ABSTRACT
The ecological and environmental consequences of large dam projects have received increasing attention in the recent decades. On the basis of daily water-level data, six periods of TM/ETM+ data and a digital elevation model, the eco-hydrological environments and vegetation area of East Dongting Lake, were compared for the years 1995–2011, spanning periods before and after the implementation of the Three Gorges Dam (TGD) in 2003. Vegetation area (including three types: forestry, reed and grass) continuously expanded, and the minimum elevation of vegetation-covered area (VCA) gradually decreased by 0·88m from 1995 to 2011. Following the implementation of the TGD, the rates of both vegetation expansion (12·3 vs 14·1 km2 year-1) and the lowering of minimum elevation of VCA (3·1 vs 7·9 cm year-1) increased rapidly. Monthly water level decreased considerably from July to November, and annual submergence duration at elevations of 22–26 and 30m was considerably decreased after the TGD was implemented. The average maximum submergence duration of VCA was 231 days. Almost equal linear equations describing elevation change from 1995 to 2011 indicated that the minimum elevation of VCA identified via analysis of TM/ETM+ images can be represented by the maximum submergence duration evaluated via daily water level. These data indicate that vegetation colonized the non-vegetation area (including mud beach or water body) more quickly after the implementation of the TGD, due to the drastic changes in eco-hydrological environments such as the decreasing water level and the minimum elevation of VCA. The present methodology might allow faster and more reliable assessment of inundation related landscape impacts on a basin scale and thereby contribute to biodiversity monitoring and policy assessment. |
