Abstract
In coastal California nitrogen (N) in runoff from urban and agricultural land is suspected to impair surface water quality of creeks and rivers that discharge into the Monterey Bay Sanctuary. However, quantitative data on the impacts of land use activities on water quality are largely limited to unpublished reports and do not estimate N loading. We report on spatial and temporal patterns of N concentrations for several coastal creeks and rivers in central California. During the 2001 water year, we estimated that the Pajaro River at Chittenden exported 302.4 Mg of total N. Nitrate-N concentrations were typically <1 mg N l–1 in grazing lands, oak woodlands, and forests, but increased to a range of 1 to 20 mg N l–1 as surface waters passed through agricultural lands. Very high concentrations of nitrate (in excess of 80 mg N l–1) were found in selected agricultural ditches that received drainage from tiles (buried perforated pipes). Nitrate concentrations in these ditches remained high throughout the winter and spring, indicating nitrate was not being flushed out of the soil profile. We believe unused N fertilizer has accumulated in the shallow groundwater through many cropping cycles. Results are being used to organize landowners, resource managers, and growers to develop voluntary monitoring and water quality protection plans.
Highlights
The Monterey Bay National Marine Sanctuary is the largest marine protected area in the U.S, consisting of more than 8000 km2 along the central coast of California
We speculate that nitrate concentrations increased as baseflow became a higher percentage of the flow compared to surface runoff. These data emphasize the importance of surface-groundwater interactions in determining stream nitrate concentrations. In both the Pajaro and Elkhorn Slough watersheds, nitrate concentrations were low in surface water passing through forested and grazing lands, and elevated where intensive agriculture was present
For the Pajaro River at Chittenden and Carneros Creek at San Miguel Canyon Road, we estimated that 302.4 and 2.7 Mg of N were exported during the 2001 water year, respectively
Summary
The Monterey Bay National Marine Sanctuary is the largest marine protected area in the U.S, consisting of more than 8000 km along the central coast of California. The Sanctuary includes Elkhorn Slough, a National Estuarine Research Reserve and one of the largest remaining tidal wetlands in California[1]. The three main watersheds that drain into the coastal habitats of the Monterey Bay Sanctuary are the Pajaro River (3394 km2), Elkhorn Slough (203 km2), and Salinas River (10,600 km). The three main watersheds that drain into the coastal habitats of the Monterey Bay Sanctuary are the Pajaro River (3394 km2), Elkhorn Slough (203 km2), and Salinas River (10,600 km2) Within these three watersheds, agriculture and livestock production accounts for approximately 75% of the total land area[5]. We developed a monitoring program to link land use with nutrient concentrations and loading in the Pajaro River and Elkhorn Slough watersheds. In this paper we present results from the 2001 water year that will be used to coordinate landowners, resource managers, and growers to develop voluntary monitoring and water quality protection plans
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