Application of an integrated framework for estimating nitrate loadsfrom a coastal watershed in south-east Sweden

Abstract

tNitrate-nitrogen (NO3-N) loading from a 734 ha coastal watershed draining into the Baltic Sea offsouth-east Sweden was simulated using a simple modelling approach in which the nitrogen modelDRAINMOD-N II and a temperature-dependent NO3-N removal equation were incorporated into the ArcHydro-DRAINMOD framework. Hydrology and water quality data collected during six periods between2003 and 2007 were used to test Arc Hydro-DRAINMOD and its performance was evaluated by consideringuncertainty in model parameters using GLUE methodology. The GLUE estimates (5th and 95th percentiles)and calculated monthly NO3-N loads were in satisfactory agreement. There are some sources of errorsthat may affect the performance of the framework, such as NO3-N load calculations, soil denitrificationand in-stream removal of NO3-N. Although additional measurements may help to improve the under-standing of these processes and reduce uncertainty, they cannot completely eliminate the uncertainty inframework predictions. These uncertainties must be evaluated by some methodology, such as the GLUEprocedure. Sensitivity analysis showed the framework to be most sensitive to changes in stream base-flow and N removal processes in the stream network. These results show that the Arc Hydro-DRAINMODframework can be an effective tool to support water stakeholders in managing NO3-N loading from smalltile-drained watersheds at monthly time step.