Hydrogeology assessment and groundwater risk analisys to nitrate pollution in the gallocanta basin (spain)
- Autores: José María Orellana Macías
- Directores de la Tesis: Daniel Merchán Elena (dir. tes.), María Jesús Perles Roselló (dir. tes.), Jesús Causapé Valenzuela (dir. tes.)
- Lectura: En la Universidad de Zaragoza ( España ) en 2022
- Idioma: inglés
- Número de páginas: 299
- Tribunal Calificador de la Tesis: Jorge Olcina Cantos (presid.), José Ángel Sánchez Navarro (secret.), Raphael Abrahao (voc.)
- Programa de doctorado: Programa de Doctorado en Geología por la Universidad de Zaragoza
- Materias:
- Enlaces
- Tesis en acceso abierto en: Zaguán
- Resumen
Groundwater quality depends on the balance among natural characteristics of the aquifer system and the anthropogenic activities carried out in the area. The territorial land use model determines the groundwater quality status and its temporal evolution, whereas, on the contrary, groundwater quality may affect dependent human activities. In order to enhance a sustainable relationship between the natural potentiality of the system and the human activities, a holistic approach must be followed. This work is based on a deep knowledge of the hydrogeological functioning of the aquifers, with the aim of analysing its quality for the last forty years, under several changes in land uses. Based on this information, the determining factors of groundwater risk to pollution in the area are analysed, a methodology is proposed to assess and map this type of risk, and the effects of pollution over socio-economic activities that depends on groundwater are estimated.
The ultimate objective of this PhD Thesis was to study the hydrogeological functioning of the Gallocanta Lake System, and the spatial-temporal evolution of groundwater quality as the starting point to develop a method for assessing groundwater risk to pollution, especially nitrates, that fits to a rural territorial model. The partial objectives were the hydrogeological characterization of the basin, the evaluation of groundwater pollution under European Union’s Directives, the analysis of the components of risk in the area (hazard, intrinsic vulnerability, social vulnerability and socio-economic impact), as well as the review of its usual methods of analysis and mapping in order to provide a new and better risk assessment method.
Regarding the sources of information used in this work, the endorheic Gallocanta Basin (540 km²) has been analysed based on qualitative and quantitative data. The geological and hydrogeological framework of the study have been based on previous studies and reports published by public administrations and researchers, which have been updated and reviewed by fieldwork. Additionally, the risk assessment has been carried out according to data obtained from national, regional and local official databases, as well as fieldwork.
The results could be separated in three research lines: contribution to the hydrogeological characterization of the Gallocanta System, spatial-temporal evolution of groundwater quality, and proposal of a method to assess groundwater risk to pollution by nitrates from agricultural sources.
According to the hydrogeological modelling, it has been proven the discharge of the Gallocanta Basin to the Piedra Basin and the Ortiz Basin (NO), and to the Jiloca Basin (SE), at the Ojos de Caminreal Springs. The estimated flow to the Piedra and Ortiz rivers was 4.77 Hm3/y, whereas the flow to the Jiloca River was 1.85 Hm3/y.
In relation to the diachronic analysis of the qualitative status at the Gallocanta Groundwater Body, overall, the average nitrate concentration within the whole study area increased from 57.2 mg L-1 in 1999, before the implementation of the action programmes related to the Nitrate Directive, to 62.4 mg L-1 in 2017. However, individually, after the implementation of the programmes, 24 % of the sampling points showed decreasing trends after the implementation of the action programmes.
Regarding to the risk analysis, a review of the hazard assessment methods to pollution is provided, and a new index is proposed to assess and map groundwater hazard to pollution by nitrates from agricultural sources, the so-called NIHI (Nitrogen Input Hazard Index). The hazard to groundwater pollution was low and moderate in 64 % of the study area according to several generic hazard indexes, whereas according to the NIHI specific hazard index, a 44 % of the area was classified as high hazard. The hazard classification proposed by the NIHI fits better to the real groundwater pollution status in the area.
The study also proposes a method to assess risk of pollution, which is based on the NIHI, the intrinsic vulnerability classification calculated by the modified DRASTIC index, which ranges between very low and high in the area, and a social vulnerability index that estimates a moderate vulnerability of the whole study area. According to this method, the risk level to groundwater pollution was high in 23 % of the study area, whereas the potential socioeconomic impact of that risk is moderate.
Thus, it is estimated a moderate and high potential risk level in 47 % of the study area. It is highlighted that the current quality control system and the strategies implemented to mitigate pollution in the area requires substantial changes and improvements at different levels. Starting from a deeper comprehension of the hydrogeology, to the rethinking of the methods used to assess risk components, as well as the effectiveness of the Nitrate Vulnerable Zone concept, the delimitation of those areas, and the territorial and social consequences of its implementation.
