Application of isotope techniques to enhance the conceptual hydrogeological model and to assess groundwater sustainability in the Pampean plain in Córdoba, Argentina

The objective of this work is to enhance the conceptual hydrogeological model in the Río Cuarto River basin by using isotope and hydrochemical techniques. The precipitation pattern, as reflected in the average values of δ ²H and δ ¹⁸O in stations located in the plains and in the mountains, showed an isotope depletion from the East to the West, attributed to continental and altitude effects. Groundwater quality is mainly the result of two controlling factors: lithology and flow distances from recharge. The aquifers show fresh calcium/sodium bicarbonate water in the upper and medium basin (coarse fluvial sediments) which evolve to sodium sulphate and chloride waters in the low basin (mainly loess and fine alluvial sediments). The confined aquifer systems in the lower basin (C and D systems) averaged more negative stable isotope values, indicating that groundwater recharged during colder climatic conditions (Pleistocene period). Groundwater dating with ¹⁴C confirmed that groundwater ages range from modern to 45,000 years BP showing that as the water flows towards deeper layers and farther from the mountainous recharge area, groundwater age increases. The confined aquifers can potentially be exploited in order to partly cover different water needs but they should be managed in a sustainable way.

Assemblage of dematiaceous and Ingoldian fungi associated with leaf litter of decomposing Typha latifolia L. (Typhaceae) in riverine wetlands of the Pampean plain (Argentina) exposed to different water quality

The purpose of this study was to analyze the rate of sporulation, richness, and spore diversity of dematiaceous and Ingoldian fungi colonizing Typha latifolia leaves during a 40-day period of decomposition, as well as the loss of mass in Typha latifolia, in four riverine wetlands of Pampean plain (Argentina) with different water quality. Higher sporulation rates, richness, and diversity of the fungi as well as loss of mass of the leaves that they colonized were associated with lower water quality. Anguilospora longissima, Arthrinium sp., Margaritispora aquatica, and Tricellula botryosa were dominant taxa. Redundancy analysis showed two fungal assemblages related to different environmental conditions. One assemblage was related to higher nutrient levels and higher temperature, characterized mainly by dematiaceous fungi. The other assemblage was related to higher levels of pH and dissolved oxygen, which was mainly represented by Ingoldian fungi. The results obtained in our study demonstrated the link between these fungal assemblages and changes in water quality, revealing their potential as indicators of environmental changes in rivers exposed to different types of land use.

Geochemical processes regulating F-, as and NO3- content in the groundwater of a sector of the Pampean Region, Argentina

The presence of F(-) and As in groundwater is common in volcanic aquifers. Excessive concentrations of these ions affect the quality of drinking water and can be harmful to health. When there is an anthropogenic source in phreatic aquifers, NO3(-) is incorporated to the groundwater components, deteriorating its quality. The objective of this work is to assess the geochemical processes that regulate the contents of F(-), As and NO3(-) of the groundwater in a sector of the Pampean Region in Argentina. This area is supplied with water by exploiting a multilayer aquifer, composed of a phreatic aquifer occurring in loess sediments and a fluvial semi-confined aquifer, separated by an aquitard. The results obtained show that the phreatic aquifer has a higher concentration of F(-), As and NO3(-) than the semi-confined aquifer. Fluoride derives from the dissolution of volcanic glass at a slightly alkaline pH and from anion exchange; however, it may also be absorbed by the reprecipitating carbonates. The As is released by desorption, with the main source being the glass and lithic fragments of the loess. The NO3(-) originates from the decomposition of organic matter, mainly in the septic tanks of the peri-urban areas. Meanwhile, the As and F(-) content in the semi-confined aquifer is lower and its origin is the result of water inflow by vertical downward infiltration from the phreatic aquifer through the aquitard. The Pampean Region is one of the areas with the largest volume of agricultural exports in the world and at present it is undergoing a strong social and economic growth. Understanding the geochemical processes that regulate the quality of drinking water is of vital importance to generate water management guidelines aiming at minimizing the deterioration of drinking water sources.