Title

Nutrient Dynamics in the Upper Clark Fork River

Presentation Type

Poster

Abstract

The Upper Clark Fork River (UCFR) has a long history of contamination from historic copper mining; restoration efforts are underway. Nutrient concentrations in the UCFR will be of central importance to ecological form and function. Excess nutrients can cause eutrophication, leading to decreased water quality. Little work
has addressed how the relative abundance of nitrogen (N) and phosphorus (P) influence rates of primary
production and algal growth within the UCFR. We hypothesized that biotic demand for N and P will differ because of inequalities between the stoichiometry of dissolved nutrients and algal biomass should dictate the stoichiometry of biological uptake. Based on availability, we predicted that N would be limiting. To test this prediction, we evaluated nutrient limitation by measuring algal growth in nutrient diffusing substrata (NDS) with different levels of N and P availability. We also performed a nutrient addition experiment during base flow. We used chloride (Cl) as a conservative tracer, and added salts of nitrogen and phosphorus. We took grab samples at two locations during the additions, and analyzed them for Cl, N, and P to determine when the solute pulse passed. Results from NDS confirmed that N is limiting to autotrophic production. Algae grown on N or N and P enriched substrates contained significantly (p<0.05) more chlorophyll than algae grown P enriched substrates. Similarly, the solute release experiment revealed no significant uptake of P, while N was consumed at 2200mg m-2 d-1. Together these data indicate that biotic demand for N is significantly higher than biotic demand for P. Our experiment will connect spiraling metrics with a measurement of nutrient limitation. In addition, since our results indicate that nitrogen is limiting to growth, reducing inputs of nitrogen to the river would be an effective method of preventing excessive autotrophic growth in the river.

Category

Life Sciences

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Apr 17th, 11:00 AM Apr 17th, 12:00 PM

Nutrient Dynamics in the Upper Clark Fork River

South UC Ballroom

The Upper Clark Fork River (UCFR) has a long history of contamination from historic copper mining; restoration efforts are underway. Nutrient concentrations in the UCFR will be of central importance to ecological form and function. Excess nutrients can cause eutrophication, leading to decreased water quality. Little work
has addressed how the relative abundance of nitrogen (N) and phosphorus (P) influence rates of primary
production and algal growth within the UCFR. We hypothesized that biotic demand for N and P will differ because of inequalities between the stoichiometry of dissolved nutrients and algal biomass should dictate the stoichiometry of biological uptake. Based on availability, we predicted that N would be limiting. To test this prediction, we evaluated nutrient limitation by measuring algal growth in nutrient diffusing substrata (NDS) with different levels of N and P availability. We also performed a nutrient addition experiment during base flow. We used chloride (Cl) as a conservative tracer, and added salts of nitrogen and phosphorus. We took grab samples at two locations during the additions, and analyzed them for Cl, N, and P to determine when the solute pulse passed. Results from NDS confirmed that N is limiting to autotrophic production. Algae grown on N or N and P enriched substrates contained significantly (p<0.05) more chlorophyll than algae grown P enriched substrates. Similarly, the solute release experiment revealed no significant uptake of P, while N was consumed at 2200mg m-2 d-1. Together these data indicate that biotic demand for N is significantly higher than biotic demand for P. Our experiment will connect spiraling metrics with a measurement of nutrient limitation. In addition, since our results indicate that nitrogen is limiting to growth, reducing inputs of nitrogen to the river would be an effective method of preventing excessive autotrophic growth in the river.