Searsville Lake: Position of the Jasper Ridge Advisory Committee – October 2007Searsville Lake is a major feature of the Jasper Ridge Biological Preserve. It plays a role in all aspects of the Preserve's mission, including research, conservation, and education. As Stanford and other stakeholders evaluate options for managing the reservoir, it is important for all parties to understand the relationship of the reservoir to the Preserve's strategic goals.
In that spirit, the Jasper Ridge Advisory Committee has assessed options for managing Searsville Lake into the future.
The goal of this assessment is to inform the decision-making process and help Stanford develop a unified and well-supported plan of action. The recommendation of the Jasper Ridge Advisory Committee is not based upon or intended to be a comprehensive analysis. It is based solely on the impacts of possible management options on the Preserve's mission. It does not account for numerous other factors that need to be addressed in the final decision, including costs, offsite environmental impacts, and consequences for upstream and downstream stakeholders.
The judgment of the Jasper Ridge Advisory Committee is that the continued existence of a reservoir provides important values for the Preserve. The available evidence indicates that careful dredging to maintain open water can sustain nearly all of these values, and that the impacts of the dredging can be managed in a way that does not create unacceptable levels of damage or risks to the Preserve's goals, operations, environment, and values. Further, none of the alternative options we have considered presents a comparable balance of environmental benefits, costs, and risks, based on the Preserve's mission.
Searsville Lake provides a number of important benefits to the Preserve. Ecologically, it supports a range of habitats, including the reservoir itself, the associated wetlands, and all of the habitats with species that use the reservoir and wetlands for feeding or breeding. Searsville Lake has a diverse aquatic community. It is a key habitat for migratory and breeding waterfowl and provides important foraging resources for bats. In addition, the reservoir helps maintain shallow water tables that support wetland habitat on the Corte Madera and Sausal Creek alluvial floodplains. The reservoir and associated wetlands are home to a number of species of conservation interest. Aquatic and wetland sites are rare on the San Francisco Peninsula, on university campuses, and in urban areas. As a consequence, Searsville Lake is a unique educational and research resource. It provides opportunities for students to have direct experience with a range of globally and locally important habitats, environmental issues, and engineering topics. It is also an important resource for research. Recent projects have pursued questions in biogeochemistry, hydrology, atmospheric chemistry, remote sensing, animal behavior, and sedimentology.
The Jasper Ridge Advisory Committee assessed the consequences for the Preserve of five general management options. Each of these could have a number of variants. We focus on impacts that are characteristic of each class of management options. These are:
From the perspective of the Jasper Ridge mission, each of these options has costs, risks from unknowns, and benefits, and each creates opportunities and challenges.
Based on the information currently available, our assessment of each of the options is:
Mosquito Report for Jasper Ridge Biological Preserve - December 2006
The San Mateo County Mosquito Abatement District works with Stanford University and the staff of the Jasper Ridge Biological Preserve (JRBP) to control mosquitoes arising from the cattail marshes surrounding Searsville Lake. This report is a summary of the work done at this site and its results to date.
Click here to download the report (PDF format)
Mosquito Abatement at JRBP
The San Mateo County Mosquito Abatement District (SMCMAD) has treated the Preserve's wetlands south and west of Searsville Lake with a bacterial agent that attacks mosquito larvae, Bacillus thuringiensis subspecies israelensis, for at least a couple of decades. However, due to the density of vegetation, especially in the tules and cattails, the District is unable to access some areas they consider to be potential mosquito threats to nearby residents.
With the increased concern about West Nile virus, SMCMAD used a helicopter to spray about 25 acres of wetlands in the Preserve with another bacterial agent, Bacillus sphaericus in September of 2003, and again in July, August, and September of 2004. Mosquito larvae ingest the bacteria, which produce a toxin that disrupts the gut in the larvae by binding receptor cells present in insects that are not found in mammals. The product is typically marketed under the trademark name of VectoLex and is generally effective for up to 4 weeks.
To date, most of the information indicates that this larvicide and Bacillus thuringiensis subspecies israelensis, have little or no significant environmental impacts. The District intends a more aggressive monitoring and management regime in 2004 than has been the case historically at Jasper Ridge Biological Preserve that includes more frequent spraying and increasing the area to include all of Searsville Lake. The Preserve not only bears the costs associated with the aerial spraying, but also makes an effort to keep nearby residents informed about upcoming spraying activity.
San Mateo County is using "sentinel" chicken flocks as an early detection mechanism for West Nile virus and Jasper Ridge Biological Preserve's flock of 10 chickens is part of the early warning network. Technicians from the San Mateo County Mosquito Abatement District take blood samples from the chickens every two weeks to test for the presence of West Nile virus and other mosquito-borne diseases.
SMCMAD posts monthly updates on West Nile virus and the sentinel chicken monitoring system in their entomology reports located at http://www.smcmad.org/news1.htm.
For further information on West Nile virus: