Preprints
https://doi.org/10.5194/hess-2021-246
https://doi.org/10.5194/hess-2021-246

  20 May 2021

20 May 2021

Review status: this preprint is currently under review for the journal HESS.

Saline groundwater evolution in Luanhe River Delta, China since Holocene: hydrochemical, isotopic and sedimentary evidence

Xianzhang Dang1,2,3, Maosheng Gao2,4, Zhang Wen1, Guohua Hou2,4, Daniel Ayejoto1, and Qiming Sun1,2,3 Xianzhang Dang et al.
  • 1School of Environmental Studies, China University of Geosciences, 388 Lumo Rd, Wuhan, 430074, China
  • 2Qingdao Institute of Marine Geology, CGS, Qingdao, 266071, China
  • 3Chinese Academy of Geological Sciences, Beijing, 100037, China
  • 4Laboratory for Marine Geology, Pilot National Laboratory for Marine Science and Technology, Qingdao, 266071, China

Abstract. Since the Quaternary Period, palaeo-seawater intrusions have been suggested to explain the observed saline groundwater that extends far inland in coastal zones. The Luanhe River Delta (northwest coast of Bohai Sea, China) is characterized by the distribution of saline, brine, brackish and fresh groundwater, from coastline to inland, with a wide range of total dissolved solids (TDS) between 0.38–125.9 g L−1. Meanwhile, previous studies have revealed that this area was significantly affected by Holocene marine transgression. In this study, we used hydrochemical, isotopic, and sedimentological methods to investigate groundwater salinization processes in the Luanhe River Delta and its links to the palaeo-environmental settings. The isotopic results (2H, 18O, 14C) show that deep confined groundwater was recharged during the Late Pleistocene cold period, shallow saline and brine groundwater was recharged during the warm Holocene period, and shallow brackish and fresh groundwater was mainly recharged by surface water. The results of hydro-geochemical modeling (PHREEQC) suggest that the salty sources of salinization are seawater and concentrated saline water (formed after evaporation of seawater). The 18O–Cl relationship diagram shows that saline and brine groundwater are formed by three end-member mixings (seawater, concentrated saline water and, fresh groundwater). In contrast, brackish groundwater is formed after the wash-out of saline groundwater by surface water. Using palaeo-environmental data from sediments, we found that palaeo-seawater intrusion during the Holocene marine transgression was the primary cause of groundwater salinization in the study region. Seawater was found to evaporate in the lagoon area during the progradation of the Luanhe River Delta; the resulting concentrated saline water infiltrated into the aquifer, eventually forming brine groundwater due to salinity accumulation. Surface water recharge and irrigation, on the other side, would gradually flush the delta plain's saline groundwater. This study provides a better understanding of saline groundwater evolution in other similar coastal zones.

Xianzhang Dang et al.

Status: open (until 29 Jul 2021)

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Xianzhang Dang et al.

Xianzhang Dang et al.

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Short summary
Due to the widespread salinity in coastal zones, the freshwater supplies are now under pressure. This study analyzes the recharge and salinity source of coastal groundwater (brine, saline, brackish, fresh), as well as the salinization and freshening processes, using hydrochemical and isotopic methods. The evolution of saline groundwate were studied using sedimentary characteristics as multiple lines of evidence. This sduty can be used to better understand groundwater evolution in coastal zone.