Hydrol. Earth Syst. Sci. Discuss., 3, 2813–2851, 2006 Hydrology and www.hydrol-earth-syst-sci-discuss.net/3/2813/2006/ Earth System © Author(s) 2006. This work is licensed Sciences under a Creative Commons License. Discussions Papers published in Hydrology and Earth System Sciences Discussions are under open-access review for the journal Hydrology and Earth System Sciences Assessing the model performance of an integrated hydrological and biogeochemical model for discharge and nitrate load predictions T. Pohlert, L. Breuer, J. A. Huisman, and H.-G. Frede Institute for Landscape Ecology and Resources Management, Justus-Liebig-University Gießen, Heinrich-Buff-Ring 26, 35392 Gießen, Germany Received: 12 July 2006 – Accepted: 28 August 2006 – Published: 12 September 2006 Correspondence to: T. Pohlert (
[email protected]) 2813 Abstract In this study, we evaluate the performance of the SWAT-N model, a modified version of the widely used SWAT version, for discharge and nitrate predictions at the mesoscale Dill catchment for a 5-year period. The underlying question is, whether the model 5 efficiency is sufficient for scenario analysis of land-use changes on both water quan- tity and quality. The Shuffled Complex Evolution (SCE-UA) algorithm is used to cali- brate the model for daily discharge at the catchments outlet. Model performance is as- sessed with a split-sampling as well as a proxy-basin test using recorded hydrographs of four additional gauges located within the catchment. The efficiency regarding ni- 10 trate load simulation is assessed without further calibration on a daily, log-daily, weekly, and monthly basis as compared to observations derived from an intensive sampling campaign conducted at the catchments outlet.