Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, United Kingdom; School of Geography and Environmental Science, University of Southampton, University Road, Southampton SO17 1BJ, United Kingdom.
Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, United Kingdom.
Sci Total Environ. 2020 Jun 20;722:137745. doi: 10.1016/j.scitotenv.2020.137745. Epub 2020 Mar 9.
Many lakes undergo anthropogenically driven eutrophication and pollution leading to decreased water and sediment quality. These effects can enhance seasonally changing lake redox conditions that may concentrate potentially toxic elements. Here we report the results of a multi-method geochemical and sediment microfabric analysis applied to reconstruct the history of cultural eutrophication and pollution of the North and South Basins of Windermere, UK. Eutrophication developed from the mid-19th to the earliest 20th centuries. Enhanced lake productivity is indicated by increased sedimentary δC, and increased pollution by a higher concentration of metals (Pb, Hg, and As) in the sediment, likely enhanced by incorporation and adsorption to settling diatom aggregates, preserved as sedimentary laminae. In the South Basin, increasing sediment δN values occur in step with Zn, Hg, and Cu, linking metal enrichment to isotopically heavy nitrate (N) from anthropogenic sources. From around 1930, decreases in Mn and Fe-rich laminae indicate reduced deep-water ventilation, whereas periods of sediment anoxia increased, being most severe in the deeper North Basin. Strongly reducing sediment conditions promoted Fe and Mn reduction and Pb-bearing barite formation, hitherto only described from toxic mine wastes and contaminated soils. From 1980 there was an increase in indicators of bottom water oxygenation, although not to before 1930. But in the South Basin, the continued impacts of sewage are indicated by elevated sediment δN. Imaging and X-ray microanalysis using scanning electron microscopy has shown seasonal-scale redox mineralisation of Mn, Fe, and Ba related to intermittent sediment anoxia. Elevated concentrations of these metals and As also occur in the surficial sediment and provide evidence for dynamic redox mobilisation of potentially toxic elements to the lake water. Concentrations of As (up to 80 ppm), exceed international Sediment Quality Standards. This process may become more prevalent in the future with climate change driving lengthened summer stratification.
许多湖泊受到人为驱动的富营养化和污染，导致水质和底质变差。这些影响可能会增强湖泊季节性的氧化还原条件，从而使潜在有毒元素浓缩。在这里，我们报告了一种多方法地球化学和沉积物微观结构分析的结果，该方法应用于重建英国温德米尔湖北部和南部盆地的文化富营养化和污染历史。富营养化从 19 世纪中叶发展到 20 世纪初。沉积物中 δC 的增加表明湖泊生产力增强，而金属（Pb、Hg 和 As）浓度的增加表明污染加剧，这可能是由于硅藻聚集体的沉降和吸附作用增强所致，这些硅藻聚集体以沉积纹层的形式保存下来。在南部盆地，随着 Zn、Hg 和 Cu 的增加，沉积物 δN 值也在增加，这将金属富集与来自人为源的同位素重硝酸盐（N）联系起来。从 1930 年左右开始，富 Mn 和 Fe 的纹层减少表明深层水通气减少，而缺氧期增加，在较深的北部盆地最为严重。强烈的还原条件促进了 Fe 和 Mn 的还原和 Pb 赋存的重晶石形成，这在以前只在有毒矿山废物和污染土壤中描述过。自 1980 年以来，底水氧合的指示物有所增加，尽管尚未达到 1930 年以前的水平。但在南部盆地，污水的持续影响表明沉积物 δN 升高。利用扫描电子显微镜进行成像和 X 射线微分析表明，与间歇性底泥缺氧有关的 Mn、Fe 和 Ba 的季节性尺度氧化还原矿化作用。这些金属和 As 的浓度升高也出现在表层沉积物中，为潜在有毒元素向湖水的动态氧化还原迁移提供了证据。As 的浓度（高达 80ppm）超过了国际沉积物质量标准。随着气候变化导致夏季分层时间延长，这种过程在未来可能会更加普遍。
