Creek Dynamics Determine Pond Subsurface Geochemical Heterogeneity in East Anglian (UK) Salt Marshes
Creek Dynamics Determine Pond Subsurface Geochemical Heterogeneity in East Anglian (UK) Salt Marshes
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DOI：
10.3389/feart.2019.00041
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发表时间：
2019-03-14
影响因子：
2.9
通讯作者：
Turchyn, Alexandra, V
中科院分区：
文献类型：
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作者：
Hutchings, Alec M.;Antler, Gilad;Turchyn, Alexandra, V
盐沼是一个复杂的系统，包括短暂的淹没，植被平台，由潮汐小溪水力喂养。在排水不良的地方，可能会形成盐水池塘。在东盎格鲁（英国）盐沼，两种类型的沉积物化学可以在这些池塘下发现;富铁沉积物，其特点是高亚铁浓度在地下孔隙水（高达2毫米以上的30厘米）;和富硫化物沉积物，其特点是高孔隙水硫化物浓度（高达8毫米）。我们提出了5年的推芯取样，探讨这两种类型的沉积物中的孔隙水的地球化学。我们认为，当有机碳的数量足以耗尽池塘沉积物中的氧和铁含量时，条件有利于富含硫化物的沉积物的存在。相比之下，在池塘沉积物中，氧气存在，主要是通过生物灌溉，还原铁可以再氧化，从而回收进一步减少，有利于永久的富铁沉积条件。我们发现这些池塘沉积物可以改变显着超过一年的时间尺度。我们进行了无人机调查，与地面真实测量，探索这些池塘的地球化学的空间分布。我们的研究结果表明，池塘的接近小溪部分决定了池塘地下地球化学，富铁池塘往往更接近大的小溪比硫化物丰富的池塘。我们建议在表面交付的有机碳的差异，由于能量的不同的落潮，或铁的表面/地下交付可能控制的分布。如果潮汐洪水更频繁地冲刷靠近小溪的池塘，去除碳并用氧气冲洗，这可能会被放大。这些结果表明，人为创造的排水沟可能会改变分布的铁和硫化物丰富的池塘，从而对盐沼生态系统中的养分，微量金属和碳循环的影响。
Salt marshes are complex systems comprising ephemerally flooded, vegetated platforms hydraulically fed by tidal creeks. Where drainage is poor, formation of saline-water ponds can occur. Within East Anglian (UK) salt marshes, two types of sediment chemistries can be found beneath these ponds; iron-rich sediment, which is characterized by high ferrous iron concentration in subsurface porewaters (up to 2 mM in the upper 30 cm); and sulfide-rich sediment, which is characterized by high porewater sulfide concentrations (up to 8 mM). We present 5 years of push-core sampling to explore the geochemistry of the porewater in these two types of sediment. We suggest that when organic carbon is present in quantities sufficient to exhaust the oxygen and iron content within pond sediments, conditions favor the presence of sulfide-rich sediments. In contrast, in pond sediments where oxygen is present, primarily through bioirrigation, reduced iron can be reoxidised and thus recycled for further reduction, favoring the perpetuation of iron-rich sedimentary conditions. We find these pond sediments can alter significantly over an annual timescale. We carried out a drone survey, with ground-truthed measurements, to explore the spatial distribution of geochemistry in these ponds. Our results suggest that a pond's proximity to a creek partially determines the pond subsurface geochemistry, with iron-rich ponds tending to be closer to large creeks than sulfide-rich ponds. We suggest differences in surface delivery of organic carbon, due to differences in the energy of the ebb flow, or the surface/subsurface delivery of iron may control the distribution. This could be amplified if tidal inundations flush ponds closer to creeks more frequently, removing carbon and flushing with oxygen. These results suggest that anthropogenic creation of drainage ditches could shift the distribution of iron- and sulfide-rich ponds and thus have an impact on nutrient, trace metal and carbon cycling in salt marsh ecosystems.