Land-use dynamics in a southern Illinois (USA) watershed

The Cache River of southernmost Illinois is used as a case study for develo ping and demonstrating an approach to quantitatively link (1) national agri cultural policy and global agricultural markets, (2) landowner's decisions on land use, (3) spatial patterns of land use at a watershed scale, and (4) hydrologic impacts, thus providing a basis to predict, under a certain set of circumstances, the environmental consequences of economic and political decisions made at larger spatial scales.. The heart of the analysis is an estimation, using logistic regression, of the affect of crop prices and Con servation Reserve Program (CRP) rental rates on farmland owner's decisions whether to reenroll in the CRP or return to crop production. This analysis shows that reasonable ranges for crop prices (80%-150% of 1985-1995 values) and CRP rental rates (0-125% of 1985-1995 rates) result in a range-of 3%-9 2% of CRP lands being returned to crop production, with crop prices having a slightly greater effect than CRP rental rates. Four crop price/CRP rental ,rate scenarios are used to display resulting land-use patterns, and their effect on sediment loads, a critical environmental quality parameter in thi s case, using the agricultural non point source (AGNPS) model. These scenar ios demonstrate the importance of spatial pattern of land uses on hydrologi cal and ecological processes within watersheds. The approach developed can be adapted for use by local governments and watershed associations whose go als are to improve watershed resources and environmental quality.