U.S. Geological Survey, Florida Water Science Center, 12703 Research Pkwy, Orlando, FL 32826, USA.
J Contam Hydrol. 2012 May 15;133:53-75. doi: 10.1016/j.jconhyd.2012.03.005. Epub 2012 Mar 23.
A stormwater infiltration basin in north-central Florida, USA, was monitored from 2007 through 2008 to identify subsurface biogeochemical processes, with emphasis on N cycling, under the highly variable hydrologic conditions common in humid, subtropical climates. Cyclic variations in biogeochemical processes generally coincided with wet and dry hydrologic conditions. Oxidizing conditions in the subsurface persisted for about one month or less at the beginning of wet periods with dissolved O(2) and NO(3)(-) showing similar temporal patterns. Reducing conditions in the subsurface evolved during prolonged flooding of the basin. At about the same time O(2) and NO(3)(-) reduction concluded, Mn, Fe and SO(4)(2-) reduction began, with the onset of methanogenesis one month later. Reducing conditions persisted up to six months, continuing into subsequent dry periods until the next major oxidizing infiltration event. Evidence of denitrification in shallow groundwater at the site is supported by median NO(3)(-)-N less than 0.016 mg L(-1), excess N(2) up to 3 mg L(-1) progressively enriched in δ(15)N during prolonged basin flooding, and isotopically heavy δ(15)N and δ(18)O of NO(3)(-) (up to 25‰ and 15‰, respectively). Isotopic enrichment of newly infiltrated stormwater suggests denitrification was partially completed within two days. Soil and water chemistry data suggest that a biogeochemically active zone exists in the upper 1.4m of soil, where organic carbon was the likely electron donor supplied by organic matter in soil solids or dissolved in infiltrating stormwater. The cyclic nature of reducing conditions effectively controlled the N cycle, switching N fate beneath the basin from NO(3)(-) leaching to reduction in the shallow saturated zone. Results can inform design of functionalized soil amendments that could replace the native soil in a stormwater infiltration basin and mitigate potential NO(3)(-) leaching to groundwater by replicating the biogeochemical conditions under the observed basin.
美国中北部佛罗里达州的一个雨水渗透盆地，从 2007 年到 2008 年进行了监测，以确定地下生物地球化学过程，重点是氮循环，这是在潮湿的亚热带气候下高度变化的水文条件下进行的。生物地球化学过程的周期性变化通常与干湿水文条件相吻合。在雨季开始时，地下的氧化条件持续了大约一个月或更短的时间，溶解氧和硝酸盐表现出相似的时间模式。在盆地长时间洪水期间，地下出现了还原条件。大约在同一时间，氧气和硝酸盐还原结束后，锰、铁和硫酸盐开始还原，一个月后甲烷生成开始。还原条件持续了长达六个月，持续到随后的旱季，直到下一次主要的氧化渗透事件发生。该地点浅层地下水中存在反硝化作用的证据，支持地下水硝酸盐氮含量中位数小于 0.016 毫克/升，氮素过剩高达 3 毫克/升，在盆地长时间洪水期间，氮同位素逐渐富集，δ15N 值高达 25‰，δ18O 值高达 15‰。新渗透雨水的同位素富集表明，反硝化作用在两天内部分完成。土壤和水化学数据表明，在土壤上层 1.4 米存在一个生物地球化学活跃区，其中有机碳可能是由土壤固体中的有机质或渗透雨水提供的电子供体。还原条件的周期性有效地控制了氮循环，使盆地下的氮命运从硝酸盐淋失转变为浅层饱和带的还原。研究结果可以为功能化土壤改良剂的设计提供信息，这些改良剂可以替代雨水渗透盆地中的天然土壤，并通过复制观察到的盆地中的生物地球化学条件来减轻潜在的硝酸盐向地下水的淋失。
