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Climate change and human activities have redefined seasonal river water quality patterns, yet their respective impacts remain unclear. Here, we propose a novel trend-based metric, the T-NM index, to isolate asymmetric human amplification and suppression effects across 195 natural and 1540 managed watersheds in China (2006–2020). Consistent trends in 52–89% of watersheds suggest climatic dominance, while anthropogenic drivers intensified or attenuated trends by 22–158% and 14–56%, especially in summer. Four independent multivariable models simulated seasonal COD and DO concentrations. Attribution analysis showed that seasonal factors explained 47.08% of the variation, while rainfall (25.37%) and slope (17.40%) accounted for COD and DO changes in natural watersheds; in contrast, Shannon Diversity Index (11.58%) and Largest Patch Index (10.66%) dominated in managed watersheds. This study establishes a generalizable framework for distinguishing natural and anthropogenic influences, offering key insights for adaptive water quality management under future climatic and socio-economic transitions.
Zhang et al. (Mon,) studied this question.