Land use change in California, USA: Nonpoint source water quality impacts

Abstract

/ 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 13% occurred on irrigated prime farmland, and 48% on wildlands or fallow marginal farmlands. Sixty-six percent of all new irrigated farmland put into production between 1984 and 1990 was of lesser quality than the prime farmland taken out of production by urbanization. Factors dictating the agricultural development of marginal farmlands include the availability and price of water and land, agricultural commodity prices, and technical innovations such as drip irrigation systems that impact the feasibility and costs of production, The increasing amount of marginal farmland being put into production could have significant water quality consequences because marginal lands are generally steeper, have more erodible soils, poorer drainage, and require more fertilizer than prime farmlands. Although no data exist to test our hypothesis, and numerous variables preclude definitive predictions, the evidence suggests that new irrigated marginal lands can increase nonpoint source (NPS) pollution for a given size area by an order of magnitude in some cases.Large-scale land use conversion can have significant impacts on both surface water and groundwater quality. These impacts are especially well illustrated in California, where rapid population increase has resulted in conversion of prime agricultural land and undeveloped wildlands to urban uses. Less obvious but more importantly, many marginal lands have been placed into agricultural production with serious water quality implications because the marginal lands are typically more erodible and require greater fertilizer application than prime farmlands.In this study, we review the principal sources of water pollution in California, consider the probable long-term water quality impacts of land use conversion trends, and suggest possible water resource protection strategies.

Integrated climate and land use change scenarios for California rangeland ecosystem services: wildlife habitat, soil carbon, and water supply

“…Despite the limited physical controls on the agriculture scenarios, historical changes demonstrate that technological innovation can often remove certain barriers to cultivation. For example, in the western San Joaquin Valley, large areas of poorly drained soils have been cultivated, while in the Sierra foothills, orchards and vineyards have been planted despite the likelihood of soil loss associated with cultivation in these areas (Charbonneau and Kondolf 1993). Our scenarios (A2 in particular) assume that agriculture will expand into marginally suited areas with the assumption that technological innovation would allow such a land use transition to be economically worthwhile for the landowner.…”

Soil suitability index identifies potential areas for groundwater banking on agricultural lands

“…5). It is possible that over time, more suitable land for groundwater banking will become available as marginal soils continue to be developed and modified for agricultural purposes (Charbonneau and Kondolf 1993).…”

Potential future land use threats to California’s protected areas

“…Air pollution from large metropolitan areas impacts ecosystems throughout California (Fenn et al 2003) while logging activity impacts slope stability and elevated sediment loads in streams resulting in habitat degradation (Neary and Hornbeck 1994) and altered biogeochemical cycling (Nave et al 2010). Agriculture activities in California's Central Valley have been implicated in elevated nitrogen pollution levels in Sequoia National Park (Bytnerowicz et al 2002) and throughout the western Sierra Nevada (Takemoto et al 2001), and have driven widespread increases in nonpoint source pollution of surface and groundwater statewide (Charbonneau and Kondolf 1993). Non-local pesticide use in summer has been shown to transport in air masses to lower elevations along the western Sierra escarpment as well (LeNoir et al 2009).…”