Simulation of monthly dissolved organic carbon concentrations in small forested watersheds

Dissolved organic carbon (DOC) plays an important role in both terrestrial and aquatic ecosystems. In-stream DOC concentration is an important indicator of water quality, because high in-stream DOC concentrations naturally lead to reductions in dissolved oxygen. Recent studies indicate that DOC is responsible in transferring toxic metals (e.g., mercury, Hg) from terrestrial sources to aquatic ecosystems. However, assessing DOC or Hg dynamics is fairly challenging as a result of extreme spatiotemporal variation. Typically, process-based models with short-to-medium term temporal resolutions are required to model DOC and Hg dynamics. The objective of this research is to develop a watershed-based monthly DOC production and export model that integrates the treatment of (i) forest-litter decomposition (DOC production), (ii) wetland-to-watershed area ratio (DOC storage), and (iii) relevant hydrological processes (DOC export) in the simulation of in-stream concentrations. Model results are compared against DOC concentrations collected at the stream outlets of two separate forested watersheds in Kejimkujik National Park, Atlantic Canada. Comparisons for the two watersheds show that predicted monthly DOC concentrations are generally in good agreement with field-based concentrations, giving R2-values of 0.61 and 0.63 for Pine Marten Brook watershed and 0.72 and 0.75 for Moose Pit Brook watershed for model calibration and validation, respectively.

► DOC production and export is modelled for two forest-dominated watersheds.
► DOC production depends on forest tree species composition and litter-fall dynamics.
► Variation in litter fall is controlled largely by climate and forest age.
► Less well-drained watersheds export more DOC than well-drained watersheds.