Department of Civil and Environmental Engineering, Western University, London, Ontario N6A 3K7, Canada.
School of Civil and Environmental Engineering, Water Research Centre, University of New South Wales, Manly Vale, NSW 2093, Australia.
Sci Total Environ. 2021 Jan 15;752:141262. doi: 10.1016/j.scitotenv.2020.141262. Epub 2020 Aug 8.
This study evaluates spatiotemporal variability in the behavior of septic system derived nutrients in a sandy nearshore aquifer and their discharge to a large lake. A groundwater nutrient-rich plume was monitored over a two-year period with the septic system origin of the plume confirmed using artificial sweeteners. High temporal variability in NO-N attenuation in the nearshore aquifer prior to discharge to the lake (42-96%) reveals the complex behavior of NO-N and potential importance of changing hydrological and geochemical conditions in controlling NO-N discharge to the lake. While PO-P was retarded in the nearshore aquifer, the PO-P plume extended over 90 m downgradient of the septic system. It was estimated that the PO-P plume may reach the lake within 10 years and represents a legacy issue whereby PO-P loads to the lake may increase over time. To provide broader assessment of the contribution of septic systems to P and N loads to a large lake, a regional scale geospatial model was developed that considers the locations of individual septic systems along the Canadian Lake Erie shoreline. The estimated P and N loads indicate that septic systems along the shoreline are only a minor contributor to the annual P and N loads to Lake Erie. However, it is possible that nutrients from septic systems may contribute to localized algal blooms in shoreline areas with high septic system density. In addition, disproportionate P and N loads in discharging groundwater may change the N:P ratio in nearshore waters and promote growth of harmful cyanobacteria. The study provides new insights into factors controlling the function of the reaction zone near the groundwater-lake interface including its impact on groundwater-derived nutrient inputs to large lakes. Further, the study findings are needed to inform septic system and nutrient management programs aimed at reducing lake eutrophication.
本研究评估了沙质近岸含水层中源于化粪池系统的养分在时空上的变化及其向大湖排放的情况。在两年的时间里，使用人工甜味剂监测了富营养化地下水流带，确认了该流带的化粪池系统来源。在排放到湖中之前，近岸含水层中硝态氮衰减的时间变化很大（42-96%），这揭示了硝态氮的复杂行为以及改变水文和地球化学条件对控制硝态氮向湖中排放的潜在重要性。尽管磷在近岸含水层中受到阻滞，但磷带延伸到化粪池系统下游 90 米处。据估计，磷带可能在 10 年内到达湖泊，这是一个遗留问题，随着时间的推移，磷负荷可能会增加到湖中。为了更广泛地评估化粪池系统对大湖磷和氮负荷的贡献，开发了一个区域尺度的地理空间模型，该模型考虑了加拿大安大略湖湖岸沿线单个化粪池系统的位置。估计的磷和氮负荷表明，湖岸沿线的化粪池系统对安大略湖的年磷和氮负荷只有很小的贡献。然而，化粪池系统的养分可能会导致岸边地区局部藻类大量繁殖，这些地区的化粪池系统密度较高。此外，排放地下水的磷和氮负荷不成比例可能会改变近岸水域的氮磷比，并促进有害蓝藻的生长。该研究提供了新的见解，了解控制地下水-湖泊界面反应区功能的因素，包括其对大湖地下水来源养分输入的影响。此外，还需要研究结果为旨在减少湖泊富营养化的化粪池系统和养分管理计划提供信息。
