PS 51-181 - Impacts of Upper Trishuli “3A” Hydropower Dam on Benthic Macroinvertebrates and Water Quality, Rasuwa, Nepal

Background/Question/Methods

Dams are one of the world's most rapidly developing infrastructures. Benthic macroinvertebrates are one of the best bio-indicators for evaluating the impacts of a wide range of water pollution, climate change, and flow alteration in river ecosystems because they are very sensitive to these stressors. This research confers the dam impacts on macroinvertebrates and water quality upstream and downstream of the Trishuli 3A hydropower dam, Rasuwa, Nepal, for two seasons, i.e., 2020 (Winter) and 2021(Spring). Five sites were selected for this study, one reference site (T1- far above the dam), three disturbed sites (T2- just above the dam; T3- just below the dam; T4- dewatered section), and a recovery site (T5- far below the dam). In upstream and downstream, the values of physico-chemical parameters were slightly different and were higher in the spring season as compared to the winter season. Multi-Habitat Sampling (MHS) method was applied in macroinvertebrates sampling, in addition to 60 water samples (6 replicates in each site). Statistical analysis such as Principal Component Analysis (PCA), Redundancy Analysis (RDA) and Two-way Analysis of Variance (ANOVA) were applied. River water quality was analyzed using GRSBIOS/ASPT, where all the sites belonged to class I, indicating good water quality

Results/Conclusions

Species richness was higher in reference sites, i.e., Upstream reference and downstream recovery sites. RDA analysis revealed that Dissolved Oxygen (DO), pH, temperature and conductivity have a close association with the benthic macroinvertebrates, and PCA analysis showed that PCA1 correlated with alkalinity and nitrate (NO₃), whereas PCA2 is correlated with free CO₂ in the winter season. Similarly, in the spring season, PCA1 is correlated with TDS and NH_3, whereas PCA2 is correlated with turbidity and calcium hardness. Although the water quality looks similar both upstream and downstream of the hydropower dam, the benthic macroinvertebrate diversity is higher in upstream (reference) and downstream (recovery) sites than in disturbed sites near the dam. Rigorous assessment studies should be carried out before the implementation of any future project, and this study could be referenced document.

Keywords: Benthic macroinvertebrates, Hydropower dam, Water quality, Upstream, Downstream