Characterizing the river water quality in China: Recent progress and on-going challenges

Area of Science:

• Environmental Science
• Water Quality
• Ecology

Background:

• Anthropogenic activities like food production and urbanization significantly impact China's river water quality by altering natural hydrological and nutrient cycles.
• River impairment, defined as water quality worse than Class V (GB3838-2002), is a major concern across China's river systems.

Purpose of the Study:

• To investigate national-scale spatial patterns of river water quality from 2003-2018.
• To identify the key anthropogenic and natural drivers of river impairment, focusing on nutrient pollution.

Main Methods:

• Compiled a comprehensive 16-year dataset (2003-2018) of river water quality, watershed characteristics, and meteorological data from 2424 sites.
• Utilized Bayesian modeling to analyze the relationships between nutrient levels (Total Phosphorus and Ammonia-Nitrogen) and various environmental/anthropogenic factors across six major river basins.

Main Results:

• Observed moderate mitigation of cultural eutrophication, decreased anoxic conditions, and alleviated heavy metal pollution over the study period.
• Identified significant spatial disparities, with eastern China exhibiting poorer water quality (17.2% impaired sites) compared to western China (4.6% impaired sites).
• Total Phosphorus (TP) and Ammonia-Nitrogen (NH3-N) were the primary causes of impairment (>85%), driven predominantly by anthropogenic factors (82.5% for TP, 79.5% for NH3-N), particularly urbanization and farmland extent.

Conclusions:

• Despite some improvements, significant challenges remain in eradicating eutrophication and achieving acceptable ecological conditions in China's rivers.
• Remedial strategies must be site-specific, considering landscape, climate, non-point source pollution, and internal nutrient loading.