Groundwater nitrate pollution and climate change: learnings from a water balance-based analysis of several aquifers in a western Mediterranean region (Catalonia)
Groundwater nitrate pollution and climate change: learnings from a water balance-based analysis of several aquifers in a western Mediterranean region (Catalonia)
SANITATION 0
AGRICULTURE 0
WATER SUPPLY PRACTICES 0
Josep Mas-Pla 0
Anna Menció 0
0 Grup de Geologia Aplicada i Ambiental (GAiA), Centre de Recerca en Geologia i Cartografia Ambiental (Geocamb), Dept. de Ciències Ambientals, Universitat de Girona , Girona , Spain
Climate change will affect the dynamics of the hydrogeological systems and their water resources quality; in particular nitrate, which is herein taken as a paradigmatic pollutant to illustrate the effects of climate change on groundwater quality. Based on climatic predictions of temperature and precipitation for the horizon of 2021 and 2050, as well as on land use distribution, water balances are recalculated for the hydrological basins of distinct aquifer systems in a western Mediterranean region as Catalonia (NE Spain) in order to determine the reduction of available water resources. Besides the fact that climate change will represent a decrease of water availability, we qualitatively discuss the modifications that will result from the future climatic scenarios and their impact on nitrate pollution according to the geological setting of the selected aquifers. Climate effects in groundwater quality are described according to hydrological, environmental, socio-economic, and political concerns. Water reduction stands as a major issue that will control stream-aquifer interactions and subsurface recharge, leading to a general modification of nitrate in groundwater as dilution varies. A nitrate mass balance model provides a gross estimation of potential nitrate evolution in these aquifers, and it points out that the control of the fertilizer load will be crucial to achieve adequate nitrate content in groundwater. Reclaimed wastewater stands as local reliable resource, yet its amount will only satisfy a fraction of the loss of available resources due to climate change. Finally, an integrated management perspective is necessary to avoid unplanned actions from private initiatives that will jeopardize the achievement of sustainable water resources exploitation under distinct hydrological scenarios.
Groundwater; Nitrate; Climate change; Scarcity; Sustainability
Introduction
Groundwater nitrate pollution is a ubiquitous worldwide
problem that has been in the managers’ as well in the researchers’
agenda for decades
(e.g., Galloway et al. 2008; Sutton et al.
2011; Rosenstock et al. 2014)
. Multiple efforts have been
devoted to improve agricultural practices so nitrogen leaching
Responsible editor: Philippe Garrigues
Institut Català de Recerca de l’Aigua (ICRA), Girona, Spain
due to fertilization is minimized
(Cameron et al. 2013;
Beaudoin et al. 2005)
, to track its movement through the
unsaturated zone and its migration beneath the water table
(Baram et al. 2017; Dimitriou and Moussoulis 2010;
Molénat and Gascuel-Odoux 2002)
, to analyze
biogeochemical processes so denitrification rates can be identified and
induced aquifer clean-up be subsequently applied to remove
nitrate from groundwater
(Böhlke 2002; Rivett et al. 2008)
,
and, finally, to treat polluted groundwater once withdrawn
from the aquifer so its nitrate content is reduced before
entering the water supply systems (Seidel et al. 2011). Moreover,
legislation has been issued to cope with these problems and
oblige those who are responsible to reduce such impact and/or
face legal prosecution (i.e., the Nitrates Directive, 1991/676/
EEC; and the Water Framework Directive, 2000/60/EEC).
Despite all these efforts, present nitrate concentrations in
groundwater reflect the impact of decades of nitrogen inputs
and its persistence in the subsurface
(e.g., Paradis et al. 2017)
. In
many aquifers, dilution has been one of the major processes that
have diminished nitrate concentration
(Altman and Parizek 1995;
Hoffman and Canace 2004)
. Mixing between polluted water
resources and less-polluted groundwater effectively reduces this
environmental pressure. In the subsurface, natural and pumping
induced mixing from different aquifer levels also has a dilution
effect. In particular, mixing in boreholes due to the exploitation of
several aquifer levels produces dilution by averaging nitrate mass
fluxes, which in many cases is not enough to reduce nitrate
concentration below the drinking standard values. However,
mixing cannot be understood as a complete positive effect, as
non-polluted groundwater resources are also at risk to reduce
their quality. In intensively exploited aquifers, well fields induce
an overall mixing process that affects the general quality of the
regional subsurface resources.
Dilution, at the end, relies on the input of non-polluted
water fluxes. Assuming that the aquifer has such inputs (i.e.,
through rainfall, stream and/or mountain front recharges), a
decrease on the amount of Bclean^ fluxes definitely reduces
the (...truncated)