FISH DIVERSITY AND ENVIRONMENTAL DRIVERS IN THE BAGMATI RIVER, KATHMANDU, CENTRAL NEPAL
DOI:
https://doi.org/10.3126/jist.v31i1.86008Keywords:
Biodiversity conservation, Fish diversity, Freshwater, Monsoon dynamics, Urban River ecologyAbstract
This study examined the spatiotemporal variation in fish diversity and its environmental drivers along the Bagmati River, Kathmandu, Nepal. Fish and water sampling was conducted across five sites during premonsoon, monsoon, and post monsoon on the year 2021-2022 A.D. Physicochemical parameters (Temperature (0C), Turbidity (NTU), EC (µS/cm), TDS (mg/L), pH, Hardness (mg/L as CaCO3), Total Alkalinity (mg/L of CaCO3), DO (mg/L), Free CO2 (mg/L), Chloride (mg/L), Zn (mg/L)) were measured to assess habitat conditions. Diversity indices, including Shannon, Simpson, Inverse Simpson, Pielou’s evenness, Margalef’s, and Menhinick’s indices, were calculated. Principal Component Analysis (PCA) and Canonical Correspondence Analysis (CCA) were used to explore the relationship between environmental gradients and species-environment respectively. Spatial variation was found on the fish abundance and diversity however no significant variation was observed between seasons. Upstream site (U1) consistently recorded the lowest abundance (21 - 34 individuals) and diversity (Shannon: 0.98 - 1.08; Simpson: 0.58 - 0.66), whereas far-downstream sites D3 - D4 showed the highest abundance (up to 166 individuals) and diversity (Shannon: 2.68 - 2.88; Simpson: 0.92 - 0.94). Environmental variables varied significantly across sites and seasons (p < 0.05). PCA revealed that the first two components explained 57.73% of the total variance, driven by electrical conductivity, total dissolved solids, hardness, and chloride. CCA indicated that fish assemblage structure was strongly associated with temperature (F = 15.54, p < 0.001), electrical conductivity (F = 7.93, p < 0.001), total alkalinity (F = 4.22, p = 0.0025), dissolved oxygen (F = 3.80, p = 0.0031), and free CO₂ (F = 2.90, p = 0.019). Overall, results indicate that fish diversity and community composition significantly varies along the location in the Bagmati River. So, conservation and management strategies should focus on maintaining habitat quality, particularly at upstream sites, to support sustainable fish diversity.
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