LAND-USE CHANGE IN CALIFORNIA, USA - NONPOINT-SOURCE WATER-QUALITY IMPACTS

California's population increased 25% between 1980 and 1990, resulting in rapid and extensive urbanization. Of a total 123,000 ha urbanized in 42 of the state's 58 counties between 1984 and 1990, an estimated 1 3% occurred on irrigated prime farmland, and 48% on wildlands or fallo w marginal farmlands. Sixty-six percent of all new irrigated farmland put into production between 1984 and 1990 was of lesser quality than t he prime farmland taken out of production by urbanization. Factors dic tating the agricultural development of marginal farmlands include the availability and price of water and land, agricultural commodity price s. and technical innovations such as drip irrigation systems that impa ct the feasibility and costs of production. The increasing amount of m arginal farmland being put into production could have significant wate r quality consequences because marginal lands are generally steeper, h ave more erodible soils, poorer drainage, and require more fertilizer than prime farmlands. Although no data exist to test our hypothesis, a nd numerous variables preclude definitive predictions, the evidence su ggests that new irrigated marginal lands can increase nonpoint source (NPS) pollution for a given size area by an order of magnitude in some cases.