THE INFLUENCE OF CATCHMENT LAND-USE ON STREAM INTEGRITY ACROSS MULTIPLE SPATIAL SCALES

1. Despite wide recognition of the need for catchment-scale management to ensure the integrity of river ecosystems, the science and policy b asis for joint management of land and water remains poorly understood. An interdisciplinary case study of a river basin in south-eastern Mic higan is presented. 2. The River Raisin drains an area of 2776 km(2), of which some 70% is agricultural land. The upper basin consists of ti ll and outwash, and both topography and land use/cover are diverse. Th e lower basin consists of fine textured lake deposits, is of low relie f, and land use is primarily agricultural. 3. The River Raisin basin h istorically was a region of oak-savannah and wetlands. It was deforest ed, drained and converted to farmland during the mid-nineteenth centur y. Human population reached a plateau at about 1880, and then underwen t a second period of growth after 1950, mainly in small urban areas. M ore recently, the amount of agricultural land has declined and foreste d land has increased, in accord with a general decline in farming acti vity. 4. It could be suggested that the influence of land use on strea m integrity is scale-dependent. Instream habitat structure and organic matter inputs are determined primarily by local conditions such as ve getative cover at a site, whereas nutrient supply, sediment delivery, hydrology and channel characteristics are influenced by regional condi tions, including landscape features and land use/cover at some distanc e upstream and lateral to stream sites. 5. Sediment concentrations mea sured during low flows were higher in areas of greater agriculture. In a comparison of two subcatchments, sediment yields were up to ten tim es greater in the more agricultural location, in response to similar s torm events. A distributed parameter model linked to a geographical in formation system predicted that an increase in forested land cover wou ld result in dramatic declines in runoff and sediment and nutrient yie lds. 6. Habitat quality and biotic integrity varied widely among indiv idual stream sites in accord with patterns in land use/cover. Extent o f agricultural land at the subcatchment scale was the best single pred ictor of local stream conditions. Local riparian vegetation was uncorr elated with overall land use and was a weak secondary predictor of hab itat quality and biotic integrity. 7. Investigation of the regulatory agencies involved in land and water management in the basin revealed a complex web of overlapping political jurisdictions. Most land-use dec ision-making occurs at the local level of township, city or village. U nfortunately, local decision-making bodies typically lack the informat ion and jurisdictional authority to influence up- and downstream event s.