Impacts of a hydroelectric dam and human land uses on water quality and aquatic macroinvertebrate assemblages in the Phong River, Thailand

Changes in land use and landcover, combined with disturbances from human activities, can impact biodiversity in water. In this study, we investigated the effects of human land uses and human constructions—specifically the Ubol Ratana hydroelectric dam—on water quality and the distribution of aquatic macroinvertebrates in the Phong River in northeastern Thailand. Fieldwork was conducted six times in 2024—three in the dry season and three in the rainy season—across 12 stations along the Phong River from its headwaters downstream covering a gradient from natural to heavily impacted land uses. Seven stations located upstream of the Ubol Ratana Dam (PO1–PO7) while five located downstream (PO8–PO12). At each station, an unmanned aerial vehicle was used to document surrounding land cover, and biological, physical, and chemical parameters were measured. Furthermore, we collected aquatic macroinvertebrates according to rapid bioassessment protocols using a D-frame aquatic dip net. We categorized the stations into three groups based on the dominant land use/land cover type: forest (2 stations), agriculture (8 stations) and residential (2 stations). We observed significant differences in temperature, electrical conductivity and total dissolved solids among three land use types (one-way ANOVA, p-value < 0.05). The level of total suspended solids, total dissolved solids, electrical conductivity, nitrate, ammonia, and orthophosphate were significantly lower after the dam, while water transparency was higher (independent t-test, p-value < 0.05). The constrained correspondence analysis (CCA) revealed that aquatic macroinvertebrate distribution was associated with ten environmental factors, i.e., temperature, depth, transparency, pH, dissolved oxygen, electrical conductivity, total dissolved solids, ammonia, nitrate, and orthophosphate. The results suggest that human land conversion and construction in the Phong River have impacted water quality and aquatic macroinvertebrate assemblages highlighting their potential as indicators of land use impacts in the Phong River.