Jeff Schell

Advisor: Dr. Stanley Dodson

Ph.D. Zoology, 2003: Detecting and understanding land use effects on zooplankton communities at multiple scales.

Alteration of the earth’s landscape for various anthropogenic enterprises is the dominant factor responsible for the loss of biological diversity worldwide, particularly in freshwater ecosystems. In aquatic habitats the watershed influences external (weather and climate) and internal (abiotic conditions and biotic interactions) factors that govern community structure (abundance, richness and composition). Therefore, changing land use in the watershed of aquatic habitats has the potential to influence biological diversity at multiple scales. To better understand how land use influences biological diversity in aquatic habitats I conducted multiple field surveys, laboratory experiments and theoretical analyses of zooplankton communities and environmental conditions of small, shallow habitats (hereafter ponds) in relation to differences in watershed land use: 1) agriculture, 2) urban, 3) recreation and 4) reference (forested) ponds. The zooplankton communities and environmental conditions of ponds were surveyed in June 1999 (22 ponds) and 2000 (36 ponds). Differences in zooplankton species composition and richness among ponds were related to land use, temperature, dissolved oxygen and turbidity, as well as macrophyte and duckweed cover. I conducted single-species bioassays to test the separate effects of: 1) periodic oxygen stress, 2) turbidity, 3) fine-filtered (0.45 µm) pond water (i.e., ambient mixtures of contaminants) and 4) course-filtered (80 µm) pond water (i.e., planktonic food resources). Periodic oxygen stress, increased turbidity and fine-filtered pond water had adverse effects on test organisms. Nine ponds were surveyed from May 6 to October 7, 2001 to determine if land use influences the temporal 1) means, 2) patterns and 3) coherence of pond environmental conditions, zooplankton taxa abundance and zooplankton diversity. Additional analyses of the 2001 survey data were performed to test predictions of non-equilibrium hypotheses of community development. These additional analyses suggested that agricultural land use increased the temporal variability of environmental conditions, which in turn increased the temporal variability of taxa abundance that, over time, may have resulted in the loss of species. Results of the research establish a clear relationship between land use and zooplankton community structure across different spatial and temporal scales and identify relevant environmental mechanisms responsible for these relationships.