Wilson George J L, Lu Chuanhe, Lapworth Dan J, Kumar Arun, Ghosh Ashok, Niasar Vahid J, Krause Stefan, Polya David A, Gooddy Daren C, Richards Laura A
Department of Earth and Environmental Sciences and Williamson Research Centre for Molecular Environmental Science, The University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, United Kingdom.
British Geological Survey, Maclean Building, Wallingford, Oxfordshire OX10 8BB, United Kingdom.
Sci Total Environ. 2023 Dec 10;903:166208. doi: 10.1016/j.scitotenv.2023.166208. Epub 2023 Aug 10.
The distribution and composition of dissolved organic matter (DOM) affects numerous (bio)geochemical processes in environmental matrices including groundwater. This study reports the spatial and seasonal controls on the distribution of groundwater DOM under the rapidly developing city of Patna, Bihar (India). Major DOM constituents were determined from river and groundwater samples taken in both pre- and post-monsoon seasons in 2019, using excitation-emission matrix (EEM) fluorescence spectroscopy. We compared aqueous fluorescent DOM (fDOM) composition to satellite-derived land use data across the field area, testing the hypothesis that the composition of groundwater DOM, and particularly the components associated with surface-derived ingress, may be controlled, in part, by land use. In the pre-monsoon season, the prominence of tryptophan-like components likely generated from recent biological activity overwhelmed the humic-like and tyrosine-like fluorescence signals. Evidence from fluorescence data suggest groundwater in the post-monsoon season is composed of predominantly i) plant-derived matter and ii) anthropogenically influenced DOM (e.g. tryptophan-like components). Organic tracers, as well as Eh and Cl, suggest monsoonal events mobilise surface-derived material from the unsaturated zone, causing dissolved organic carbon (DOC) of more microbial nature to infiltrate to >100 m depth. A correlation between higher protein:humic-like fluorescence and lower vegetation index (NDVI), determined from satellite-based land use data, in the post-monsoon season, indicates the ingression of wastewater-derived OM in groundwater under the urban area. Attenuated protein:humic-like fluorescence in groundwater close to the river points towards the mixing of groundwater and river water. This ingress of surface-derived OM is plausibly exacerbated by intensive groundwater pumping under these areas. Our approach to link the composition of aqueous organics with land use could easily be adapted for similar hydrogeochemical settings to determine the factors controlling groundwater DOM composition in various contexts.
溶解有机物（DOM）的分布和组成会影响包括地下水在内的环境基质中的众多（生物）地球化学过程。本研究报告了印度比哈尔邦巴特那市快速发展地区地下水DOM分布的空间和季节控制因素。利用激发-发射矩阵（EEM）荧光光谱法，对2019年季风前和季风后季节采集的河流和地下水样本中的主要DOM成分进行了测定。我们将水体荧光DOM（fDOM）组成与整个研究区域的卫星衍生土地利用数据进行了比较，检验了以下假设：地下水DOM的组成，特别是与地表来源入渗相关的成分，可能部分受土地利用的控制。在季风前季节，近期生物活动产生的类色氨酸成分的突出性掩盖了类腐殖酸和类酪氨酸荧光信号。荧光数据表明，季风后季节的地下水主要由以下成分组成：i）植物源物质和ii）受人为影响的DOM（如类色氨酸成分）。有机示踪剂以及氧化还原电位（Eh）和氯离子（Cl）表明，季风事件会使非饱和带中的地表来源物质发生移动，导致更多具有微生物性质的溶解有机碳（DOC）渗入到100米以下的深度。季风后季节，基于卫星土地利用数据确定的较高蛋白质：类腐殖酸荧光与较低植被指数（归一化植被指数，NDVI）之间的相关性表明，城市地区地下水中存在源自废水的有机物的入渗。靠近河流的地下水中蛋白质：类腐殖酸荧光减弱表明地下水与河水发生了混合。这些区域密集的地下水抽取可能会加剧地表来源有机物的这种入渗。我们将水体有机物组成与土地利用联系起来的方法可以很容易地应用于类似的水文地球化学环境，以确定在各种情况下控制地下水DOM组成的因素。
