Paleoecological Environmental Assessment and Research Lab, Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada; Department of Ecology and Environmental Science, Umeå University, 90187 Umeå, Sweden.
Paleoecological Environmental Assessment and Research Lab, Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada.
Sci Total Environ. 2020 Jul 10;725:138347. doi: 10.1016/j.scitotenv.2020.138347. Epub 2020 Apr 1.
Since the implementation of large-scale lake monitoring in the ~1980s, water color and dissolved organic carbon (DOC) concentrations have increased in many northern lakes (i.e., lake browning), impacting the functioning of aquatic ecosystems. In regions that formerly experienced high levels of acid deposition, this browning trend has been largely attributed to the recovery from the impacts of past acid deposition. However, the extent to which DOC levels have now returned to naturally higher, pre-industrial conditions is still poorly understood. In this study, we assessed whether DOC levels are still influenced by acid deposition in lakes near Sudbury, Ontario, a region that has been heavily affected by sulfur dioxide emissions from local metal smelting during the 20th century. We analyzed water chemistry monitoring data (1981-2018), together with comparisons between modern and pre-industrial DOC levels inferred from sediment spectroscopy, for 51 acid-sensitive and 24 buffered reference lakes across the Sudbury landscape. Since 1981, DOC concentrations doubled in acid-sensitive lakes, with a mean increase of +1.6 mg/L, whereas in more buffered reference lakes, mean DOC levels increased by only 0.8 mg/L. Similarly, sediment-inferred DOC trends indicate that current DOC levels are, on average, ~22% below pre-industrial levels in acid sensitive systems compared to only ~10% in buffered lakes. Weakening correlations between DOC and acidification-related water chemistry variables (e.g., pH, alkalinity, metals) further indicate a diminishing influence of acid deposition on DOC in Sudbury lakes. These results highlight the strong impact that acid deposition has historically had on lake-water DOC dynamics in this region, but also suggest that DOC levels are approaching natural baseline levels in less acid-sensitive lakes, and that other drivers, such as changes in climate or vegetation cover, are now becoming the dominant controls on changes in DOC concentrations.
自 20 世纪 80 年代大规模开展湖泊监测以来，许多北方湖泊（即湖泊变褐）的水色和溶解有机碳（DOC）浓度都有所增加，这影响了水生生态系统的功能。在过去酸沉降水平较高的地区，这种变褐趋势主要归因于过去酸沉降影响的恢复。然而，DOC 水平现在已经恢复到自然的、工业化前的较高水平的程度仍知之甚少。在这项研究中，我们评估了安大略省萨德伯里（Sudbury）附近的湖泊中，DOC 水平是否仍然受到酸沉降的影响，该地区在 20 世纪曾受到当地金属冶炼厂排放的二氧化硫的严重影响。我们分析了水质监测数据（1981-2018 年），并结合现代和从沉积光谱推断的工业化前 DOC 水平的比较，对萨德伯里景观内的 51 个酸性敏感湖泊和 24 个缓冲参考湖泊进行了研究。自 1981 年以来，酸性敏感湖泊的 DOC 浓度增加了一倍，平均增加了+1.6mg/L，而在缓冲性更强的参考湖泊中，平均 DOC 水平仅增加了 0.8mg/L。同样，从沉积推断的 DOC 趋势表明，与缓冲湖泊相比，目前酸性敏感系统的 DOC 水平平均比工业化前水平低约 22%，而缓冲湖泊的 DOC 水平平均低约 10%。DOC 与酸化相关的水质变量（例如 pH、碱度、金属）之间的相关性减弱，这进一步表明酸沉降对萨德伯里湖泊 DOC 的影响正在减弱。这些结果突出表明，酸沉降在过去对该地区湖泊水中的 DOC 动态具有很强的影响，但也表明在酸性敏感度较低的湖泊中，DOC 水平正在接近自然基线水平，而其他驱动因素，如气候变化或植被覆盖的变化，现在正成为控制 DOC 浓度变化的主要因素。
