Fachbereich Geowissenschaften

Nitrate dynamics under climate and land-use change

How does the change in agricultural practices and in climate influence the nitrate load of a small Mediterranean catchment?

PhD Researcher: Carolin Paneru, née Thesenvitz
Supervisors: Olaf Cirpka (University of Tübingen), Claus Haslauer (University of Tübingen), David L. Rudolph (University of Waterloo)

Motivation

Irrigated agriculture enables higher efficiency: harvests are more secure and productive. But it increases nitrate loads in the related water bodies. Today, nitrate is the top chemical contaminant in groundwater worldwide (Exner, Hirsh & Spalding 2014). It is a threat for human health and the environment. Forecasting the terrestrial and aquatic pathways of nitrates is imperative for appropriate water management. Physically-based hydrological modelling achieves best results at catchment scale (Goderniaux et al. 2011). Integrating the relevant processes of the nitrogen life cycle is the next step. Input, turnover, and transport occur at the surface, the root and vadose zone. The characteristics of the aquifer attenuate and retard the transport processes. An approach comprising all relevant zones is necessary. A resulting model may investigate real water management problems.

Approach

This research project aims to include solute transport (of nitrate) to a model based on partial differential equations. This is closely linked to previous research work on integrated surface and groundwater model, see Figure 1. Von Gunten and colleagues (2014) calibrate the water balance in the Lerma catchment with a physically-based approach. Using this model, von Gunten and co-workers (2015) investigate the impact varying climate scenarios on this catchment. The Mediterranean small-scale Lerma catchment in northern Spain is an ideal study area. The main land-use in the catchment is agriculture. In the recent 10 years, it had undergo the transformation from a rain-fed to irrigated agriculture. The associated evolution of the water basin is well monitored (Merchán, Causapé & Abrahão 2013, Merchán et al. 2014). A comprehensive data base for water quality and quantity is the result. An ideal situation to calibrate and validate a physically-based model on nitrate transport. Key parameter in nitrate transport, computational costs, and data-requirements need to be determined. This model would then be useful to answer questions on the impact of varying land-use (different crops, their respective water and fertilization demand) on the water quality of the catchment.

Figure 1: Interrelation of the research project to previous research

References

  • Duncan, J. M., L. E. Band, P. M. Groffman, and E. S. Bernhardt (2015), Mechanisms driving the seasonality of catchment scale nitrate export: evidence for riparian ecohydrologic controls, Water Resources Research, 51, doi:10.1002/2015WR016937.
  • Exner, M. E., A. J. Hirsh, and R. F. Spalding (2014), Nebraska’s groundwater legacy: Nitrate contamination beneath irrigated cropland, Water Resources Research, 50, 4474-4489, doi:10.1002/2013WR015073.
  • Goderniaux, P., S. Brouyere, H. J. Fowler, S. Blenkinsop, S, R. Therrien, P. Orban and A. Dassargues (2011), How can large-scale integrated surface-subsurface hydrological models be used to evaluate long-term climate change impact on groundwater reserves?, In Wang, X. Y., S. Ge, M. C. Hill and C. M. Zheng, Calibration and Reliability in groundwater modelling: managing groundwater at the environment. Paper presented at 7th International Conference on Calibration and Reliability in Groundwater Modeling September 20-23, 2009, Wuhan (China) (115-120). IAHS Publication.
  • Merchán, D., J. Causapé and R. Abrahão (2013), Impact of irrigation implementation on hydrology and water quality in a small agricultural basin in Spain. Hydrological Sciences Journal, 58 (7), 1400-1413, doi:10.1080/02626667.2013.829576.
  • Merchán, D., J. Causapé, R. Abrahão and I. Garciá-Garizábal (2014), Assessment of a newly implemented irrigated area (Lerma basin, Spain) over a 10-year period. II: Salts and nitrate exported. Manuscript submitted for publication in September 2014.
  • Von Gunten, D., T. Wöhling, C. Haslauer, D. Merchán, J. Causapé and O. A. Cirpka (2014), Efficient calibration of a distributed pde-based hydrological model using grid coarsening, Journal of Hydrology, 519, 3290-3304, doi: 10.1016/j.jhydrol.2014.10.025.
  • Von Gunten, D., T. Wöhling, C. Haslauer, D. Merchán, J. Causapé and O. A. Cirpka (2015), Estimating Climate-Change Effects on a Mediterranean Catchment under Various Irrigation Conditions, Manuscript submitted for publication in May 2015.