Understanding Subsurface Pathways of Nitrate Transport on the Catchment Scale: A Case Study in the Semi-Arid Mediterranean Lerma Catchment
2 Geological Survey of Spain – IGME, Zaragoza, Spain
3 Department of Earth and Environmental Sciences, University of Waterloo
O 15.4 in Forum Junge Hydrogeologen
13.04.2016, 13:30-13:45, Plank Hörsaal, Geb. 40.32
Most pronounced effects of climate change are expected in semi-arid areas (von Gunten et al. 2015 submitted). In Europe, these areas are typically located around the Mediterranean, and are also heavily populated and farmed. Both factors pose a significant threat to groundwater resources in terms of quantity and quality. Today, nitrate is the most commonly encountered contaminant in groundwater worldwide (Exner, Hirsch, and Spalding 2014). Forecasting the terrestrial and aquatic pathways of nitrates is imperative for appropriate water management.
Our study site is located in such a critical area, is experiencing increasing nitrate contamination in both surface and subsurface water, and is trying to alleviate water problems by irrigation. The study site – the small Lerma catchment (~7 km) lies in the Ebro basin. The main land use was transformed within only two years, from 2006-2008, from rain-fed to irrigated agriculture on nearly half of the catchment surface (~48 %) lead to an overall change of the hydrological condition: The Lerma which grounded in summer is permanently auriferous today. This shift monitored in detail hydro-geologically. The Mediterranean small-scale Lerma catchment in northern Spain is intensively monitored regarding water quality and quantity since 2004 (Merchán 2015).
Von Gunten and collegues (2014) worked on an efficient way of calibrating PDE (partial differential equations) based hydrological models. Based on the same study site, hydrological processes of groundwater and surface water processes are coupled at catchment scale. Von Gunten and coworkers (2015a, b) comprehensively studied the interrelationship of climate and land use changes using this model. Now, the integration of nitrate transport is the next step towards an integrated model comprising the most relevant processes at catchment scale.
Additionally to the hydrological data set, nitrate data (measurements in the gully and observation wells) and fertilizing and agricultural methods are available to integrate to the PDE based model of the Lerma catchment. The actual physical processes are spatially described within the domain. The study site needs to be described in detail (hydrological conductivity, porosity, Van Genuchten parameter, etc.). The computational grid will be constrained by the main hydrological features as well as the boarders of the agricultural plots to ensure an appropriate nitrate input. The validation and calibration will be performed using surface and groundwater nitrate measurements from University of Zaragoza & IGME.
EXNER, M.E., HIRSH, A.J., SPALDING, R.F. (2014). Nebraska’s groundwater legacy: Nitrate contamination beneath irrigated cropland. Water Resour. Res., 50(5), 4474–4489. doi:10.1002/2013WR015073
MERCHÁN, D. (2015). Hydrological Assessment of a Newly Implemented Irrigated Area in Span: Sanlinization and Nitrate Pollution from Irrigation Return Flows. PhD. University of Zaragoza, Spain.
MERCHÁN, D., OTERO, N., SOLER, A., CAUSAPÉ, J. (2014). Main sources and processes affecting dissolved sulphates and nitrates in a small irrigated basin (Lerma Basin, Zaragoza, Spain): Isotopic characterization. Agric. Ecosys. Envir., 195, 127–138. doi:10.1016/j.agee.2014.05.011
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