Ecological Conditions of Luetshokha Lake and its Recharge Potential using Rooftop Rainwater Harvesting, Samtengang, Wangdue Bhutan

Abstract

Luetshokha lake is noted to harbour invasive aquatic plants and experiences reduction in water level. This research assessed the water variables and floristic and macroinvertebrate compositions of Luetshokha lake in Samtengang, Wangdue and its potential to increase water level using rooftop rainwater harvesting (RWH). Presence of aquatic plants such as Brasenia schreberi, Schnoeplectus pungens and Potamogeton distinctus indicates organic pollution of water in the lake. Coenagrionidae and Baetidae families were the dominant macroinvertebrate taxa present in the lake. There was a positive relationship between aquatic plants and macroinvertebrate diversity indices (rs = 0.20, p = 0.25), richness (rs = 0.24, p = 0.16) and evenness (rs = 0.29, p = 0.04). The relationships between aquatic plants and physico-chemical variables studied were negative; pH (rs = -0.02, p = 0.90), conductivity (rs = -0.45, p = 0.00), Total Dissolved Solids (TDS) (rs = -0.43, p = 0.01) and salinity (rs = -0.34, p = 0.56). However, temperature was positively correlated (rs = 0.25, p = 0.14) with aquatic plants. Similarly,
macroinvertebrate diversity was negatively correlated with pH (rs = -0.31, p = 0.07), temperature (rs = -0.11, p = 0.54), conductivity (rs = -0.24, p = 0.17), TDS (rs = -0.24, p = 0.16) and salinity (rs = -0.27, p = 0.12). Family-level Biotic Index indicated good physical condition of lake water with low organic pollution. The lake water level was estimated to rise by 5 cm through a potential RWH of 1,784.37 m3 from the roof catchment area of 2,221.01 m2.