California State Water Resources Control Board (SWRCB) | November 1st, 2008
Summary
Section 305(b) of the Federal Clean Water Act (CWA) requires each state submit biennial reports describing the health of its surface water, including wetlands, to the USE
Section 305(b) of the Federal Clean Water Act (CWA) requires each state submit biennial reports describing the health of its surface water, including wetlands, to the USEPA. This document reports on the health of California’s perennial, saline estuarine wetlands. Estuaries are partially enclosed bodies of water along the coast where freshwater runoff meets and mixes with salt water from the ocean. Based on the draft definition of wetlands for California, an estuarine wetland is an area within an estuary that is exposed at low tide and covered with rooted vegetation. The health of the state’s estuarine wetlands is estimated from a statewide survey of the distribution, abundance, and ambient condition of estuarine wetlands.
The survey had three components: 1) landscape profile; 2) probability-based assessment of ambient condition; and 3) assessment of selected estuarine wetland restoration and mitigation projects. The results help answer four fundamental management questions: 1) where are the State’s estuarine wetlands and how abundant are they; 2) what is the ambient condition of estuarine wetlands statewide and how does their condition vary by region; 3) what are the major stressors and how do they vary among coastal regions; and 4) what is the condition of permitted restoration projects relative to ambient condition. This fourth question demonstrates how data could be used to evaluate policies and programs affecting the distribution, abundance, and condition of estuarine wetlands.
The landscape profile described the distribution and abundance of the State’s estuarine wetlands relative to other estuarine habitats and explored the underlying causes through a detailed examination of trends in San Francisco Estuary. A probability-based survey was used to assess the ambient condition of saline, perennial estuarine wetlands. The statewide ambient survey involved 120 sites allocated equally among four regions: North Coast, San Francisco Estuary, Central Coast, and South Coast. An additional 30 sites were allocated to South Coast to test for a difference between large and small estuaries. The field survey was conducted in the Fall of 2007. The statewide ambient survey in turn served as a regional frame of reference for project assessments.
Both the ambient survey and the project assessments utilized the California Rapid Assessment Method (CRAM; Version 5.0.2). CRAM is a field-based method to assess wetland condition based on visible indicators of four wetland attributes: Landscape Context, Hydrology, Physical Structure, and Biological Structure. Results were reported as the percent of the total area of estuarine wetland in California likely to fall within four categories equally-spaced categories of possible CRAM index or attribute scores, which range from 25-100: Scores greater than 82 = Category 1; scores between 63 and 82 = Category 2; scores between 44 and 63 = Category 3; and scores less than 44 = Category 4.
Landscape Profile. Approximately 91% of the historical amount acreage of California wetlands has been lost due to reclamation and land use. Accurate estimates of estuarine wetland loss in particular are only available for the San Francisco Estuary. In spite of losing approximately 85% of its saline wetlands and almost 92% of its freshwater tidal wetlands, the SF Estuary has almost 44,500 acres of estuarine wetlands at this time, about 77% of all the estuarine wetlands in the state. Although land use varies among the estuaries of California, it has affected the distribution, abundance, size, and shape of estuarine wetlands in consistently deleterious ways. It has decreased the amount of estuarine wetland and increased the number of small wetlands, thus increasing the distance between wetlands.
In the more urbanized estuaries of the South Coast, Central Coast, and SF Estuary, many wetlands are embedded in intensive land uses and bounded by levees. These conditions diminish the hydrological and ecological connectivity among the wetlands, increase their susceptibility to invasion and local catastrophic events, and reduce their overall capacity to serve society.