Contribution of aquatic plants to ienitrification in lakes and marshes

摘要

Denitrifying bacteria have been found in biofilms on aquatic plant surfaces, but so far it is still very difficult to measure denitrification activity in-situ. It is important to understand the denitrification activity in these biofilms in the field and to be able to quantify nitrogen (N) losses through denitrification. In this study, we conducted an in-situ field experiment to measure denitrification activity by aquatic plants and to assess N dynamics in this controlled experiment. We used a special measurement device and acetylene inhibition technique. The experiment was carried out at the ponds connected to the Lake Kasumigaura, the second largest freshwater lake in Japan. The result of the in-situ field experiments showed that higher N_2O concentrations were observed in chambers with vegetation than without vegetation. Denitrification activity varied seasonal, and the ratio of NO_3~- removal by denitrification varied seasonal too. The result of incubation experiments showed that withered plants surface had a higher denitrification activity than fresh plant surfaces. Withered plant surfaces also had more denitrifying bacteria than fresh plant surface. It is suggested that presence of aquatic plant on lakes and marshes are important for N elimination from lakes and marshes.