Identifying the Impacts Of Water Quality On Macroinvertebrate Degradation In The Taizi River With A Reconsideration Of Water Quality Grades In China

The degradation of macroinvertebrate communities was studied in the Taizi River in northeast China. By applying cluster analysis (CA) and non-metric multidimensional scaling (NMS) analysis, macroinvertebrate communities were classified into four groups, or clusters. Geological variation of macroinvertebrates was confirmed from cluster I to cluster III, corresponding to the upstream mountainous regions and downstream floodplains, respectively. Meanwhile, the degradation of water quality and macroinvertebrate communities was identified from cluster I to cluster IV. By applying indicator species analysis, the dominant indicator species confirmed the degradation of macroinvertebrates, resulting from low water quality found among different clusters. Canonical correspondence analysis (CCA) identified the geological variable of altitude, the physical variable of temperature, and water quality variables of conductivity, suspended solids, dissolved oxygen, pH, ammonia, and total nitrogen as the most important variables significantly affecting macroinvertebrate community composition. The NMS methods were used to assess the effects of water quality levels on the status of the macroinvertebrate community. The water quality variables determined as significant in the CCA analysis, in addition to total phosphorus, were classified into different grades according to the Chinese surface water standards. The degradation of macroinvertebrates was identified when the concentrations of total phosphorus and ammonia were lower than the third grade. Dissolved oxygen values higher than 7.5 mg/L gave a slight indication of macroinvertebrate status. A conductivity value of 400µs/cm was recommended as the threshold value, above which the macroinvertebrate community degrades in the Taizi River. Due to persistently high concentrations of total nitrogen throughout the watershed, the spatial effects of the nutrient on community degradation could not be elucidated in the Taizi River.