Invasive Water Hyacinth (Eichhornia crassipes) Increases Methane Emissions from a Subtropical Lake in the Yangtze River in China

Abstract

Lakes represent an important source of atmospheric methane (CH4); however, there are few studies on which lake-dwelling invasive aquatic plants generate CH4. Therefore, in this study, CH4 emissions were measured using a floating chamber and gas chromatography in a subtropical lake in China. We considered four community zones of invasive plants (Eichhornia crassipes), emergent vegetation (Zizania latifolia), floating-plant (Trapa natans) and open-water zones. The results indicate that the flux of CH4 emissions varied between −5.38 and 102.68 mg m−2 h−1. The higher emission values were attributed to lake eutrophication. Moreover, the flux of CH4 emissions in the invasive plant zone was 140%–220% higher than that in the open-water and the floating-plant zones. However, there was no significant difference in CH4 emissions between the invasive plant and the emergent vegetation zones. This may be due to a higher production of plants, as well as the rapid reproductive rate of the invasive plants. Finally, CH4 emissions were positively associated with the air and water temperature; however, the emissions were also negatively associated with water depth. Our results suggest that invasive plants enhance freshwater CH4 emissions, thus contributing to global warming.

Effects of Lotus (Nelumbo nucifera Gaertn.) on the Methane Emission in Littoral Zones of a Subtropical Lake, China

“…The research area lay in the Hong Lake Natural Reserve in the middle reach of the Yangtze River, located between 29 • 40 N and 29 • 58 N, and between 113 • 12 E and 113 • 26 E [28]. Hong Lake is the seventh largest freshwater lake in China and the largest lake in Hubei Province [27].…”

“…Hong Lake is the seventh largest freshwater lake in China and the largest lake in Hubei Province [27]. The lake has a surface area of 344 km 2 , with an open water area of 308 km 2 , a littoral area of 36 km 2 , and a mean water depth of 1.34 m [28,29]. This region is in the northern fringe of a humid subtropical monsoon climate, with an average annual temperature of 15.9-16.6 • C and average annual precipitation of 1060-1331 mm, as well as around 74% of precipitation, which occurs from April to October [27][28][29].…”

“…Paddy and fluvoquic soil are the typical soils. Additionally, Hong Lake became one of the international important wetlands of the Ramsar convention in 2008 and one of the Chinese Wetland Ecosystem Research Stations in 2014 [28].…”

“…CH 4 gases were sampled from April to December in 2021, and from April to October in 2022, and gas samples were collected once per month on a clear day between 8:30 and 11:30 a.m. (Beijing standard time, GMT + 8 h), with sampling carried out twice in September 2021 and June 2022, and three times in September 2022. The chamber was composed of acrylic organic glass (40 cm height × 35 cm diameter) [28]. Air inside the chambers was circulated with battery-driven fans during the measurement to ensure the gas samples were well mixed.…”

“…Hubei, located in the middle reaches Yangtze River, is one of the largest provinces in lotus cultivation [26]. Hong Lake, covering an area of around 350 km 2 , is the largest freshwater lake in Hubei province [27,28]. The lake was originally connected with the Yangtze River in the 1950s when the area of the lake was 760 km 2 ; now, it is semi-connected to the Yangtze River because of the construction of sluices around the lake between the years 1955 and 1975 [27].…”