The purpose of this paper is to combine data on climate conditions with an understanding of the runoff cleaning mechanisms in cinstructed stormwater wetlands to better assess issues and opportunities specific to the use of these systems in the San Francisco Bay Area. Currently there is great interest across the country in the use of constructed stormwater wetlands to treat urban runoff. Analysis of these systems and their success has been done almost exclusively around the Chesapeake Bay, which differs from the San Francisco Bay Area in that the monthly average rainfall is relatively consistent, while the Bay Area experiences about three months of no rain. This study has two parts. First, an analysis of tainfall and evaporation data from Maryland and the Bay Area were compared to determine the nature of this climatic difference. Second, a literature search was conducted on mechanisms by which these sustems clean heavy metals from stormwater runoff. The analysis of this data points to five questions of particular concern for Bay Area constructed wetlands related to heavy metal pollution:
1. the ability of standing dead stalks of emergent vegetation and their roots to slow runoff for maximum sedimentation and to hold accumulated sediment;
2. the viability of dead vegetatiuon as a site for microbial action;
3. the delay between the first rain and point where the full complex mechanisms of wetland treatment will begin operation;
4. chemical changes in the water column over the season;
5. the bioabsorption and water demand characteristics of annual wetland species.
