Enviromental dynamics of chlorine in water and soil - transport patterns and transformation rates

自20世纪40年代以来，人们普遍认为土壤中的氯是保守的，在流域内其他物质的预算计算中，氯通常被用作保守的示踪剂。然而，过去十年的研究表明，氯参与了一个复杂的生物地球化学循环。有强有力的证据表明，由于微生物的活动，土壤中普遍存在氯化作用(氯的消耗)，而氯化有机物的降解(氯的释放)主要是生物的还是非生物的，目前还不清楚。然而，很明显，土壤既可以充当氯的汇，也可以充当氯的来源，这取决于矿化或形成/挥发/淋溶过程占主导地位。该项目分为三个相互关联的部分，作为现场和实验室研究的结合，重点是与土地利用和环境变量对氯循环的影响有关的基础研究问题。第一个目标是在流域尺度上量化氯循环的主要组成部分。第二个目的是通过检验三个假设来评价氯化的生态作用：i)活性氯被用来抑制竞争微生物，ii)氯化与微生物抵御O2胁迫有关，iii)氯化增加土壤有机质的微生物利用率并提高土壤呼吸速率。第三个目的是通过用36-氯检验四个假设来研究氯离子在土壤中的去向和动力学：i)在好氧条件下，土壤中相当一部分的氯-in被转化为氯-org，ii)在厌氧条件下，由于氯化有机物的降解，氯-in从有机质中缓慢地释放出来，3)现行的氯离子行为的地球化学模型是不可靠的，因为它们没有考虑土壤中的氯离子向氯离子有机化合物的转化，以及(4)由于模型中没有包括土壤中氯-有机化合物的形成/降解，低估了放射性氯进入生物圈的速度和程度。

Since the 1940s, it has been widely accepted to assume that chloride is conservative in soil and chloride is commonly used as a conservative tracer in budget calculations of other substances within watersheds. However, the past decade of research suggests that chloride participates in a complex biogeochemical cycle. There is strong evidence that a widespread chlorination (consumption of chloride) in soil as a result of microbial activity whereas it is still unknown whether degradation of chlorinated organic matter (release of chloride) is mainly biotic or abiotic. However, it is clear that soil can act both as a sink and a source of chloride, depending on whether the mineralization or formation/volatilization/leaching processes dominate.The project is outlined in three interrelated parts conducted as combined field and laboratory studies with focus on fundamental research questions related to the impact of land-use and environmental variables on the chlorine cycle.The first aim is to quantify major components of the chlorine cycle at a watershed scale. The second aim is to evaluate the ecological role of chlorination by testing three hypotheses: i) reactive chlorine is used to inhibit competing microbes, ii) chlorination is related to microbial defense against O2 stress and iii) chlorination increases the microbial availability of soil organic matter and enhances soil respiration rates.The third aim is to investigate the fate and kinetics of Cl-in in soil by using 36-Cl to test four hypotheses: i) a considerable portion of Cl-in in soil is transformed to Cl-org under aerobic conditions, ii) Cl-in is slowly released from organic matter under anaerobic conditions due to degradation of chlorinated organic matter, iii) prevailing geochemical models of Cl-in behavior are unreliable due to that they do not take transformation of Cl-in to Cl-org in soil into account and, iv) the rate and extent to which radioactive chlorine enters the biosphere is underestimated due to that formation/degradation of Cl-org in soil is not included in the models.