Peninsula Lake, Ontario, Canada, is a Precambrian Shield lake that has experienced many environmental stressors since European settlement of the watershed in the mid-1800s, including forest clearance, water-level management, sewage inputs, and land-use changes. The deterioration of water quality by the 1970s prompted mitigation efforts intended to reduce inputs of nutrients and untreated sewage to the lake. Paleolimnological analysis of a sediment core from Peninsula Lake, collected in 1995, revealed that efforts to address eutrophication had been somewhat successful, in that the lake had returned to oligotrophic status by the early 1990s. Nevertheless, there had been little to no improvement in inferred deepwater oxygen conditions. We used similar paleolimnological techniques on a core collected in 2014 to examine ecological responses to environmental stressors and remediation efforts in the intervening years, with a particular focus on changes in the amount of oxygenated habitat available to lake trout. Specifically, we inferred trends in volume-weighted hypolimnetic oxygen (VWHO), through analysis of sedimentary chironomid assemblages, to assess long-term changes in coldwater fisheries habitat. Potential drivers of VWHO were also investigated, and included diatom-inferred total phosphorus, spectrally derived trends in sedimentary chlorophyll a and its main diagenetic products, and lake-water dissolved organic carbon. The sedimentary chironomid assemblages indicate a long period of VWHO depletion, concurrent with known anthropogenic activities from the early twentieth century to the 1990s, followed by recent recovery to near pre-impact levels. The sedimentary diatom assemblages indicate nutrient enrichment throughout most of the twentieth century, which was also followed by a return to pre-impact conditions, albeit with recent indications of renewed nutrient enrichment. In contrast, strikingly different trajectories were observed in two other regional waterbodies that support lake trout, but experienced relatively little nutrient enrichment over the past ~ 150 years. Peninsula Lake appears to be recovering from nutrient enrichment and hypolimnetic oxygen depletion, but water quality improvements have nevertheless been accompanied by increased primary production, perhaps because climate warming has extended the ice-free season and stratification period. Therefore, instead of returning to pre-impact conditions, Peninsula Lake appears to be developing a novel ecological state. Any future improvements in lake trout habitat that result from nutrient abatement may be offset by rising temperatures.

加拿大安大略省半岛湖是一个前寒武纪地盾湖，自 1800 年代中期欧洲人在该流域定居以来，该湖经历了许多环境压力，包括森林清理、水位管理、污水输入和土地利用变化。到 1970 年代水质的恶化促使采取缓解措施，旨在减少向湖中输入的营养物质和未经处理的污水。对 1995 年收集的半岛湖沉积物岩心的古湖泊学分析表明，解决富营养化问题的努力取得了一定的成功，因为到 1990 年代初，该湖已恢复到贫营养状态。尽管如此，推断的深水氧气条件几乎没有改善。我们在 2014 年收集的岩心上使用了类似的古湖泊学技术，以检查对环境压力因素的生态反应和随后几年的修复工作，特别关注湖鳟鱼可利用的含氧栖息地数量的变化。具体来说，我们通过对沉积摇蚊组合的分析，推断出体积加权水下氧 (VWHO) 的趋势，以评估冷水渔业栖息地的长期变化。还研究了 VWHO 的潜在驱动因素，包括硅藻推断的总磷、沉积叶绿素的光谱衍生趋势 我们通过对沉积摇蚊组合的分析，推断出体积加权水下氧 (VWHO) 的趋势，以评估冷水渔业栖息地的长期变化。还研究了 VWHO 的潜在驱动因素，包括硅藻推断的总磷、沉积叶绿素的光谱衍生趋势 我们通过对沉积摇蚊组合的分析，推断出体积加权水下氧 (VWHO) 的趋势，以评估冷水渔业栖息地的长期变化。还研究了 VWHO 的潜在驱动因素，包括硅藻推断的总磷、沉积叶绿素的光谱衍生趋势一种及其主要成岩产物、湖水溶解有机碳。沉积的摇蚊组合表明 VWHO 长期耗竭，同时伴随着从 20 世纪初到 1990 年代的已知人为活动，随后最近恢复到接近撞击前的水平。沉积硅藻组合表明在 20 世纪的大部分时间里营养丰富，随后又恢复到撞击前的条件，尽管最近有迹象表明营养丰富。相比之下，在支持湖鳟鱼的另外两个区域水体中观察到明显不同的轨迹，但在过去的 150 年中营养物质的富集相对较少。半岛湖似乎正在从营养丰富和水下氧耗竭中恢复，但水质的改善仍然伴随着初级生产的增加，这可能是因为气候变暖延长了无冰季节和分层期。因此，半岛湖并没有恢复到撞击前的状态，而是正在形成一种新的生态状态。由于养分减少而导致的湖鳟栖息地的任何未来改善都可能被气温上升所抵消。