The overgrowth of Zizania latifolia in a subtropical floodplain lake: Changes in its distribution and possible water level control measures

• Remote sensing and ArcGIS were used to analyze the changes in distribution of Zizania latifolia in a subtropical lake.
• We tested the effects of altered water level on the distribution of Z. latifolia.
• We proposed specific water level regulation measures to control the overgrowth of Z. latifolia.

Wuchang Lake is a shallow lake located in the middle reaches of the Yangtze River. Historically, it was freely connected with the Yangtze mainstem and dominated by submerged macrophytes. For fishing and flood control, the river–lake connection was blocked by the Wanhe sluice in 1959; this led to large changes in water level and ultimately the overgrowth of the emergent macrophyte Zizania latifolia in Wuchang Lake. In order to devise a way to control the expansion of Z. latifolia, remote sensing and a geographic information system (GIS) were used in this study to analyze the changes in distribution of Z. latifolia. The results showed that the distribution area of Z. latifolia linearly increased from 1981 to 2009, and the annual average growth rate was about 1.8 km2/year. In 2009, the plant covered about 53% of the whole lake, and the lake was presenting a serious tendency for terrestrialization. Analyses of the hydrological data indicated that the significantly decreased water level during the plant's germination period (February–March) may be the main cause for the overgrowth of Z. latifolia. By assessing the February–March mean water level before the building of sluice, and the plant's germination threshold for water depth, we recommend increasing the February–March mean water levels from 11.0 m at present to 12.0 m; this would reduce the potential distribution area of Z. latifolia from 56.8% at present to 8.9%. The results of this study should be useful for the control of aquatic macrophytes in other lakes subject to similar water level regulations.