Lopez Samuel F, Janssen Sarah E, Tate Michael T, Fernandez Diego P, Anderson Christopher R, Armstrong Grace J, Wang Thomas C, Johnson William P
Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, United States; U.S. Geological Survey, Utah Water Science Center, West Valley City, UT 84119, United States.
U.S. Geological Survey, Upper Midwest Water Science Center, Madison, WI 53726, United States.
Sci Total Environ. 2024 Dec 20;957:177374. doi: 10.1016/j.scitotenv.2024.177374. Epub 2024 Nov 13.
Great Salt Lake is a critical habitat for migratory birds that is threatened by elevated metal concentrations, including mercury (Hg) and lead (Pb), and is subject to severe hydrologic changes, such as declining lake level. When assessing metal profiles recorded in Great Salt Lake sediment, a large data gap exists regarding the sources of metals within the system, which is complicated by various source inputs to the lake and complex biogeochemistry. Here, we leverage Hg and Pb stable isotopes to track relative changes in metal source contributions to Great Salt Lake over time. Mercury and Pb concentrations increase in sediments deposited after 1920 and peak between 1965 and 1995, following closure of several local smelters and the onset of increased emission controls. The nominal associations above are confirmed via Hg stable isotopes in pre-1920 background sediments, which reflect atmospheric inputs from regional and global origin, whereas Hg and Pb stable isotopes together indicate that elevated metal concentrations in mid-late 20th century sediments reflect increased mining/smelting inputs. The observed minimal rebound towards pre-1920 Pb isotope signatures in 21st century sediments indicates that mining/smelting inputs, though reduced, remain a primary source of Pb to Great Salt Lake. In contrast, the more pronounced rebound of Hg stable isotope signatures to pre-1920 values indicate a greater contribution of atmospheric inputs of regional/global origin to current Hg inputs, though Hg concentrations are ∼10 times greater than pre-1920 background values due to global increases in atmospheric Hg concentrations or possibly slow recovery from local contamination. The importance of regional/global Hg sources to the system suggests that reductions in Hg bioaccumulation in the open water food webs of Great Salt Lake are more dependent on national and global reductions in Hg emissions and management strategies to limit methylmercury production within system. This work highlights the utility of using coupled Hg and Pb stable isotope values to assess trace metal pollution sources and pathways in aquatic systems.
大盐湖是候鸟的重要栖息地，受到包括汞（Hg）和铅（Pb）在内的金属浓度升高的威胁，并且面临严重的水文变化，如湖面下降。在评估大盐湖沉积物中记录的金属分布时，关于该系统内金属来源存在很大的数据空白，湖泊的各种源输入和复杂的生物地球化学使情况变得复杂。在这里，我们利用汞和铅的稳定同位素来追踪随着时间推移金属源对大盐湖贡献的相对变化。1920年后沉积的沉积物中汞和铅的浓度增加，并在1965年至1995年间达到峰值，这发生在几个当地冶炼厂关闭和排放控制增加之后。上述名义关联通过1920年之前背景沉积物中的汞稳定同位素得到证实，这些同位素反映了来自区域和全球来源的大气输入，而汞和铅的稳定同位素共同表明20世纪中后期沉积物中升高的金属浓度反映了采矿/冶炼输入的增加。在21世纪的沉积物中观察到向1920年之前铅同位素特征的最小反弹，这表明采矿/冶炼输入虽然减少，但仍然是大盐湖铅的主要来源。相比之下，汞稳定同位素特征向1920年值的更明显反弹表明区域/全球来源的大气输入对当前汞输入的贡献更大，尽管由于全球大气汞浓度增加或可能从局部污染中缓慢恢复，汞浓度比1920年之前的背景值高约10倍。区域/全球汞源对该系统的重要性表明，大盐湖开放水域食物网中汞生物累积的减少更多地依赖于国家和全球汞排放的减少以及限制系统内甲基汞产生的管理策略。这项工作突出了使用汞和铅稳定同位素耦合值来评估水生系统中痕量金属污染源和途径的实用性。
