Long-term phosphorus loading from onsite wastewater systems to surface waters

• Online Access: http://hdl.handle.net/2047/D20290515

Accelerated eutrophication caused by oversupply of nutrients from anthropogenic sources has impaired surface waters, especially lakes, in many places in the United States and worldwide. Nitrogen and phosphorus oversupply to surface waters has frequently caused overgrowth of aquatic plants and blooms of phytoplankton (algae) that damage fisheries, recreation, and property values. In many surface waters, phosphorus is the limiting nutrient, without which this overgrowth or bloom does not occur. Efforts to prevent, remediate, and mitigate the effects of phosphorus oversupply generally focus on surface sources and transport pathways of phosphorus, but review of the research literature suggests that phosphorus transport from domestic onsite wastewater systems (OWSs) via groundwater has not been considered a significant source because of sorption, and this source is not effectively addressed in lake management. We hypothesize that, with increasing time-in-use of an OWS, phosphorus may be transported via the groundwater surficial aquifer to a down-gradient surface water in ecologically relevant amounts. Here we develop a model of this transport and quantify the total phosphorus load transported in a time-variable manner from all the OWSs in a watershed via the groundwater to surface waters, especially lakes. The results suggest that the phosphorus load from OWSs may be significant and should be considered in efforts to manage the effects of lake eutrophication.