Small-Scale Geochemical Heterogeneities and Seasonal Variation of Iron and Sulfide in Salt Marshes Revealed by Two-Dimensional Sensors
Small-Scale Geochemical Heterogeneities and Seasonal Variation of Iron and Sulfide in Salt Marshes Revealed by Two-Dimensional Sensors
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DOI：
10.3389/feart.2021.653698
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
Qingzhi Zhu;J. Cochran;C. Heilbrun;H. Yin;H. Feng;J. Tamborski;P. Fitzgerald;W. Cong
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文献类型：
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作者：
Qingzhi Zhu;J. Cochran;C. Heilbrun;H. Yin;H. Feng;J. Tamborski;P. Fitzgerald;W. Cong
潮汐湿地的消失是一个世界性的现象。许多因素可能导致这种损失，但其中包括地球化学压力源，例如沼泽植物暴露在沼泽泥炭孔隙水中硫化氢含量升高的环境中。在这里，我们报告了牙买加湾未恢复（JoCo）和部分恢复（Big Egg）盐沼不同季节铁和硫化物地球化学的研究结果。牙买加湾是纽约市高度城市化的河口，近年来盐沼面积的消失加速。首次利用高分辨率平面传感器原位绘制了盐沼中溶解的 Fe2+ 和 H2S 的时空二维分布模式。还通过对离散深度的孔隙水取样来评估沼泽中 Fe2+ 和硫化氢的垂直剖面以及相关溶质和氧化还原电位。采集不同季节的沉积物岩心，进一步研究不同深度沼泽泥炭中固相Fe、S、N、C和铬还原性硫化物的含量，以研究不同季节Fe、S循环及其与有机质循环的关系。我们的研究结果表明，氧化还原敏感元素Fe2+和S2-在盐沼中表现出显着的异质性和复杂的三维分布模式，在毫米到厘米尺度上，由于根部的氧泄漏和氧化还原成岩反应而与植物根部直接相关。我们假设根部周围形成的含有低/未检测到的 H2S 和 Fe2+ 的氧化层通过减少硫化物吸收来帮助沼泽植物在高水平 H2S 中生存。 Fe2+和H2S的总体浓度和分布模式也随温度变化而季节性变化。 JoCo 采样点的 H2S 水平在秋季可能会从 5 mM 变化，反映了该沼泽地有机物细菌氧化速率的显着季节性变化。固相 Fe 和 S 表明，JoCo 和 Big Egg 中非常高比例的成岩活性铁与黄铁矿有关，黄铁矿可以在缺氧沉积物中长期存在。这意味着没有足够的成岩活性铁来通过在 JoCo 和 Big Egg 处形成硫化铁来缓冲孔隙水硫化氢。
Loss of tidal wetlands is a world-wide phenomenon. Many factors may contribute to such loss, but among them are geochemical stressors such as exposure of the marsh plants to elevated levels on hydrogen sulfide in the pore water of the marsh peat. Here we report the results of a study of the geochemistry of iron and sulfide at different seasons in unrestored (JoCo) and partially restored (Big Egg) salt marshes in Jamaica Bay, a highly urbanized estuary in New York City where the loss of salt marsh area has accelerated in recent years. The spatial and temporal 2-dimensional distribution patterns of dissolved Fe2+ and H2S in salt marshes were in situ mapped with high resolution planar sensors for the first time. The vertical profiles of Fe2+ and hydrogen sulfide, as well as related solutes and redox potentials in marsh were also evaluated by sampling the pore water at discrete depths. Sediment cores were collected at various seasons and the solid phase Fe, S, N, C, and chromium reducible sulfide in marsh peat at discrete depths were further investigated in order to study Fe and S cycles, and their relationship to the organic matter cycling at different seasons. Our results revealed that the redox sensitive elements Fe2+ and S2– showed significantly heterogeneous and complex three dimensional distribution patterns in salt marsh, over mm to cm scales, directly associated with the plant roots due to the oxygen leakage from roots and redox diagenetic reactions. We hypothesize that the oxic layers with low/undetected H2S and Fe2+ formed around roots help marsh plants to survive in the high levels of H2S by reducing sulfide absorption. The overall concentrations of Fe2+ and H2S and distribution patterns also seasonally varied with temperature change. H2S level in JoCo sampling site could change from 5 mM in fall season, reflecting significantly seasonal variation in the rates of bacterial oxidation of organic matter at this marsh site. Solid phase Fe and S showed that very high fractions of the diagenetically reactive iron at JoCo and Big Egg were associated with pyrite that can persist for long periods in anoxic sediments. This implies that there is insufficient diagenetically reactive iron to buffer the pore water hydrogen sulfide through formation of iron sulfides at JoCo and Big Egg.