Avloppsslam på åkermark : Analys av långsiktiga effekter på mikrobsamhället och kväveomvandlande mikroorganismer

Sammanfattning: One major environmental challenge is to manage agricultural soil in asustainable way. Since nutrients in the soil are taken away every harvest, there is a need to recycle nutrients back to the soil. One solution is to use sewage sludge as a fertilizer. However, sludge can also contain substances that could potentially be harmful to crops or humans. This study examined the long-term effect of sewage sludge amendment in agricultural soil. The aim of this study was to analyse the general effects on the microbial community by sequencing the 16SrRNA gene, as well as studying the response to the amendments of nitrifying and denitrifying microorganisms. This was done by qPCR quantification of marker genes and activity tests of potential denitrification and N2O production in the soil. The main conclusion is that long-term effects of sewage sludge amendments on the microbial community, as well as on microorganisms involved in nitrogen cycling,are relatively small compared to effects caused by differences in soils. Moreover, the effects on the microbial community differed between soils, implying that attention needs to be paid to the characteristics of the soil when evaluating effects of sludge amendments. It was clear that the ratio of ammonia oxidising bacteria and archaea differed between treatments, however further studies are needed to conclude the reason for this. Finally, positive correlations between both measured activities and denitrifying marker genes were found, which suggests that quantification of marker genes can be used for studying reactions in the soil.