Epsilon Archive for Student Projects

Abstract

The eutrophication of lakes and seas with the algal bloom and deficiency in
oxygen that follow, has been given priority by the Swedish government as one
of 16 environmental objectives. The purpose of this project was to develop a tool
based on a simple model, limited amount of data and geographic information
system (GIS) to identify areas with risk for phosphorus losses due to surface
runoff. This tool can act as a decision support to decide where appropriate
measures should be applied with the aim of reducing phosphorus losses and by
that the eutrophication.

The method that has been used is a combination of two models, one calculating
the potential erosion while the other one identifies areas of erosion (net erosion)
or deposition. This ability is of great importance because potential erosion
should be calculated on areas with net erosion. Areas with high potential erosion
have 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-factor
was improved with a modified equation to adapt the calculation for a complex
terrain. The C- and K-factor were adapted to Swedish conditions by using the
same classification as a similar Swedish method. A Finnish survey was used to
adapt the R-factor to the local climate.

Values of the LS-, C-, K- and R-factors as well as the potential erosion were
compared with similar studies to assure they were reasonable. For the same
reason the total sediment yield was calculated and compared with values based
on water chemistry data. Because the calculated sediment yield was much
higher, most likely due to the high percentage of lakes and forest within the
catchment, this method was considered not to be used.

Several interesting areas have been identified inside the catchment. These should
be investigated in the field before any suggestion of measures can be given
because of the uncertainty in the calculation, mainly related to the elevation
model and the K-factor. Therefore, this method needs to be developed. Examples
of improvements are higher resolution of the elevation model and an improved
classification of the K-factor, as well as including, for Scandinavian conditions,
important aspects such as snow melt.