Carbon dioxide exchange across water-air interface and its influencing factors in middle reaches of Yellow River during winter

River systems strongly contribute to CO(2 )emissions. However, despite numerous reports on gas emissions from ice, the current understanding of CO(2 )exchange of rivers in winter and the factors affecting it is still relatively limited. To shed light on CO(2 )exchange and the factors influencing it for rivers during winter. Based on intensive field measurements using floating chambers, riverine CO(2 )exchange in middle reaches of Yellow River in China was examined. Our results showed net emissions of CO(2 )across the ice-free interface (51.874 similar to 162.478 mg/m(2)<middle dot>h). Compared with other rivers worldwide, the CO(2 )exchange is higher than most major rivers, such as the Lena and Kolyma Rivers. However, at the ice-covered river monitoring site, CO(2 )exchange across the water-air interface exhibited a net uptake, ranging from -36.336 to 0 mg/m(2)<middle dot>h. Furthermore, the relationships between CO(2 )exchange and relevant physicochemical variables showed that CO(2 )emissions negatively correlated with pH and ice thickness and positively correlated with water velocity, wind speed, water temperature, atmospheric temperature, ammonia nitrogen levels, and total phosphorous content. This study is scientifically valuable as the findings provide insight into the CO(2 )exchange pattern that occurs at the water-air interface of rivers during winter both ice-covered and ice-free sites.