Brown Lauren E, Chen Celia Y, Voytek Mary A, Amirbahman Aria
Department of Civil and Environmental Engineering, University of Maine, Orono, ME 04469, USA.
Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
Mar Chem. 2015 Dec;177(Pt 5):731-741. doi: 10.1016/j.marchem.2015.10.011.
Estuarine sediments store particulate contaminants including mercury (Hg). We studied Hg sediment dynamics in two intertidal mudflats at Great Bay estuary, NH, over multiple years. Sediments at both mudflats were physically mixed down to ~10 cm, as determined by Be measurements, albeit via different mechanisms. Portsmouth mudflat (PT) sediments were subject to bioturbation by infaunal organisms and Squamscott mudflat (SQ) sediments were subject to erosion and redeposition. The presence of higher concentrations of fresh Fe(III) hydroxide at PT suggested bioirrigation by the polychaetes (). At depths where infaunal bioirrigation was observed, pore-water inorganic Hg (Hg) and methylmercury (MeHg) were lower potentially due to their interaction with Fe(III) hydroxide. Methylmercury concentrations increased immediately below this zone in some samples, suggesting that the observed increase in material flux in bioirrigated sediments may initiate from lower depths. Pore water in sediment at PT also had higher fractions of more protein-like and labile DOC than those at SQ that can lead to increased MeHg production in PT, especially at depths where Hg is not removed from solution by Fe(III) hydroxide. Where sediment erosion and redeposition were observed at SQ, Hg species distribution was extended deeper into the sediment column. Moreover, methyl coenzyme M reductase (MCR) and mercury reductase (-A) genes were higher at SQ than PT suggesting differences in conditions for Hg cycling. Results showed that the near-surface region of high MeHg concentrations commonly observed in unmixed sediments does not exist in physically mixed sediments that are common in many estuarine environments.
河口沉积物储存着包括汞（Hg）在内的颗粒污染物。我们多年来研究了新罕布什尔州大湾河口两个潮间带泥滩中的汞沉积物动态。通过铍测量确定，两个泥滩的沉积物在约10厘米深度内都发生了物理混合，尽管混合机制不同。朴次茅斯泥滩（PT）的沉积物受到底栖生物的生物扰动，而斯夸姆斯科特泥滩（SQ）的沉积物则受到侵蚀和再沉积作用。PT处较高浓度的新鲜氢氧化铁（III）的存在表明多毛类动物进行了生物灌溉。在观察到有底栖生物进行生物灌溉的深度，孔隙水中的无机汞（Hg）和甲基汞（MeHg）含量较低，这可能是由于它们与氢氧化铁（III）发生了相互作用。在一些样品中，甲基汞浓度在该区域下方立即增加，这表明在生物灌溉的沉积物中观察到的物质通量增加可能始于较深的深度。PT处沉积物中的孔隙水还含有比SQ处更多的类蛋白和不稳定溶解有机碳（DOC），这可能导致PT处甲基汞产量增加，特别是在汞没有被氢氧化铁（III）从溶液中去除的深度。在SQ处观察到沉积物侵蚀和再沉积的地方，汞形态分布延伸到沉积物柱更深的位置。此外，甲基辅酶M还原酶（MCR）和汞还原酶（-A）基因在SQ处比PT处更高，这表明汞循环条件存在差异。结果表明，在许多河口环境中常见的物理混合沉积物中不存在未混合沉积物中通常观察到的高甲基汞浓度近地表区域。
