Hydrogeochemical Evolution of an Aquifer Regulated by Pyrite Oxidation and Organic Sediments

Abstract

Detailed full-scale groundwater monitoring was carried out over a period of nine years, sampling at selected points along the groundwater flow direction in its final stretch. This established the hydrogeochemical evolution along the flow of a natural system formed by a calcareous aquifer which discharges and then passes through a quaternary aquifer of lake origin which is rich in organic matter. This evolution is highly conditioned by the oxidation of pyrites that are abundant in both aquifers. In the first aquifer, one kilometre before the discharge location, oxidizing groundwater crosses a pyrite mineralization zone whose oxidation produces an important increase in sulphates and water denitrification over a short period of time. In the quaternary aquifer with peat sediments and pyrites, water experiences, over a small 500 m passage and residence time of between three and nine years, a complete reduction by way of pyrite oxidation, and a consequent increase in sulphates and the generation of hydrogen sulphuric acid. This is an example of an exceptional natural hydrogeological environment which provides guidance on hydrogeochemical processes such as denitrification.

The Vulnerability of Shallow Groundwater on a Small Tropical Indonesian Island

“…TOC is a measure of organic matter content, which can be used as a parameter to evaluate water pollution (Lee et al, 2020). High TOC values imply lower dissolved oxygen (Al-Said et al, 2018), which further in uences chemical reactions in the water (Sanz et al, 2021). The results of this analysis showed that groundwater from the west and middle areas (W1-W6, except W2) had higher TOC values than those in the east area (W7-W10).…”

Hydrogeochemical Characteristics and Genetic Analysis of Karst Groundwater in the Fengfeng Mining Area

“…When the δ value is greater than 0, it indicates that stable isotopes in groundwater are depleted. The δ values of D and 18 O are calculated as follows:…”

“…The δD-δ 18 O relationship is plotted in Figure 8. The karst water sample points are all located at the lower right of the atmospheric precipitation line, indicating that although the main source is atmospheric precipitation, they are influenced by strong evaporation during precipitation and infiltration, which leads to isotopic enrichment.…”

“…In recent years, domestic and foreign scholars have carried out a lot of research on the evolution mechanism of regional groundwater chemical field [17][18][19][20][21][22]. Carmine Apollaro et al [23] studied the geochemical characteristics of rocks, stream sediments, and soils in the Fumg Grande Valley.…”

“…Guo Xiaojiao et al [26] studied the hydrochemical characteristics and evolution of groundwater in Baiyangdian Wetland by comparing and analyzing the hydrochemical characteristics and spatial distribution of surface water and groundwater. Pankaj Kumar et al [27] analyzed the hydrogeochemical evolution of the Panna region in central India by using the Piper trilinear diagram, ion proportional coefficient and δ 18 O-δD relationship. Kaveh Pazand et al [28] analyzed the groundwater hydrochemical evolution process of the igneous rock sedimentary aquifer system in the Bamnan region, southeastern Iran, using multivariate statistical methods.…”