Identifiering av områden med risk för fosforförluster genom ytavrinning : metodutveckling med GIS

Abstract: The eutrophication of lakes and seas with the algal bloom and deficiency inoxygen that follow, has been given priority by the Swedish government as oneof 16 environmental objectives. The purpose of this project was to develop a toolbased on a simple model, limited amount of data and geographic informationsystem (GIS) to identify areas with risk for phosphorus losses due to surfacerunoff. This tool can act as a decision support to decide where appropriatemeasures should be applied with the aim of reducing phosphorus losses and bythat the eutrophication.The method that has been used is a combination of two models, one calculatingthe potential erosion while the other one identifies areas of erosion (net erosion)or deposition. This ability is of great importance because potential erosionshould be calculated on areas with net erosion. Areas with high potential erosionhave an increased risk for phosphorus losses due to surface runoff.The potential erosion was calculated based on factors which describe how topography(LS), land use (C), soil type (K) and precipitation (R) effect the erosion.All of them have been modified to a greater or lesser extent. The LS-factorwas improved with a modified equation to adapt the calculation for a complexterrain. The C- and K-factor were adapted to Swedish conditions by using thesame classification as a similar Swedish method. A Finnish survey was used toadapt the R-factor to the local climate.Values of the LS-, C-, K- and R-factors as well as the potential erosion werecompared with similar studies to assure they were reasonable. For the samereason the total sediment yield was calculated and compared with values basedon water chemistry data. Because the calculated sediment yield was muchhigher, most likely due to the high percentage of lakes and forest within thecatchment, this method was considered not to be used.Several interesting areas have been identified inside the catchment. These shouldbe investigated in the field before any suggestion of measures can be givenbecause of the uncertainty in the calculation, mainly related to the elevationmodel and the K-factor. Therefore, this method needs to be developed. Examplesof improvements are higher resolution of the elevation model and an improvedclassification of the K-factor, as well as including, for Scandinavian conditions,important aspects such as snow melt.