Internal nutrient loading in the lake Skråmträsket: : Action proposal based on data from Skellefteå municipality and own water- and sediment samples

Eutrophication is one of the most obvious and visible global environmental problem. The problems with eutrophication in Sweden is mainly in the south where agriculture has affected the areas for a long time. Skråmträsket is a lake in north of Sweden who has been affected from anthropogenic activities such as wastewater and runoff from agriculture. The lake has high phosphorus concentrations, originating both from catchment runoff and internal loading from the sediments. Skråmträsket have had algal blooms during the last 20 years. The municipality of Skellefteå and the local water group have collaborated during the last years to mitigate external sources of phosphorus, focusing mainly on the deepest area of the lake. This report’s a continuation of the work and investigates the internal loading of phosphorous in the lake sediments and possible actions to restore the lake. The internal loading tends to be more widespread than previously studies have shown, also the shallow sediment areas tend to show signs of internal loading. The conclusions are based on previous samplings from the lake including own sampling made for this report. As a complement is a literature study done to investigate more about possible methods to restore Skråmträsket. There are two possible methods to proceed with, aluminum treatment of the sediments or bottom water pumping. It’s important that the measure will be long-lived. Therefore, it is important to continue the samplings and expand the areas for sampling. The focus of the actions must include both the deep areas and the shallow areas of the sediment.