Coastal Resources Management Program, East Carolina University, 379 Flanagan, Greenville, NC 27858, USA.
Environmental Health Sciences Program, East Carolina University, 3408 Carol Belk Building, Greenville, NC 27858, USA; Coastal Water Resources Center, Institute for Coastal Science and Policy, East Carolina University, 354 Science and Technology Building, Greenville, NC 27858, USA.
J Environ Manage. 2018 Apr 1;211:206-217. doi: 10.1016/j.jenvman.2018.01.063. Epub 2018 Feb 4.
Septic systems (SSs) have been shown to be a significant source of nitrogen and phosphorus to nutrient-sensitive coastal surface and groundwaters. However, few published studies have quantified the effects of SSs on nutrient inputs to water supply watersheds in the Piedmont region of the USA. This region consists of rolling hills at the surface underlain by clayey soils. There are nearly 1 million SSs in this region, which accounts for approximately 50% of all SSs in North Carolina. The goal of this study was to determine if significant differences in nutrient concentrations and exports exist between Piedmont watersheds with different densities of SSs. Water quality was assessed in watersheds with SSs (n = 11) and a sewer and a forested watershed, which were designated as controls. Stream flow and environmental readings were recorded and water samples were collected from the watersheds from January 2015-December 2016. Additional samples were collected from sand filter watersheds in April 2015-March 2016 to compare to septic and control watersheds. Samples were analyzed for total dissolved nitrogen (TDN) and orthophosphate (PO-P). Results indicated that watersheds served by a high-density (HD) of SSs (4.9 kg-N yr ha; 0.2 kg-P yr ha) exported more than double the median masses of TDN and PO-P, respectively, relative to low-density (1.0 kg-N yr ha; <0.1 kg-P yr ha) and control watersheds (1.4 kg-N yr ha; <0.1 kg-P yr ha) during baseflow. Isotopic analysis indicated that wastewater was the most likely source of nitrate-N in HD watersheds. In all other watersheds, isotopic results suggested non-wastewater sources as the dominant nitrate-N provider. These findings indicated that SS density was a significant factor in the delivery of septic-derived nutrients to these nutrient-sensitive, water supply watersheds of the North Carolina Piedmont.
污水系统（SSs）已被证明是向营养敏感的沿海地表水和地下水输送氮和磷的重要来源。然而，很少有已发表的研究量化了 SSs 对美国皮埃蒙特地区供水流域养分输入的影响。该地区表面为丘陵，下面是粘土层。该地区有近 100 万个 SSs，占北卡罗来纳州 SSs 的 50%左右。本研究的目的是确定 SSs 密度不同的皮埃蒙特流域之间的养分浓度和输出是否存在显著差异。在 2015 年 1 月至 2016 年 12 月期间，从 SSs（n=11）流域、污水处理厂和森林流域采集水样，评估水质。记录溪流流量和环境读数，并从流域收集水样。此外，还于 2015 年 4 月至 2016 年 3 月从砂滤池流域收集样本，以与 SS 和对照流域进行比较。对样本进行总溶解氮（TDN）和正磷酸盐（PO-P）分析。结果表明，高密度（HD）SSs 服务的流域（4.9 kg-N yr ha；0.2 kg-P yr ha）分别比低密度（1.0 kg-N yr ha；<0.1 kg-P yr ha）和对照流域（1.4 kg-N yr ha；<0.1 kg-P yr ha）在基流期间，输出的 TDN 和 PO-P 中位数质量多一倍以上。同位素分析表明，硝酸盐-N 最有可能是 HD 流域污水的来源。在所有其他流域，同位素结果表明，非污水源是硝酸盐-N 的主要提供者。这些发现表明，SSs 密度是这些营养敏感的北卡罗来纳州皮埃蒙特供水流域输送 SS 衍生养分的重要因素。
