Changes in the flux of dissolved organic carbon (DOC) into and out of lakes are important to the biogeochemistry of aquatic environments. The ability to estimate or model DOC fluxes and concentrations in lakes and other surface waters is of great benefit for investigations of aquatic systems. Spatial attributes of catchments were derived using GIS techniques and combined with published DOC mass balance models from 20 small study catchments and seven lakes to estimate DOC concentrations for hydrologically connected lakes (i.e. connected by surface or ground waters) of the Muskoka River Watershed, a large tertiary watershed (904 lakes) in southern Ontario. Predicted DOC concentrations were very dependent on the method used to estimate wetland area. When a Rapid Assessment Technique (RAT) was used to estimate wetland area, predicted and observed DOC concentrations were linearly related. Most of the DOC residuals were < 1 mg L−1. Inclusion of riparian wetlands or small lakes in the contributing catchments resulted in a slight improvement of model predictions, but not beyond the variability of the model. Model predictions of DOC were reasonable (according to model fit and residuals), especially considering it was a regional-scale study, but substantial variability was still unaccounted for. Applying the model to other regions with similar landscapes (i.e. other watersheds on the Precambrian Shield in North America and Nordic countries) is feasible.

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