Rates of trace metal and nutrient diagenesis in an intertidal creek bank
Rates of trace metal and nutrient diagenesis in an intertidal creek bank
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DOI：
10.1016/j.gca.2010.09.040
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发表时间：
2011
影响因子：
5
通讯作者：
T. Riedel;K. Lettmann;B. Schnetger;M. Beck;H. Brumsack
中科院分区：
文献类型：
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作者：
T. Riedel;K. Lettmann;B. Schnetger;M. Beck;H. Brumsack
海洋沉积物中的碳矿化是碳、营养物质和微量金属循环的关键过程。然而，由于海洋沉积物通常以扩散为主，元素和养分循环的速度很慢，因为孔隙水中通过微生物活动消耗的氧化剂和/或养分往往超过了再补给。在这样的系统中加入平流成分应该会大大改变生物地球化学动力学。数值模拟表明，受潮汐力影响的浅海沿岸含水层可以建立高达7cmh−1的地下水流速，驱动海水在沉积物中循环并随后排出。虽然已知平流可以促进溶质交换，但对早期成岩作用的影响尚未得到重视。为了解决这个问题，我们绘制了间质水化学图，沿着潮间带溪岸的样带，沉积物深度为2.5米，受到周期性平流的影响。此外，还应用了最近发展的河滩水文地质模拟来计算采样孔隙水的年龄。获得的样品年龄用于量化（流动路径集成）痕量金属、营养物质和硫酸盐的产量或耗竭率。我们发现年轻海水在靠近小溪的沉积物中渗透相对较快，表现出强烈的蚀变迹象，而来自扩散主导区域的孔隙水则变化较小。无机营养物质和一些微量元素在流动路径上的增加需要高的周转率。200天后，硫酸盐、钼和铀几乎完全耗尽，而溶解的无机碳（DIC）、氨和锰则增加。当平流主导地下流动时，DIC的平均产量似乎高出三倍。我们的结果表明，以平流为主的位点通常显示出更快的成岩反应速率的迹象。
Carbon mineralization in marine sediments is a key process involved in the cycling of carbon, nutrients and trace metals. However, as marine sediments are usually diffusion dominated, the pace of element and nutrient cycling is slow, because consumption of oxidants and/or nutrients in the pore waters via microbial activity often outpaces resupply. Adding an advective flow component to such a system should change the biogeochemical dynamics considerably. Numerical simulations show that shallow coastal aquifers affected by tidal forces can establish ground water velocities of up to 7cmh−1, driving a circulation of sea water through the sediments with subsequent discharge. Although known to enhance solute exchange, the impact of advection on early diagenesis has not received much attention. To address this issue we mapped the interstitial water chemistry down to 2.5m sediment depth along a transect on an intertidal creek bank that is subject to a periodic advective flow. Additionally a recently developed hydrogeological simulation of the creek bank was applied to calculate ages of the sampled pore waters. Sample ages obtained were used to quantify (flow path integrated) production or depletion rates for trace metals, nutrients, and sulphate. We find young sea water percolating relatively fast through sediments close to the creek showing strong signs of alteration, whereas pore waters from diffusion dominated regions are less altered. The increase in inorganic nutrients and some trace elements along the flow path requires high rates of turnover. Sulphate, molybdenum, and uranium are almost completely depleted after 200days, while dissolved inorganic carbon (DIC), ammonia, and manganese increase. Averaged production rates for DIC appear to be three times higher when advection dominated the subsurface flow regime. Our results demonstrate that sites dominated by advection generally show signs of faster rates of diagenetic reactions.