Water Quality and Fish Community Structure Characteristics of Third/Fourth-Order Streams in the Mississippi Alluvial Plain Ecoregion

Agriculture has influenced stream water quality and fish communities in the Mississippi Alluvial Plain (MAP). In this study, water quality and fish community structure were assessed seasonally (April, June, and October) at three sites each in four agricultural streams and four forested streams. Composite mean values for water quality parameters and fish community indices were generated seasonally for each stream.  Repeated-measures ANOVA was used to test whether water quality and fish communities varied between agricultural and forested streams. Percent similarity (PSI) was used to compare forested stream and agricultural stream fish communities. Water quality and fish community differences between forested and agricultural streams were detected, but the effects varied seasonally for many variables (i.e., stream type × season interaction). Nitrate, phosphate, and total phosphorus concentrations were significantly greater in agricultural streams, and the effect was consistent seasonally.  Fish communities from agricultural and forested streams were not similar (PSI=25%).  Relative abundances of Percidae and Cyprinidae were significantly greater in forested streams, while Centrarchidae relative abundances were greater in agricultural streams. Results of this study will be useful to enhance further understanding of agricultural impacts on water quality and biological communities in MAP streams, which have been largely ignored by management agencies.