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A mass-balance approach is used to explore the effect of several hydrologic and geographic variables on humic matter concentrations in surface waters of Labrador–Ungava. Water-color measurements from 67 dilute oligotrophic lakes are used to evaluate model predictions of aquatic humus concentration from basin hydrology, catchment vegetation, and internal loss rates. The major trend in water color in the Labrador region — increasing north to south — results from differences in external humus loading from catchment vegetation and soils. Hydrologic influences on aquatic humus concentrations reside in the dilution of catchment drainage by direct precipitation to the lake — effective only when catchments are small — and in water residence time which controls losses due to mineralization and sedimentation.
Daniel R. Engstrom (Wed,) studied this question.