Sedimentprovtagning av dagvattendammar som ett alternativ till flödesproportionell vattenprovtagning

Sammanfattning: Stormwater run-off from surfaces such as roads or rooftops is often polluted with heavy metals and nutrients. Many of these substances can cause great damage in biota if they end up in the recipient. In Sweden constructed wetlands and ponds for treatment of stormwater are frequently used, since research has shown that these treatment ponds are reducing stormwater pollution considerably to a low cost. The knowledge of these pollutant removal mechanisms and how follow-up and assessment of the ponds should be performed is still limited. To determine the pollutant removal efficiency of the stormwater ponds it is recommended that flow-weighted water samples are collected from both the inflow and the outflow of the pond. This method demands considerable resources of time and money for installations and analysis. Alternative methods for assessing pollutant removal are requested, methods with lower costs but relevant results. This thesis is investigating whether sediment sampling could be such an alternative. Sediment core samples were taken in four stormwater ponds where flow-weighted water sampling has been performed as well. This makes it possible to compare the two methods. A method of sampling recently sedimented material was also tried out by constructing and placing sediment traps on the pond floor. Analysis of concentration of six heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) and phosphorus were carried out. The results show i.e. that the concentrations of heavy metals and phosphorus in the pond sediments decrease as the distance from the pond inlet increase. Comparing the two methods shows that the results from the sediment sampling are in the same order of magnitude as the results from the water sampling. Consequently, the conclusion states that a well executed sediment sampling may be an alternative to flow-weighted water sampling.