Dissolved organic carbon load variability in the rainfall season dominated its interannual variability in the snowmelt driven basin: Evidence from 41 years data of headwater streams

Abstract

AbstractNumerous reports have observed variations of dissolved organic carbon (DOC) under the changing environment. From the DOC load variability perspective, however, how much of the variability in DOC load occurred among different seasons, and which season was most synchronized with the interannual variability remains unknown. The weekly DOC concentration and daily discharge records from four headwater streams with long‐term (1978–2018) records in the snowmelt driven basin of Harp Lake, south‐central Ontario, Canada, were used to answer these issues. We also examined the contributions of variabilities in discharge and DOC concentration to the variability in DOC load. We found that the variability of DOC load in the rainfall season (autumn) instead of snowmelt season (spring) was most closely synchronized with its interannual variability, suggesting that if the DOC variability in the rainfall season stabilized, the interannual variability would be more stable. The interannual variabilities for discharge, DOC concentration and DOC load showed an insignificant decreasing trend in the monitored 41 years, and the respective contributions of the variability trend of discharge and DOC concentration to DOC load in rainfall season increased from 28.82% to 144.58% and decreased from 71.18% to −44.58% because the change trend of discharge variability was greater than that in DOC concentration. This study provides a case information in determining which factors contribute most to the variability of DOC load in the watershed, and which season may dominate its variability throughout the year.