Wang Ting, Obrist Daniel
Department of Environmental, Earth, and Atmospheric Sciences, University of Massachusetts Lowell, Lowell, MA, 01854, USA.
Environ Pollut. 2022 Feb 1;294:118657. doi: 10.1016/j.envpol.2021.118657. Epub 2021 Dec 7.
Salt marsh estuaries serve as sources and sinks for nutrients and elements to and from estuarine water, which enhances and alleviates watershed fluxes to the coastal ocean. We assessed sources and sinks of mercury in the intertidal Plum Island Sound estuary in Massachusetts, the largest salt marsh estuary of New England, using 25-km spatial water sampling transects. Across all seasons, dissolved (FHg) and total (THg) mercury concentrations in estuarine water were highest and strongly enhanced in upper marshes (1.31 ± 0.20 ng L and 6.56 ± 3.70 ng L, respectively), compared to riverine Hg concentrations (0.86 ± 0.17 ng L and 0.88 ± 0.34 ng L, respectively). Mercury concentrations declined from upper to lower marshes and were lowest in ocean water (0.38 ± 0.10 ng L and 0.56 ± 0.25 ng L, respectively). Conservative mixing models using river and ocean water as endmembers indicated that internal estuarine Hg sources strongly enhanced estuarine water Hg concentrations. For FHg, internal estuarine Hg contributions were estimated at 26 g yr which enhanced Hg loads from riverine sources to the ocean by 44%. For THg, internal sources amounted to 251 g yr and exceeded riverine sources six-fold. Proposed sources for internal estuarine mercury contributions include atmospheric deposition to the large estuarine surface area and sediment re-mobilization, although sediment Hg concentrations were low (average 23 ± 2 μg kg) typical of uncontaminated sediments. Soil mercury concentrations under vegetation, however, were ten times higher (average 200 ± 225 μg kg) than in intertidal sediments suggesting that high soil Hg accumulation might drive lateral export of Hg to the ocean. Spatial transects of methylated Hg (MeHg) showed no concentration enhancements in estuarine water and no indication of internal MeHg sources or formation. Initial mass balance considerations suggest that atmospheric deposition may either be in similar magnitude, or possibly exceed lateral tidal export which would be consistent with strong Hg accumulation observed in salt marsh soils sequestering Hg from current and past atmospheric deposition.
盐沼河口是河口水中营养物质和元素的源与汇，这增强并缓解了流域向沿海海洋的通量。我们利用25公里的空间水样断面，评估了马萨诸塞州潮间带李子岛海峡河口（新英格兰最大的盐沼河口）汞的源与汇。在所有季节中，与河流水体汞浓度（分别为0.86±0.17纳克/升和0.88±0.34纳克/升）相比，河口水中溶解态汞（FHg）和总汞（THg）浓度在上部盐沼中最高且显著增强（分别为1.31±0.20纳克/升和6.56±3.70纳克/升）。汞浓度从上部盐沼到下部盐沼逐渐降低，在海水中最低（分别为0.38±0.10纳克/升和0.56±0.25纳克/升）。使用河水和海水作为端元的保守混合模型表明，河口内部汞源显著提高了河口水体汞浓度。对于FHg，河口内部汞贡献估计为26克/年，这使从河流来源到海洋的汞负荷增加了44%。对于THg，内部来源达251克/年，超过河流来源六倍。河口内部汞贡献的推测来源包括大气沉降到广阔的河口表面积以及沉积物再活化，尽管沉积物汞浓度较低（平均23±2微克/千克），属于未受污染沉积物的典型情况。然而，植被下土壤汞浓度比潮间带沉积物高十倍（平均200±225微克/千克），这表明高土壤汞积累可能推动汞向海洋的横向输出。甲基汞（MeHg）的空间断面显示河口水中浓度没有增强，也没有内部MeHg来源或形成的迹象。初步的质量平衡考虑表明，大气沉降可能与横向潮汐输出量相当，或者可能超过横向潮汐输出，这与在盐沼土壤中观察到的从当前和过去大气沉降中封存汞的强烈汞积累情况一致。
