Saline groundwater evolution in the Luanhe River delta (China) during the Holocene: hydrochemical, isotopic, and sedimentary evidence

[摘要] Since the Quaternary Period, paleo-seawater intrusions have been suggestedto explain the observed saline groundwater that extends far inland incoastal zones. The Luanhe River delta (northwest coast of the Bohai Sea, China)is characterized by the distribution of saline, brine, brackish, and freshgroundwater from the coastline inland. The groundwater in this region exhibits a wide range of total dissolvedsolids (TDS): 0.38–125.9 g L −1 . Meanwhile, previous studies haverevealed that this area was significantly affected by Holocene marinetransgression. This study used hydrochemical, isotopic, and sedimentologicalmethods to investigate groundwater salinization processes in the LuanheRiver delta and its links to paleo-environmental settings. Isotopicresults ( 2 H, 18 O, 14 C) allowed old groundwater recharge to be distinguished fromnew groundwater recharge. Hydrochemical analysis using the PHREEQC codeindicated that the salt in saline and brine groundwater originates from amarine source. The 18 O–Cl relationship diagram yields three-end-membergroundwater mixing, and two mixing scenarios are suggested to explain thefreshening and salinization processes in the study area. When this was interpretedalong with data from paleo-environmental sediments, we found that groundwatersalinization may have occurred since the Holocene marine transgression. Thebrine is characterized by radiocarbon activities of ∼  50–85 pMC and relatively depleted stable isotopes, which are associated withseawater evaporation in the ancient lagoon during delta progradation andmixing with deeper fresh groundwater, which was probably recharged in the coldLate Pleistocene. The brackish and fresh groundwaters arecharacterized by river-like stable isotope values, where high radiocarbonactivities (74.3–105.9 pMC) were formed after the washing out of the salinizedaquifer by surface water in the delta plain. This study presents an approachthat utilizes geochemical indicator analysis with paleo-geographicreconstruction to better assess groundwater evolutionary patterns in coastalaquifers.

[学科分类] 妇产科学