The humble beaver could hold the key to saving our water, according to a new research that has found how their dam building skills protect the rivers threatened by climate change.

The research, done on rivers in Colorado, found the wooden barriers built by beavers raise water level upstream. As it builds up, the water flows into surrounding soils and secondary waterways. These acts separate out extra nutrients and pollutants before water reenters the main channel downstream.

Extreme weather events, such as severe storms, impact water quality in major river systems. Droughts and floods are becoming more frequent, and the scientists have also found they are contributing to an increase in the American be aver in the US, and consequently an explosion of dam building.

The team chose to monitor a 40-kilometer stretch of the East River. They reviewed data on water levels gathered hourly by sensors fixed in the river and the areas along the river.

They also collected water samples, including from below the ground’s surface to monitor nutrient and pollutant levels. The researchers compared water quality along the stretch during a historically dry year, to water quality the following year when water levels were unusually high. They also compared these year-long datasets to water quality during the nearly three- month period, starting in late July 2018, when the be aver dam blocked the river.

The study revealed the dams increased nitrate (硝酸盐) by nearly 50% by increasing the pressure of the water flow upstream 10 times over, which pushed more water out into the surrounding areas. This decrease in nitrates, which are absorbed and digested by tiny organisms in the soil, helped increase the oxygen content and quality in the rivers.

Beavers’ handiwork is responsible for the land they love.

【小题1】What do the wooden barriers created by beavers act as?

A．Waterways.

B．Samples.

C．Dams.

D．Sensors.

【小题2】What is the direct result of frequent droughts and floods?

A．More dams emerge on the river.

B．More American beavers appear in the US.

C．More pollutants are removed from the river.

D．More oxygen is created in the river.

【小题3】Why did the researchers collect water samples from below the ground’s surface?

A．To keep an eye on the water quality.	B．To compare water quality of the stretch.
C．To reveal the damage caused by floods.	D．To save the river from drying up.

【小题4】What can be a suitable title for the text?

A．Organisms help decrease nitrate.

B．Beavers contribute to climate change.

C．Extreme weather catches researcher’s eyes.

D．Beavers help protect rivers against climate change.