Ecological Characteristics of Reference Locations in Lotic Ecosystems of East Himalaya (India)

This work outlines the present state of the reference conditions of East Himalayan Rivers. The East Himalayan region experiences primarily a humid subtropical climate due to intense monsoon rainfall (>1000 mm per year). As altitude decreases, there’s an observed increase in water temperature (WT), discharge, turbidity, dissolved oxygen (DO), and a slight rise in electrical conductivity (EC) and total dissolved solids (TDS). Total alkalinity (TA) ranges between 10 and 84 ppm and total hardness (TH) between 12 and 40 ppm, generally increasing with decreasing altitude. Conversely, chlorophyll a generally decreases with altitude, except for an increase observed in Lachung at rates of 0.6–2.5 and 0.8–2 compared to other locations. Several catfish species are confined to Lohit and Dibang rivers. High densities of benthic diatoms and macroinvertebrates, representing producer and consumer communities, are present. These assemblages exhibit exceptional uniqueness, as does the piscine fauna. With few localized deviations due to human activities, all serve as suitable reference points or periods in the historical past.