Seasonal dynamics of dissolved organic matter in high arsenic shallow groundwater systems

• DOI: 10.1016/j.jhydrol.2020.125120
• Publication Date: 2020-06-04T06:00:55Z
• Authors: Yijun Yang; Xiaofang Yuan; Yamin Deng; Xianjun Xie; Yiqun Gan; Yanxin Wang
• Keywords: 13. Climate action; 15. Life on land; 01 natural sciences; 6. Clean water; 0105 earth and related environmental sciences

Abstract Dissolved organic matter (DOM) plays critical roles in biogeochemistry of arsenic in groundwater systems. To characterize the spatial–temporal variations of groundwater DOM and its impacts on arsenic dynamics, surface water and shallow groundwater from two different depths were collected during monsoon and non-monsoon periods in Jianghan Plain, central Yangtze River Basin. Parallel factor analysis (PARAFAC) of the three-dimensional fluorescence excitation–emission matrix (EEM) reveals that DOM comprises three major components, one microbial humic-like component (C1) and two terrestrial humic-like components (C2 and C3). Abundant terrestrially-derived humic-like components were observed during monsoon while more microbially-derived DOM occurred in groundwater during non-monsoon season. These seasonal DOM variations are found to be related to groundwater-surface water (GW-SW) interactions, which is evidenced by stable H and O isotopes and Cl/Br mass ratios. During monsoon season, groundwater is recharged from dilute rainwater, evaporated surface water, and polluted surface water. More terrestrial humic-like components are introduced by precipitation and local agricultural activities (e.g. irrigation, paddy cultivation) during monsoon. The fluorescence spectroscopy and stable carbon isotopes (δ13CDIC and δ13CDOC) results indicate that seasonal As variations are affected by seasonal DOM dynamics. Smaller Δδ13C values (defined as δ13CDIC – δ13CDOC) with higher As concentrations are found during non-monsoon while larger Δδ13C values with relatively lower As concentrations are observed during monsoon season. The strong correlation between DOC and Fe(II) concentrations (r = 0.64, p