Anthropogenic lead releases into the environment often end up in aquatic sediments. Ecotoxicologists have historically studied biological effects of toxicants, such as lead, using individuals or populations as models in laboratory settings. It has recently been suggested that because such bottom-up approaches can be difficult to extrapolate to actual effects of contaminants in the field, more research should take a top-down perspective. My project therefore aimed to investigate sediment lead effects at the community level, as well as on ecosystem function. Studies were conducted in a lake with a gradient of low-level sediment lead contamination. An assessment of benthic macroinvertebrate communities at fifty points in the lake revealed a negative correlation between sediment lead concentration and community abundance and diversity. Leaf-litter bags were deployed at thirty of the same points and decomposition rate was assessed after thirty days. Analyses indicated that decomposition rate decreased with increasing sediment lead concentration. Acute lead bioassays, using benthic macroinvertebrates collected from different areas of the lake, revealed that communities from the contaminated area were more tolerant to lead than were communities from uncontaminated areas. The pattern of increased community tolerance as a result of chronic exposure to low-level sediment lead was confirmed with macrobenthic communities that had been pre-exposed to environmentally-relevant lead concentrations for eighteen months in sediment mesocosms. Communities exposed to elevated lead levels had an increased tolerance when exposed to lethal lead levels. This was supported by the observed reduction in abundance and diversity that correlated with an increase in benthic macroinvertebrate community tolerance to lead. Additionally, reductions in leaf-litter decomposition, a vital ecosystem function in lentic systems, were also correlated with reductions in benthic macroinvertebrate abundances. Overall, the low-levels of sediment lead in the lake system appeared to have adverse effects on both structural and functional aspects of ecological integrity. Because sediment concentrations in the lake system were largely below widely accepted guidelines that are considered to be protective of benthic macroinvertebrates, my results have implications for risk-assessment in lentic systems contaminated with lead.
|Advisor:||Klerks, Paul L.|
|Commitee:||Leberg, Paul L., Mopper, Susan, Wagener, Stephen, Wallace, William|
|School:||University of Louisiana at Lafayette|
|Department:||Environmental and Evolutionary Biology|
|School Location:||United States -- Louisiana|
|Source:||DAI-B 75/10(E), Dissertation Abstracts International|
|Subjects:||Ecology, Environmental Health, Environmental science, Limnology|
|Keywords:||Benthic macroinvertebrates, Lead contamination, Leaf-litter decomposition, Pollution-induced community tolerance, Sediment, Sediment quality|
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