Non-point source nutrient loading into our waterways is one of the leading causes of coastal eutrophication and subsequent harmful algae bloom (HAB) events. In Suffolk County, N.Y, septic systems treat 70% of the domestic waste and have been identified as a leading cause for degraded coastal water quality in Long Island coastal waters and an important factor contributing to massive outbreaks of HABs in the Great South Bay, Peconic Bay and Long Island Sound. The HAB Cochlodinium polykrikoides (C. poly) causes toxic algal blooms in Suffolk County as well as coastal waters worldwide, and has been found to be lethal to multiple species and life stages of fish and shellfish.

Green infrastructure (i.e. bioswales, bioretention systems, and rain gardens) has been gaining recognition as an effective low-impact best management approach for mitigating stormwater related nutrient loading into waterways and may have the potential to address septic leaching as well. However, the design of these systems is passive and as a result their water interception and nutrient removal capacity has been shown to be highly variable and inconsistent.

The project objectives are to (1) conduct controlled ecoWEIR mesocosm studies to evaluate nutrient removal efficiency from septic effluent and (2) carry out time-series incubations with the C. poly with mesocosm inflows and outflows to determine how ecoWEIR treatment offsets growth of this HAB species. This study will inform residents and coastal ecosystem managers of a cost-effective solution to groundwater contamination from onsite wastewater treatment via engineered drain fields.