Wetland ecosystem services in California's Central Valley and implications for the Wetland Reserve Program

Primary ecosystem services provided by freshwater wetlands in the California Central Valley, USA, include water quality improvement, biodiversity support, and flood storage capacity. We describe these services for freshwater marshes, vernal pools, and riparian wetlands and the implications for wetlands restored under USDA programs in the Central Valley. California's Central Valley is a large sedimentary basin that was once covered by grasslands, extensive riparian forests, and freshwater marshes that today have been converted to one of the most intensive agricultural areas on earth. Remaining freshwater wetlands have been heavily altered, and most are intensively managed. Nitrogen loading from agriculture to surface and groundwater in the Central Valley was estimated to be 34.7 x 10(6) kg N/yr. Atmospheric deposition of nitrogen in the Central Valley was estimated to be 44.3 x 10(6) kg N/yr, of which similar to 1.5 x 10(6) kg N/yr was introduced directly to wetlands. Our analysis indicates that wetlands enrolled in the USDA Wetland Reserve Program (WRP) may potentially denitrify the NO3-N load from relatively unpolluted source water in < 18 days, but the potential to denitrify the NO3-N load from highly polluted source water is uncertain. Water management strongly influences use, diversity, and abundance of avian fauna as well as other biota. Freshwater marshes in the region continue to support important populations of breeding and wintering waterfowl and shorebirds whose populations fluctuate seasonally. Avian diversity in the little remaining area of Central Valley's riparian wetlands is also high and influenced by stand maturity, heterogeneity, and diversity. USDA conservation practices that promote these characteristics may support avian diversity. Effects of USDA conservation practices on non-avian fauna are poorly understood and warrant further study.