Vegetative buffer strips in a Mediterranean climate: Potential for protecting soil and water resources

摘要

My research goal was to compare the efficiency of different vegetation as vegetative buffer strips (VBS) in a Mediterranean climate. VBS bordering Elkhorn Slough, draining into Monterey Bay, California received one of three treatments: annual non-native grasses, perennial native grasses, or an unseeded treatment of weedy volunteers. I tested native grasses to determine whether VBS can serve to restore biodiversity while simultaneously capturing sediment and nutrients from conventional row-cropped agriculture.;I measured vegetation composition, canopy cover, above- and below-ground biomass, rooting depth, and plant nitrogen content (Chapter 2). Annual grasses established early while perennial and unseeded treatments had more exposed ground in the first year. Perennial grasses established a dense cover by the second year; however, weeds dominated in all treatments by the fourth year. These results suggest that it may be impossible to restore native grasses on agricultural lands.;Sediment transport was investigated by measuring gullies, micro-topographic change, suspended sediment capture and deposition along the upper plot boundary (Chapter 3). Annual grasses were most efficient in preventing gully formation in the first year. Perennial grasses were most effective in trapping sediment in the second and, possibly, third years. Overall, sediment was lost in the first two years and captured in the third year. All treatments demonstrated approximately a 93% reduction in sediment concentration from the top to the bottom of the VBS in the third year.;Precipitation, groundwater and surface water chemistry, infiltration, and hydraulic conductivity were quantified (Chapter 4). Nitrate concentrations were significantly reduced in groundwater but not in surface runoff. Ammonium and phosphorus showed no significant reduction in groundwater or surface water. Vegetative treatment did not significantly effect nutrient concentrations.;I evaluated environmental costs and benefits of implementing VBS, both to the grower and to society, as a means of capturing non-market ecosystem values (Chapter 5). A net economic benefit to growers for installing VBS was realized within the first year, if the economic costs of erosion were considered. The installation of VBS also has extensive economic benefits to society. These results support installing VBS as a management strategy in an erosion-prone watershed to protect water quality.