Rådgivningsverktyg våtmarker: optimerad placering och storlek för fosforretention

The aim of this project has been to increase knowledge regarding phosphorus (P) retention in wetlands and thereby improve reduction of the load of P to our waters. To be able to do this, measured P retention was collected from 16 wetlands that had high-frequency sampling for 1-13 years. The retention was related to the hydraulic and P load. Only measurements from 12 wetlands were used, as the other four were excluded due to that the entire water flow was not led into the wetland, or because retention and load were outliers that affected the relationships too much. The results showed that phosphorus retention varied greatly between wetlands and different years. The same wetland had the lowest retention in the first year and 7 years later had amongst the highest retention. With such large annual variation, it becomes difficult to compare wetlands that have been studied in different years and at different ages. Most of the measurements have been carried out when the wetlands were relatively new. In order to get a better estimate of long-term P retention, wetland management needs and optimal hydraulic load, long-term measurements are needed at the same time in all these wetlands. Phosphorus retention, based on annual average for the 12 wetlands, increased with higher P load. The obtained equation was used to estimate potential P retention, based on the developed maps with modelled P load. Another map was created to estimate the recommended wetland size based on modelled flow accumulation and an optimal hydraulic load of 100 m per year.