Sustainability of groundwater resources of weathered and fractured schists in the rural areas of Galicia (Spain)

Jorge Dafonte,Bruno Pisani,Acacia Naves,Aitor García-Tomillo,Javier Samper,Luis Montenegro

doi:10.1007/s12665-022-10264-5

Abstract

Water supply deficits in droughts, groundwater pollution and climate change are the main challenges for the sustainability of groundwater resources from hard-rock aquifers in rural areas of Galicia (Spain). Here, we address the sustainability of groundwater resources of weathered and fractured schists in the rural areas of the Abegondo municipality. The conceptualization of the hydrogeology of the study area includes: (1) The weathered schist (regolith), (2) The decompressed highly fractured schist layer; and (3) An underlying slightly fractured schist. Groundwater flows mostly through the regolith and the highly fractured rock. Rainfall infiltration is the source of aquifer recharge. Groundwater discharges in seepage areas, springs and along creeks and valleys. The water table is generally shallow and shows seasonal oscillations of up to 4 m. The equivalent transmissivity of the regolith and the highly fractured schist ranges from 15 to 35 m2/days. The electrical resistivity tomography identifies a shallow water table and attests that the contact of the highly fractured schist and the slightly fractured schist is highly heterogeneous. Groundwater resources were quantified with a hydrological water balance model. The mean annual recharge is about 185 mm. Groundwater recharge at the end of the twenty-first century could decrease from 6 to 10% due to climate change. The decline in groundwater table could aggravate the shortages during droughts. Groundwater quality data show bacteriological and nitrate contamination due to the poor management of the manure in the fields and occasional discharges of slurry from pig and mink farms. Groundwater management and protection actions are proposed to prevent groundwater pollution and achieve a sustainable groundwater supply in the study area.

Highlights

The European regulations concerning the water protection and management (Directive 2000/60/EC) and the quality of water for human consumption (Directive 98/83/EC) pose a great challenge for water supply in dispersed rural communities such as those of Galicia in the northwestern corner of the Iberian Peninsula (Fig. 1) (Naves et al 2019, 2021)
The results reported by Rodríguez-Suárez et al (2011, 2014) show that fast-growing trees reduces the availability of the water resources in dry periods, leading to a decline of the water table and the drying up of springs and small creeks
We address the sustainability of groundwater resources of weathered and fractured schists in the rural areas of Abegondo (Galicia, Spain)

Summary

Introduction

The European regulations concerning the water protection and management (Directive 2000/60/EC) and the quality of water for human consumption (Directive 98/83/EC) pose a great challenge for water supply in dispersed rural communities such as those of Galicia in the northwestern corner of the Iberian Peninsula (Fig. 1) (Naves et al 2019, 2021). Hard rock aquifers usually present: (1) A shallow regolith layer with clay-rich material derived from the in situ weathering of the bedrock; (2) A fractured rock layer, which often presents a dense horizontal network of fractures in the first few meters and a. Previous hydrological research and water resources assessment were performed in the Abelar pilot watershed in Abegondo by Soto et al (2005) and Rodríguez-Suárez et al (2011, 2014) (Fig. 1). This small watershed has a surface area of about 10.7 ha. The results reported by Rodríguez-Suárez et al (2011, 2014) show that fast-growing trees reduces the availability of the water resources in dry periods, leading to a decline of the water table and the drying up of springs and small creeks

Methods

Results

Conclusion