Casey R E, Taylor M D, Klaine S J
Dep. of Chemistry, Environmental Science and Studies Program, Towson Univ., MD 21252, USA.
J Environ Qual. 2001 Sep-Oct;30(5):1732-7. doi: 10.2134/jeq2001.3051732x.
Riparian wetlands are transition zones between terrestrial and aquatic environments that have the potential to serve as nutrient filters for surface and ground water due to their topographic location. We investigated a riparian wetland that had been receiving intermittent inputs of NO3- and PO4(3-) during storm runoff events to determine the mechanisms of nutrient attenuation in the wetland soils. Few studies have shown whether infrequent pulses of NO3- are sufficient to maintain substantial denitrifying communities. Denitrification rates were highest at the upstream side of the wetland where nutrient-rich runoff first enters the wetland (17-58 microg N2O-N kg soil(-1) h(-1)) and decreased further into the wetland. Carbon limitation for denitrification was minor in the wetland soils. Samples not amended with dextrose had 75% of the denitrification rate of samples with excess dextrose C. Phosphate sorption isotherms suggested that the wetland soils had a high capacity for P retention. The calculated soil PO4(3-) concentration that would yield an equilibrium aqueous P04(3-) concentration of 0.05 mg P L(-1) was found to be 100 times greater than the soil PO4(3-) concentration at the time of sampling. This indicated that the wetland could retain a large additional mass of PO4(3-) without increasing the dissolved P04(3-) concentrations above USEPA recommended levels for lentic waters. These results demonstrated that denitrification can be substantial in systems receiving pulsed NO3- inputs and that sorption could account for extensive PO4(3-) attenuation observed at this site.
河岸湿地是陆地和水生环境之间的过渡区域，由于其地形位置，有可能作为地表水和地下水的营养过滤器。我们调查了一个河岸湿地，该湿地在暴雨径流事件期间间歇性地接收硝酸根离子（NO3-）和磷酸根离子（PO4(3-)）的输入，以确定湿地土壤中营养物质衰减的机制。很少有研究表明，不频繁的硝酸根离子脉冲是否足以维持大量的反硝化群落。反硝化速率在湿地的上游最高，富营养径流首先进入湿地的地方（17 - 58微克一氧化二氮 - 氮每千克土壤（-1）每小时（-1）），并在湿地中进一步降低。湿地土壤中反硝化的碳限制较小。未用葡萄糖修正的样品的反硝化速率是有过量葡萄糖碳的样品的75%。磷酸盐吸附等温线表明，湿地土壤具有很高的磷保留能力。计算得出的土壤磷酸根离子（PO4(3-)）浓度，该浓度会产生平衡的水相磷酸根离子（P04(3-)）浓度为0.05毫克磷每升（-1），发现该浓度比采样时的土壤磷酸根离子（PO4(3-)）浓度大100倍。这表明，湿地可以保留大量额外的磷酸根离子（PO4(3-)），而不会使溶解的磷酸根离子（P04(3-)）浓度增加到超过美国环境保护局（USEPA）对静水水体推荐的水平。这些结果表明，在接受脉冲式硝酸根离子输入的系统中，反硝化作用可能很大，并且吸附可以解释在该地点观察到的大量磷酸根离子（PO4(3-)）衰减。
