Svensson Teresia, Redon Paul-Olivier, Thiry Yves, Montelius Malin, Bastviken David
Department of Thematic Studies - Environmental Change, Linköping University, 581 83 Linköping, Sweden.
Andra, Research and Development Division, 1/7 rue Jean-Monnet, 92298 Chatenay-Malabry Cedex, France.
Sci Total Environ. 2022 Feb 1;806(Pt 2):150478. doi: 10.1016/j.scitotenv.2021.150478. Epub 2021 Sep 25.
The levels of natural organic chlorine (Cl) typically exceed levels of chloride in most soils and is therefore clearly of high importance for continental chlorine cycling. The high spatial variability raises questions on soil organic matter (SOM) chlorination rates among topsoils with different types of organic matter. We measured Cl formation rates along depth profiles in six French temperate soils with similar Cl deposition using Cl tracer experiments. Three forest sites with different humus types and soils from grassland and arable land were studied. The highest specific chlorination rates (fraction of chlorine pool transformed to Cl per time unit) among the forest soils were found in the humus layers. Comparing the forest sites, specific chlorination was highest in mull-type humus, characterized by high microbial activity and fast degradation of the organic matter. Considering non-humus soil layers, grassland and forest soils had similar specific chlorination rates in the uppermost layer (0-10 cm below humus layer). Below this depth the specific chlorination rate decreased slightly in forests, and drastically in the grassland soil. The agricultural soil exhibited the lowest specific chlorination rates, similar along the depth profile. Across all sites, specific chlorination rates were correlated with soil moisture and in combination with the patterns on organic matter types, the results suggest an extensive Cl cycling where humus types and soil moisture provided best conditions for microbial activity. Cl accumulation and theoretical residence times were not clearly linked to chlorination rates. This indicates intensive Cl cycling between organic and inorganic forms in forest humus layers, regulated by humic matter reactivity and soil moisture, while long-term Cl accumulation seems more linked with overall deep soil organic carbon stabilization. Thus, humus types and factors affecting soil carbon storage, including vegetation land use, could be used as indicators of potential Cl formation and accumulation in soils.
在大多数土壤中，天然有机氯（Cl）的含量通常超过氯化物的含量，因此对于陆地氯循环显然极为重要。高空间变异性引发了关于不同类型有机质表土中土壤有机质（SOM）氯化速率的问题。我们使用氯示踪实验测量了六种法国温带土壤（具有相似的氯沉降）沿深度剖面的氯形成速率。研究了三个具有不同腐殖质类型的森林站点以及草地和耕地的土壤。在森林土壤中，腐殖质层的比氯化速率（单位时间内转化为Cl的氯库比例）最高。比较森林站点，在以高微生物活性和有机质快速降解为特征的腐殖质型腐殖土中，比氯化作用最高。考虑非腐殖质土壤层，草地和森林土壤在最上层（腐殖质层以下0 - 10厘米）具有相似的比氯化速率。在此深度以下，森林中的比氯化速率略有下降，而草地土壤中则急剧下降。农业土壤的比氯化速率最低，沿深度剖面相似。在所有站点中，比氯化速率与土壤湿度相关，结合有机质类型的模式，结果表明存在广泛的氯循环，其中腐殖质类型和土壤湿度为微生物活动提供了最佳条件。氯的积累和理论停留时间与氯化速率没有明显关联。这表明森林腐殖质层中有机和无机形式之间存在强烈的氯循环，受腐殖质反应性和土壤湿度调节，而长期的氯积累似乎更多地与深层土壤有机碳的整体稳定有关。因此，腐殖质类型和影响土壤碳储存的因素，包括植被土地利用，可以用作土壤中潜在氯形成和积累的指标。
