During summer 1967 an ecological study of the zonation of different macrophytes was made in the three basins of Chielgat, Venematen and Zuideindigerwiede in North-West Overijssel, the Netherlands. Chemical properties of sapropels, microclimatic conditions and composition of mud gases in habitats of different macrophyte zones were studied. The three basins show various degrees of trophism and different qualities of humic substances in sapropels. The habitats of different macrophytes in the same basin are also different. Each vegetation zone is characterized by a special temperature course in different water and air layers. The temperature course is dependent on the position and structure of the vegetation zone and on weather conditions. Water temperature is influenced by the duration of insolation, and by the direction and strength of wind. Time-shifts in the warming-up of the lower water layers are also of interest. The relative amounts of C02, 02, N2 and CH4 were estimated both under and in the plant cover of the vegetation zones under study. While under the plant cover CH4 prevails in the gas mixture, in the plant cover C02, 02 and N2 are of higher importance. The amount of C02 + CH4 on the one hand and the amount of N2 on the other hand reflect the outputs of C and N metabolisms which take place in the basins. The gaseous output of C and N metabolisms in the basins under study are related to the trophisms of individual basins.