Impact of invasive alien plant species on aquatic biodiversity of Koshi Tappu Wetlands : Ramsar Site, Nepal

Abstract

Koshi Tappu Wetlands play a significant role in the conservation of many rare and endangered species of flora and fauna. However, this wetland is threatened by several natural and anthropogenic stressors; among others, invasion by invasive species is the most serious problem. The objective of this study was to prepare an inventory list of wetlands, categorize the wetlands based on the coverage of alien species, identify the problematic aquatic invasive plant species, and assess their impact on water quality and aquatic biodiversity (fish and macroinvertebrates). This study was conducted in winter and spring seasons of 2018. Composite water samples were collected from the wetlands with different covers of invasive species. Macroinvertebrate samples were collected using hand net of 500µm mesh following the habitat specific sampling approach, and fishes were sampled using Cast Net. The analysis of water quality parameters, macroinvertebrates and fishes were performed for different levels of invasion. Altogether, 66 wetlands were documented in the Buffer Zone located in the east of eastern embankment of the KTWR. Out of the total 66 wetlands, 33.33% were found to be non-invaded while 66.67% were found to be invaded by the invasive macrophytes. The invaded wetlands were further subdivided into abundant 'A' (>75% coverage), common 'C' (50-75% coverage) frequent 'F' (25-50%coverage), occasional 'O' (5-25% coverage), and rare 'R' (1-5% coverage) which were found to have occupied 19.69%, 16.67%, 12.12%, 13.63% and 4.50%, respectively, of the invaded wetlands (66.61%). The most problematic invasive species were found to be Eichhornia crassipes and Ipomoea carnea. The dissolved oxygen (DO) decreased while the total alkalinity and free CO₂ increased significantly with the increased coverage of invasive macrophytes. The macroinvertebrate diversity was observed high in common and abundant coverage, but the fish diversity was high in the frequent coverage of invasive species. The taxa compositions shifted from “Decapoda” and “Ephemeroptera” to “Odonata” and “Mollusca” in none to abundant coverage of invasive species. The findings of this research are expected to help wetland managers and related stakeholders to understand the level of impact of different coverage of invasive species on wetlands, help to develop the conservation strategy and action plans to mitigate the spread of these invasive species, and wise use of wetlands.