Assessment of chemical integrity based on ecological thresholds in one of the largest basins in China

Abstract

Chemical integrity plays a crucial role in maintaining the ecological integrity of aquatic ecosystems. Despite its significance, assessments of ecological integrity often prioritize biological evaluations, leading to infrequent and inadequate scrutiny of chemical integrity. Additionally, a comprehensive framework for separately assessing chemical integrity has not been established. To address this issue, we established a new index for evaluating chemical integrity, achieved through indicator screening, normalization, and weight assignment. Combined with the threshold indicator taxa analysis (TITAN) and Pearson correlation analysis, main evaluation indicators and their indicator species were identified and the corresponding response threshold was determined. These thresholds were then applied to improve the normalization method, with weights determined by indicator species proportions. This index was applied to evaluate the chemical integrity of the Huai River Basin, which is one of the largest basins in China. The results indicated that ammonia nitrogen (NH3-N), nitrate nitrogen (NO2-N), pH, and turbidity (Turb) were identified as the core parameters for evaluating chemical integrity. The conventional normalization method (max–min normalization) led to overestimation of the assessment results, whereas improved normalization method based on ecological threshold yielded better and more reasonable results. This study provided a reference for the selection of appropriate indicators and improvement of normalization method to better assess chemical integrity. And it would become a useful tool for monitoring and rehabilitating the chemical integrity in such basins.