Relative Importance of Water Quality and Habitat to Fish Communities in Streams Influenced by Agricultural Land Use in the Cedar Creek Watershed, Indiana

摘要

Agricultural land use has been shown to negatively impact fish communities in headwater streams that also serve as agricultural drainage ditches. The objective of this study was to determine the relative contributions of water quality and habitat on fish community diversity in streams surrounded by agriculture using a two-step process. First, by determining the relative contributions of water quality and instream habitat to fish community diversity; and second, by using streamside bioassays at sites of varying contamination to determine differences in survivorship, growth, hepatosomatic index (HSI), and condition factor (K). Fish from headwater streams dominated by agriculture were sampled, and habitat characteristics were measured from the same stream reaches. Streamside bioassays were constructed to pump water directly from the stream to expose fishes to seasonal and daily variations in contaminations and contaminant concentrations. Principal components analysis was used to determine important trends in water quality and habitat data, which were then used in multiple linear regressions with fish community data. Ten fish community response variables were best explained by instream habitat, three were best explained by riparian habitat, and four fish community response variables were best explained by stream water contaminants. This indicates instream habitat may be a greater predictor of fish communities than water quality.Results from streamside bioassays suggest water quality does not have a noticeable effect on survivorship, growth, HSI, or K, supporting the hypothesis that fish community integrity may be less influenced by water quality than by habitat quality in agricultural drainage ditches.