Abstract The contribution of septic systems to watershed nutrient loads is poorly quantified although septic systems are often cited as potentially important nutrient sources. The study uses a geospatial model to estimate phosphorus loads from septic systems to the tributaries of the Canadian Lake Erie Basin to inform Lake Erie nutrient management initiatives. There is currently no inventory of septic systems in the Lake Erie Basin (e.g., numbers and locations of septic systems). Therefore a geospatial model was first developed to automatically locate individual septic systems with these locations then used to estimate phosphorus load contributions to tributaries. The model was tested on three subwatersheds in the Canadian Lake Erie Basin before being applied across the Basin. Present-day basin-wide phosphorus load estimates that consider: (i) only a fraction of septic effluent is currently reaching the tributaries due to slow transport and other delays, and (ii) phosphorus attenuation in the subsurface, range from 23 ± 11 to 68 ± 32 MT/yr. Based on these estimates, septic systems may currently contribute between 1.7 ± 0.8to 5 ± 2.3% of the phosphorus loads to Lake Erie from Canada. However, maximum phosphorus load estimates and transient model results show that the contribution of septic systems to phosphorus loads will increase over time as slow moving septic-derived groundwater phosphorus plumes reach tributaries and if aging septic systems are not maintained. This study provides widely applicable new knowledge and methodology; as well as specific findings needed to inform nutrient and septic system management in the Lake Erie Basin.

中文翻译：

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估算从化粪池系统到加拿大伊利湖盆地支流的磷负荷

摘要 化粪池系统对流域养分负荷的贡献很难量化，尽管化粪池系统经常被认为是潜在的重要营养源。该研究使用地理空间模型来估计从化粪池系统到加拿大伊利湖盆地支流的磷负荷，以告知伊利湖养分管理计划。目前伊利湖盆地没有化粪池系统的清单（例如，化粪池系统的数量和位置）。因此，首先开发了地理空间模型来自动定位具有这些位置的单个化粪池系统，然后用于估计对支流的磷负荷贡献。在应用于整个盆地之前，该模型在加拿大伊利湖盆地的三个子流域上进行了测试。当前全流域磷负荷估算考虑：(i) 由于缓慢的运输和其他延迟，目前只有一小部分化粪池流出物到达支流，以及 (ii) 地下的磷衰减范围为 23 ± 11 至 68 ± 32 MT/yr。根据这些估计，化粪池系统目前可能对加拿大伊利湖的磷负荷贡献 1.7 ± 0.8 至 5 ± 2.3%。然而，最大磷负荷估计和瞬态模型结果表明，随着缓慢移动的化粪池衍生的地下水磷羽流到达支流，并且如果不维护老化的化粪池系统，化粪池系统对磷负荷的贡献将随着时间的推移而增加。这项研究提供了广泛适用的新知识和方法；以及为伊利湖盆地的营养和化粪池系统管理提供信息所需的具体发现。