Cooperative Fish and Wildlife Research Units Program: California
Education, Research and Technical Assistance for Managing Our Natural Resources

Primary ecosystem services provided by freshwater wetlands in the California’s Central Valley 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 agriculture 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 106 kg N/yr. Atmospheric deposition of nitrogen in the Central Valley was estimated to be 44.3 X 106 kg N/yr, of which about 1.5 X 106 kg N/yr was introduced directly to wetlands. Our analysis indicates that wetlands enrolled in the USDA Wetland Reserve Program may potentially denitrify the NO3-N load from relatively unpolluted source water in less than 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. Nevertheless, 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 riparian wetlands is also high and is 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.