Developing a lake management strategy by dovetailing lake monitoring with paleolimnological techniques: a case study from a kettle lake on the Oak Ridges Moraine (Ontario, Canada)

Moos MT, Ginn BK. 2016. Developing a lake management strategy by dovetailing lake monitoring with paleolimnological techniques: a case study from a kettle lake on the Oak Ridges Moraine (Ontario, Canada). Lake Reserv Manage. 32: 234–245. In response to concerns about declining water quality, increased aquatic plant biomass, and harmful algal blooms, a lake monitoring program was undertaken on a suburban kettle lake near Toronto, Canada. We identified environmental conditions consistent with eutrophication, and the largest source of phosphorus (P) loading was from sediment release during an extended period of low dissolved oxygen during thermal stratification of the water column. To put these current environmental conditions in perspective, account for long-term limnological trends, and develop a sustainable lake management strategy, we also undertook paleolimnological analysis of a sediment core. Using diatoms as proxy indicators, historic limnological conditions were reconstructed. Although pre-European settlement conditions were typical of lakes with forested catchments in this region, the lake was mesotrophic (total phosphorus [TP] ∼17.5 µg/L), likely from P bound to dissolved organic carbon. P concentrations increased with the use of chemical fertilizers and establishment of seasonal lakeside cottages and resorts starting in the 1920s (the beginning of the diatom-inferred (DI-) TP upward trend). With the conversion of these cottages into year-round homes (since 1960) and further urbanization of the catchment, including servicing with municipal water supply but continued reliance on septic tanks, P has increased further (TP ∼26.1 µg/L). For restoration to a sustainable state, methods of preventing sediment P release (capping the sediment surface or oxygenation of the hypolimnion) should be considered, along with installation of municipal wasterwater servicing and stewardship projects to prevent further P loading from septic systems and surface runoff.

Moos MT与Ginn BK于2016年在《湖泊与水库管理》（*Lake Reserv Manage*）第32卷第234–245页发表了题为《通过整合湖泊监测与古湖沼学（paleolimnology）技术制定湖泊管理策略：加拿大安大略省橡树岭冰碛层锅穴湖（kettle lake）实例研究》的论文。针对水质下降、水生植物生物量增加以及有害藻华暴发等问题，研究团队于加拿大多伦多近郊的一处城郊锅穴湖（kettle lake）开展了湖泊监测项目。研究识别出与富营养化相符的环境特征，其中磷（P）负荷的最大来源为水体热分层（thermal stratification）期间长时间低溶解氧状态下的沉积物磷释放。为客观评估当前环境状况、厘清长期湖沼学变化趋势并制定可持续的湖泊管理策略，研究团队同时对该湖的沉积物岩芯（sediment core）开展了古湖沼学分析。研究以硅藻作为代用指标，重建了该湖的历史湖沼学环境。尽管欧洲殖民前的环境特征符合该地区森林集水区湖泊的典型状态，但该湖当时处于中营养水平（总磷（total phosphorus, TP）约17.5 µg/L），其磷负荷大概率来源于结合在溶解有机碳（dissolved organic carbon）上的磷。自20世纪20年代起，随着化肥的使用以及湖滨季节性度假小屋与度假村的兴建，磷浓度持续上升，硅藻反演总磷（diatom-inferred total phosphorus, DI-TP）的上升趋势即始于这一时期。自1960年起，这些度假小屋被改造为常年居住住宅，加之集水区进一步城市化——虽配套了市政供水系统，但仍依赖化粪池处理污水——磷浓度进一步攀升至约26.1 µg/L。若要将该湖恢复至可持续健康状态，可考虑采用抑制沉积物磷释放的手段（如沉积物覆盖法或下层滞水带（hypolimnion）充氧），同时配套建设市政污水收集处理设施，并开展管护项目以阻止化粪池系统与地表径流带来的额外磷负荷。