Bakgrundshalt av fosfor i sjön Skråmträsket : Analys av den naturliga fosforkoncentrationen genom kiselalgsrekonstruktion

Sammanfattning: Skråmträsket acts as a pilot case in the Bothnian Bay water district for eutrophic lakes. Recently the symptoms caused by eutrophication has gone from occasionally occurring to annual heavy algal blooms. The overall objective of the study was to determine the natural TP content in the lake by studying the development of TP. This was supposed to serve as a basis for future measures to reduce the amount of phosphorus in the lake. Another objective was to evaluate the oxygen conditions in the bottom waters to assess whether the internal load is present or not. To determine the natural TP a sediment core was taken in the lake's deep burrow. A reconstruction of the TP was done on ten samples from the sediment core by studying diatoms. Oxygen levels in Skråmträskets bottom water was analyzed at 25 coordinate points. The result of the reconstructed background level of phosphorus showed that it varied between 18-20 µg TP/l. Oxygen measurement showed that oxygen deficiency occurs in the bottom water of the lake, which means that internal load can occur. However, further studies are needed for an accurate assessment regarding the natural background level of the TP.