Projektet Raseborgs å: an investigation into the impact of water protection structures on nutrient release mitigation in the Gulf of Finland

Abstract

The Raseborg river is a river in Southern Finland that empties into the Gulf of Finland. Past modification of the river for drainage of agricultural activities has contributed to the decline in ecological status of the river and the Gulf of Finland. Projektet Raseborgs å, or Project Raseborg River, commenced in 2018 with the aim of attaining a good ecological status, in line with EU Directive 2000/60/EC. The aims of the project include the reduction of phosphorus load in the river, making sediment less prone to resuspension from increases in water level, and reduction of total phosphorus concentration in Landbofjärden, the bay the river flows into. The objective of the thesis was to assess the effect of the project on the river basin and the bay it flows into. This includes studying the change in turbidity and phosphorus in the river during the project, how affected riverbed sediments are by changes in water level following the implementation of water protection structures, and the change in total phosphorus concentration in the bay in which the river flows into. Data collected by the project was grouped by month. The data includes hourly readings for turbidity, water level, total phosphorus, and temperature. Correlations and statistical significance tests were calculated for phosphorus and turbidity, and turbidity and water level. Comparisons of monthly and seasonal averages for turbidity over time were made to study the changes over the duration of the study and to account for seasonal variations. Readings of total phosphorus in the bay were graphed to study its change over the project duration. The study shows that the water protection structures implemented in the river have reduced turbidity and phosphorus readings over the studied duration. Landbofjärden saw an increase in phosphorus concentrations during the period studied. An expansion of the project to include other waterways flowing into the bay may be beneficial to the area by decreasing other sources of phosphorus entering the bay, and by extension the Gulf of Finland.