Contributions of streamflow variability, concentration-discharge shifts and forested wetlands to terrestrial-aquatic solute export in Precambrian Shield headwater catchments

Hydrological and biogeochemical processes in terrestrial watershed compartments are an important source of short- and long-term physico-chemical dynamics in Precambrian Shield headwater lakes. In this study, a residual analysis of concentration discharge models based on the composite method of stream solute flux estimation was conducted to quantify two key factors contributing to terrestrialaquatic export of sulphate (SO42-), dissolved organic carbon (DOC), hydronium ion (H+) and colour for ten Precambrian Shield catchments in three lake basins: (1) advective transport capacity, as influenced by variations in runoff, and (2) the terrestrial supply of mobilizable solute, as influenced by terrestrial biogeochemical cycling and associated controlling variables. Overall, annual fluxes associated with mechanism (2) were approximately equal to those associated with mechanism (1) in driving inter-annual deviations from long-term mean annual solute export. There was considerable variation in the relative contributions of these mechanisms among solutes and watersheds, and % wetland area could not explain these differences. However, mean annual terrestrial-aquatic fluxes of DOC and colour were highly correlated with % wetland area, as were inter-annual variations in mean annual flux. The corresponding relationships between H+ and % wetland area were moderate but also significant. Annual fluxes SO42- were negatively associated with wetlands but there was no relationship between inter-annual variations in mean annual SO42- flux and % wetland area. The contribution of forested wetlands to annual flux variability for DOC, colour and H+ was primarily driven by inter-annual differences in runoff and associated mobilization of large solute pools within these critical source areas of organic carbon and acidity. Copyright (C) 2011 John Wiley & Sons, Ltd.