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Modeling the Effects of Onsite Wastewater Treatment Systems on Nitrate Loads Using SWAT in an Urban Watershed of Metropolitan Atlanta
Author(s) -
Hoghooghi Nahal,
Radcliffe David E.,
Habteselassie Mussie Y.,
Jeong Jaehak
Publication year - 2017
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2016.08.0322
Subject(s) - atlanta , metropolitan area , watershed , environmental science , wastewater , nitrate , environmental engineering , sewage treatment , waste management , hydrology (agriculture) , water resource management , geography , engineering , archaeology , chemistry , geotechnical engineering , computer science , machine learning , organic chemistry
Onsite wastewater treatment systems (OWTSs) can be a source of nitrogen (N) pollution in both surface and ground waters. In metropolitan Atlanta, GA, >26% of homes are on OWTSs. In a previous article, we used the Soil Water Assessment Tool to model the effect of OWTSs on stream flow in the Big Haynes Creek Watershed in metropolitan Atlanta. The objective of this study was to estimate the effect of OWTSs, including failing systems, on nitrate as N (NO 3 –N) load in the same watershed. Big Haynes Creek has a drainage area of 44 km 2 with mainly urban land use (67%), and most of the homes use OWTSs. A USGS gauge station where stream flow was measured daily and NO 3 –N concentrations were measured monthly was used as the outlet. The model was simulated for 12 yr. Overall, the model showed satisfactory daily stream flow and NO 3 –N loads with Nash–Sutcliffe coefficients of 0.62 and 0.58 for the calibration period and 0.67 and 0.33 for the validation period at the outlet of the Big Haynes Watershed. Onsite wastewater treatment systems caused an average increase in NO 3 –N load of 23% at the watershed scale and 29% at the outlet of a subbasin with the highest density of OWTSs. Failing OWTSs were estimated to be 1% of the total systems and did not have a large impact on stream flow or NO 3 –N load. The NO 3 –N load was 74% of the total N load in the watershed, indicating the important effect of OWTSs on stream loads in this urban watershed. Core Ideas We examined the importance of OWTSs on stream NO 3 –N load in the urban watershed. The SWAT model sufficiently predicted the effect of OWTSs on NO 3 –N load. The NO 3 –N load was the main component of the total N load in the watershed.