Treating Runoff using California Native Plants As Biofilters, Poster Board #179

Nitrate contamination of water systems from agricultural runoff is a pervasive problem in California. A substantial number of water bodies have been included on the State 303(d) list due to impairments that include benchmark exceedances of nutrients. The use of different types of vegetated buffers (bioswales, filter strips and constructed wetlands) has proved to be effective to filter the excess of pesticides, fertilizers and other pollutants from different sources of urban and agricultural runoff. These buffers intercept surface and subsurface flow reducing the movement of sediment and the delivery of different contaminants to water systems. As runoff water moves across the vegetated strips, it is filtered by physical, biological and chemical processes. Roots and rhizomes obstruct flow, facilitate sedimentation and provide surface areas for microbial activity. Nutrients and pesticides are taken up by plant root systems, decomposed by microorganisms or adsorbed into soil particles. However, the effectiveness of vegetative buffers depends on several factors, such as size, runoff flow, climate, soils, vegetation cover, and plant species. Our goal was to analyze the nutrient uptake efficiency of different California native plants that can be used to optimize the function of vegetated buffers to reduce nitrogen (N) and phosphorus (P) runoff and leaching. We compared the growth response and the accumulation of N and P in shoots of Carex pansa, Carex praegracilis, Juncus patens, Juncus xiphioides, Sporobolus airoides and Muhlenbergia rigensthat were grown for twelve weeks with 0, 50, 100, and 150 ppm of N. The content of nitrate and orthophosphate in leachates collected from the different plants was also analyzed. As the N rate increased, the shoot and total dry mass of all the plant species increased and their root:shoot ratio decreased. M. rigens was the largest plant at all N rates. It had the greatest shoot, total dry mass and the highest content of N and P in shoots. When grown at 150 ppm of N, M. rigens had about three to four times more shoot dry mass than C. praegracilis and J. xiphiodes and about twice the content of shoot N and P. However, there were no significant differences in the content of nitrate and orthophosphate in leachates collected from these species. The relation between biomass production, shoot N and P, and leachate volume, on the content of N and P in leachates collected from the different species will be discussed.