Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
The processes of pollutant transport and spreading in catchments are complex, but their quantification is crucial for mitigation of several important water resource problems, such as eutrophication. This thesis investigates nutrient transport in the Swedish Norrström drainage basin, which suffers from eutrophication of its inland water bodies and is also one of the main Swedish contributors of nutrient loads to the Baltic Sea. A widely used approach for describing, quantifying and predicting pollutant spreading and testing management and climate scenarios is basin scale hydrological modelling. The water flow and nutrient loads in the Norrström basin are simulated using Soil and Water Assessment Tool (SWAT) which is a semi-distributed, process-based, continuous-time river basin model.
The results indicate that SWAT model was successfully implemented to simulate water discharge, total nitrogen and total phosphorus fluxes in the Norrström drainage basin. The performed multi-variable and multi-site calibration has yielded satisfactory results with correlation coefficients equal to 0.93 between modelled and observed average annual water flows, 0.96 between modelled and observed average annual total nitrogen loads and 0.85 between modelled and observed average annual total phosphorus loads. However, it was found out that the SWAT model is not designed for large-scale watersheds containing large water bodies, which causes important limitations for its application to the Norrström drainage basin and thus requires modelling of lakes Hjälmaren and Mälaren using, for example, one of the distributed water quality models that are linked with SWAT. Several other problematic issues were also identified in the study, such as modelling of in-stream processes, input data demands and extensive parameterization.
The possible future scenarios that could be of interest to investigate using SWAT for the Norrström drainage basin in the context of eutrophication, such as climate change, economic development and population growth scenarios, as well as practices intended to mitigate eutrophication are discussed. In conclusion, SWAT application to the Norrström basin is a promising tool for analysing water flows and nutrient loads and could serve for water quality management purposes, provided that identified model limitations and uncertainties are accounted for and addressed.
2009. , 36 p.