SIMoN
  Sanctuary Integrated Monitoring Network
Monitoring Project

Elkhorn Slough Tidal Wetland Project

Principal Investigator(s)

  • Monique Fountain
    Elkhorn Slough National Estuarine Research Reserve

Funding

  • NOAA Coastal Impact Assistance Program
  • David and Lucile Packard Foundation
  • Resources Legacy Fund Foundation
  • U.S. Environmental Protection Agency
  • California Coastal Conservancy
Start Date: June 01, 2004

Elkhorn Slough, an estuary located on the central coast of California, provides a rich ecosystem for over 780 aquatic bird, marine invertebrate, marine mammal, and fish species. Elkhorn Slough is an important nursery for commercially and recreationally harvested fish and a premier migratory stopover for birds. In the Elkhorn Slough watershed, there are over two dozen rare, threatened, or endangered species. The estuary provides many beneficial uses, including boating and kayaking, hiking, educational experiences, and research opportunities. The hundreds of acres of coastal wetlands also decrease shoreline erosion, reduce flooding, and filter polluted waters. Elkhorn Slough is recognized as a Globally Important Bird Area and Western Hemisphere Shorebird Reserve. The National Oceanic and Atmospheric Administration has designated areas of Elkhorn Slough as a National Estuarine Research Reserve and National Marine Sanctuary. Sections of Elkhorn Slough are also designated as a State Ecological Reserve and State Wildlife Management Area by the California Department of Fish and Game.

The Elkhorn Slough Tidal Wetland Project is a collaborative effort to develop and implement strategies to conserve and restore estuarine habitats in the Elkhorn Slough watershed. It involves over a hundred coastal resource managers, representatives from key regulatory and jurisdictional entities, leaders of conservation organizations, scientific experts and community members.

The main goals of the Tidal Wetland Project are to:
(1) conserve existing high quality estuarine habitats,
(2) restore and enhance degraded estuarine habitats, and
(3) restore the physical processes that support and sustain estuarine habitats.

Particular emphasis in the restoration planning process has been placed on the first goal, which aims to stop the ongoing marsh loss and estuarine habitat erosion in Elkhorn Slough. The Tidal Wetland Project builds upon a number of past planning reports and efforts including the 1989 Elkhorn Slough Wetland Management Plan. The conservation and restoration of Elkhorn Slough’s estuarine habitats are considered a priority to California due to the loss of approximately 80 percent of coastal marshes in the state alone.

Summary to Date

Parsons Slough Project

The primary objective of the Parsons Slough Project is to reduce the tidal prism in Elkhorn Slough to minimize tidal marsh loss and habitat degradation as a result of tidal erosion and flooding, while maintaining sufficient tidal exchange and flushing to provide acceptable water quality. A secondary objective is to increase habitat diversity in Parsons Slough such that it better represents historic conditions.

The slough is under construction! A restoration project years in the making is now underway. The project will address erosion in the slough and will use heavy machinery to construct an underwater wall, called a sill, that will slow the movement of water as it moves out of the slough with the tide. The project will also improve the parking lot at Kirby Park, including the construction of a new dock.

This restoration has been carefully planned to minimize disturbance to slough life, but from November 2010 through February 2011 you can expect to see and hear this amazing project in action.

Discussion

Elkhorn Slough contains approximately 2,690 acres of distinct habitat types. This includes 293 acres of subtidal channels and tidal creeks, 1,605 acres of mudflats, and 796 acres of intertidal salt marshes and tidal creeks. These habitats provide a rich ecosystem for over 340 bird (135 aquatic species), 550 marine invertebrate, and 102 fish species. The climate, geomorphology, and tidal hydrology have gradually shaped the spatial distribution of Elkhorn Slough’s estuarine habitats throughout the past 20,000 years.

Over the past 150 years, human actions have altered the tidal, freshwater, and sediment processes that are essential to support and sustain Elkhorn Slough’s estuarine habitats. Approximately 50 percent, or 1000 acres, of the tidal marsh in Elkhorn Slough has been lost since 1870 due to human activities. Major physical modifications to the estuary have caused and are currently causing high rates of habitat loss and degradation in Elkhorn Slough. Human impacts have resulted in ongoing marsh loss and estuarine habitat erosion, degraded water quality conditions, increased levels of pollution, eutrophication, and increased numbers of invasive species. Almost 73,250 cubic yards of sediment are exported each year from Elkhorn Slough into Monterey Bay from habitat erosion. Bank erosion rates along the main channel of Elkhorn Slough range from 1 to 2 feet per year. These rapid changes not only affect the estuary’s animals and plants, but also impact neighboring private lands, public access sites, and railroad and road infrastructure.

Broad restoration strategies have been developed by the Tidal Wetland Project teams to conserve and restore Elkhorn Slough’s estuarine habitats. The first key restoration strategy aims to reduce interior marsh dieback and estuarine habitat erosion. The restoration alternatives included under this strategy propose to change the estuary’s entrance to reduce the tidal influence and habitat erosion and restore or add sediment to promote marsh growth. The next step for this strategy will be to make a decision about whether to pursue a large-scale restoration project for Elkhorn Slough based on ongoing technical evaluations. The purpose of the second restoration strategy is to restore and enhance degraded estuarine habitats in Elkhorn Slough. These restoration alternatives include actions to restore marsh habitat in the Parsons Slough and North Marsh wetland complexes, enhance water quality conditions in degraded areas, and restore tidal brackish marsh habitats. The next steps will be to obtain funding for a Parsons Slough restoration project, priority research and monitoring activities, restoration planning for degraded wetland sites, and pilot restoration projects.

The implementation of restoration projects requires a thorough understanding of relevant regulations, technical and political feasibility, funding needs, stakeholder interests, and research gaps. Potential large-scale restoration projects to reduce interior marsh dieback and habitat erosion in Elkhorn Slough are being evaluated over the next few years using an ecosystem-based management approach. The analysis of options to modify the estuary’s entrance and add sediments to rebuild marshes will include predictions about changes to tidal hydrodynamics, morphology, estuarine habitats and species, water quality, socioeconomic values, and political constraints. Restoration planning has been initiated for the Parsons Slough wetland complex. Funding is needed to support restoration projects, priority research and monitoring efforts, and community involvement activities.

Study Parameters

  • Erosion
  • Habitat