Influences of watershed land use on habitat quality and biotic integrity in Wisconsin streams

We analyzed relationships between watershed land use and habitat quality, and between watershed land use and biotic integrity for 134 sites on 103 streams located throughout Wisconsin. Habitat quality and index of biotic integrity (IBI) scores were significantly positively correlated with the amount of forested land and negatively correlated with the amount of agricultural land in the entire watershed and in a 100-m-wide buffer along the stream. Correlations were generally stronger for the entire watershed than for the buffer. Relationships between forested land and habitat and biotic integrity were linear, although there were several outlying sites with lower-than-expected IBI scores. Relationships with agricultural land use were more complex, with an obvious decline in habitat quality and IBI scores apparent only when agricultural land use exceeded 50%. Even when agricultural land use exceeded 80%, some sites maintained relatively good habitat quality and biotic integrity. These ''good'' sites tended to have relatively high gradients and rocky substrates, and had not been channelized. High urban land use was strongly associated with poor biotic integrity and was weakly but significantly associated with poor habitat quality. There appeared to be a threshold. value of urbanization between 10% and 20% beyond which IBI scores were consistently very low. Overall, watershed land uses had strong effects on habitat quality and biotic integrity in Wisconsin streams.