Is phosphorus limiting the nitrogen removal in constructed wetlands?
Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
Two mesocosm studies were performed in a laboratory to figure out the relevance of the phosphorus concentration to the nitrogen removal in wetlands. The main intention was to see if phosphorus is limiting the process of denitrification. In both experiments, plastic beakers (n=20) were filled with inlet water and plant litter material from the ground of a constructed wetland near Halmstad, Sweden.. The litter consisted mainly of dead leaves of Phragmites australis and the water, originating from an agricultural site, had a high concentration of total nitrogen (around 9 mg/L), but a low concentration of phosphorus (around 20 µg/L). The experiment was performed in darkness and in the mesocosms prevailed anaerobic conditions. Half of the beakers were filled with phosphorus enriched water and water samples were obtained at several times and analyzed for nitrate, total nitrogen and total phosphorus to determine the nitrogen removal. In addition the plant material was analyzed for nitrogen and carbon content before and after the experiment with a carbon/nitrogen-analyzer. The mean removal rates of nitrogen were higher in the mesocosms which were treated with additional phosphorus. In a long-term perspective from the second experiment, the mean removal rates are declining faster in the non phosphorus treated beakers. The analysis of the plant litter material could not show if nitrogen was removed from systems through denitrification or just taken up and stored by microorganisms. The experiment was carried out under controlled conditions. The results show that the effect of P on denitrification is not completely understood yet and further research especially on the N uptake by microorganisms and long-term experiments are needed.
Place, publisher, year, edition, pages
IdentifiersURN: urn:nbn:se:hh:diva-26257OAI: oai:DiVA.org:hh-26257DiVA: diva2:738950
Per Magnus Ehde