Damming effects on hydrological abundance and eco-hydrological alteration in upstream wetlands of Eastern Himalaya

Abstract

The effects of dams on hydrological conditions and ecological functioning of wetlands downstream are less well studied. Rivers and wetlands are vital environmental elements linked to natural and human ecosystems, so it is extremely important to study ecohydrological planning and human well-being. This study investigates the impact of the dam on the hydrological abundance and eco-hydrological alterations of Loktak Lake, which is located upstream of the Ithai barrage. For this purpose, the Indicator of Hydrological Alteration (IHA) was used to examine the ecohydrological threshold, failure rate, impact magnitude and ecohydrological deficit/surplus in a river section and the adjacent wetland in three temporal phases (I, 1996–2001; II, 2006–2011; and III, 2016–2021). The results show that the hydrological surplus has recently increased to 27.22% (phase III), while in phase I it was only 1.1%. Due to the decreasing failure rate of ecological optima, eco-hydrological surplus was recorded in both Loktak lakes, which is an obvious indication of a reduction in ecological distress that may lead to negative impacts on natural and human well-being. However, due to the constant high-water level in the lake, Phumdi is no longer able to reach the bottom of the lake during the dry season. Since it cannot absorb nutrients, the lake's vegetation declines and rotting sediments settle. Since the Ithai Dam closed the outlet that once connected the lake to the sea, fishermen can no longer dispose of the decomposing biomass. This study is important for dam management and planning to consider the impacts on wetlands downstream and to take measures to mitigate these impacts.