Eutrophication is one of the most serious threats to the Baltic Sea environment. Nutrient loading into the sea therefore needs to be quantified by available mathematical models. The Generalised Watershed Loading Functions (GWLF), a lumpedparameter model that predicts hydrology and monthly nutrient loads, was applied to the Daugava River Basin, discharging into the Baltic Sea. The aim of the study was to model historic transport of nutrients into the Baltic Sea and thereby produce estimates of parameters and input data needed for a spatial extension of the GWLF to surrounding river basins.Calibration data were taken from the 1990’s and validation data from the 1980’s. Yearly nitrogen loads were modelled with an R2 value of 0.78 for the calibration period. Predicted yearly nitrogen loads for the validation period were about 30 % lower than reported values, probably depending on decreasing groundwater and runoff concentrations between the 1980’s and 1990’s. Phosphorus loads were underestimated compared to reported values, the main reason probably being the exclusion of septic systems and too low reported point sources.Modifications of the model are suggested for longterm predictions of nutrient loads and the need for harmonised, uptodate and generally accessible data for nutrient transport modelling discussed.
Contents
1. INTRODUCTION
2. BACKGROUND
2.1 EUTROPHICATION OF THE BALTIC SEA
2.2 FEATURES OF THE NITROGEN AND PHOSPHORUS CYCLES
2.2.1 NITROGEN RETENTION AND LEAKAGE
2.2.2 PHOSPHORUS LEAKAGE AND EROSION
2.3 GENERAL MODEL DESCRIPTION
3. MATERIALS AND METHODS
3.1 SITE DESCRIPTION – THE DAUGAVA RIVER BASIN
3.1.1 GEOGRAPHY AND HYDROGRAPHY
3.1.2 HYDROLOGY AND CLIMATE
3.1.3 GEOLOGY AND LAND USE
3.1.4 POPULATION AND ANTHROPOGENIC INFLUENCE
3.1.5 INTERNATIONAL COOPERATION IN THE DAUGAVA BASIN
3.2 MODEL DESCRIPTION
3.2.1 AN OVERVIEW OF THE MODEL
3.2.2 WATER FLOW
3.2.3 NUTRIENTS
3.3 AVAILABLE OBSERVATION DATA USED IN THE STUDY
3.3.1 CLIMATE DATA
3.3.2 STREAMFLOW AND NUTRIENT LOAD DATA
3.4 CALIBRATION AND VALIDATION
3.5 IMPACT OF THE CURVE NUMBER ON NUTRIENT SOURCE APPORTIONMENT
3.5 SENSITIVITY ANALYSIS
4. RESULTS
4.1 CALIBRATION AND VALIDATION
4.2 IMPACT OF THE CURVE NUMBER ON NUTRIENT SOURCE APPORTIONMENT
4.3 SENSITIVITY ANALYSIS
5. DISCUSSION
6. CONCLUSIONS
7. REFERENCES
APPENDIX A. INPUT DATA AND PARAMETERS USED BY THE GWLF MODEL
APPENDIX B. DETERMINATION OF SURFACE RUNOFF
Author: Wallin, Andrea
Source: Uppsala University Library
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