Browsing by Author "Niederlehner, Barbara R."

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    A comparison of techniques for estimating the hazard of chemicals in the aquatic environment
    Niederlehner, Barbara R. (Virginia Polytechnic Institute and State University, 1984)
    Estimates of the concentration of cadmium constituting a threat to aquatic ecosystems were derived from laboratory tests conducted at two levels of the biological hierarchy. A population level estimate was derived from single species toxicity tests and a community level estimate was derived from laboratory tests on microbial communities. Estimates were compared to each other and to an ecosystem level estimate derived from reports of ecological health and ambient cadmium levels in rivers, lakes, and streams. Estimates of permissible levels for short term exposures differed by an order of magnitude. Single species toxicity tests indicated that a level of 46.1 ug Cd/L would affect only 5% of taxa. The corresponding estimate from the community level test was 459.4 ug Cd/L. Similar estimates of permissible levels for chronic exposures were not significantly different (1.02 and 0.20 ug Cd/L, single species arid community level tests, respectively). Both of the laboratory derived estimates of permissible levels for chronic exposure fell within a rational range; the minimum level defined by median cadmium levels reported in healthy aquatic systems (0.05 ug Cd/L), and the maximum level defined by median cadmium levels reported in damaged aquatic systems (9.2 ug Cd/L). However, the community level estimate was obtained more efficiently, permitting an estimate of effects on diversity from a single test. Single species level tests, community level tests, and field studies each contributed unique information to hazard evaluation. Using information from all levels will strengthen predictions.
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    Developing a field of landscape ecotoxicology
    Cairns, John Jr.; Niederlehner, Barbara R. (Ecological Society of America, 1996-08)
    Since toxicants are spread over ecological landscapes, it seems likely that they have effects at that level of ecological organization. Landscape ecotoxicology examines the effects of toxic chemicals on larger scales than traditional environmental toxicology. This approach is characterized by the use of endpoints appropriate to the spatial scale across which a toxicant is dispersed, attention to interactions between physical and temporal patterns and the process of ecological impairment, and integration of multiple lines of evidence for toxicity at various scales. In addition, landscape ecotoxicology seeks predictive models in order to influence human actions before environmental damage occurs. Integrating information from damaged systems, toxicity tests, simulation models, and biomonitoring of healthy systems provides the best basis for decisions. Rapid progress in landscape ecotoxicology is expected as scientists incorporate tools, such as remote sensing and spatially explicit simulation models, and then calibrate these models using data from longterm biomonitoring of large areas. Further integration into combined socio-economic-ecological models is also possible.
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    Ecosystem Function in Appalachian Headwater Streams during an Active Invasion by the Hemlock Woolly Adelgid
    Northington, Robert M.; Webster, Jackson R.; Benfield, Ernest F.; Cheever, Beth M.; Niederlehner, Barbara R. (PLOS, 2013-04-22)
    Forested ecosystems in the southeastern United States are currently undergoing an invasion by the hemlock woolly adelgid (HWA). Previous studies in this area have shown changes to forest structure, decreases in canopy cover, increases in organic matter, and changes to nutrient cycling on the forest floor and soil. Here, we were interested in how the effects of canopy loss and nutrient leakage from terrestrial areas would translate into functional changes in streams draining affected watersheds. We addressed these questions in HWA-infested watersheds at the Coweeta Hydrologic Laboratory in North Carolina. Specifically, we measured stream metabolism (gross primary production and ecosystem respiration) and nitrogen uptake from 2008 to 2011 in five streams across the Coweeta basin. Over the course of our study, we found no change to in-stream nutrient concentrations. While canopy cover decreased annually in these watersheds, this change in light penetration did not translate to higher rates of in-stream primary production during the summer months of our study. We found a trend towards greater heterotrophy within our watersheds, where in-stream respiration accounted for a much larger component of net ecosystem production than GPP. Additionally, increases in rhododendron cover may counteract changes in light and nutrient availability that occurred with hemlock loss. The variability in our metabolic and uptake parameters suggests an actively-infested ecosystem in transition between steady states.