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Modification of AGNPS for Agricultural Land and Climate Conditions in Central Germany

UFZ Centre for Environmental Research Leipzig-Halle, Dep. of Inland Water Research Magdeburg, Heydeckstrassse 9, D-39104 Magdeburg, Germany

H.-G. Frede

Dep. of Landscape Development, University of Giessen, Senckenbergstraße 3, D-35390 Giessen, Germany

^* Corresponding author (rode{at}water.gm.ufz.de).

ABSTRACT

Until recently, no suitable computer model was available to quantify P and N yields of nonpoint sources into surface water in central German watersheds. The event-based erosion and nutrient transport model AGNPS (Version 3.65), developed in the USA, was adapted to central German landscape conditions and linked to a GIS. Drawing on a 2-yr program of water quality measurements and on hydrologic data collected during 33 yr, this modified model was tested in two medium-sized agricultural watersheds in the state of Hesse, Germany. With deviations of 1.7 and 3.8%, runoff volumes for all observed and simulated flood events showed a high level of agreement in both watersheds. Peak flows showed larger errors averaging 14.8 and 24%. Only for one of the two watersheds were sediment and total P yield computed satisfactorily, with average errors of 5% (sediment) and 6% (total P). Deviations for the second watershed were considerably greater. The same is true for the dissolved P and N yields. In the case of small events, AGNPS consistently overestimated the particulate P yield in both watersheds. However, the model correctly registered the overall dynamics of the system as well as the differences of sediment and total P yield between the two watersheds. The modified AGNPS model can thus be employed by environmental agencies as a useful planning tool.