| Using GIS to Identify Functionally Significant Wetlands in the Northeastern United States |
| Of the several automated wetland assessment methods currently available, none are comprehensive in considering all of the primary functions a wetland can perform. We developed a methodology particularly suited to the Northeastern United States that enumerates spatial predictors of wetland function for three primary wetland functions: flood flow alteration, surface water quality improvement and wildlife habitat. Predictors were derived from several wetland assessment techniques and directly from the literature on wetland structure and function. The methodology was then automated using a Geographic Information System (GIs). The resulting Automated Assessment method for Northeastern Wetlands (AMNEW) consists of a suite of eight ARC/INFO GRID module. Using remotely senses land use information and digital elevation models (DEMs), AMNEW produces three separate grids of wetlands that perform each function. The method was tested on four watersheds in Vermont's Lake Champlain Basin. Results and preliminary verification indicate that the method can successfully identify those wetlands in the Northeastern region that have the potential to be functionally important. |
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| Aquatic ecosystems in agricultural landscapes: a review of ecological indicators and achievable ecological outcomes |
| The impacts of agricultural land uses on surface water quality continue to command attention nationwide. In contrast, less consideration has been given to understanding aquatic communities in agricultural ecosystems or what measures might be used to indicate how these communities are responding to changing conditions in the surrounding landscape. This review discusses (1) the role of natural processes in agricultural watersheds; (2) the use of biological indicators in aquatic systems; (3) assessments of the effects of agriculturally-derived pollutants both in-stream and at the landscape scale; (4) achievable ecological outcomes; and (5) recommendations for developing ecological indicators and identifying appropriate restoration goals for agricultural systems. If ecological indicators are to be used effectively, it is necessary to identify those taxa and responses that are most closely associated with agricultural stressors. Once such tools are developed, an overall framework for designing holistic management plans will help identify realistic and achievable restoration goals that maximize the environmental benefits in a watershed. |
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| Toxicity identification evaluation of metal-contaminated sediments using an artificial pore water containing DOC as the dilution media |
| Recent investigations of sediment-associated pollutants in Lake Champlain indicated significant contamination with As, Mn, and Ni in Outer Malletts Bay, Vermont, USA. Ceriodaphnia dubia exposed to sediment pore water from several sites in Outer Malletts Bay showed repeatable, acute mortality at only one site. A toxicity identification evaluation (TIE) was conducted on pore water to determine the contaminants causing mortality at this site. Unlike most TIE applications, the dilution water used in these tests was formulated to match the hardness, alkalinity, pH, conductivity, and dissolved organic carbon content of the pore water. Results from phase I of the TIE indicated that divalent metals may be responsible for toxicity. Phase II results revealed levels of Mn above LC50 values. Spiking experiments employed in phase III confirmed Mn as the principal toxicant in sediment pore water. The formulated pore water worked well and helped ensure that toxicant behavior was influenced primarily by each TIE manipulation and not be physical and chemical differences between the dilution and site water. Although the Mn toxicity at this site may be the result of its unique geomorphology, this situation underscores the need to look broadly for potential toxicants when evaluating contaminated sites. |
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| Sediment organic matter content as a confounding factor in toxicity tests with Chironomus tentans |
| Physicochemical characteristics of sediment unrelated to contaminant levels and bioavailability may influence the outcome of toxicity tests. In particular, sediment organic matter content has the potential to be a confounding factor in toxicity tests using the midge larva Chironomus tentans because the larvae are infaunal and feed on organic matter in the sediments. To examine this possibility, we conducted a series of tests using formulated sediments with varying organic matter contents (0-20%) following the standard U.S. Environmental Protection Agency (U.S. EPA) 10-day C. tentans growth and survival protocol. Formulated sediments made with peat moss, a-cellulose, and maple leaves were tested. An organic-rich natural sediment diluted with formulated sediment to achieve a range of organic matter contents was also examined. In a final experiment, sediments containing each of the four organic matter sources at the same concentration were tested against one another. Survival was not greatly affected by concentration of organic matter, except at the lowest concentrations in natural sediment (6-7%), where survival dipped below 70%. In experiments using peat moss, a-cellulose, and maple leaves, significant differences in C. Tentans growth (measured as ash-free dry weight) were found at different organic matter concentrations. In contrast, concentration of organic matter in the natural sediment dilution series had little effect on growth, perhaps because much of this material was highly refractory. In the comparison experiment, growth differed significantly among the four sediments, with best growth achieved with a-cellulose and leaves. These results suggest that both organic matter quantity and quality can be confounding factors in toxicity tests using C. tentans. |
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| Trophic interactions between yellow perch and their benthic prey in a littoral zone community |
| Yellow perch (Perca flavescens) growth rates in northern lake Champlain have declined in recent years while densities have increased, suggesting resource limitation. At high densities, predators have the potential to influence prey communities, but these effects can be highly complex. Using in situ mesh cages in an unmanipulated littoral zone setting, we examined the effects of two densities (0.5 and 1.5/m2) of yellow perch on (i) their growth and (ii) the abundance of major prey groups in the benthic community. Yellow perch growth rates were significantly lower in the high-density treatment than in the low-density treatment. Because site characteristics were not manipulated, measured covariates reflecting sediment and vegetation variation between cages were used to help clarify treatment effects on benthos. Fish predation on invertebrate prey was significant only in the high-density predator treatment for three of the six prey groups examined (predatory chironomids, prey chironomids, and isopods). For this littoral zone community, availability and abundance of benthic prey strongly influenced yellow perch growth rates; but the effect of yellow perch predation on benthic community structure was only moderate. |
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| Assessing sediment quality in highly heterogeneous environments: a case study of a small urban harbor in Lake Champlain |
| Relatively few case studies have been conducted demonstrating the utility of multiple endpoint approaches to sediment quality assessment in areas with moderate contaminant levels and heterogeneous conditions. Because variability is commonplace in natural systems, assessment approaches must be designed explicitly for these conditions. In an assessment of highly heterogeneous freshwater sediments in Lake Champlain, Vermont, USA, we measured multiple endpoints, including physical and chemical characteristics of the sediment, acute and chronic toxicity in three tests (Ceriodaphnia dubia, Chironomus tentans, and Pimephates promelas), and benthic community composition, at 19 sites throughout Inner Burlington Harbor. Multiple regression techniques were used to investigate whether significant relationships existed between biological endpoints and the physical and chemical characteristics of the sediments. Although all three laboratory exposures indicated toxicity at some sites, little correspondence was found among the tests. No changes in the benthic community could be attributed to trace contaminants. Multiple regression was useful in showing associations between contaminants, grain size, toxicity,and benthic community composition. Although not demonstrating causal linkages, these statistical analyses suggested which factors might be important in driving measured responses. In heterogeneous sites, an individualized assessment approach based on a preliminary analysis of variability might provide the most useful information. |
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| The effects of zinc contamination on the recruitment and early survival of benthic invertebrates in an estuary |
| Using formulated sediment as the test substrate and field exposures, we examined the effects of zinc contamination on the benthic invertebrate community in Mobile Bay. Formulated sediment was mixed to match field sediment in grain size and organic matter content. Clean sediments and sediments dosed with zinc to target concentrations from 250-5000 ug g-1 were exposed in field holding racks anchored on the bottom. The abundance and diversity of benthic invertebrate recruits were used as indicators of sediment quality. We found significant differences in both indicators between clean and zinc contaminated sediments. All taxa did not respond similarly to changing zinc concentrations. Several families of polychaetes, harpacticoid copepods and ostracods appeared to be most sensitive to zinc. Under certain conditions, some taxa, particularly gastropods, were attracted to zinc-contaminated sediments. Taken together, the results suggest that zinc contamination can profoundly affect the nature of the benthic community recruiting into such sediments. Published by Elsevier Science Ltd. |
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| Low levels of dietary methylmercury inhibit growth and gonadal development in juvenile walleye (Stizostedion vitreum |
| Mercury levels in the aquatic environment of North America have been increasing, raising the possibility that this highly toxic heavy metal might alter fish populations. Previous investigations have demonstrated toxic effects of mercury on teleost reproduction, but these findings were observed following unrealistically high exposures. In this study, we used concentrations frequently observed in North American lakes to investigate the effects of dietary methylmercury on growth, gonadal development, and plasma cortisol levels in juvenile walleye (Stizostedion vitreum). For a period of 6 months, two groups of walleye were reared on untainted catfish fillets, while two test groups were fed fillets injected with methylmercury, one group receiving 0.1 ug Hg g-1 food (low-mercury diet) and the other receiving 1.0 ug Hg g-1 food (high-mercury diet). After the exposure period, fish fed the low- and high-mercury diets had mean body burdens of 0.254 ± 0.015 ug Hg g-1 and 2.37 ± 0.09 ug Hg g-1, respectively. Dietary mercury significantly impaired both growth and gonadal development in males, which was apparent as reduced fish length, weight, and gonadosomatic index. Testicular atrophy was observed in fish fed the mercury-tainted fillets, but was nonexistent in control animals. Mercury also suppressed plasma cortisol in juveniles (sexes combined). The findings of this study suggest that dietary methylmercury, at levels currently found in the aquatic environment, might reduce juvenile survival by impairing growth and immune function. Furthermore, these results suggest that methylmercury might also affect reproductive potential of teleosts by impairing testicular development in young. |
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| Role of wetlands in reducing phosphorus loading to surface water in eight watersheds in the Lake Champlain Basin |
| A landscape-level approach was applied to eight rural watersheds to assess the role that wetlands play in reducing phosphorus loading to surface waters in the Lake Champlain Basin. Variables summarizing various characteristics of wetlands within a watershed were calculated using a geographic information system and then compared to measured phosphorus loading through multiple regression analyses. The inclusion of a variable based on the area of riparian wetlands located along low- and medium-order streams in conjunction with the area of agricultural and nonwetland forested lands explained 88% of the variance in phosphorus loading to surface waters. The best fit model coefficients (Pload = 0.86Ag = 0.64For - 30 Ripwet + 160) suggest that a hectare of riparian wetland may be many times more important in reducing phosphorus than an agricultural hectare is in producing phosphorus. These results provide additional support for the concept that protection of riparian wetlands is an important management strategy for controlling stream water quality in multiuse landscapes. |
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| Response of aquatic communities from a Vermont stream to environmentally realistic atrazine exposure in laboratory microcosms |
| The direct and indirect effects of the herbicide atrazine were assessed at the community level under exposure patterns likely to be experienced by stream organisms in Vermont. Both attached algae and benthic invertebrates were collected from a clean site using artificial substrates and established in recirculating 120-L laboratory microcosms. On day 1 of the 14-d experiment, three of six microcosms were treated with 5 ug/L atrazine. Concentrations were gradually reduced by replacing a portion of the water in the systems over time so that by day 7, atrazine concentrations were only about 1 ug/L. Direct effects of atrazine on algal biomass between treatment and control microcosms. Potential indirect effects of reduced algal food availability on benthic invertebrate communities were assessed by comparing assemblages in treatment and control microcosms using both a functional (feeding) group classification and taxonomic composition. There were no significant differences in the functional or taxonomic composition of the benthic invertebrate communities; however, a greater number of insects emerged from the treatment microcosms early in eh experiment compared to controls, suggesting some response to atrazine. Further community-level testing is needed to more clearly determine if atrazine is affecting stream organisms. |
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| Effects of environmental mercury on gonadal function in Lake Champlain northern pike (Esox lucius) |
| Levels of mercury in the environment have increased steadily over the past two centuries, primarily because of human activity (Nater and Grigal 1992). Common point sources of this heavy metal include industrial waste discharge from chloralkali and paper pulp plants. More diffuse emissions, which become widely distributed by global wind currents, result from the combustion of fossil fuels and incineration of municipal wastes. Stricter laws in the United States have decreased the amount of pollution from point sources. In contrast, mercury from diffuse atmospheric origins has been increasing, causing a rise in rainwater concentrations and aquatic environments frequently distant from the source of pollution. Once in aquatic systems, mercury is readily converted to the more toxic methylated form and is the only heavy metal that indisputably biomagnifies through the food web (WHO 1990). Acid rain compounds the environmental impact of anthropogenic mercury because aquatic organisms concentrate more mercury when living in waters with lower alkalinity (Spry and Wiener 1991). The persistence of this heavy metal in teleosts is illustrated by the finding that mercury, unlike cadmium, arsenic, and lead, did not decrease in North American freshwater fish between 1976 and 1984 (Schmitt and Brumbaugh 1990). |
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| Patterns of herbicide contamination in selected Vermont streams detected by enzyme immunoassay and gas chromatography/mass spectrometry |
| The patterns of contamination of the heavily used herbicide atrazine were determined in four Vermont streams. Over two seasons, 600 streamwater samples were collected following rain events and analyzed for atrazine content using a low-cost enzyme immunoassay (EIA). To ensure the accuracy of the EIA and to determine the concentration patterns of five other herbicides commonly used in Vermont (alachlor, cyanazine, metolachlor, pendimethalin, and simazine), 30% of the water samples were also analyzed using standard gas chromatography/mass spectrometry (GC/MS) techniques. Fifty stream sediment samples were also analyzed by GC/MS. The atrazine concentrations detected in the water samples varied from less than 1 to over 7 ug/L, depending on the rainfall patterns during the season, the location of the sampling site within the watershed, and the intensity of the agricultural activity surrounding the sites. Combined water concentrations in all six herbicides were often several times higher than atrazine concentrations. Except in the largest stream, herbicide contamination usually occurred in pulses that dissipated within a few days after each rain event. Only trace amounts of two of the six herbicides were found in stream bottom sediment samples. |
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| Comparison of an enzyme immunoassay and gas chromatography/mass spectrometry for the detection of atrazine in surface waters |
| To determine the reliability of an enzyme immunoassay (EIA) for atrazine, we collected water samples and analyzed them for herbicide content by both EIA and standard gas chromatography/mass spectrometry (GC/MS) techniques. The commercially available EIA uses antibodies linked to magnetic particles to determine sample atrazine concentrations and requires less than 2 h to analyze a run of 50 samples. The EIA was internally consistent with variation of less than 3% between 156 duplicate standards that were run to develop standard curves. For the 217 samples examined, atrazine concentrations measured by the two analytical techniques were highly correlated (r=0.96). Compared to concentrations measured by GC/MS, the EIA produced no false negatives and few false positives (5.53%). The EIA tended to overestimate atrazine concentrations slightly probably the result of cross-reaction in the EIA by atrazine metabolites and structurally related triazine herbicides. Even so, the EIA proved to be a reliable, relatively simple, and cost-effective screening technique for atrazine contamination. |
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| Community-level field method for testing the toxicity of contaminated sediments in estuaries |
| The objective of this study was to demonstrate a method for testing the toxicity of contaminated sediments under field conditions. An artificial sediment that matches field sediment in grain-size distribution and organic matter content was mixed from 11 components and used as the test substrate. Clean sediments and sediments spiked with zinc (~8,000 mg/kg) were exposed in the field on a holding rack anchored on the bottom of Mobile Bay, Alabama. The abundance and diversity (species richness) of benthic invertebrate recruits were used as indicators of sediment quality. The number of recruits was significantly reduced by the presence of zinc in one-week exposures. |
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| Interactions among temporary and permanent meiofauna: observations on the feeding and behavior of selected taxa |
| Meiofauna diets and behavioral patterns are relatively unknown despite the fact that in any system, predatory relationships and behavioral responses may play an important role in determining community structure. Therefore, observations on food preferences, feeding behavior, and encounter interactions of members of a meiofauna assemblage were made in the laboratory in dishes of natural sediment. The diets and behavior of two turbellarian species, Neochildia fusca and Archiloa wilsoni were examined in detail. Both are predators and both feed on a variety of other taxa, including the temporary meiofauna. Based upon the results of these experiments, a potential food web was constructed among the temporary and permanent meiofauna. The behavioral responses of these turbelliarians and other members of the meiofaunal assemblage at times of encounter were also observed, categorized, and quantified. Implications of these behaviors are discussed. |
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Last modified February 24 2003 02:35 PM
