Balancing wildlife needs and nitrate removal in constructed wetlands:The case of the Irvine Ranch Water District's San Joaquin Wildlife Sanctuary

摘要

The San Joaquin Wildlife Sanctuary (SJWS),Irvine,CA,is a 32 ha series of shallow ponds created to maximize nitrate removal rates while maintaining 90% open water and episodically exposed shoreline for avian habitat.Design elements created non-ideal denitrification conditions by diminishing an organic carbon source (emergent vegetation) and increasing sediment exposure to oxygen.SJWS aqueous nitrogen and avian data (1999-2002) were analyzed to discern whether design and operating conditions allowed for simultaneous nitrate removal and diverse,abundant avian habitat.Average TIN removal efficiency was 80% while average TN removal efficiency was 60%;the difference reflects Org-N production in the marsh.Based on Chl-a measurements,roughly 40% of Org-N produced in the system was present as algae.The highest annual nitrate removal rates occurred April-May (350-500 mg/m~2/d) and September-October (250-425 mg/m~2/d).First order rate constants ranged 30.7-47.5 m year~(-1).Seasonal plantings of barnyard grass (Echinocloa crus-galli) were intended to serve as a carbon amendment for denitrification,however,there was no difference in nitrate removal between amended and non-amended conditions,likely because data averaging obscured a small,localized enhancement signal.Average avian species richness was high,ranging between 65 and 76 species month~(-1),while average relative abundance was mid-range,at 65-83 birds ha~(-1) month~(-1).Birds observed included common and rare species.