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Alternative leach fields: nitrogen removal and response to saltwater intrusion
Citation:
Janiec, J., T. Hill, AND Rick Mckinney. Alternative leach fields: nitrogen removal and response to saltwater intrusion. OneCape Summit, Harwich, MA, August 16 - 17, 2018.
Impact/Purpose:
Coastal communities in the eastern United States have experienced significant human development over the past few decades resulting in an increase in nutrients, particularly nitrogen, entering their local waterbodies. Impacts from nitrogen over enrichment to estuaries include eutrophication, habitat degradation, and increased occurrence of algal blooms. In many localities, existing mechanisms have not been fully successful in mitigating nitrogen impacts to waterbodies. Communities are presently evaluating alternative methods of nitrogen removal including wetland and watershed restorations, living shorelines, permeable reactive barriers, and rain gardens. This study examined the nutrient removal efficiency of permeable reactive barriers (PRBs) under conditions typically encountered in both inland and estuarine environments. In an experiment utilizing PRB bioreactor columns, we examined how saltwater intrusion could affect nitrogen removal efficiency of low-lying woodchip barriers, and will ultimately provide estimates of biogeochemical process rates and co-benefits associated with the removal of nitrogen. Preliminary analysis showed significant reduction in nitrogen levels in effluent subjected to the bioreactor columns, and that seawater intrusion does not appear to significantly alter the nitrogen reduction capability of the columns. Our results will help inform coastal zone managers and local decision makers by reducing uncertainty in estimates of the magnitude and efficiency of nitrogen interception of PRBs. Results of this study will also provide information on potential co-benefits that could help inform a cost-benefit analysis. Our findings on the efficacy of PRBs in the presence of seawater intrusion will help inform decisions regarding their placement in communities where they may be susceptible to coastal flooding.
Description:
Communities are presently evaluating alternative methods of nitrogen removal from groundwater including wetland and watershed restorations, living shorelines, permeable reactive barriers, and rain gardens. As part of a larger project seeking to identify components of vulnerability and opportunities for improvement in systems threatened by nutrient enrichment, this study examined the nutrient removal efficiency of permeable reactive barriers (PRBs) under conditions typically encountered in both inland and estuarine environments. In an experiment utilizing PRB bioreactor columns, we examined how saltwater intrusion could affect nitrogen removal efficiency of low-lying woodchip barriers, and will ultimately provide estimates of biogeochemical process rates and co-benefits associated with the removal of nitrogen. Preliminary analysis showed significant reduction in nitrogen levels in effluent subjected to the bioreactor columns, and that seawater intrusion does not appear to significantly alter the nitrogen reduction capability of the columns. Our results will help inform decisions regarding the placement of PRBs I communities where they may be susceptible to coastal flooding.