Temporal Variations of Water Chemistry in the Wet Season in a Typical Urban Karst Groundwater System in Southwest China

Min Xiao; Zenglei Han; Sen Xu; Zhongliang Wang

doi:10.3390/ijerph17072520

Temporal Variations of Water Chemistry in the Wet Season in a Typical Urban Karst Groundwater System in Southwest China

Int J Environ Res Public Health. 2020 Apr 7;17(7):2520. doi: 10.3390/ijerph17072520.

Authors

Min Xiao¹, Zenglei Han¹, Sen Xu², Zhongliang Wang¹

Affiliations

¹ Tianjin Key Laboratory of Water Resources and environment, Tianjin Normal University, Tianjin 300387, China.
² Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China.

Abstract

It is important to investigate temporal variations of water chemistry for the purpose of improving water quality in karst groundwater systems. Groundwater samples were collected daily under various land uses of Guiyang. Major ions and stable carbon isotope composition of dissolved inorganic carbon (δ¹³C_DIC) were analyzed to understand the biogeochemical processes. The water chemistry was dominated by Ca²⁺, Mg²⁺, HCO₃^-, and SO₄^2-, which mainly derived from the dissolution of carbonate rocks (limestone and dolomite) and oxidation of sulfide. The groundwater was defined as of the HCO₃-Ca Mg and HCO₃·SO₄-Ca·Mg type, according to its hydrochemical characteristics. Results suggested that hydrochemical concentrations changed quickly, in response to rainfall events. The fast response revealed that karst groundwater was easily impacted by rainfall and anthropogenic inputs according to temporal variation of water chemistry. The distribution of DIC (dissolved inorganic carbon) and δ¹³C_DIC showed that DIC is mainly sourced from soil CO₂(g) influx and carbonate dissolution. δ¹³C_DIC and major ions ratios suggested that carbonate minerals were dissolved by H₂SO₄ at groundwater in wooded area, contributing an important source for DIC due to the slight enrichment of heavy δ¹³C_DIC. More negative δ¹³C_DIC values were observed after rainfall reflected the fact that soil CO₂(g) and organic carbon oxidation influxes accounted for a large share during DIC formation. Various δ¹³C_DIC and hydrochemical patterns were observed under various land use and human activity conditions. Meanwhile, relative high nitrate loads were found in groundwater after rainfall, suggesting high anthropogenic inputs following rainwater as having side effects on water quality. This study suggests that water chemistry and isotopic proof provide a better understanding of water quality and carbon dynamics responding to rainfall events in the karst groundwater systems.

Keywords: carbon isotope; carbonate rock weathering; dissolved inorganic carbon; groundwater; water chemistry.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

China
Environmental Monitoring
Groundwater* / chemistry
Humans
Seasons