Epsilon Archive for Student Projects

Abstract

Lerbodaälven is a river in the municipality of Kil which, due to high phosphorus content is not meeting the requirements for good ecological status according to the Water Framework Directive. The purpose of this report is to investigate the causes for the high content of phosphorus that has been measured in Lerbodaälven between 1995-2010. Four questions will be answered in this report.

1. Does the sewage treatment work affect the phosphorus level in Lerbodaälven?
The result from the time series analysis shows that the sewage treatment works have a small impact on the phosphorus level in Lerbodaälven. The reduction of phoshorus is high (94 %) and the phoshorus load from the sewage treatment works is approximately 9 kg per year.

2. Does Lerbodaälven differ from other rivers nearby?
Water samples from ten other rivers close to Lerbodaälven have been collected and analysed two times during the spring 2010: one time during high water flow and one time during normal water flow. The purpose of that was to examine if Lerbodaälven differ or if similar results are shown in waters nearby, with the same kind of land use. The results from the high water flow period show that Lerbodaälven does not differ, since the results were similar in adjacent rivers. The results also show that much of the measured phosphorus is bound to particles or organic material.

3. Is the soil type the reason why the phosphorus level vary within the catchment?
This was one of the first questions that came up when the project started. But due to lack of data, a local soil type map could not be done. It is therefore not possible to draw any conclusions about how the soil type affect the phosphorus levels. Although it has been verified that silty clay is the dominant soil type within the catchment, by other maps.

4. Is it the natural or man made sources that contribute the most to the phosphorus load?
Both natural causes and man-made causes have been studied. The largest source of phosphorus load is farming, (1370 kg gross phosphorus/year). The net phosphorus load from the private waste water is approximately 320 kg. The atmospheric deposition and the leakage from forest, swamps and open fields is all together approximately 390 kg gross phosphorus/year, natural sources that are hard to decrease. There are a lot of lakes in the Lerbodaälven catchment and it is likely that much of the phosphorus that load the area settles.

Measures.

A model, such as the Fyrismodel, would give better approximations of the phosphorus load than the ones made in this report. The Fyrismodel is a tool for catchment-scale modelling of source apportioned gross and net transport of both nitrogen and phosphorus. With the Fyrismodel it is also possible to better/more precisely calculate the natural sources. An effective reduction of the phosphorus leakage from arable land would require measures that are specific to each field and that are implemented during the periods in which the flow of phosphorus is high. A dialog with the farmers about problem with phosphorus leakage could give rise to improved routines.