Modeling the dissolved organic carbon output from a boreal mire using the convection‐dispersion equation: Importance of representing sorption

Abstract

In this paper we present a model of the dissolved organic carbon (DOC) concentrations and fluxes in mire water based on the convection‐dispersion equation. The dynamics of sorbed, potentially soluble organic carbon (SPSOC) in the peat matrix are simulated in parallel with DOC. First, the model is applied solely to stagnant water conditions in order to interpret the results of laboratory peat incubations, with the focus on sorption processes. Some important model parameters are derived using literature data complemented by information from new incubation experiments. Second, the model is fully applied to simulate the DOC concentrations in the outlet of a steam draining a small headwater mire in northern Sweden during the period 1993–2001. A relatively good model fit (mean bias error (MBE) = −0.6–2.2 mg L−1, Willmott index of agreement d > 0.7 for the daily concentrations) was found for all the categories of stream discharge, except periods with very low flow (q < 0.3 mm d−1). When seeking explanations for the interannual variability in DOC concentrations, we, like previous authors, could find the influence of temperature, flow path, and intensity. However, the model has helped to demonstrate that the system also has a “memory”: the store of sorbed, potentially soluble organic carbon in a year affects the DOC concentrations and fluxes in the following year.