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Project: Extent and Condition of Depressional Wetlands

Background and Objectives

Freshwater depressional wetlands are the state’s most diverse wetland class and comprise approximately 45% of the California’s 3.6 million wetland acres. This class includes vernal pools, freshwater marshes, and wet meadows. Depressional wetlands may have near-persistent to intermittent surface water flows that connect them to other surface waters or other wetlands. They may be natural, actively maintained manmade features, or abandoned manmade features. While they perform the entire suite of functions typically associated with wetlands, depressional wetlands are particularly important as seasonal refugia and breeding areas in dry habitats. Cumulatively, they contribute to groundwater recharge and attenuation of surface runoff. They reduce the impact of excessive flow to streams, lentic waterbodies, and coastal environments downstream, while fostering improved water quality.

To date, the state’s Surface Water Ambient Monitoring Program (SWAMP) has focused almost entirely on assessing the condition of wadeable streams. As a result, most depressional wetland monitoring is associated with specific impact studies or mitigation projects. Available monitoring data is limited in spatial and temporal coverage, and there is little information about the overall extent and condition of depressional wetlands.

The goal of this project is to establish a foundation for a statewide ambient monitoring and assessment program for depressional wetlands by developing a pilot program in southern California.


This project was initiated in 2011 with anticipated completion in 2014.


The depressional wetland assessment will address the following questions of importance to regulatory agencies and regulated communities, and public:

  1. What is the extent and distribution of depressional wetlands in Southern California?
  2. What is the condition of depressional wetlands in Southern California?
  3. What are the major stressors affecting depressional wetland condition in Southern California?

To answer these questions, researchers will:

  1. Map the location and distribution of depressional wetlands;
  2. Assess the condition of depressional wetlands using a general wetland condition or health indicator, as well as a set of more intensive indicators to characterize hydrologic, water quality, and habitat conditions;
  3. Measure sediment chemistry, toxicity, and potential stressors in the surrounding landscape (e.g., agriculture, flow diversions, industrial activities), and then investigate potential stressor‐response relationships.

The data produced will be compatible with SWAMP, and the sampling design and indicators used in this pilot may be adaptable to new depressional wetland monitoring programs in other regions.


This project is being conducted in collaboration with the State Water Resources Control Board and Regional Water Quality Control Boards 2, 4, 8, and 9.

For more information on Extent and Condition of Depressional Wetlands, contact Eric Stein at (714) 755-3233.
This page was last updated on: 6/30/2014