The Combined Effect of Water Hardness and Metribuzin Herbicides on Some Population Parameters of Microalgae Scenedesmus quadricauda

Metribuzin (Met) is a triazinone herbicide that is widely used for the control of grasses and easily arrived to aquatic ecosystems. Met has different biological effects in the various waters with different water hardness. In this research, combined effects of different water hardness (0, 50, 150, and 200 mg/l as CaCO3) and Met (0, 1, 5 and 10 mg/l) were investigated on population dynamic, growth, and chlorophyll a in green microalgae Scenedesmus quadricauda under laboratory conditions of temperature of 22±2 ºC, photoperiod of 12 hours light : 12 hours dark, and light intensity of 80 µmol photons/m2/s. The experiment was carried out as completely randomized design with three replications for a 14 days period. Results showed that the maximum population density was obtained at hardness of 200 mg/L CaCO3 and 0, 1 and 5 mg/l of Met while the highest amount of chlorophyll a was 6.73 mg/L at hardness of 150 mg/L CaCO3 and 0 mg/l of Met that had significant differences with other treatments. For chlorophyll a content, there were not significant differences among 0, 1, 5 and 10 mg/l of Met at hardness of 0 while significant and considerable reduction was observed due to different hardness. Generally, the suitable hardness for S. quadricauda was obtained 150 mg/L CaCO3. In addition, this study illustrated that S. quadricauda has capability of growth on high concentration of Met and low (or without) water hardness.