Abstract

Lac à la Truite (Trout Lake) from the municipality of Irlande (southern Quebec, Canada) suffers from eutrophication and siltation. More than 100 years of mining activities in the Thetford Mines region (1877–2011 CE) and the accumulation of gigantic mining waste piles have often been blamed for these problems, but their real impacts have never been demonstrated. Paleolimnological analyses were undertaken on a sediment core collected in Lac à la Truite to provide insights into its long-term evolution since pre-mining times. Results indicate that its degradation was greatly enhanced by the drainage of upstream Lac Noir (Black Lake) from 1955 to 1959 CE for mining purposes. Radiometric dating (¹³⁷Cs, ²¹⁰Pb, ¹⁴C) showed that this event caused a strong increase in sediment inputs, which afterwards remained high (0.6–1.3 cm yr⁻¹; 0.4–1.0 g cm⁻² yr⁻¹). Loss-on-ignition and spectrometry (ICP-AES/ICP-MS) analyses revealed that sediments deposited since 1960 CE mostly originate from the mining waste piles as they are organic-poor and highly enriched in metals associated with asbestos tailings (magnesium, chromium, nickel). During the drainage of Lac Noir, the emergence of diatom taxa typical of nutrient-rich waters in the sedimentary assemblages (e.g., Cyclotella meneghiniana, Cyclostephanos invisitatus) and the concomitant shift of biochemical proxies (C/N, δ¹³C) indicate that the disappearance of this water body has also caused the rapid eutrophication of Lac à la Truite by facilitating municipal wastewater inputs. Moreover, the pH and conductivity of the lake water are now considerably higher than during pre-mining times. Pollution generated by the mining waste piles and wastewater must be rapidly controlled to ensure the sustainability of Lac à la Truite.

摘要

来自爱尔兰（加拿大魁北克省南部）市的 Lac à la Truite（鳟鱼湖）饱受富营养化和淤积的困扰。Thetford Mines 地区 100 多年的采矿活动（公元 1877 年至 2011 年）以及巨大的采矿废料堆的堆积常常被归咎于这些问题，但它们的真正影响从未得到证实。对在 Lac à la Truite 收集的沉积物岩心进行了古湖沼学分析，以深入了解其自采矿前时代以来的长期演变。结果表明，从 1955 年到 1959 年，出于采矿目的，上游黑湖（黑湖）的排水大大增强了其退化。辐射测年 ( ¹³⁷ Cs, ²¹⁰ Pb, ¹⁴C) 表明该事件导致沉积物输入的强烈增加，之后保持高位（0.6-1.3 cm yr ^-1；0.4-1.0 g cm ^-2 yr ^-1）。烧失量和光谱法 (ICP-AES/ICP-MS) 分析表明，自公元 1960 年以来沉积的沉积物主要来自采矿废物堆，因为它们缺乏有机物并且富含与石棉尾矿相关的金属（镁、铬，镍）。在 Lac Noir 的排水过程中，沉积组合中富含营养水的典型硅藻类群（例如Cyclotella meneghiniana、Cyclostephanos invisitatus）的出现以及伴随的生化指标的变化（C/N，δ ¹³C) 表明该水体的消失也通过促进城市废水的输入而导致 Lac à la Truite 的快速富营养化。此外，现在湖水的 pH 值和电导率比开采前时期要高得多。必须迅速控制采矿废料堆和废水产生的污染，以确保 Lac à la Truite 的可持续性。