Water Quality in Estuarine Wetland Restoration: An Examination of Dissolved Oxygen and Nutrients in the South Bay Salt Pond Restoration Project

The South Bay Salt Pond Restoration Project (SBSPRP) was established in 2003 from 15,100 acres of former Cargill salt harvesting ponds in the San Francisco Bay Area. Since then, the SBSPRP has utilized an adaptive management framework to restore the ponds with the goal of habitat restoration, public access, and flood protection as its guiding principles. The SBSPRP is the largest wetland restoration project on the West Coast and the complexity of the project is compounded by nearby land use, including wastewater facilities and urban development. The majority of previous water quality studies in the area have primarily focused on legacy pollutants, such as methylated mercury. For a selection of Alviso ponds with diverse management histories, the spatial and temporal variability of water quality parameters including dissolved oxygen (DO), nitrate (NO3), and ammonium (NH4) were examined during summer 2016. Two ponds (A21 and A17) are tidally controlled, with water entering and exiting the ponds based on changes in tide levels; these ponds also receive treated wastewater via Coyote Creek slough. Two other ponds (A3W and A8) are managed ponds, with elevated gates partially controlling the water level and no direct flow of wastewater entering these ponds. DO varied between 2.48-9.25 mg/L across all ponds, with significantly lower DO in tidal ponds (mean = 3.9 mg/L) compared with the managed ponds (mean = 6.7 mg/L). Nutrient concentrations also differed between the managed ponds and tidal ponds. 70% of samples in the managed ponds were below the detection limit of 0.81 µM NO3-N. NO3 concentrations in the tidal ponds, located closest to the wastewater facilities, ranged from 47.6 - 111.8 µM NO3-N; DO values were negatively correlated with both NO3 and NH4 in the tidal ponds. These results suggest that greater considerations for DO and other water quality parameters may be of use in future adaptive management strategies in the SBSPRP.