Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

2005

Thesis Director

Robert Fischer

Thesis Committee Member

Scott Meiners

Thesis Committee Member

Charles Pedersen

Abstract

In recent years stream ecologists have come to realize that in order to better understand the processes that occur within streams it is important to incorporate some knowledge of the surrounding landscape into their studies. Previous work on Hurricane Creek indicated that agricultural activities and the proportion of cropland has an impact on stream water chemistry and community metabolism within Hurricane Creek, Illinois. Thus, this study examined stream community composition and food-chain length to ascertain the effects of water quality differences resulting from agricultural land-use practices. The four sites chosen for this study on Hurricane Creek were sampled four times and separated into two groups for analysis of community composition and food chain length: sites heavily impacted by agricultural land-use (more than 69% cropland; sites 11 and 5) and sites less impacted by agricultural land-use (less than 69 % cropland; sites 9 and 6). Examination of benthic macroinvertebrate and stream fish communities did not indicate any significant difference between sites characterized as highly impacted or less impacted based on water chemistry. However, macroinvertebrate community metrics varied significantly with sampling period while fish community metrics were related to stream order. These results suggest that land-use effects on water chemistry and biotic communities may operate on different spatial and temporal scales making it difficult to predict biotic changes from observed abiotic factors. Nitrogen isotopes concentrations have been shown to be particularly useful for quantifying trophic position because organisms become slightly, but detectably, enriched in 1N compared to their food source. In this study food-chain length was determined using stable nitrogen isotope ratios, with macroinvertebrates serving as baselines and fish as top predators. Food-chain length did not vary significantly with productivity, as predicted, but was related to stream size. While the importance of productivity in determining food-chain length remains unclear, these results indicate ecosystem size may play a key role in structuring food webs and trophic interactions.

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