Näringsbelastning på en anlagd våtmark från åker, skog och enskilda avlopp

Sammanfattning: This work is a part of the project "Våtmarker i odlingslandskapet – uppföljning av miljömålen" (Wetlands in arable land – following-up of the environmental goals). The main objective with this project is to study nitrogen and phosphorus retention in a constructed wetland by using mass balance calculations. Continuous measurements of nutrients and water flow through the inlet and the outlet of the wetland are made. However, substantial amounts of nitrogen and phosphorus were assumed to reach the wetland with a drain-pipe transporting wastewater from nearby houses (10 persons). This drain-pipe is located after the inlet and in order to make reliable mass balance calculations it was important to quantify this flow of nutrients through measurements, which was the main objective with this thesis. Another objective was to quantify nitrogen and phosphorus load from forest and arable land by using literature and a nitrogen leaching model. The aim was also to describe how water moves through the catchment toward the wetland. The catchment area is 98 hectares of which 82 % is drained through the inlet of the wetland. This 82 % represented 77 % of the total nitrogen load (per year) and 60 % of the total phosphorus load to the wetland respectively. The total nitrogen load to the wetland was estimated to be 730 kg /year. The arable land, which constitutes only about one third of the catchment contributed with 89 % of the total nitrogen load. From the forest land was 8 % estimated to origin and only 3 % from wastewater. The total phosphorus load was 19 kg/year, of which 63 % originated from arable land, 13 % from forest and 24 % from wastewater. An important conclusion from this work is that wastewater has a large impact on the phosphorus supply to this particular wetland, especially during periods when drainage flow from the surrounding land is low. Another conclusion is that arable land was an important source of both nitrogen and phosphorus.