Twentieth-century historic industrial activity in Cornwall, ON loaded high amounts of metals and metalloids to the St. Lawrence River. Despite industrial improvements and the eventual closure of point-source polluters, sedimentary contamination in the Cornwall waterfront remains above provincial guidelines, causing concern for ecosystem management. We analysed chironomid (Order: Diptera) subfossils from modern-day surface-sediment samples and a sediment core from the Cornwall waterfront in order to better understand historic pollution impacts and potential recovery. Modern-day chironomid assemblages were diverse (48 genera, >70 species) and overall assemblage structure was weakly related to sedimentary zinc concentrations, with Procladius, Paratanytarsus, and Ablabesmyia identified as zinc-tolerant and Rheotanytarsus, Polypedilum and Paratendipes identified as zinc-sensitive. The sediment core showed peak total mercury (THg) concentrations were an order of magnitude higher than in modern-day surface sediments. In sections of the core below 10 cm in depth, THg concentrations were high (~30–50 µg/g) and chironomids were nearly absent from the record. Above 10 cm (c. 1980) THg concentrations decreased and chironomid taxa returned in low abundances. Subsequent intervals displayed an increase in diversity, abundance, and the relative abundance of metal-sensitive taxa. This study provides evidence of ecological change which co-occurs with Cornwall’s historic industrial activity and indicates progress toward related ecological goals identified in the current management strategy.

康沃尔郡二十世纪的历史性工业活动向圣劳伦斯河装载了大量金属和类金属。尽管工业改善和点源污染源最终关闭，康沃尔滨水区的沉积物污染仍然高于省级指导方针，引起对生态系统管理的担忧。我们分析了现代地表沉积物样本中的摇蚊（订单：双翅目）亚化石和康沃尔海滨的沉积物核心，以更好地了解历史污染影响和潜在的恢复。现代摇蚊组合多种多样（48 属，> 70 种），整体组合结构与沉积锌浓度微弱相关，包括Procladius、Paratanytarsus和Ablabesmyia认定为锌宽容和Rheotanytarsus，Polypedilum和Paratendipes鉴定为锌敏感。沉积物核心显示总汞 (THg) 峰值浓度比现代表层沉积物高一个数量级。在深度低于 10 cm 的岩心部分，THg 浓度很高（~30-50 µg/g），并且几乎没有记录中的摇蚊。高于 10 cm (c. 1980) THg 浓度下降，摇蚊类群以低丰度返回。随后的间隔显示出金属敏感类群的多样性、丰度和相对丰度的增加。这项研究提供了与康沃尔历史工业活动同时发生的生态变化的证据，并表明在当前管理战略中确定的相关生态目标方面取得了进展。