LAND-USE AND AQUATIC BIOINTEGRITY IN THE BLACKFOOT RIVER WATERSHED, MONTANA

Benthic macroinvertebrate samples representing 151 tars were collected in August 1995 to examine the linkage between land use, water quality , and aquatic biointegrity in seven tributaries of the Blackfoot River watershed, Montana. The tributaries represent silvicultural (timber h arvesting), agricultural (irrigated alfalfa and hay and livestock graz ing), and wilderness land uses. A 2.4 km (1.5 mile) reach of a recentl y restored tributary also was sampled for comparison with the other si x sites. A geographic information system (GIS) was used to characteriz e the seven subwater-sheds and estimate soil erosion, using the Modifi ed Universal Soil Loss Equation, and sediment delivery. The wilderness stream had the highest aquatic biointegrity. Two agricultural streams had the largest estimated soil erosion and sediment delivery rates, t he greatest habitat impairment from nonpoint source pollution, and the most impoverished macroinvertebrate communities. The silvicultural su bwatersheds had greater rates of estimated soil erosion and sediment d elivery and lower aquatic biointegrity than the wilderness reference s ite but evinced better conditions than the agricultural sites. A multi ple-use (forestry, grazing, and wildlife management) watershed and the restored site ranked between the silvicultural and agricultural sites . This spectrum of land use and aquatic biointegrity illustrates both the challenges and opportunities that define watershed management.