Dramatic variations in emergent wetland area in China’s largest freshwater lake, Poyang Lake
Freshwater wetlands are important ecosystems experiencing rapid degradation around the world. As much as 64% of world’s wetland area has been lost since 1900; the situation is even more serious in Asia, where land reclamation and anthropogenic modifications of rivers are increasing the rate of wet- land disappearance. In this study, we provide a first complete estimation of daily Emergent Wetland Area (EWA) in Poyang Lake, China’s largest freshwater lake, from 1955 to 2012. A wavelet analysis indicates a strong periodicity in the monthly EWA time series with two oscillations having a period of 12 and 60–72 months, respectively. A dramatic increase in mean annual EWA is detected since 2003, when the Three Gorges Dam (TGD) was completed, mainly due to the seasonal drying of 1078 km 2 of wetlands in Octo- ber. It is found that the timing of wetland emergence during the dry season has been anticipated of one month, from November to October, since the establishment of TGD. It is argued that a significant increase in wetland exposure and an observable shift in the seasonal timing of flooding and drying will seriously degrade the wetland system and threaten the endangered migratory birds that inhabit it unless effective countermeasures are implemented.
Fig. 1. Map of Poyang Lake catchment in China. (a) Poyang Lake’s location in relation to the Changjiang River, the Three Gorges Dam and the East China Sea; (b) Poyang Lake catchment; (c) Poyang Lake bathymetry (referred to the 1985 National Elevation datum); and (d) relationship between water level and emergent wetland area (blue circles represent the measured data while the red line denotes the polynomial fitting curve).
Fig. 9. Decadal variations of monthly exposed wetland area (EWA) from 1963 to 2012, the red curve denotes the decadal EWA fluctuation pattern in each month.
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