Water Environment Federation (WEF)

A study of the compatibility of habitat and water quality enhancement objectives in urban wetlands of southern California, USA

With the rising urbanization of the coastal watersheds of California, requirements for control of urban runoff have created demand for treatment wetlands to improve surface water quality and attenuate storm flows. Concurrent with this need, significant wetland and riparian habitat have been lost. Pressure is mounting to restore, enhance, and create wetlands with multiple objectives (i.e., habitat support, treatment of nonpoint source pollution, flood attenuation, and recreation). Information is lacking on the potential risk to wildlife associated with using wetlands for treatment of nonpoint source runoff. The goal of this study is to provide information on how urban wetlands can be better managed to increase compatibility with wildlife protection. In spring 2006, a baseline biological survey was conducted to evaluate the condition of habitat provided by these sites. The survey focused on both freshwater basins and small streams or channel systems and was conducted in three tiers:

1) wetland and vegetation habitat mapping and 2) rapid assessment of wetland condition using the California Rapid Assessment Method (CRAM) for wetlands at 40 sites, and 3) a more intensive biological survey of 26 sites including vascular plant and benthic macroinvertebrate community composition and bird use. Results of the survey showed that, while urban infrastructure provide some basic constraints on the achievable condition of wetland basins and channels, site-specific conditions can mitigate or exacerbate these constraints. The site-specific factors include, but are not limited to: 1) wetland size, 2) project objective and design criteria, 3) intensity of maintenance, and 4) origin of site.

We found that habitat wetlands could achieve what could be considered good condition if: 1) the sites can support wetland hydrology, 2) the hydrology can be managed to mimic natural hydroperiod, 3) the site is designed to have good physical structure, 4) the wetland and buffer have appropriate native vegetation, 5) the wetland is maintained frequently to manage stressors, but not in manner which is incompatible with the seasonal cycles of nesting and reproduction, and 6) issues of bioaccumulation and toxicity are not a factor. This last factor has not been evaluated as a part of the baseline biological survey, but will be addressed in the subsequent phases of the project.

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