This study investigated water quality and aquatic insects above, in, and below the measuring weir of Happen Creek, the No. 1 watershed of the Fushan Experimental Forest, to assess the effects of the measuring weir on water quality. The results revealed that the measuring weir engendered significant changes in five basic quality parameters-
water temperature, pH, turbidity, electrical conductivity (EC), and dissolved oxygen (DO)-in water that passed
through it (p < 0.001). The average temperature and EC decreased slightly, whereas the pH, turbidity, and DO increased slightly. The study analyzed the concentrations of 12 anions and cations, and the results indicated no significant changes,except for the concentration of only sulfate ions, which decreased slightly (p < 0.05). The nutrient budget measurements taken from the weir station were assumed to be similar to those for the free-flowing stream water. Additionally, the family-level biotic index (FBI) of aquatic insects above the measuring weir was 4.1, and that below the measuring weir was 3.9, indicating that the water quality could be classified as “very good.” The FBI inside the measuring weir was 5.9, indicating a classification of “fairly poor.” These results demonstrate that the measuring weir had substantial effects on stream water quality, particularly regarding the composition of aquatic insects.
Key Words: measuring weir, water quality, family-level biotic index (FBI)