Department

Program in Earth Systems Science

First Advisor

Erin Hotchkiss

Description

Streams receive, transform, sequester, and transport nitrogen (N). Stream N fluxes and tr ansformations are of particular interest due to the large anthropogenic influence on N movement through the biosphere. Though regional estimates quantifying N fluxes have been proposed, these represent averages that may vary drastically given different loc al geomorphology and species composition. These fluxes are also highly variable at different time scales. In order to characterize short - term N cycling in a (relatively) pristine sub - alpine stream, we added 퐾 푁 15 푂 3 to North Fork Little French Creek in Me dicine Bow National Forest. We measured travel time and ecosystem metabolism in three reaches downstream of the isotope tracer addition. We collected plant, organic matter, invertebrate and water column samples over a period of 45 days before and after the 푁 15 addition. The relative isotopic enrichment in these samples will allow us to calculate uptake length and the degree of biological N assimilation over time. Preliminary indicators for in - stream biological activity and turnover rates can be deduced fro m comparisons of travel time (salt tracer additions) and ecosystem metabolism (diel 푂 2 measurement). Area - specific reconstructions of the fate of N in freshwater ecosystems will increase our understanding of the impact of human - induced changes on Wyoming’ s watersheds.

Comments

Oral Presentation, Wyoming NSF EPSCOR

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Nitrogen Cycling in an Open Canopy Mountain Stream

Streams receive, transform, sequester, and transport nitrogen (N). Stream N fluxes and tr ansformations are of particular interest due to the large anthropogenic influence on N movement through the biosphere. Though regional estimates quantifying N fluxes have been proposed, these represent averages that may vary drastically given different loc al geomorphology and species composition. These fluxes are also highly variable at different time scales. In order to characterize short - term N cycling in a (relatively) pristine sub - alpine stream, we added 퐾 푁 15 푂 3 to North Fork Little French Creek in Me dicine Bow National Forest. We measured travel time and ecosystem metabolism in three reaches downstream of the isotope tracer addition. We collected plant, organic matter, invertebrate and water column samples over a period of 45 days before and after the 푁 15 addition. The relative isotopic enrichment in these samples will allow us to calculate uptake length and the degree of biological N assimilation over time. Preliminary indicators for in - stream biological activity and turnover rates can be deduced fro m comparisons of travel time (salt tracer additions) and ecosystem metabolism (diel 푂 2 measurement). Area - specific reconstructions of the fate of N in freshwater ecosystems will increase our understanding of the impact of human - induced changes on Wyoming’ s watersheds.