DNA metabarcoding reveals human impacts on macroinvertebrate communities in polluted headwater streams: Evidence from the Liao River in northeast China.

Headwater streams are a hotspot of freshwater biodiversity, carrying indispensable resource pools of aquatic species. However, up to now, there remain many challenges to accurately and efficiently characterize the responses of this vulnerable ecosystem to human-induced changes. Here, we collected macroinvertebrate data from 12 different headwater streams in the Liao River of northeast China by DNA metabarcoding approach, to reveal biodiversity changes and ecological thresholds affected by human beings. Our data showed that the community composition and structure of headwater streams had unique and significant differences under human impacts, and 5-day biological oxygen demand (BOD5) and ammonia nitrogen (NH3-N) were the key variables explaining the variation in community structure. Although α diversity had a unimodal relationship with nutrients and organic loads, β diversity and its turnover component (species replacement) increased significantly. In addition, 22 and 33 indicative taxa were identified to have significant negative responses to BOD5 and NH3-N, respectively, and the change points derived from Threshold Indicator Taxa Analysis (TITAN) for the negative response of their frequency and abundance were BOD5 >3.42 mg/L and NH3-N >0.14 mg/L. Overall, this study reveals the biodiversity changes in headwater streams from the aspects of α and β diversity, and also determines the thresholds of BOD5 and NH3-N pollutants for one reach at one date from 12 headwater streams, suggesting the potential of DNA metabarcoding approach for threshold analyses in headwater streams.