Orsaker till algblomning i Avan : Förslag till möjliga åtgärder för att minska blomningen

The water chemistry of a blooming lake in Tavelsjö, west of Umeå, was analysed after the break-up of the ice and during the summer of 2014. The phosphorous (P) content of the sediment and the inflows, the composition of macrophytes, minor invertebrates and diatoms in the water and diatom fossils in sediments were also looked at. The results show high P, nitrogen and oxygen (O) content in the lake, and the inflows have a high P content. The P content in the sediment is within normal range, but in the upper limit and this could be partly the reason for high P in the water. The lake has neutral pH and is O saturated, to over-saturated in late summer. Composition of macrophytes, invertebrates and diatoms is conferring this high nutritious water. The private sewage-wells were not well maintained, and some need immediate restoration action. It is also shown that excess P is coming from inflow in the south of the lake. This may be due to leakage from farmlands in Västerbacka, or badly maintained sewage wells in Östibyn. The proposed actions are to install columns with P absorbing material in the south inflow and to use straw, leaf litter and alum (AlSO4 or AlOH) to reduce the internal loading