Keywords: 
• total nitrogen /
• total phosphorus /
• insertion algae /
• indicator species /
• habitat optimum value

Abstract: Periphyton is an important part of aquatic communities in rivers and is closely related to habitat water environment factors. This relationship is commonly studied using multivariate statistical analysis. The environmental elements of algal colonies can affect their space-time distribution. However, qualitative analysis can only judge the driving environmental factor, whereas a quantitative analysis can provide accurate information on the relationship between the algal colony and environmental factors (such as nitrogen, phosphorus). This study was based on three entire river basins and investigated 141 stations in Taizi River, Liaoning Province. The quantitative evaluation of the response of the algal colony to nitrogen and phosphorus nutrients (optimum value and threshold) was conducted by thresholds indicator taxa analysis (TITAN) and weighted averaging. Twenty-two indicator species of total nitrogen (TN) were identified by TITAN in the Taizi River basin, among which 13 were negative and 9 were positive response species. Navicula placentula had the highest TN threshold value of 3.68 mg·L^-1 among the negative response species. When the TN content of water reached 3.68 mg·L^-1, most of the periphyton communities no longer produced a significant threshold response except for Navicula placentula. Euglena caudata was the species with the highest TN threshold value of 8.70 mg·L^-1 for a positive response. When the TN content of water reached 8.70 mg·L^-1, most of the periphyton no longer produced a significant threshold response except for Euglena caudata. Among the 19 total phosphorus (TP) index species identified by TITAN in the Taizi River basin, 9 were negative and 10 were positive response species. The negative response species, Cymbella affinis, had the highest TP threshold value of 0.06 mg·L^-1, and when the TP content of water reached 0.06 mg·L^-1, most of the periphyton communities no longer produced a significant threshold response except for Cymbella affinis. The highest positive response was for Melosira granulata with a TP threshold value of 0.19 mg·L^-1. When the TP content of water reached 0.19 mg·L^-1, most of the periphyton communities no longer produced a significant threshold response except for Melosira granulata. Moreover, the optimal range of TN and TP for the periphyton was 0.025～0.47 mg·L^-1 and 0.65～12.14 mg·L^-1, respectively, in the Taizi River basin. Melosira and Nitzschia are suitable for living in water environments with high TP, whereas Gomphonema and Cymbella are suitable for living in those with low TP. Euglena and Nitzschia are suitable for living in water environments with high TN, while Cymbella and Navicula are suitable for living in those with low TN. Through quantitative analysis of the relationship between the algal colony and water environmental factors (nitrogen and phosphorus), we can accurately evaluate the relationship between the algal colony and nutrient content in the Taizi River basin. This study can provide basic data for management decisions and a scientific basis for environmental protection by controlling emissions of nitrogen, phosphorus, and other pollutants.