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Varying redox potential affects P release from stream bank sediments

机译：氧化还原电位的变化会影响河岸沉积物中磷的释放

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Sediments in streams that drain agricultural watersheds may be sinks that can adsorb P from the stream or sources that can release P to the stream. Sediment characteristics and environmental factors, including the oxidation-reduction (redox) potential of the water associated with the sediment, determine whether P will be adsorbed or released by the sediment. We investigated P adsorption and release by four sediments [three Holocene-age sediments (Camp Creek, Roberts Creek and Gunder) as well as Pre-Illinoian-age Till] that occur in Walnut Creek, a second-order stream in Jasper County, Iowa, that is representative of many small streams in the glaciated upper Midwest of the US. The effects of two redox potentials on phosphorus buffering capacity (PBC) and equilibrium phosphorus concentration (EPC) were evaluated in batch adsorption experiments. We also simulated aerobic and anerobic conditions over a 24-day period and measured solution-phase P concentrations in stirred systems where the sediments were isolated from the water by dialysis tubing. The batch experiment indicated that the EPCs of the three Holocene-age sediments were similar to one another and increased with decreasing redox potential. In the stirred flow reactors, more dissolved P was released from the Camp Creek and Roberts Creek sediments under anaerobic conditions than from the other sediments. This observation suggests that these two sediments, which are younger and higher in the stratigraphic sequence, are more likely to be P sources in suboxic settings. The P buffering capacity was greatest in the till. Where it is in contact with the stream water, the till is likely to serve as an adsorbing sink for P in the water column.
机译：排放农业集水区的河流中的沉积物可能是可以吸收河流中P的汇，也可能是可以释放P到河流中的源。沉积物的特性和环境因素，包括与沉积物相关的水的氧化还原（氧化还原）电势，决定了磷是否会被沉积物吸附或释放。我们调查了在爱荷华州贾斯珀县的二次流核桃溪中发生的四种沉积物（三种全新世时代的沉积物（坎普克里克，罗伯茨溪和冈德以及伊利诺伊时期前的耕种）对磷的吸附和释放。 ，代表了美国中西部冰川上游的许多小溪。在分批吸附实验中评估了两种氧化还原电势对磷缓冲能力（PBC）和平衡磷浓度（EPC）的影响。我们还模拟了24天的好氧和好氧条件，并测量了搅拌系统中溶液相P的浓度，在这些系统中，透析管通过水将沉积物分离出来。批处理实验表明，三种全新世年龄沉积物的EPC彼此相似，并且随着氧化还原电位的降低而增加。在搅拌流反应器中，在厌氧条件下，Camp Creek和Roberts Creek沉积物中释放的溶解磷比其他沉积物中释放的磷更多。该观察结果表明，这两种沉积物在地层层序中越来越年轻，在亚氧环境中更有可能是磷源。直到现在为止，P缓冲能力最大。在与溪流水接触的地方，耕till很可能充当水柱中P的吸附槽。

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