Identification of Natural and Anthropogenic Geochemical Processes Determining the Groundwater Quality in Port del Comte High Mountain Karst Aquifer (SE, Pyrenees)

Abstract

The Port del Comte Massif (SE, Pyrenees) contains one of the most important vulnerable and strategic karst aquifers for supplying freshwater to the city of Barcelona (Spain). It is a fragile system, whose possible environmental impact is highly conditioned by land use. To improve the hydrogeological knowledge of the system, between September 2013 and October 2015, a detailed fieldwork was carried out for the revision of the geological model, the inventory of water points, and the in situ physico-chemical characterization on major elements and isotopes of up to a total of 43 springs, as well as precipitation water. This paper focuses on the characterization of the geochemical processes that allow explanation of the observed chemical variability of groundwater drained by the pristine aquifer system to determine the origin of salinity. The results show that the main process is the dissolution of calcite and dolomite, followed by gypsum and halite, and a minor cation exchange-like process. Sulfur and oxygen isotopes from dissolved sulfate in the studied springs point out a geogenic origin related to the dissolution of gypsum from Triassic and Tertiary materials, and that the contribution from anthropogenic sources, like fertilizers, is lower. Nitrate in groundwater is not an important issue, with a few localized cases related with agricultural activities. The multidisciplinary approach has allowed the development of a consistent hydrogeological conceptual model of the functioning of the aquifer system, which can be replicated in other places to understand the geogenic character of the hydrogeochemistry.

Identification and apportionment of groundwater nitrate sources in Chakari Plain (Afghanistan)

“…The BSIMM (Parnell et al, 2013 is a new version of the Bayesian isotope mixing model SIAR (Parnell et al, 2010). This approach can include uncertainty sources, isotopic fractionation and various nitrate sources (Herms et al, 2021;Zaryab et al, 2022). The equations of the SIAR model are as follows (Parnell et al, 2010).…”

“…A conventional approach for identification of NO3̄ origins as well as transformation of nitrate is the use of dual-isotopic compositions of nitrate (δ 15 Over the past two decades, many nitrate source apportionment models were developed to quantitatively estimate the contribution of natural and anthropogenic nitrate sources to the total nitrate concentrations in different aquatic systems. These models, range from a simple dual stable isotopic linear mixing model based on mass balance (Phillips and Koch, 2002;Deutsch et al, 2006), to end-member mixing analysis (Ogrinc et al, 2019), and Bayesian stable isotope mixing model (BSIMM) (Herms et al, 2021;Ji et al, 2022). BSIMM considers the denitrification process and its related fractionation, while previous models rarely consider these factors.…”