Date of Award:

5-1-2004

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Michelle A. Baker

Committee

Michelle A. Baker

Committee

James W. Haefner

Committee

Todd A. Crowl

Abstract

I investigated the environmental control of consumer-mediated nutrient recycling (CNR) in sub-alpine streams by evaluating the effects of water temperature and food elemental composition on the rates and ratios of nitrogen (N) and phosphorus (P) excretion by macroinvertebrates. I predicted that biomass-specific excretion rates would be positively correlated with temperature whereas N:P ratios would primarily relate to food N:P ratio. I measured nutrient release by heptagenaiid larvae eating periphyton of varying elemental composition grown on nutrient-diffusing substrates. I hypothesized that skewed ratios of N:P release would result from differential retention of nutrients in the food. Excretion rates of N and P from macroinvertebrates fed unmanipulated periphyton nearly doubled with increasing water temperature ( > 18°C: 7.97 × 10-3 ± 8.35 × 10-4 μg-N/mg-dry mass/min vs. < 10°C: 4.73 × 10-3 ± 4.33 × 10-4 μg-N/mg-dry mass/min; > 18°C: 9.67 × 10-4 ± 8.58 × 10-5 μg-P/mg-dry mass/min vs. < 10°C: 4.34 × 10-4 ± 7.22 × 10-5 μg-P/mg-dry mass/min). When I used unmanipulated periphyton in feeding trials, excretion N:P ratios were lower in warm water than in cold ( > 18°C: 20.4 ± 1.79 vs. < 10°C: 29.9 ± 3.13). Food N:P ratio affected consumer N:P release in cold water (high-P food excretion N:P= 15.3 ± 3.01 vs. low-P food excretion N:P= 29.9 ± 3.13), but not in warm water. While these results suggest that environmental factors affect macroinvertebrate nutrient release, these effects are small compared to those observed in planktonic ecosystems. Data from a large-scale observational study that I also conducted support these findings.

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