Occurrence and influencing factors of high groundwater manganese in the oxbow lakes of the middle reaches of Yangtze River

Oxbow lake, acting as an efficient factory, plays an important role in the attenuation and accumulation of groundwater contamination. However, there are few concerns on the enrichment of manganese in the oxbow lakes. Based on 113 groundwater samples collected from Wuhan Geological Survey Center, China Geological Survey in 2019, the distribution and influencing factors of high groundwater Mn were studied in the oxbow lakes of the middle reaches of Yangtze River. The results showed that the elevated groundwater Mn were mainly distributed in the concave bank with 75 % of Mn concentration exceeded 0.10 mg/L, and up to 3.79 mg/L. Moreover, groundwater Mn concentrations were related to the depth and the well types. According to principal component analysis, Mn and HCO3 -, Mg2+, Fe, NH4-N, Ca2+, As, Eh and NO3- dominated in PC1 with significantly correlations which may result from natural attenuation processes. The sedimentary environments including geological properties and reducing conditions in the studied area were responsible for the enrichment. Not only the dissolution of rich Mn-bearing minerals in the studied area driven by redox conditions provided the source of groundwater Mn but also the unique sedimentary architecture characteristics and the slow flow limited the transfer of dissolved Mn in groundwater, resulting in the enrichment of Mn. This study provides us understand the occurrence and influencing factors of high groundwater manganese in the oxbow lakes/wetlands.