Citation:

WALTERS, D., K. M. FRITZ, AND D. L. PHILLIPS. REACH-SCALE GEOMORPHOLOGY AFFECTS ORGANIC MATTER AND CONSUMER Ä 13C IN A FORESTED PIEDMONT STREAM. Presented at North American Benthological Society, Columbia, SC, June 03 - 07, 2007.

Impact/Purpose:

The objective of this task is to addres the risk management LTG for the Contaminated Sites Research Program in the area of contaminated sediments. The contaminated sediments LTGs of "How can we better assess and document the short- and long-term effectiveness of remediation approaches (e.g., dredging vs capping vs monitored natural attenuation (MNA)?" and "How can any short-term negative impacts from the use of one of these options be reduced?" are partially addressed under this task. The research areas in this task includes: the miniturization of sediment toxicity tests & elutriate comparability with whole sediment assays; and bioassays, development and demonstration of ecological tools for sediment monitoring to assess toxicity, gene expression ecological impacts and the use of stable isotope analysis, to develop a mechanistic understanding of energy and material flux within PCB contaminated streams and lakes and their food webs. Stable isotopes techniques will be used to track biomagnification of PCBs and other persistent bioaccumulative contaminants in lake food and stream food webs using a site based approach in collaboration with other ORD labs' contaminanted sediment research.

Description:

We investigated seasonal (spring, autumn) and spatial variation of stream organic matter and consumer δ 13C in a Piedmont stream. Sites were sampled along a continuum and fit into two geomorphic categories: high-gradient, rock-bed ("rock") or low-gradient, sand-bed ("sand") sites. δ 13C was generally enriched in spring, but this response varied among foodweb components. CPOM, Seston, and 5 of 9 trophic guilds (e.g., grazers, insectivorous fish) showed spring enrichment, whereas FBOM and one guild were enriched in autumn. Biofilm, seston, FBOM, and 8 guilds were enriched at rock sites. δ 13C of biofilm and 4 guilds were also positively correlated with drainage area, but the magnitude of enrichment was less than between bed-types. Consumer δ 13C enrichment at rock sites suggests greater reliance on algal carbon than at sand sites; however, biofilm δ 13C was also enriched at rock sites. Thus, geomorphic differences in consumer δ 13C could be related to increased utilization of biofilm at rock sites, consumption of biofilm at rock sites that is enriched relative to biofilm at sand sites, or both mechanisms. Numerous studies have found downstream enrichment of δ 13C in stream foodwebs, but longitudinal (and seasonal) effects were minor compared with site-scale geomorphic effects in this study.

Record Details: