PARENT SESSION
Oral Session 1: Aquatic Ecology I: Rivers, Nutrients, and Water Quality.
Presiding: D Kashian
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room A 105.
Towards linking nitrogen and phosphorus cycling in stream ecosystems.
Thomas, Steven*,1, Valett, Maurice2, 1 Department of Ecology and Evolutionary Biology, Ithaca, NY, USA2 Department of Biology, Blacksburg, VA, USA
ABSTRACT- Nutrient cycling is examined in streams using the concept of nutrient spiraling. Though an active topic of research for nearly 25 years, rarely have multiple elements been assessed in unison and a conceptual framework for examining coincident spiraling is necessary for advancing our understanding of stream biogeochemistry. In this presentation, ecological stoichiometry (ES) is used to provide the basis for developing a conceptual model of coupled nitrogen (N) and phosphorus (P) spiraling in streams. We demonstrate how stoichiometric constraints manifest themselves in indices of nutrient spiraling. Specifically, ES is related to nutrient spiraling through nutrient uptake rates (U) using nutrient availability and biomass stoichiometry. Various scenarios (e.g., differential recycling, biomass homeostasis) are developed to assess controls over variation in UN:UP. Preliminary results suggest that UN:UP and biomass N:P will be equivalent when the water column is the sole nutrient source and that departures are expected as organisms exploit alternative nutrient pools. Longitudinal variation in nutrient availability is also explored by combining nutrient regeneration rates (R) with U. Modest variation in NU:R:PU:R are demonstrated to have a substantial influence on the absolute and relative concentration of N and P over distance. Lastly, existing field data are reviewed to assess the validity of the model results and specific research questions are developed to help stimulate future research activity in this arena.
Key words: streams, nitrogen and phosphorus, biogeochemistry, ecological stoichiometry