The Yellow River, often called the birthplace of Chinese culture, has seen big changes in its environment. This is mostly because of fast city growth, which has led to more wastewater going into the river. This has changed how the water flows and its quality.  The Dahei River, a key part of the Yellow River, has been watched closely for almost ten years. Over 20 spots in this river were checked for seven important water quality signs. These signs were looked at in places with different amounts of human activity and various weather conditions. The checks happened during wet, normal, and dry years.

The results showed that the best way to understand how water quality changes over time is with a simple line graph. This method was very reliable, with scores from 0. 82 to 0. 99. The water quality signs changed slowly over time. When looking at different places, the best way to show changes was with a curve that goes up quickly. This also had high reliability scores, from 0. 85 to 0. 99. This means that water quality can suddenly get worse in some places.  In areas with lots of human activity, the water quality was always worse than in quieter areas. The bad signs were 1. 66 to 63. 25 times higher in busy areas.  Water quality was also worse during wet years. For example, the amount of total nitrogen was too high in all parts of the river during wet years. In normal years, 81. 05% of the river had too much nitrogen. In dry years, this number was even higher, at 90. 36%.

This information is very useful for people who manage the river. It shows that they need to focus on fixing water quality problems and stopping pollution.  It is important to note that the Yellow River is not the only river facing these issues. Many rivers around the world are dealing with similar problems because of city growth and climate change. This makes the findings from the Yellow River even more important. They can help other places understand and fix their own water quality problems.

The Yellow River's Water Quality: A Decade of Change

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