Enhanced Role of Streamflow Processes in the Evolutionary Trends of Dissolved Organic Carbon
Jiefeng Wu, Huaxia Yao
Abstract
Investigating dissolved organic carbon (DOC) dynamics and drivers in rivers enhances the understanding of carbon–environment linkages and support sustainability. Previous studies did not fully consider the dynamic nature of key drivers that influence the long-term changing trends in DOC concentration over time (the controlling factors and their roles in DOC trend can undergo alterations over time). We analyzed 42 years (1979–2018) of hydrometeorology, sulfate SO 4, and DOC data from a 5.42 km 2 watershed in central-southern Ontario, Canada. Our findings reveal a significant ( p ≤ 0.01) overall increase in DOC concentrations, mainly due to the coevolution of SO 4 and streamflow trends, especially the extreme flows. Over the 42-year period, the changing trend of streamflow (especially the extreme high or low flows) have significantly ( p < 0.05) intensified their influence on DOC trends, increasing by an average of 30%. Conversely, the impact of SO 4 has weakened, experiencing an average decrease of 32.6%. The upward trend in the annual average DOC concentration is attributed to the increasing number of maximum flow days within a year, while the decreasing trend in the number of minimum flow days has a contrasting effect. In other words, changes in maximum and minimum flow days have a counteracting effect on the DOC concentration trends. These results underscore the importance of considering the effects of altered streamflow processes on carbon cycle changes under evolving environmental conditions.