Variable Specific Discharge and Its Influence on Mass Export of Carbon, Sulphur, Calcium and Magnesium in a Boreal Forest Catchment

Sammanfattning: Considerable research efforts are made in order to understand the global carbon cycle and how it will affect future climate change and vice versa. To be able to calculate the export of carbon from a certain area, discharge is one of the most important variables together with stream concentrations. Measuring discharge in every catchment would be impossible, as it is both time consuming and expensive. To come around these obstacles, the majority of studies on element export use known discharge data from gauging stations at a single catchment outlet and assumes the same discharge per unit area from nearby catchments, known as the assumption of uniform specific discharge. A few studies in recent years, have come to the conclusion that this questionable assumption can lead to large errors in estimated discharge volumes and it should therefore be reconsidered.This study aims to analyse how the export of elements changes if actual measured variable discharge is applied in comparison to uniform specific discharge. The results of this study shows that the assumption of uniform discharge leads to an overestimation of the export of dissolved organic carbon (DOC), sulphur, calcium and magnesium from forest-dominated catchments by up to 30%. At the same time this assumption leads to an underestimation of export from wetland-dominated catchments by up to 26% over a five year period.