burrowing by animals increased O2 consumption in the diffusion- dominated system but produced the opposite effect in the advection-dominated system. The influence of bioturbation was also negatively related to interstitial flow rate, the bioturbation having a higher influence on O2 consumption in the diffusion-dominated system than in the advection-dominated system. According to our hypothesis, bioturbation modified microbial processes in sediments depend on the hydrological characteristics of the system. In the diffusion-dominated system, invertebrate bioturbation can produce water fluxes at the watersediment interface that may strongly influence microbial processes in sediments. In contrast, in the advectiondominated system, invertebrate bioturbation can only modify the water circulation patterns in sediments, moderately affecting microbial processes. Consequently, it is necessary to use a conceptual framework which takes into account the features of sediment habitats in order to allow a better prediction of bioturbation effects on sediment biogeochemistry. With this aim, the conceptual scheme of ecosystem engineers can be an organizing principle to integrate the complex relationships among physical habitat, bioturbation mode and microbial activity.

The comparative biodiversity of seven globally important wetlands: A synthesis

Abstract: The species diversity data of seven globally important wetlands (Canadian peatlands, Florida Everglades, Pantanal, Okavango Delta, Sundarban, Tonle Sap, and Kakadu National Park) were compared. The available data for most groups of lower plants and animals are insufficient for a comparative analysis. Data on vertebrates and higher plants are more complete and show high species diversity. The large habitat diversity allows the coexistence of amphibious species with many immigrants from connected deepwater and terrestrial habitats. Several of these immigrant species find an important permanent refuge in the wetlands; some use the wetlands as periodic habitats. All wetlands are important habitats for long-distance migratory bird species. The species composition reflects the biogeography of the respective regions, e.g. the high diversity of large ungulates characteristic for Africa is also found in the Okavango Delta in Botswana, and the high fish species diversity typical for South America is also reflected in the Pantanal in Brazil. The number of endemic species in most wetlands is low, except in the Everglades. The low numbers are explained to some extent by the dramatically changing paleo-climatic conditions that increased extinction rates, but also by the connection with large river systems that act as migratory and transport routes for species from large catchment areas and hinder the genetic isolation of wetland populations. The high number of endemic species in the Everglades is explained in part by its isolation on a peninsula. The relatively low nutrient status of most wetlands does not negatively affect species diversity and often leads to high animal densities. Large populations of endangered or rare species in all wetlands contribute to the great value of these areas for biodiversity protection. All wetlands are subjected to an increasing degree to human pressure through, e.g. water abstraction, changes in the natural flood regime, land reclamation, pollution, over-utilization of natural resources, and poaching. High habitat diversity and a pronounced natural disturbance regime make some of the wetlands vulnerable to invasion by exotic species, as shown for the Everglades. All studied wetlands are at least in part protected by national and international conventions. This provides perspectives for long-term protection only to a limited extent because of major environmental changes in their surroundings. Further strong efforts are required to match protection and sustainable use of the wetlands proper with management activities in their catchments.

Controls on the export of C, N, P and Fe from undisturbed boreal catchments, Finland

Abstract: Associations between catchment characteristics (altitude, slope, proportion of peatland, site fertility, total stem volume, and its distribution among the main tree species), climatic drivers (temperature sum, latitude, precipitation and runoff) and atmospheric deposition and concentrations and export of C, N, P and Fe in 21 unmanaged boreal catchments (0.07 to 14 km2) were examined in data sets spanning 3 to 32 years. In the entire data base including catchments from southernmost Finland to the Arctic Circle, N and P concentrations were associated with climatic drivers and deposition, while a catchment characteristic, peatland percentage, reflecting topography and site fertility was the best predictor for TOC (total organic carbon) and total Fe concentrations and export. In a subgroup of 18 catchments located in similar climatic conditions and low N deposition in eastern Finland (<600 kg N km–2 yr–1), peatland percentage accounted for 52–75% of the export of TOC, TN (total nitrogen), TON (total organic nitrogen), NH4-N and total Fe, while slope was the best predictor of TP (total phosphorus) export (r2 = 0.56, p < 0.001). Furthermore, among these 18 catchments TOC export accounted for as much as 95% of the variance in TON export, and 61–73% of the variance in NH4-N, total Fe and TP export. Total stem volume of the tree stands and their distribution between tree species and vegetation types were not important predictors for concentrations/export. The peatland percentage of the 21 catchments ranged widely, from 0 to 88% , with an average value of 34% as in entire Finland. Consequently, among the 21 catchments there was also a large variability both in average TOC and pH, 1.2–30 mg l–1 and 4.2–7.1, respectively. The average annual TOC export was 6,200 kg km–2 yr–1 , significantly lower values were recorded for the export of TN, TP and total Fe (130, 5 and 280 kg km–2 yr–1, respectively). N and P export was mainly in an organic form. The TIN (total inorganic N) proportion averaged 13% and elevated NO3-N export occurred only in fertile, high pH sites in southernmost Finland, where stream C/N ratio was lowest. On average, 97% of the TOC, 94% of the TN and 79% of the TP was in a dissolved form.

Species diversity and ecology of Tonle Sap Great Lake, Cambodia

Abstract: Tonle Sap Great Lake in Cambodia, the largest natural freshwater lake in southeast Asia, is situated within the floodplain of the Mekong River. Water levels in the lake vary by about 8 m between the dry season minimum and the wet season maximum when waters from the Mekong River back up the Tonle Sap River. The lake is highly productive – the annual fish catch from the Lake is estimated at between about 180,00–250,000 tonnes while the dai fishery on Tonle Sap River annually harvests about 12,000 tonnes of fish migrating from the lake to the Mekong River early in the dry season. At least 149 species of fish are recorded from the lake and it provides habitat for 11 globally threatened and 6 near-threatened species of vertebrates including globally important populations of Spot-billed Pelican, Greater Adjutant, Bengal Florican, Darter, Grey-headed Fish Eagle and Manchurian Reed Warbler. It also supports significant reptile populations including formerly Siamese Crocodiles, now hunted close to extinction, and probably the world’s largest harvest of freshwater snakes. The inundation area around the permanent lake is highly modified, with areas having been cleared for farming and settlements, and many semi-natural areas altered by burning, firewood and timber harvesting. Nevertheless some 200 species of higher plants have already been recorded. Threats to the lake include pressure through growth of the local population dependant on the lake for subsistence and livelihoods, overharvesting of fish and other aquatic species and potential changes in the hydrology of the River due to the construction and operation of dams which could reduce the amplitude of the lake flood cycle. However concerns that the lake is rapidly filling with sediment are unfounded.

Species diversity of the Okavango Delta, Botswana

Abstract: In the Okavango Delta (about 28,000 km2) the number of identified species is 1,300 for plants, 71 for fish, 33 for amphibians, 64 for reptiles, 444 for birds, and 122 for mammals. The local occurrence of different species of these taxonomic groups in the Okavango Delta is mainly due to a hydrological gradient from permanent streams and swamps to seasonal floodplains, riparian woodlands, and dry woodlands. This level of species diversity is normal for the southern African region, and all analyzed aquatic groups are composed of ubiquitous species with an additional significant proportion of species originating from northern, more tropical systems. Cyclical variations in climate over thousands of years have created a huge wetland complex in the upper Zambezi and Okavango Rivers during wet phases. This wetland complex has fragmented into the Okavango Delta and other large wetlands in Zambia during dry phases. There are no endemic species in the Okavango Delta while the South-central African wetland complex is a centre of endemism. Species diversity of the Okavango Delta is a consequence of this unique environment, with dynamic shifts in flooding patterns that in turn force constant changes in patterns of plant succession and dependent animals. Temporal variations in flooding also cause accumulation and sudden mobilization of nutrients which are readily used by well adapted plant species. As a consequence, locally high biological productivity occurs, which in turn results in high numbers of grazing mammals.

Distribution of diatoms, chironomids and cladocera in surface sediments of thirty mountain lakes in south-eastern Switzerland

Abstract: Surface sediments from 30 mountain lakes in south-eastern Switzerland (Engadine, Grisons) were analysed for subfossil diatom, chironomid, and cladoceran assemblages. Ordination techniques were used to identify relevant physical and chemical environmental parameters that best explain the distribution of these biota in the studied lakes. Diatom assemblage composition showed a strong relationship with physical (e.g., lake depth, temperature, organic content of surface sediments) and chemical variables (e.g., lake-water pH, alkalinity, silica concentration). The greatest variance in chironomid and cladoceran assemblages is explained by dissolved organic carbon (DOC) content of lake water, temperature, and the organic content of surface sediments, all parameters which are highly correlated with lake elevation. Increasing lake depth is reflected in diatom and cladoceran assemblages by higher percentages of planktonic species, whereas chironomid assemblages in the deep Engadine lakes are characterised by a high proportion of lotic taxa. In contrast to similar studies in the Northern and Southern Alps, subfossil assemblages in the Engadine mountain lakes showed a strong relationship with DOC, which in these weakly buffered lakes is negatively correlated with altitude. According to our findings, chironomid and cladocera remains have a considerable potential as quantitative palaeotemperature indicators in the Engadine area. This potential is somewhat weaker for diatoms which seem to be more strongly influenced by water chemistry and lake bathymetry.

Water clarity modeling in Lake Tahoe: Linking suspended matter characteristics to Secchi depth

Abstract: An additive semi-analytic model of water clarity for the forward problem of calculating apparent optical properties (AOPs) of diffuse attenuation and Secchi depth from the inherent optical properties (IOPs) due to suspended matter in oligotrophic waters is presented. The model is general in form, taking into account algal concentration, suspended inorganic sediment concentration, particle size distribution, and dissolved organic matter to predict Secchi depth and diffuse attenuation. The model’s application to ultra-oligotrophic Lake Tahoe, California-Nevada, USA is described. The function of the clarity model is to quantify the relative effect of phytoplankton or phytoplankton-derived organic materials, other particles such as suspended mineral sediment, and dissolved organic matter on the lake’s clarity. It is concluded that suspended inorganic sediments and phytoplanktonic algae both contribute significantly to the reduction in clarity, and that suspended particulate matter, rather than dissolved organic matter, are the dominant causes of clarity loss.

Landscape predictors of stream dissolved organic matter concentration and physicochemistry in a Lake Superior river watershed

Abstract: We examined landscape predictors of dissolved organic matter (DOM) concentration, molecular weight (Mw), and molar absorptivity at 280 nm (ɛ280) in 60 streams from the Ontonagon River watershed in northern Michigan. During our sampling period (September 19–22, 2002), DOM concentration ranged from 4 to 35 mg C L−1 across streams. DOM Mw and ɛ280 also showed considerable variation among streams. Multiple factor regression showed that stream DOM concentrations were related to watershed area, mean watershed slope, and the percentage of watershed area in certain types of land cover (lake, total wetlands, emergent wetlands, and lowland conifer forests). Streams with higher DOM concentration also had higher DOM Mw and molar absorptivity. Moreover, DOM Mw and ɛ280 were negatively related to the % lake and positively related to the % total wetlands in the watershed. In general, landscape variables explained more among stream variation in DOM concentration than in DOM Mw or ɛ280 in this watershed. It thus appears that the many biogeochemical processes controlling DOM input, transportation, and degradation weaken relationships between stream DOM composition and terrestrial organic matter dynamics in this relatively large watershed. Our results indicate that the total proportion of wetlands alone may be inadequate to predict DOM concentration or physicochemistry in streams flowing from large watersheds of variable morphology and land cover composition.

Can algal photosynthetic inorganic carbon isotope fractionation be predicted in lakes using existing models

Abstract: Differential fractionation of inorganic carbon stable isotopes during photosynthesis is an important cause of variability in algal carbon isotope signatures. Several physiological models have been proposed to ex- plain algal photosynthetic fractionation factors (ep). These models generally consider CO2 concentration, growth rate, or cell morphometry and have been supported by empirical evidence from laboratory cultures. Here, we explore the applicability of these models to a broad range of lakes with mixed phytoplankton communities. Under- standing this fractionation is necessary for using carbon stable isotopes for studies ranging from food webs to paleolimnology. In our largest comparative study, values

Biodiversity of the wetlands of the Kakadu Region, northern Australia.

Abstract: The biodiversity values of the wetlands in the Kakadu Region of northern Australia have been recognised as being of national and international significance, as demonstrated through their listing by the Ramsar Convention on Wetlands. Analyses of the wetland biodiversity have resulted in the production of species list for many taxa, and some population and community-level analyses of biomass and abundance, and the mapping of habitats at multiple scales. Wetland habitats include inter-tidal mud-flats, mangroves, hyper-saline flats, freshwater flood plains and streams. The tidal influence on the saline wetlands is pronounced, as is the influence of the annual wet-dry cycle of the monsoonal climate on the flood plains and streams. The vegetation is diverse and highly dynamic with rapid turnover of organic material and nutrients. The fauna is abundant with endemism being high in some habitats. Most fauna analyses have focussed on vertebrates with a large amount of information on waterbirds and fish in particular. However, despite extensive effort over the past two decades much is still unknown about the biota. While the invertebrate fauna in the streams has received some attention, a large taxonomic classification effort is required. The functional inter-relationships between habitats and species have largely not been assessed. Further, the ecology of many species is only cursorily known. At the same time there has been increased attention to pressures on the wetlands, such as weeds and feral animals, water pollution, and the potential impact of climate change and salinisation of freshwater habitats. Importantly, given the social context of the region, increased attention is being directed towards traditional use and management of the wetlands.

Species diversity in the Florida Everglades, USA: A systems approach to calculating biodiversity

Abstract: The Everglades, a complex wetland mosaic bounded by human development at the southern tip of the Florida Peninsula, is home to a wide array of species, including 68 threatened or endangered animal species. Species richness within Everglades National Park, at the southern extreme of the Greater Everglades ecosystem, is 1033 plant taxa, 60 reptile taxa, 76 mammal taxa, 432 fish taxa, 349 bird taxa and 38 amphibian taxa. This paper briefly introduces the flora and fauna of the Greater Everglades, focusing on species of special conservation concern and those non-native species that are altering native ecology. While there is conservation utility in cataloging biodiversity, we argue that counts of species alone are inadequate descriptors of ecosystem condition because they fail to effectively indicate emergent ecosystem properties (resilience, productivity). We develop an approach to calculating biodiversity based on systems theory that can be applied across trophic levels to provide a condition benchmark that accounts for food web interactions. The Everglades, for which detailed flow data between ecosystem components have been compiled as part of ongoing modeling efforts (DeAngelis et al., 1998), is among the few ecosystems globally for which this technique is currently feasible. Flow data are coupled with exogenous forcing energies (in emergy units – Odum, 1996) to compute transformity values (Odum, 1988) for biotic and abiotic components of an Everglades graminoid marsh community. We calculate across-trophic level biodiversity using the Shannon information equation applied to ecosystem emergy flows. Results suggest that the graminoid marsh is operating at 42% of theoretical maximum ecosystem flow diversity. By comparing observed flows with theoretical maximum flows, we provide a measure of component conservation value; we observe strong overlap between species with lower than expected emergy-based importance and those known to be currently threatened or endangered. A significant positive association between this conservation value and transformity in the marsh suggests systematic uppertrophic level biodiversity degradation.

Seasonality in UV transparency of an alpine lake is associated to changes in phytoplankton biomass

Abstract: We studied the temporal variation in ultraviolet (UV) radiation transparency in the water column of a low dissolved organic carbon (DOC) lake (range: 0.12–0.65 mg L−1) located above the treeline. After ice-break, the water column was spatially segregated into an upper zone (0–4 m depth) with relatively constant UV transparency and a lower zone (4–9 m depth) where transparency decreased over time, for example at 380 nm, by up to 70%. This temporal decrease in UV transparency was significantly correlated with the increase in phytoplankton chlorophyll a. For the entire study period, there was no clear relationship between changes in UV transparency and colored dissolved organic matter (CDOM) absorptivity. Furthermore, changes in DOC concentration were not reflected in CDOM absorptivity or fluorescence, indicating a discrepancy between estimates of concentration and optical properties of this material. Use of spectral slope to track signals of CDOM photobleaching resulted in no consistent pattern. An indication of the low proportion of UV-absorbing chromophores in the dissolved organic matter (DOM) pool was obtained by applying size-exclusion chromatography combined with simultaneous measurements of DOC and UV absorption. These results indicated that more than the 50% of the DOM did not have significant UV absorption. Electrospray mass spectrometry analysis of DOM also showed a low diversity of organic compounds which exhibited relatively low molecular weight (< 250 D). These results, in combination with measurements of DOC-specific absorptivity and fluorescence, indicated that DOM in this lake is mainly autochthonous. Overall, our results show that factors which have been established to explain temporal changes in UV transparency of high DOC lakes may have little application in this and similar alpine lakes. Finally, reconstruction of the UV-exposure history in alpine lakes may have to take into account the discrepancy between DOC and CDOM.

Carbon sources of fish in an Amazonian floodplain lake

Abstract: In a tropical floodplain lake in central Amazon (L. Camaleao), we investigated seasonal shifts in primary carbon sources for commercially important fish species over an hydrological cycle. Carbon and nitrogen stable isotope and stomach content analyses were conducted to investigate the feeding preferences of six species with different feeding habits: Cichla monoculus (piscivorous species), Schizodon fasciatus (herbivorous), Prochilodus nigricans (detritivorous), and the omnivorous species Triportheus angulatus, Colossoma macropomum and Mylossoma duriventre. Stomach content and isotopic analyses exhibited a high seasonal variation for four out of the six species. The dominant food items were fruits and seeds, plant material, zooplankton and aquatic and terrestrial insects. Over the hydrological cycle, C3 plants were the major carbon source for all fish species. In addition, seston and aquatic C4 macrophytes were very important carbon sources for most species. Our findings underpin the complex trophic linkages between floodplain lakes and the aquatic terrestrial transition zone as postulated by the Flood Pulse Concept.

Comparison between the fish communities of lakes, reservoirs and rivers: can natural systems help define the ecological potential of reservoirs?

Abstract: The European Water Framework Directive (WFD) aims at improving the ecological status of continental waters, including man-made water bodies. Thereby it raises the question of the reference conditions for reservoirs. A number of limnologists consider reservoirs as intermediate systems between lakes and rivers. Hence, the aim of this study is to contribute to the implementation of the WFD by comparing the fish communities across these three types of ecosystems. This was achieved using fish sampling data from 21 natural lakes, 50 reservoirs and 549 river stations. The lists of occurring species are very similar between lakes and reservoirs, and appear as a subset of the species occurring in rivers. Lakes and reservoirs are also very similar in terms of common and rare species. Conversely, the comparison of community structures (summarised by correspondence analysis axes) supports the hypothesis of an intermediate position of reservoirs between lake and river systems. This latter result could reflect the effect of large-scale processes undergone by freshwater ecosystems whatever their type and the non-independence of water bodies within their catchments, particularly when considering the communities of highly mobile organisms like fishes. Although the major conservation concerns are about natural systems, artificial ones should also be considered in monitoring and assessment programs in order to allow efficient catchment-scale management policies.

Biological diversity of peatlands in Canada

Abstract: Knowledge about the biodiversity of Canada’s vast peatlands is poor largely because peatlands have not been routinely differentiated from other types of habitats. Plants are better known than the animals. Systematic surveys of peatland plants began in the late 1800s, but did not begin in earnest until the 1950s. With the exception of a few marshes, peatlands are classified into bogs (18 forms), fens (17 forms), and swamps (21 forms). Bogs are the most widespread compared to fens and swamps. Peatlands occur throughout most of Canada but are most common in the Boreal, Subarctic, and Arctic Wetland Regions. Species richness for plants clearly separates bogs and fens. Average number of total species is greater in fens than in bogs. Species richness of herbs, fern and fern allies, and bryophytes is greater in fens than in bogs, and it is greater in bogs for trees and lichens. Bryophytes contribute the most to species richness in bogs, while herbs are most important in fens. Bogs on the Atlantic coast appear to have greater species numbers of lichens and shrubs than bogs on the Pacific coast. Herbs likely contribute more to total species numbers in fens in eastern Canada than in western Canada. There are species of mammals, birds, herptiles, biting flies, beetles, dragon-flies, water mites, rotifers, and protozoans that are restricted to peatlands or are found in both peatlands and other habitats.

Polychlorinated biphenyls, mercury, and potential endocrine disruption in fish from the Hudson River, New York, USA

Abstract: Tissue residues of total mercury (Hg), total polychlorinated biphenyls (PCBs), and lipid-based PCBs; plasma concentrations of endocrine biomarkers; and reproductive and histologic biomarkers were assessed in 460 carp (Cyprinus carpio), bass (Micropterus salmoides and Micropterus dolomieui), and bullhead (Ameiurus nebulosus) collected from eight sites across the Hudson River Basin in the spring of 1998 to determine if endocrine disruption was evident in resident fish species and to evaluate contaminant-biomarker interrelations. Total PCBs in bed sediments (maximum 2,500 μg kg−1) could explain 64 to 90% of the variability in lipidbased PCB residues in tissues (maximum 1,250 μg PCB g-lipid−1) of the four species. The 17β-estradiol to 11-ketotestosterone ratio, typically less than 1.0 in male fish and greater than 1.0 in females, exceeded 1.4 in all male largemouth bass and 35% of male carp and bullhead at one site 21 km downstream from a major PCB source. Endocrine biomarkers were significantly correlated with total Hg in female smallmouth bass and carp, and with lipid-based PCBs in males of all four species. Empirical evidence of endocrine modulation in blood plasma of male and female fish from sites with and without high PCB residues in bed sediments and fish tissues suggest that PCBs, Hg, or other contaminants may disrupt normal endocrine function in fish of the Hudson River.

Organic carbon and bacterial heterotrophic activity in the maximum turbidity zone of the Seine estuary (France)

Abstract: The aim of this study is to understand the sources, biodegradability and fate of organic carbon entering the maximum turbidity zone (MTZ) of the Seine estuary. Dissolved (DOC) and particulate organic matter (POC), and their biodegradable fractions (BDOC and BPOC) were investigated immediately upstream and within the MTZ in various hydrological conditions together with bacterial production of free-living and particle-associated cells. At the entrance of the MTZ, average DOC was 3.6 mg C l−1 with a biodegradable fraction of 23%. The DOC and BDOC/DOC ratio decreased linearly with increasing salinity, indicating a dilution of river freshwater with a higher DOC and higher BDOC/DOC ratio than marine waters. The organic content of suspended matter (SM) at the entrance of the MTZ was high (POC/SM ratios up to 10.6%), especially during phytoplankton blooms when high BPOC/POC ratios were also found. Within the MTZ, the carbon content of SM was lower and less variable; the biodegradable fraction of POC in the MTZ was lower than upstream, illustrating the progressive bacterial degradation of BPOC within the MTZ. Total bacterial production in the MTZ fluctuated between 0.2 and 5.1 μg C l−1 h−1; average production of free-living bacteria was 0.77 μg C l−1 h−1 while that of attached bacteria was 1.47 μg C g SM−1 h−1. Growth rates of attached bacteria were, on average, three times higher than those of free-living ones. Bacterial activity can explain the decrease in the POC/SM ratio observed between summer and fall in the MTZ.

Scale-dependent influences on water quality, habitat, and fish communities in streams of the Kalamazoo River Basin, Michigan (USA)

Abstract: In 2002, we investigated regional versus local influences of 22 streams in the Kalamazoo River basin, MI (USA) to: 1) determine how stream water quality, habitat, and fish communities were influenced by environmental variables at multiple spatial scales, and 2) examine linkages among watershed, riparian corridor (total and local stream corridors), and instream characteristics. Our data show that environmental patterns and processes operating at different spatial scales regulated stream water quality, habitat, and fish communities in Michigan streams. Broader spatial scales, including the watershed and total stream corridor (100-m riparian buffer extending the entire stream length upstream of the site), were the best predictors of water quality (R 2 = 0.26–0.74), whereas the local stream corridor (50-m riparian buffer extending 200 m upstream of the site) was the best predictor of stream habitat (R 2 = 0.23–0.59). Fish community structure was explained by various factors operating at both the watershed and local scales (R 2 = 0.24–0.61). Anthropogenic factors (e.g., land use) had a greater influence on fish species composition (46% of the explained variation) than did natural environmental features (e.g., geology; 16%) or spatial variables (e.g., latitude, 13%). Understanding how environmental factors constrain stream ecosystem structure at multiple scales will help water resource specialists target appropriate scales and factors for management and restoration efforts.

Biogenic silica accumulation in the sediments of Iron Gate I Reservoir on the Danube River

Abstract: Damming of rivers can result in severe downstream effects such as changing sediment and nutrient fluxes that potentially affect coastal ecosystems. Closing of the Iron Gates Dams in the lower Danube River was linked to a decrease in dissolved silica flux to the Black Sea of 600,000 t yr−1. A recent study on the Iron Gate I, however, indicated a dissolved silica removal within the reservoir of only 16,000 t yr−1. Such an order of magnitude difference between actual budgets and earlier estimates is unlikely to be caused by changes in hydrological or biogeochemical conditions. In order to separate annual variations and downstream effects of damming, we analyzed the sedimentary records of biogenic silica using dated sediments. Results confirm the detailed budgets of dissolved silica. In 2001, a total biogenic silica accumulation in the sediments of the Iron Gate I Reservoir of 19,000 t Si yr−1 was determined and represents the highest retention over the past 20 years. The accumulation of biogenic silica in the Iron Gate I Reservoir was compared with data from the coastal Black Sea. Biogenic silica in the sediments of the coastal Black Sea start decreasing before Iron Gate I Dam was completed in 1971. In conclusion, construction of the largest impoundment on the Danube River, the Iron Gate I Reservoir, was not solely responsible for decreasing the silica loads downstream at the coastal Black Sea.

Influence of hydraulic conductivity on communities of microorganisms and invertebrates in porous media: a case study in drinking water slow sand filters

Abstract: The impact of reduced hydraulic conductivity on the abundance and diversity of microorganisms and invertebrates was examined in an artificial ecosystem consisting of a slow sand-filter. Sand-filters processed pre-treated lake water under high flow rates and acted as small ecosystems inhabited by a complex community. The first trophic level consisting of microorganisms serves as a food source for a dense community of protists, micro- and macro-invertebrates. The reduction of hydraulic conductivity due to the development of larger bacterial and fungal biomass induced a shift of the microbial community towards anaerobiosis that may increase clogging by carbonate precipitation. The presence of more bacterial prey seems to favour the development of higher trophic levels. Predation and bioturbation by eukaryotes were not able to counteract the reduction of hydraulic conductivity due to prokaryotic clogging.

Comparative influence of resuspended glacial sediment on physicochemical characteristics and primary production in two arctic lakes

Abstract: We compared physicochemical properties and rates of phytoplankton and epipelic primary production in two shallow lakes in the Alaskan arctic on eight occasions over three years. The two morphometrically similar lakes lacked defined inlets and had a mean depth of 2.2 m. The lakes differed with respect to glacial influence. Lake GTH 112 was continuously turbid due to resuspension of glacial silt from the lake bed, while GTH 114 showed higher clarity as it was situated on coarser glacial drift. The two lakes contrasted sharply in euphotic zone nutrient concentrations. Soluble reactive phosphorus, NO 3 − -N and NH 4 + -N concentrations averaged 0.17, 2.5 and 12.6 μM, respectively, in GTH 112, but were generally at or below the detection limit of 0.05 μM in GTH 114. Reduced light limited the ability of phytoplankton in GTH 112 to use the increased nutrients, and volume-based rates of phytoplankton primary production were similar between lakes. High turbidity in GTH 112 decreased the average percentage of total lake volume and sediment surface within the euphotic zone to 63% and 47%, respectively, compared with values of 88% and 85%, respectively, for GTH 114. Consequently, the average whole lake (phytoplankton plus epipelic) primary production rate in GTH 112 (8.5 mmol m−2 d−1) was significantly lower than the mean rate (12.3 mmol m−2 d−1) for GTH 114. The increase in turbidity affected benthic and pelagic habitats proportionately, as epipelon accounted for about 25% of total whole lake primary production in both lakes.

A carbon budget for an oligotrophic clearwater lake in mid-Sweden

Abstract: In this study, a whole-lake carbon budget for the oligotrophic, clearwater Lake Eckarfjarden was established both on an annual and seasonal basis. For budget calculations, the lake was divided into three habitats (pelagial, littoral and benthic) and the biota into 19 functional groups. In the lake, major parts of biomass (97%) and primary production (91%) are concentrated in benthic and littoral habitats and to a few functional groups. Respiration on the other hand, is focused on benthic and pelagial habitats where 60% and 39%, respectively, of the respiration took place. Our conceptual model indicates strong interactions between habitats. For instance, the pelagial is fed with carbon fixed by primary producers in the benthic and littoral zones. On an annual basis, total primary production exceeds total respiration and the lake is net autotrophic. However, there are clear differences between habitats and between seasons. For instance, the littoral is net autotrophic during spring, summer and autumn, the benthic habitat is net autotrophic only during summer, and the pelagial is always net heterotrophic. Our results demonstrate clear couplings between habitats and organisms and the importance of a holistic view when studying lake ecosystems.

Effect of nutrients on culture dynamics of marine phytoplankton

Abstract: The effects of nitrate, ammonium and phosphate on the abundance, chlorophyll a content (chl a), in vivo fluorescence, particulate organic carbon, nitrogen, phosphorus and cell morphology of the diatom Skeletonema costatum, the dinoflagellate Prorocentrum micans and the coccolithophore Emiliania huxleyi were investigated in the laboratory. The carbon:chlorophyll a ratio (as weight), a parameter often used in productivity estimates, differed substantially among the three species as well as at different nutrient concentrations at the end of the exponential growth phase. The cell chl a content was higher in the earlier phases of growth in all three species in agreement with previous investigations. Average chl a content per cell during the experiments was higher in P. micans (8 pg) than in S. costatum (0.4 pg) and E. huxleyi (0.2 pg). However, chl a content per unit volume was higher in E. huxleyi (~15 fg μm−3) than in S. costatum (~7 fg μm−3) and P. micans (~1 fg μm−3). Prorocentrum micans cultures reached the highest total biovolume (74 mm3 L−1 and was 3 and 5 times higher than S. costatum and E. huxleyi cultures, respectively) under high nutrient concentrations. Nevertheless, total chl a concentration of S. costatum culture was almost twice higher (122 μg L−1) than that of the other two species at the end of the exponential growth phase. Phosphate consumption by S. costatum occurred at higher rates compared to the other two species during the experimental period, probably showing that this nutrient was more favourable for this species. Our findings from these laboratory experiments emphasize that chl a values in the natural habitat may not accurately indicate actual phytoplankton biomass.

Phosphate uptake by seston and epilithon in the Grand River, southern Ontario

Abstract: Phosphate uptake and release by epilithon and seston were measured in the eutrophic Grand River during May to October over three years. Measurements were performed in stirred beakers of freshly collected river water containing seston and, for measurements of uptake by epilithon, unglazed ceramic tiles that had been colonized by epilithon in the river. Areal PO43− uptake was dominated by the epilithon, especially when the water level was low, although uptake per ash-free dry mass was greater for seston. Uptake rates varied on both short ( 1 h. On average, about half of sestonic PO43− uptake was by the picoplankton (0.2 − 2.0μm) size-fraction, and this fraction was most important when total uptake was low. Net changes in SRP during incubations of river water were consistent with both epilithon and seston regenerating PO43−, at least at times, so that net uptake is less than gross uptake and probably near zero at low flow. These net uptake experiments also served to highlight some difficulties with measuring P dynamics in microcosms, especially that uptake and regeneration are high enough that PO43−, and therefore PO43− uptake, can change rapidly in microcosms filled with river water.

Changes in bacterial community composition along a solar radiation gradient in humic waters

Abstract: It has been demonstrated that solar and particularly UV-radiation has strong effects on the production, activity and abundance of bacterioplankton, whereas effects on bacterial community composition (BCC) are unclear. We performed 3 independent experiments where humic water (either from a lake or a swamp) was incubated at different depths to create a gradient of intensity of exposure to natural solar radiation. Bacterial community composition, as assessed by terminal restriction fragment length polymorphism analysis (t-RFLP), changed gradually with increasing depth in parallel to decreasing sunlight exposure. Vertical changes in the production of dissolved inorganic carbon, oxygen consumption and bacterial production coincided with changes in BCC, suggesting a relationship between bacterial community composition and function.

Position of the Gulf Stream influences lake nitrate concentrations in SW Ireland

Abstract: A positive relationship was observed between winter nitrate concentrations in two lakes in SW Ireland and the latitudinal position of the Gulf Stream in the previous spring. Weaker but statistically significant relationships were apparent between the Gulf Stream position and weather variables, as well as soil moisture levels, in the same year. Wind speed, cloud cover and precipitation in May and June were negatively related to the Gulf Stream position in April. In contrast, air temperature and sunshine hours in May and June and the magnitude of the soil moisture deficit in June were positively related. There was also a positive correlation between the magnitude of the early summer soil moisture deficit and lake nitrate concentrations in the following winter. This three way linkage implies that the concentration of winter nitrate in these lakes is influenced by a sequence of related factors that are initiated by the latitudinal position of the Gulf Stream. In this sequence the position of the Gulf Stream appears to influence early summer weather in SW Ireland which in turn dictates the extent of moisture deficit in catchment soils and, consequently, the degree of nitrate loss to surface waters in the autumn. This connection, between events in the Atlantic Ocean, weather systems in the North West Atlantic and processes in catchment soils in SW Ireland has implications for both the quality and quantity of biota in lakes and catchments in the region.

Competition between pelagic and benthic microalgae for phosphorus and light

Abstract: In freshwater ecosystems production of both pelagic and benthic microalgae tends to be limited by phosphorus and light. However, the availability of these resources to pelagic and benthic communities differs due to differences in habitat structure. In a well mixed epilimnion individual phytoplankton cells should receive similar light intensities and nutrient concentrations per unit time. Benthic microalgae colonize substrates forming three-dimensional mats. Their access to nutrients and light is partially determined by the vertical architecture of the mat and often restricted to the canopy layer algae. In addition, algal mats will always be shaded by the phytoplankton inhabiting the water column above.

Inhibition of primary production by UV-B radiation in an arctic bay - : model calculations

Abstract: Inhibition of primary production by UV-B radiation (UVBR) in Kings Bay, western Spitsbergen, was modelled using measured physical and biological data. The underwater radiation regime was modelled using continuous measurements of incoming radiation and repeated measurements of underwater attenuation of Photosynthetic Active Radiation (PAR) and UVBR. By using attenuation measurements, P/I curves and UVBR sensitivity measurements, we modelled the reduction of primary production in the photic zone for 14 days. We also calculated how the estimate was dependent on the different factors. The model showed that, on average, 2.9 % of the primary production was inhibited by UVBR, assuming that the inhibition is a function of the UVBR irradiance. If the ozone layer were reduced to 200 DU, the inhibition would increase to 4.4% using unweighted UVBR values. The model indicated that at ambient ozone levels the inhibition was practically independent of the chosen weighting function, but the choice was critical when predicting the effects of a depleted ozone layer. At 200 DU, using DNA weighting, the inhibition was 14.4% but using erythema weighting it was 6.5%. Different P/I curves did not change the estimate while changes in water attenuation gave results in the range 1.6–5.2%. The most uncertain factor in the model was the estimate of the sensitivity of primary production. Using four different in situ incubations, the estimated integrated reduction in primary production caused by UVBR ranged from 0.05–4.1%.