Abstract:
Denitrification and emission of greenhouse gases and oxygen are all important biochemical processes occurring in aquatic ecosystems. To define extent of the impact of aquatic plants, relative to type, on these processes, dynamics of N
2, CH
4 ,O
2 ,CO
2 and N
2O emissions from eutrophied waters in Caohai of Lake Dianchi, rank with emergent plants (
Acorus calamus), floating-leaved plants (
Nymhaea tetragona,
Nelumbo nucifera), floating plants (
Eichhornia crassipes) and submerged plants (
Myriophyllum verticillatum, Hydrilla verticillata) and in control (waters without plants) were studied in July and August, 2012. Gases released from the waters were
in-situ collected using a self-developed bubble trapping device, while water temperature, dissolved oxyen(DO), oxidative redox potential(ORP) and pH were also measured. Results show that the gas emitted from the waters with or without aquatic plants, were composed mostly of N
2, CH
4 and O
2, and the rest of CO
2 and N
2O. The submerged plants obviously improved O
2 releasing process via photosynthesis, resulting in higher gas emission rate and higher emission fluxes of various fractions of gass. The leaves of
Nymhaea tetragona,
Nelumbo nucifera, and
Eichhornia crassipes created shadow over the water surface, thus decreasing photosynthetic capacity of algae in the water, and consequently the gas emission rate of the water, with its median being even lower than that in the control. Moreover, the shadow also reduced emission fluxes of various fractions of gases. No significant difference was found in CH
4 concentration in emitted gas between the experimental plots, while the concentration of N2 in the gas emitted from the waters grown with
Acorus calamus or
Nymhaea tetragona was significantly higher than that from the control. The study provides a new method and idea for studying how different aquatic plants affect the gas releasing process in waters.