Diversity and Distribution Patterns of Freshwater Macroinvertebrates in Modi River System, Gandaki Province, Nepal

Abstract

In the face of several stressors in Modi River system, this research was conducted with the aim of assessing diversity and distribution patterns of benthic macroinvertebrates along the altitudinal gradient including the ecological health of a River system. Benthic macroinvertebrates sampling was conducted in 20 different (13-river's mainstem and 7- tributaries) following a multi-habitat sampling approach based on Moog (2007). Macroinvertebrates were collected by kicking the substrate or jabbing with a D-frame dip net and transferred into labeled vials and preserved in 99.9% ethanol for sorting and identification in the lab. Threats were identified from direct observation and key informant interview. Taxa richness was assessed using Shannon Diversity Index, Simpson Diversity Index, and Evenness. Similarly, Shapiro-Wilk normality test, One way ANOVA, Turkey HSD test and Wilcoxon pair test were conducted to know the difference between groups. R studio (1.2.5 version) and CANOCO (4.5 version) was used for statistical analysis. In total, 40 families belonging to 10 orders were recorded in the study area. 29 families belonging to eight orders were recorded in river’s mainstem while 39 families belonging to 9 orders were recorded in tributaries. Lowest numbers of taxa were recorded at higher elevations of both river (9 families at 1654m) and tributaries (14 families at 1719m). Among 40 families, order Diptera has the highest family richness. Turkey HSD test showed taxa richness between 1550-1800m and 1050-1300m (p=0.0004), and 15501800m and

1350-1500m (p=0.0389) differ significantly. Taxa richness is highest at the elevation of 1050-1300m and lowest at 1550-1800m. Similarly, Shannon Diversity index is highest in the sampling sites located at 1265m elevation and lowest at 1533m. Test Showed that the diversity index differs significantly (p=0.049) with altitude. Wilcoxon pair test did not show the difference in the Simpsons Diversity Index between river's mainstem and tributaries (p=0.195). Likewise, RDA diagram showed the temperature as the most important variable governing the BMI composition . Furthermore, river's mainstem are less polluted than the tributaries. Hydropower construction, sewage, sand and stone quarry, waste dumping, bathing and washing were the major threats for the river system. Keywords: Benthic macroinvertebrates, freshwater, diversity, distribution, stressors