Wetland plays a crucial role in removal of nitrogen through some microbial processes like denitrification. Denitrification has been shown to be affected by organic carbon concentrations. The aim of the study is to determine the impact of dissolved organic carbon (DOC) concentration and composition on nitrogen removal in wetland. This study consists of two parts. Firstly, a laboratory experiment to investigate the effect of concentration and composition of DOC on nitrogen removal. Secondly, analysis of the data collected from 10 constructed wetlands in different catchment areas to investigated which environmental factors affect nitrogen removal. The laboratory experiments involves nitrogen- rich wetland water that is treated with different types of DOC (glucose, cellulose and acetate) in different concentrations (control, 0.05 mol/L, 0.1 mol/L and 0.2 mol/L). Then the nitrogen removal was measured over 5 days. The result shows there is no significant difference in nitrogen removal between treatments with different concentrations for any of the carbon sources such as glucose, cellulose and acetate. In the field analysis only one wetland named Fjelkner showed a significant positive correlation between the TOC and the nitrogen removal that is r= 0.637 and p= 0.008, but in case of all other wetlands there is no significant relationship between TOC and nitrogen removal. The ratio of colour/TOC will indicates the composition of the carbon and the site-specific trends, and, in some wetlands like Vennestad and Viderup that shows positive significant correlation and some of the wetlands like Toarp shows negative significant correlation. Therefore, an increasing concentration of carbon does not reliably increase nitrogen removal but in the case of carbon quality some factors like hydrology, vegetation and land use plays an important role. Our study shows mismatched concentrations of DOC and quality of carbon are the problems for nitrogen removal in wetlands. To improve these solutions there are some strategies: site specific carbon addition, increasing the water residence time to control the flow structures, increasing wetland vegetation and reformulate the biofilms, it’s a microbial strategy, that will support the denitrification.