Grantee Research Project Results

Nutrient Cycling in Detrital-Dominated Headwater Streams: The Influence of Stoichiometric Imbalances on Nutrient Uptake and Particulate Nutrient Export

EPA Grant Number: F07E10832
Title: Nutrient Cycling in Detrital-Dominated Headwater Streams: The Influence of Stoichiometric Imbalances on Nutrient Uptake and Particulate Nutrient Export
Investigators: Hood II, James M.
Institution: University of Minnesota
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2007 through September 1, 2009
RFA: STAR Graduate Fellowships (2007) RFA Text |  Recipients Lists
Research Category: Fellowship - Aquatic Ecology and Ecosystems , Academic Fellowships , Fellowship - Aquatic Ecosystem Ecology

Objective:

In small headwater streams, detritivores consume decaying leaf litter (organic matter), transforming a proportion of this material into fine particles. It is unclear how changes in organic matter stoichiometry (carbon: nitrogen: phosphorus, C:N:P) affects the formation of fine particles (FPOM) by detritivores or how FPOM quality ultimately impacts nutrient uptake. This project has three objectives. 1) Determine how litter-detritivore stoichiometries influence the quality of detritivore fecal material. 2) Determine how the stoichiometry of fecal particles affects bacterial metabolism and nutrient uptake rates. 3) Determine how stoichiometric imbalances effect the dynamic between top-down (consumptive) and bottom-up (nutrient regeneration) influences of detritivores on stream metabolism and nutrient cycles.

Approach:

This project will explore how litter-detritivore stoichiometries influences the role of fine particles in stream nutrient cycles. Three experiments will be conducted. First, feeding trials and nutrient egestion measurements will be used to determine how litter and detritivore identity interact to shape fine particle stoichiometry. The second group of experiments will examine how FPOM stoichiometry influences bacterial metabolism and nutrient uptake rates. Finally, a field experiment will be used to evaluate how consumer-resource stoichiometries influence the role of detritivores in stream nutrient cycles.

Expected Results:

Within watersheds, headwater streams play an important role in the assimilation and processing of N and P. These services are influenced, in part, by the stoichiometric balance of leaf litter, detritivores, FPOM, and microbes. This work will help clarify how these four compartments interact and impact nutrient cycles. This work may demonstrate that the role of detritivores in headwater nutrient cycles is dependant upon both the detritivores’ identity as well as the identity of the riparian tree species. Results from this work will improve our understanding of stream nutrient cycling and the export of nutrients to lakes and costal systems.

Project Synopsis:

Globally, small streams play an important role in mediating the impact of nitrogen and phosphorus pollution. In these streams, nutrient cycles are, in part, influenced by organic matter decomposition. During decomposition, detritivores consume bacteria and indirectly shape bacterial metabolism by creating high quality substrates. This project will determine how detritivores shape the nutrient content of fine particles. Then, further work will evaluate how substrate quality influences bacterial metabolism and nutrient uptake. Both detritivore and litter species identity will likely influence nutrient uptake rates. In sum, this work will clarify our understanding of headwater nutrient cycles.

Supplemental Keywords:

Stream, nutrient dynamics, nitrogen, phosphorus, uptake, detritus, ecological stoichiometry, shredders, aquatic ecosystems, biogeochemistry, stream macroinvertebrates,

Progress and Final Reports:

2008

Final