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Downstream Sites (downstream + site)
Selected AbstractsMolluscan shellfish biomarker study of the Quebec, Canada, Saguenay Fjord with the soft-shell clam, Mya arenariaENVIRONMENTAL TOXICOLOGY, Issue 3 2002C. Blaise Abstract A spatial and temporal survey of six sites in the Saguenay Fjord and of one adjacent site in the St. Lawrence River estuary (Quebec, Canada) was undertaken to study the possible effects of anthropogenic contaminant input on soft-shell clam (Mya arenaria) populations. Bivalve sampling sites were selected because they reflected a range of areas representative of either no known (or apparent) pollution sources or of areas potentially influenced by different gradients and types of contamination sources. The most upstream site selected in the Saguenay Fjord, nearest to a highly populated and industrialized sector, and the most downstream site, near its mouth with the St. Lawrence River estuary, spanned a distance of some 70 km and encompassed the entire intertidal area suitable for Mya arenaria habitat. To measure effects in collected animals, we used a comprehensive battery of biomarkers composed of metallothionein-like proteins (MT), 7-ethoxyresorufin O-deethylase activity (EROD), DNA damage (DD), lipid peroxidation (LPO), vitellinlike proteins (Vn), phagocytosis (PHAG), nonspecific esterase (NspE) activity, and condition factor (weight-to-length ratio of clams). Vn, PHAG, DD, and NspE biomarkers were assayed in hemolymph (or hemocytes), whereas others (MT, EROD, LPO) were determined in the digestive gland. Whole-tissue metal content was also quantified in clams collected in the spatial survey. The spatial survey conducted in June 1997 showed significant effects at all sites, and principal component analysis indicated in addition that the more important responses were linked to the MT, LPO, and NspE biomarkers. Clams collected from sites closest to the upstream reaches of the fjord generally displayed higher levels of tissue metals (cadmium, manganese), as well as greater responses of NspE activity, MT, LPO, and PHAG. Animals collected from sites influenced by municipal wastewaters had higher levels of Vn, suggesting the presence of environmental estrogens. The results of the temporal survey (six monthly samplings of clams at three sites from May through October, 1997) showed that the bivalve reproductive cycle (vitellogenesis and spawning) can modulate the expression of several biomarkers. Vn levels, for example, were positively correlated with DD and EROD and negatively correlated with MT, suggesting that reproduction can influence the susceptibility of clams to some contaminants. Discrimination analysis over the 6 months of sampling revealed that the mean value of the discriminant function changed significantly over time, suggesting important changes in the relative contribution of each biomarker. In short, this study has provided evidence that clam populations in the Saguenay Fjord are impacted by multiple sources of contamination whose effects can be modulated by reproduction. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 170,186, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10048 [source] Day,night changes in the spatial distribution and habitat preferences of freshwater shrimps, Gammarus pulex, in a stony streamFRESHWATER BIOLOGY, Issue 4 2005J. M. ELLIOTT Summary 1. As many invertebrates are nocturnal, their spatial distribution and habitat preferences may change from day to night. Both aspects are examined for Gammarus pulex by testing the hypotheses: (i) a power function was a suitable model for the spatial distribution of the shrimps in both day and night; (ii) diurnal and nocturnal spatial distributions were significantly different; (iii) diurnal and nocturnal habitat preferences were significantly different. Five different life-stages were treated separately. To ensure that the conclusions were consistent, large samples were taken near midday and midnight in April, June and November over 4 years at two sites about 3 km apart in a stony stream: downstream (n = 30) and upstream (n = 50). 2. The first and second hypotheses were supported at both sites. A power function, relating spatial variance (s2) to mean (m), was an excellent fit in all analyses (P < 0.001, r2 > 0.91), i.e. the spatial variance was density-dependent. All five life-stages were aggregated in the day. At night, the degree of aggregation increased for juveniles at higher densities but decreased for juveniles at lower densities, increased for immature females and males, but decreased slightly for mature females and especially mature males, the latter being close to a random distribution. There were no significant differences between sites, in spite of the lower numbers at the downstream site. 3. The third hypothesis was tested at only the upstream site and supported by comparisons between shrimp densities and 13 physical variables (distance from bank, water depth, water velocity, ten particle size-classes), and three non-physical variables (dry weights of bryophytes, leaf material, organic detritus). During the day, densities were strongly related to particle sizes with the following preferences: 0.5,8 mm for juveniles, 8,256 mm for the other life-stages with a weaker relationship for males. There were no significant positive relationships with the other variables, apart from bryophytes for immature shrimps and adults. At night, densities were unrelated to particle size; juveniles and immature shrimps preferred low water velocities near the banks, often where leaf material and organic detritus accumulated, females often preferred medium water velocities slightly away from the banks, and males showed no habitat preferences. 4. Day samples do not provide a complete picture of habitat preferences and probably identify refuge habitats. Day,night changes in spatial distribution and habitat preferences are an essential part of the behavioural dynamics of the shrimps and should be investigated in other species. [source] Presence of natural and anthropogenic organic contaminants and potential fish health impacts along two river gradients in Alberta, CanadaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2010Ken M. Jeffries Abstract In the current study, 28 organic contaminants were measured, many with estrogen-like activity, in water collected from 16 sites on two rivers in the South Saskatchewan River Basin, Alberta, Canada. The compounds detected included synthetic estrogens (birth control pill compounds and hormone therapy drugs) downstream of municipal wastewater effluents and natural hormones downstream of municipal wastewater effluents and in agricultural areas. Greater concentrations of cholesterol and derivatives, phytosterols, and fecal sterols were measured at the most downstream sites, which indicates cumulative inputs of such compounds in these rivers. A native minnow (longnose dace, Rhinichthys cataractae) was sampled to assess pathophysiological responses to exposure to compounds with estrogen-like activity. Hepatic vitellogenin protein was detected in at least one adult male longnose dace from 14 of 15 sites sampled for fish. Vitellogenin was negatively correlated with hepatosomatic (r,=,,0.47, p,<,0.001) and gonadosomatic (r,=,,0.44, p,<,0.003) indices, which suggests potential health impacts in male longnose dace in the South Saskatchewan River Basin. The current study demonstrates that organic contaminants, many with estrogen-like activity, are distributed over hundreds of kilometers throughout the South Saskatchewan River Basin and not just downstream of major point-sources. Therefore, many activities within these basins impact water quality in the South Saskatchewan River Basin and affect endemic longnose dace populations. Environ. Toxicol. Chem. 2010;29:2379,2387. © 2010 SETAC [source] Reproductive health of bass in the Potomac, USA, drainage: Part 2.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2009Seasonal occurrence of persistent, emerging organic contaminants Abstract The seasonal occurrence of organic contaminants, many of which are potential endocrine disruptors, entering the Potomac River, USA, watershed was investigated using a two-pronged approach during the fall of 2005 and spring of 2006. Passive samplers (semipermeable membrane device and polar organic chemical integrative sampler [POCIS]) were deployed in tandem at sites above and below wastewater treatment plant discharges within the watershed. Analysis of the samplers resulted in detection of 84 of 138 targeted chemicals. The agricultural pesticides atrazine and metolachlor had the greatest seasonal changes in water concentrations, with a 3.1- to 91-fold increase in the spring compared with the level in the previous fall. Coinciding with the elevated concentrations of atrazine in the spring were increasing concentrations of the atrazine degradation products desethylatrazine and desisopropylatrazine in the fall following spring and summer application of the parent compound. Other targeted chemicals (organochlorine pesticides, polycyclic aromatic hydrocarbons, and organic wastewater chemicals) did not indicate seasonal changes in occurrence or concentration; however, the overall concentrations and number of chemicals present were greater at the sites downstream of wastewater treatment plant discharges. Several fragrances and flame retardants were identified in these downstream sites, which are characteristic of wastewater effluent and human activities. The bioluminescent yeast estrogen screen in vitro assay of the POCIS extracts indicated the presence of chemicals that were capable of producing an estrogenic response at all sampling sites. [source] Metal toxicity inferred from algal population density, heterotrophic substrate use, and fatty acid profile in a small streamENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2000Robert B. Genter Abstract The purpose of this study was to examine relations between metal concentrations in periphyton and the abundance of algal species, heterotrophic use of 95 carbon sources, and phospholipid fatty acids (PLFA) of the periphyton in a small stream spanning a mine in Lemhi County, Idaho, USA. Two upstream, two mine, and two downstream sites were examined. Elevated concentrations of As and Cu at the mine sites were associated with communities that were depleted of diatoms and filamentous blue-green algae and characterized by a low-diversity community dominated by a single blue-green alga and patchy populations of the diatom Achnanthidium minutissimum and a filamentous green alga. Carbon source use and PLFA profiles provided a rapid assessment of stream conditions that were consistent with algal taxonomy and with our hypotheses constructed from previous reports on periphyton responses to metal stress. [source] Morphological clines in dendritic landscapesFRESHWATER BIOLOGY, Issue 9 2007A. CHAPUT-BARDY Summary 1. In complex landscapes such as river networks, organisms usually face spatio-temporal heterogeneity and gradients in geomorphological, water, ecological or landscape characteristics are often observed at the catchment scale. These environmental variables determine developmental conditions for larval stages of freshwater insects and influence adult phenotypic characteristics. Environmental clines are therefore expected to generate morphological clines. Such a process has the potential to drive gradual geographical change in morphology-dependent life history traits, such as dispersal. 2. We studied the influence of aquatic and terrestrial environmental factors on morphological variations in Calopteryx splendens across the Loire drainage. To investigate these effects we took explicitly into account the hierarchical structure of the river network. 3. We analysed eight morphological traits. Results showed significant body size variation between tributaries and the presence of a morphological cline at the drainage scale. We observed an effect of pH and water temperature on body size. Individuals in downstream sites were larger than individuals in upstream sites, and adults whose larval stages were exposed to alkaline pH and high temperatures during summer were larger. 4. Body size affects flight abilities in insects. Thus, our results suggest that morphological clines may generate an asymmetric dispersal pattern along the downstream,upstream axis, downstream populations dispersing farther than upstream ones. Such a process is expected to influence population genetic structure at the drainage scale if larval drift and floods do not balance an asymmetrical dispersal pattern of adults along the downstream,upstream gradient. To assess the influence of environmental gradients on the variation of life history traits it is important to understand the population biology of freshwater insects, and more generally of riverine organisms. It is also essential to integrate such data in conservation or restoration programmes. [source] Effects of stream restoration and wastewater treatment plant effluent on fish communities in urban streamsFRESHWATER BIOLOGY, Issue 10 2006ROBERT M. NORTHINGTON Summary 1. Fish community characteristics, resource availability and resource use were assessed in three headwater urban streams in Piedmont North Carolina, U.S.A. Three site types were examined on each stream; two urban (restored and unrestored) and a forested site downstream of urbanisation, which was impacted by effluent from a wastewater treatment plant (WWTP). Stream basal resources, aquatic macroinvertebrates, terrestrial macroinvertebrates and fish were collected at each site. 2. The WWTPs affected isotope signatures in the biota. Basal resource, aquatic macroinvertebrate and fish ,15N showed significant enrichments in the downstream sites, although ,13C signatures were not greatly influenced by the WWTP. Fish were clearly deriving a significant part of their nutrition from sewage effluent-derived sources. There was a trend towards lower richness and abundance of fish at sewage-influenced sites compared with urban restored sites, although the difference was not significant. 3. Restored stream sites had significantly higher fish richness and a trend towards greater abundance compared with unrestored sites. Although significant differences did not exist between urban restored and unrestored areas for aquatic and terrestrial macroinvertebrate abundances and biotic indices of stream health, there appeared to be a trend towards improvements in restored sites for these parameters. Additional surveys of these sites on a regular basis, along with maintenance of restored features are vital to understanding and maximising restoration effectiveness. 4. A pattern of enriched ,13C in fish in restored and unrestored streams in conjunction with enriched ,13C of terrestrial invertebrates at these sites suggests that these terrestrial subsidies are important to the fish, a conclusion also supported by isotope cross plots. Furthermore, enriched ,13C observed for terrestrial invertebrates is consistent with some utilisation of the invasive C4 plants that occur in the urban riparian areas. [source] Integration of lakes and streams in a landscape perspective: the importance of material processing on spatial patterns and temporal coherenceFRESHWATER BIOLOGY, Issue 3 2000George W. Kling 1. We studied the spatial and temporal patterns of change in a suite of twenty-one chemical and biological variables in a lake district in arctic Alaska, U.S.A. The study included fourteen stream sites and ten lake sites, nine of which were in a direct series of surface drainage. All twenty-four sites were sampled between one and five times a year from 1991 to 1997. 2. Stream sites tended to have higher values of major anions and cations than the lake sites, while the lake sites had higher values of particulate carbon, nitrogen, phosphorous and chlorophyll a. There were consistent and statistically significant differences in concentrations of variables measured at the inlet versus the outlet of lakes, and in variables measured at upstream versus downstream sites in the stream reaches which connect the lakes. In-lake processing tended to consume alkalinity, conductivity, H+, DIC, Ca2+, Mg2+, CO2, CH4, and NO3,, and produce K+ and dissolved organic carbon (DOC). In-stream processing resulted in the opposite trends (e.g. consumption of K+ and DOC), and the magnitudes of change were often similar to those measured in the lakes but with the opposite sign. 3. Observed spatial patterns in the study lakes included mean concentrations of variables which increased, decreased or were constant along the lake chain from high to low altitude in the catchment (stream sites showed no spatial patterns with any variables). The strongest spatial patterns were of increasing conductivity, Ca2+, Mg2+, alkalinity, dissolved inorganic carbon and pH with lake chain number (high to low altitude in the basin). These patterns were partly determined by the effect of increasing catchment area feeding into lakes further downslope, and partly by the systematic processing of materials in lakes and in the stream segments between lakes. 4. Synchrony (the temporal coherence or correlation of response) of variables across all lakes ranged from 0.18 for particulate phosphorus to 0.90 for Mg2+ the average synchrony for all twenty-one variables was 0.50. The synchronous behaviour of lake pairs was primarily related to the spatial location or proximity of the lakes for all variables taken together and for many individual variables, and secondarily, to the catchment to lake area ratio and the water residence time. 5. These results illustrate that, over small geographic areas, and somewhat independent of lake or stream morphometry, the consistent and directional (downslope) processing of materials helps produce spatial patterns which are coherent over time for many limnological variables. We combine concepts from stream, lake and landscape ecology, and develop a conceptual view of landscape mass balance. This view highlights that the integration of material processing in both lakes and rivers is critical for understanding the structure and function of surface waters, especially from a landscape perspective. [source] Surprises from the crystal structure of the hepatitis C virus NS2-3 protease,HEPATOLOGY, Issue 6 2006Jerome Gouttenoire Ph.D. Hepatitis C virus is a major global health problem affecting an estimated 170 million people worldwide. Chronic infection is common and can lead to cirrhosis and liver cancer. There is no vaccine available and current therapies have met with limited success. The viral RNA genome encodes a polyprotein that includes 2 proteases essential for virus replication. The NS2-3 protease mediates a single cleavage at the NS2/NS3 junction, whereas the NS3-4A protease cleaves at 4 downstream sites in the polyprotein. NS3-4A is characterized as a serine protease with a chymotrypsin-like fold, but the enzymatic mechanism of the NS2-3 protease remains unresolved. Here, we report the crystal structure of the catalytic domain of the NS2-3 protease at 2.3 Å resolution. The structure reveals a dimeric cysteine protease with 2 composite active sites. For each active site, the catalytic histidine and glutamate residues are contributed by one monomer, and the nucleophilic cysteine by the other. The carboxy-terminal residues remain coordinated in the 2 active sites, predicting an inactive postcleavage form. Proteolysis through formation of a composite active site occurs in the context of the viral polyprotein expressed in mammalian cells. These features offer unexpected insights into polyprotein processing by hepatitis C virus and new opportunities for antiviral drug design. [source] Survival and growth of brown trout Salmo trutta L. embryos and the timing of hatching and emergence in two boreal lake outlet streamsJOURNAL OF FISH BIOLOGY, Issue 4 2008J. Syrjänen Survival, growth and hatching of brown trout Salmo trutta embryos were studied using in situ incubation experiments in two lake outlet streams in Finland. The experimental design in both streams included an outlet site and a reference site far downstream. The date of hatching was recorded and the Elliott,Hurley model was then used to predict the time of emergence based on water temperature. For data analyses, the incubation period was divided into ,winter' (from fertilization to mid March) and ,spring' (from mid March until the end of the experiment). Temperature of the large-lake outlet remained at 1° C through the winter, while in other sites temperature was close to 0° C. In spring, temperature increased more slowly in the large-lake outlet. The survival of embryos was overall very high, from 83 to 98%, and they were larger in the outlets than in the downstream sites. Embryos hatched at the large-lake outlet in March, and 3,5 weeks later in the other sites. Although there were considerable between-site differences in hatching intervals, difference in expected 50% emergence dates of the earliest and latest site was only 4 days. Thus, any growth advantage that the outlet embryos had in winter disappeared by the end of the alevin period. Lake outlets, however, may be important for age 0 year brown trout later during the summer when other stream habitats do not provide adequate food resources. [source] DAM-INDUCED MODIFICATIONS TO UPPER ALLEGHENY RIVER STREAMFLOW PATTERNS AND THEIR BIODIVERSITY IMPLICATIONS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2002C. Mark Cowell ABSTRACT: This study evaluates the streamflow characteristics of the upper Allegheny River during the periods preceding (1936 to 1965) and following (1966 to 1997) completion of the Kinzua Dam in northwestern Pennsylvania. Inter-period trends in seasonal patterns of discharge and peak flow at three downstream sites are compared to those at two upstream sites to determine the influence of this large dam on surface water hydrology. Climatic records indicate that significant changes in annual total and seasonal precipitation occurred over the twentieth century. Increased runoff during the late summer through early winter led to increased discharge both upstream and downstream during these months, while slightly less early-year rainfall produced minor reductions in spring flood peaks since 1966. The Kinzua Dam significantly enhanced these trends downstream, creating large reductions in peak flow, while greatly augmenting low flow during the growing season. This reduction in streamflow variability, coupled with other dam-induced changes, has important biodiversity implications. The downstream riparian zone contains numerous threatened/endangered species, many of which are sensitive to the type of habitat modifications produced by the dam. Flood dynamics under the current post-dam conditions are likely to compound the difficulties of maintaining their long-term viability. [source] | |||||||||||||