Evaluating temporal changes in stream condition in three New Jersey rive basins by using an index of biotic integrity

An index of biotic integrity (!B!) modified for New Jersey streams was used to compare changes in stream condition from the 1970s to the 1990s in Delaware, Passaic, and Raritan River Basins. Stream condition was assessed at 88 sampling locations. Mean IBI scores for all basins increased from the 1970s to the 1990s, but the stream-condition category improved (from fair to good) only for the Delaware River Basin. The number of benthic insectivores and the proportion of insectivorous cyprinds increased in all three basins; however, the number of white suckers decreased significantly only in the Delaware River Basin. Results of linear-regression analysis indicate a significant correlation between the percentage of altered land in the basin and change in IBI score (1970s to 1990s) for Delaware River sites. Results of analysis of variance of the rank-transformed IBI scores for the 1970s and 1990s indicate that the three basins was equal in the 1970s. Results of a multiple-comparison test demonstrated that the 1990s IBI values for the Delaware River Basin differed significantly from those for the Passaic and Raritan River Basins. Many factors, such as the imposition of the more stringent standards on water-water and industrial discharges during the 1980s and changes in land-use practices, likely contributed to the change in the Delaware River Basin. A general increase in IBI values for the Passaic, Raritan, and Delaware River Basins over the past 25 years appears to reflect overall improvements in water quality.