Grantee Research Project Results

Biological Controls on Chemical Pollution: How Aquatic Microbial Communities Regulate and Respond to Inputs from Land Use Change

EPA Grant Number: F13F11094
Title: Biological Controls on Chemical Pollution: How Aquatic Microbial Communities Regulate and Respond to Inputs from Land Use Change
Investigators: Bier, Raven
Institution: Duke University
EPA Project Officer: Lee, Sonja
Project Period: August 25, 2014 through August 25, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Fellowship - Ecology , Academic Fellowships

Objective:

Weathering of exposed coal strata releases potential ecological stressors, including metals and sulfur into downstream waterways. This research asks how these stressors alter the fate of nitrogen by differentially affecting those microorganisms responsible for anaerobic nitrogen cycling processes. It further seeks to understand the extent to which microbial responses to these stressors can inform thermodynamic and geochemical predictions for the fate of inorganic nitrogen.

Approach:

This work will take place in the streams of neighboring catchments in southern West Virginia. One catchment drains the largest surface coal mine in West Virginia: the Hobet Mine complex, and the other catchment is absent of surface coalmining. Water and sediment environmental variables will be collected, including substrates (C and N) and stressors (SO₄²−, pH and metals) across a gradient of contaminants. In an observational approach, regression analysis will be used to investigate the extent to which contaminant concentrations and anaerobic nitrogen functional genes of sediment microbes in the field can help explain N₂O fluxes. In an experimental approach, ¹⁵NO₂- will be traced in sediment microcosms exposed to different combinations of stressors and will compare the fate of ¹⁵NO₂- along with the expression of anaerobic nitrogen cycling genes in contaminated and uncontaminated assays. The difference between observed and thermodynamically predicted N pool concentrations will be examined.

Expected Results:

At low concentrations, contaminants may provide additional electron donors for denitrification processes, stimulating nitrogen export from aquatic ecosystems as N₂O and N₂. But at high concentrations they
may serve as toxicants, reducing nitrogen export by the denitrifying community. Thus, the results are expected to show a nonlinear, concentration-dependent relationship between contaminants and N₂O fluxes. Incorporating contaminants and denitrification gene abundances into the regression analysis is expected to increase the explanatory power for denitrification in these aquatic ecosystems. Furthermore, it is anticipated that in laboratory assays with high contaminant loads, using biological information (such as the activity of sediment-denitrifying microorganisms) will improve thermodynamically based predictions for the fate of nitrite.

Potential to Further Environmental/Human Health Protection

Contamination of water resources is widespread, and microorganisms are employed to clean up these sites through bioremediation. By improving the understanding of the relative importance of contaminants in predicting microbially mediated processes, the results from this work could refine current approaches to nutrient management at contaminated sites. For example, at anoxic locations with elevated nitrate and high metal contaminant levels, contaminant-removal strategies may need to incorporate denitrification-management plans if reducing contaminants inhibits rather than stimulates denitrification.

Supplemental Keywords:

alkaline mine drainage, metal contamination, mountaintop mining

Progress and Final Reports:

2015

Final