Date of Graduation

5-2013

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

J. Thad Scott

Committee Member

Michelle A. Evans-White

Second Committee Member

Mary Savin

Third Committee Member

Brian E. Haggard

Abstract

Anthropogenic enrichment of nitrogen and phosphorus is one of the most pervasive and detrimental threats to aquatic ecosystems worldwide. In streams that rely on allochthonous basal food resources, such as leaves, nutrient pollution can result in altered food quality and decreased carbon (C) standing stocks. However, the magnitude and mechanisms of this change in quality are poorly understood. Laboratory microcosm studies were conducted to 1) quantify the response of litter C:P to a gradient of phosphorus (P) enrichment (0, 0.05, and 0.5 mg SRP/L) across leaf species with variable levels of degradability (sugar maple and oak), and 2) quantify the response of litter C:P to a range of P concentrations (0, 0.05, and 0.5 mg SRP/L) and light availability (15 and 500 µmol photons m-2 s-1). Results of the first experiment showed that litter %P increased and C:P decreased with increasing water column P concentrations and this response was greater for the more labile maple species. Carbon:P remained relatively constant through time in the low-P treatments (2600 for both maple and oak) and declined significantly in the high-P treatments (480 and 1040 for maple and oak, respectively). Results of the second experiment demonstrated that phosphorus concentrations and light availability differentially affected algal biomass (as chlorophyll a), microbial metabolic rates, and litter stoichiometry. Algal biomass responded to increased P enrichment only when coupled with greater light intensity, and respiration rates increased with P enrichment in both light levels. Litter C:P ratios decreased significantly with P enrichment with a differential response across light intensities. Our results demonstrate the complexities of nutrient pollution on forested stream ecosystem functioning where allochthonous food resources are important. The effects of nutrient enrichment on detrital quality can provide an important link to understanding how nutrient loading impacts aquatic consumers and potential biodiversity losses.

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