Research - Category II: Aquatic Ecosystems

Linking Upland Landcover Change with Wetland Structure in Elkhorn Slough, CA
(Funded 2002-2003)

Principal Investigator: Nina M. Kelly
Environmental Sciences Policy and Management
UC Berkeley
(510) 642-7272
mkelly@nature.berkeley.edu

Executive Summary:
Elkhorn Slough is considered on of the most important wetland/estuarine systems in Central California. The State of California has designated Elkhorn Slough as an ecological reserve, and the National Oceanic and Atmospheric Administration has established a National Estuarine Research Reserve within 1,400 acres of the slough. Elkhorn Slough serves as an important nursery for fish in Monterey Bay, and provides habitat for numerous rare plants and animals. However, this important natural resource is being impacted by severe sedimentation originating from cultivated fields on steep slopes within the Elkhorn Slough watershed. As such, it is similar to many other coastal wetlands along the California coast that serve as important aquatic habitat while facing impacts from land use practices.

The impact of land use changes (most important of these being increased agriculture) in the watershed of Elkhorn Slough on the wetlands needs to be assessed for two reasons. First, it is important to quantify how increased sedimentation from agriculture has altered physical habitat features of the marsh, which are a key element in the success of fisheries in Monterey Bay. Shallow tidal channels provide protection, food, and reduced osmoregulatory stress for juvenile fish, and salt marsh detrital provides part of the fish diet. Second, the ability to design successful marsh restoration projects depends upon the capability to consider inputs to the wetland form upland land use activities in the restoration design. Elkhorn Slough can serve as a case study to assess the changes to a wetland system caused by such upland inputs.

Wetland scientists have begun to pay more attention to processes operating at a watershed or ecoregion scale when considering wetland management strategies. The cumulative alteration of landscapes has been called one of the greatest constraints to wetland restoration. Wetland structure and processes are relate3d to their position in the landscape, and changes to the landscape should therefore alter wetlands contained within them. The properties of the landscape, such as slope and topography, distribution of glacial deposits, percent area in wetlands, and spatial configuration of different land-use types, greatly determines the type of inputs to wetlands. Wetland restoration planning should be conducted within the context of a cumulative effects analysis that addresses landscape degradation and controls on wetland development in order to ensure a successful project.

This proposal will address the following questions: Have there been changes to the structure of tidal wetlands within Elkhorn Slough since 1970? If yes, can these changes be linked to increased agriculture and subsequent sedimentation in the watershed? Are there differences in wetland changes between sub-catchments of the watershed? This project will assist wetland managers and restoration experts in understanding the larger-scale effects on wetland structure by extending methods developed for understanding linkages between upland landcover change and instream aquatic habitats.

We propose to map upland landcover change in the watershed of Elkhorn Slough through remote sensing imagery analysis in accordance with NOAA's Coastal Change Analysis Project (C-CAP) for the years of 1973, 1986, and 2000. The C-CAP project has completed this work for 1983 and 1996, and we will extend these results to an earlier and more recent time period. In addition, we will map plant community type and distribution, width of tidal channels, length of channels, and sinuosity of the channel network from high-resolution aerial photography. Statistical analyses will be conducted to identify any linkages between watershed attributes and wetland structural features.

This study will assist in guiding future wetland restoration projects that occur in highly impacted watersheds. A number of organizations and agencies are actively involved in managing and restoring Elkhorn Slough. The groups that would serve to benefit most from this research are the Natural Resource Conservation Service (NRCS), the Nature Conservancy, and th3e Elkhorn Slough Foundation. NRCS is actively working with farmers in the watershed to reduce erosion and off-farm sediment and improve wetland habitat. The Elkhorn Slough Foundation is involved with several wetland monitoring and restoration projects. My research will identify the wetlands that have been most altered by sedimentation and how they have been altered; these results will be used to prioritize areas for land-use management. The research will also provide information about wetland conditions prior to intensive agriculture, and the extent to which changes have occurred, which will guide decisions related to wetland restoration and management.