Land use can affect biological communities directly by introduction of contaminants and indirectly by altering the physical habitat.
Humans also can alter biological communities by stocking non-native fish.
Evaluation of invertebrate and fish communities provides the opportunity to assess responses to changes in environmental conditions using organisms with different life spans. Collection of these data can provide some of the multiple lines of evidence needed to assess water-quality conditions. Although most of these compounds have been banned since the 1970's, they can persist in the environment for decades, which is important because of the multiple pathways for these contaminants to become part of the natural food chain. Organochlorine pesticides and PCBs in bed sediment and fish tissue were related to land use. Few organochlorine pesticides and PCBs were detected, and concentrations were low in bed sediment or fish tissue in forested or rangeland areas.