Impacts of Manwan Dam construction on aquatic habitat and community in Middle Reach of Lancang River

Abstract

Aquatic habitats have been affected worldwide by dams for hydroelectric generation, resulting in biological impactts. Great changes in Manwan Reservoir area had been taken place on aquatic habitat in pre-and post-dam periods. The storage resulted in area increase of water body from other habitats. The flow at Gajiu hydrological station gave rise to divergent oscillation in dry season and changed smoothly in wet season after the completion of dam, respectively. Besides, months of maximum discharge also was found to be oscillatory during construction period. Surface water temperature, ammonia nitrogen (NH3-N) and total phosphorus (TP) content were higher in pre-dam period than that in post-dam period. The variation of habitats led to number increase and structure change of species, includeing algae, zooplankton, fishes, plant, birds and mammals. Dramatic growth of chlorophyta and appearance of euglenaphyta were associated with higher surface water temperature and NH3-N and TP content. The change of aquatic habitat and introduction of alien fishes, such as neosalanx taihuensis, tilapia nilotica, carassius auratus and so on, influenced fish assemblage composition in reservoir. Despite disappearance of some shrub species, such as homonoia riparia and syzygium fluviatilis, the number of plant species also was higher in post-dam period because of the flood with herbs from mountain ridge or tributaries.