Implications of intra-ecoregion variability on Gulf of Mexico coastal plain stream biological assessment

Ecoregion is generally regarded as the greatest source of variability in composition of fish communities and water quality parameters for streams throughout Louisiana.  A biotically-based stream monitoring program with assessments specific to ecoregion is currently under consideration.  Disparity among major river basins, however, suggests that sub-ecoregion variability could further reduce the discriminating power of locally-applied biometrics.  Biogeographical differences among Louisiana’s aquatic communities are a consequence of the state’s geological legacy, particularly the physical barrier presented by the Mississippi River.  Data used in this study were collected from 1990 to 2008 by the U. S. Environmental Protection Agency, U. S. Geological Survey, U. S. Fish and Wildlife Service, Louisiana Department of Environmental Quality, and the Louisiana State University Agricultural Center.  Canonical discriminant function analysis of water quality data for eight river basins revealed significant differences among basins.  A multivariate analysis of variance on fish abundance data that were reduced in dimensionality with non-metric multidimensional scaling demonstrated the significant effect of basin on community composition.  Results from similar analyses using benthic macroinvertebrate data will be compared for the two aquatic communities.  Implications of intra-ecoregion variability on biological assessment of Louisiana’s coastal plain streams will be discussed.