Sub-Project 5

 

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Scenario analysis of water quantity and quality in the Havel river basin

Main objectives

The aim of the subproject is to verify and improve existing estimations of nutrient emission from diffuse (mainly agricultural) sources in a lowland region using a dynamic model. Based on the results, the application of some known methods to reduce nutrient leaching will be tested in the modelling framework. 

More exactly, the subproject aims are: 

·   Estimation of nutrient emission from diffuse sources in selected mesoscale subbasins of the Havel (e.g. Nuthe, Rhin) by means of dynamic modelling of hydrological and ecohydrological processes involved,

·   Scenario analysis of options to reduce nutrient leaching from diffuse sources resulting from  modified land use and land management strategies,

·   Improved  estimation of nutrient retention in a large river basin (the lower Havel) using the coupled drainage basin (SWIM) and river (HYDRAIN) modelling.

This subproject in collaboration with subproject 3 should provide a tool to link processes in the drainage basin area with those in the main river system (Havel) and to estimate retention processes at the basin level. It is strongly linked to subproject 6 (data and parameterization), subproject 2 (modelling of inputs), and subproject 3 (transport in the water system). 

Scheduled work and methods

The ecohydrological model SWIM (Soil and Water Integrated Model), developed at PIK, simulates hydrological processes, plant growth, nutrient cycles (nitrogen, phosphorous) and erosion at the river basin level using regionally available data. Another objective is the study of climate and land use change impacts on ecohydrological processes. SWIM was already successfully validated in a number of meso- and macroscale basins (mainly in the Elbe catchment area) and applied for impact studies. However the detailed validation for water quantity and water quality in a lowland basin like Havel is missing. 

A.      Validation of SWIM in a selected mesoscale subbasin of the Havel

First of all, a mesoscale basin in the catchment area of the Havel has to be selected (e. g. Rhin, Nuthe or Hammerfließ), whereby the quality of data is the substantial criterion of choice. The following data will be used: a digital elevation model (DEM), a land use map, a soil map and related soil parameters, a ground water table map, meteorological data, land management (crop rotation, fertilization regime), water discharge, measured concentrations of nitrogen in the river and in the ground water. The model SWIM will be validated for the selected basin with special consideration of hydrological processes and nitrogen and phosphorous fluxes. 

Different data already exist at PIK (e.g. a DEM, meteorological data, a land use map), other data will be supplied by project partners (subprojects 1, 6). In this context the improvement of spatial and temporal resolution of the input data, such as land use, soils and hydrology, is of particular importance.

 B.      Estimation of nutrient emission from diffuse sources

After the validation of SWIM nutrient emission from diffuse (mainly agricultural) sources will be estimated. The monthly accumulated emissions will be compared with existing estimations for the selected subbasins of the Havel (Behrendt et al, 1999). In addition, this work will contribute to subproject 2.

C.     Simulation experiments considering different scenarios of land use change

Different scenarios of land use change will be created based on available information (LUA). Thereby possible changes of the relative areal share (e.g. of arable land, grassland, forest, and fallow land) or changes within the classes (e.g. of the crop rotation within arable land, the fertilization regime, the forest management) have to be considered. 

For this purpose the results of the project MESSAGE (Mesoscale Simulation Study Assessing the Consequences of Global Change) can be adopted and transferred to the scale of land use for the districts in Brandenburg. MESSAGE is coordinated at PIK and uses the agroeconomical model RAUMIS. Other scenarios will be provided by subprojects 1 and 6. Afterwards, the analysis of options to reduce nutrient emissions from diffuse sources by modified strategies of land use and land management will be performed.

D.     Spatially differentiated modelling of the river basin 

After validation of the model for the selected subbasin, SWIM will be applied to the total area of the lower Havel in a spatially-distributed mode. Hydrological processes (evapotranspiration, runoff, groundwater recharge) as well as nitrogen and phosphorous fluxes (plant uptake, wash-off by surface runoff, leaching to groundwater) will be simulated for existing land use and recent climate conditions. This work will provide an input for the hydraulic model HYDRAIN simulating river transport of nutrients. In addition, the estimation of retention processes should be improved by linking SWIM and HYDRAIN in cooperation with subproject 3. 

Target results 

A.  Results of validation of the ecohydrological model SWIM in a selected subbasin of the Havel with a focus on hydrological processes and the nitrogen and phosphorous fluxes.

B.  Comparison of the existing estimations of nutrient emissions from diffuse sources with those simulated dynamically by SWIM.

C.  Analysis of options to reduce non-point nutrient emissions by investigating different scenarios of land use change and using the dynamic model SWIM.

D.  Estimation of nutrient fluxes for the whole lower Havel (spatially-distributed) for the existing land use and recent climate.

E.   Recommendation of methods to reduce nitrogen and phosphorous emissions from agriculture.

 

Please respond to W. Lahmer (werner@wernerlahmer.de or webmaster@havelmanagement.net)
02/07/05

Layout: W. Lahmer