Tuesday, May 19, 2009
207

Estimation of microbial and animal mineralization across a gradient of nutrient availability

B.M. Cheever1, Jackson R. Webster2, and E.B. Kratzer1. (1) Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, (2) Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061

Animals are both pools of organic nutrients and sites of nutrient transformation. The importance of nutrient regeneration by animals to meeting stream inorganic nutrient demand will depend on the relative importance of microbial mineralization and exogenous nutrient supply. To explore temporal and spatial patterns in microbial mineralization, we placed packs of red maple leaves in five southern Appalachian streams, which spanned a range of nitrogen (N) and phosphorus (P) availability. Packs were collected four times from each stream. Leaf disks from these packs were incubated in filtered stream water, spiked to increase NH4-N or PO4-P concentrations and sampled periodically over four hours to determine microbial uptake rates. Microbial mineralization rates were calculated using these uptake rates and steady state nutrient concentrations. To then compare animal and microbial mineralization, we measured N and P excretion rates of dominant macroinvertebrate taxa and measured microbial mineralization rates from disks cut from two abundant leaf species. We used animal and leaf biomass estimates to scale these rates to reach-level fluxes. These fluxes were compared to whole stream N and P demand determined by step-wise solute injections. This study contributes to our understanding of the role of animal mineralization in stream nutrient dynamics.


Web Page: microbial mineralization, animal excretion, stream nutrient dynamics

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