Effect of water level changes in the middle reaches of the Yellow River in summer on CO2 emissions from wetlands dominated by Phragmites

Abstract

The purpose of this study was to investigate the effect of water level changes (WLC) in the middle reaches of the Yellow River in summer on CO2 emissions from wetlands dominated by Phragmites. The rate of CO2 emissions (RCE) from soil was measured in some Phragmites wetlands selected along the Yumenkou-Tongguan section in this river’s middle reaches. An artificial recharge experiment was conducted and the data about this section’s water levels for the past 15 years was analyzed. This study found that the water level of this river section changed frequently in the last 11 summers. The effect of WLC depended on air temperature. At low temperatures of between 18.0 and 28.0 °C, WLC contributed to a RCE change from 10.19 mmol·m−2·h−1 to 13.43 mmol·m−2·h−1. When the temperature fell within the normal range of 29.0-35.0 °C, the corresponding changes were from 4.07 mmol·m−2·h−1 to 7.35 mmol·m−2·h−1. When the temperature was higher than 35.0 °C, the corresponding changes increased slightly from 6.47 mmol·m−2·h−1 to 12.41 mmol·m−2·h−1. These suggest that WLC had a considerable effect on CO2 emissions at high and low temperatures. As the water level rose, the RCE increased and then decreased in both types of wetlands. At low temperatures, the most favorable water levels for CO2 emissions were −10 cm and 0 cm. At normal temperatures, the RCE from the two types of wetlands decreased with rising water level. At high temperatures, the most favorable water level was −60 cm for Phragmites wetlands. These results demonstrate that frequent WLC can slow CO2 release from Phragmites wetlands along the middle reaches of the Yellow River. Therefore, research on the effect of WLC on CO2 emissions has practical significance.