Projects Funded for David Lewis


Best Management Practices to Mitigate Water Quality Impairments: What Are the Benefits and Costs?

Tina L. Saitone, David Lewis, and Kenneth W. Tate


Specific Objectives of the Project:
Nonpoint source pollution is the leading cause of water quality impairments in California. Many sources, including cattle grazing in or around streams, lakes, and wetlands, may contribute to the pollution of surface waters. Grazing best management practices (e.g., riparian fencing, off-stream water, etc.) have been shown to reduce fecal-based microbial pollutants and improve surface water quality. Objectives of this project are threefold: i) estimate the biophysical reductions in fecal indicator bacteria over time, ii) estimate the costs associated with grazing best management practices, and iii) compare these costs to biophysical results in the literature on efficacy to estimate benefit/cost of practice implementation.

Project Report/Summary of Results:
Coastal areas support multiple important resource uses including recreation, aquaculture, and agriculture. Unmanaged cattle access to stream corridors in grazed coastal watersheds can contaminate surface waters with fecal-derived microbial pollutants, posing risk to human health via activities such as swimming and shellfish consumption. Improved managerial control of cattle access to streams through implementation of grazing best management practices (BMPs) is a critical step in mitigating waterborne microbial pollution in grazed watersheds. This work reports trend analysis of a 19-year dataset to assess longterm microbial water quality responses resulting from a program to implement 40 grazing BMPs within the Olema Creek Watershed, a primary tributary to Tomales Bay, USA.

Stream corridor grazing BMPs implemented included: 1) Stream corridor fencing to eliminate/control cattle access, 2) hardened stream crossings for cattle movements across stream corridors, and 3) off stream drinking water systems for cattle. We found a statistically significant reduction in fecal coliform concentrations following the initial period of BMP implementation, with overall mean reductions exceeding 95% (1.28 log10)—consistent with 1—2 log10 (90 – 99%) reductions reported in other studies. Our results demonstrate the importance of prioritization of pollutant sources at the watershed scale to target BMP implementation for rapid water quality improvements and return on investment. Our findings support investments in grazing BMP implementation as an important component of policies and strategies to protect public health in grazed coastal watersheds. In total, this suite of practices cost over $870,000 to implement. The remaining work on this project (in progress) uses spatial and temporal variation in practice implementation to determine the benefits and costs associated at the practice level.