SULPHATE DYNAMICS IN RELATION TO GROUNDWATER–SURFACE WATER INTERACTIONS IN HEADWATER WETLANDS OF THE SOUTHERN CANADIAN SHIELD
✍ Scribed by K. J. DEVITO; A. R. HILL
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 290 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0885-6087
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✦ Synopsis
The spatial and temporal distribution of sulphate (SO 4 ) concentrations in peat pore water and the outlet streams of two forested swamps was related to variations in the magnitude of upland runo, wetland water levels and ¯ow path. The swamps were located in headwater catchments with contrasting till depths typical of the southern Canadian Shield. Inputs of SO 4 from shallow hillslope tills and streams showed little seasonal variation in either source or concentration in both swamps. Sulphate dynamics at the outlet stream re¯ected hydrological and biogeochemical processes within the valley wetlands, which in turn were partly controlled by catchment hydrogeology. During high runo, maximum water table elevations and peak surface ¯ow in the swamps resulted in upland inputs largely bypassing anoxic peat. Consequently, SO 4 concentrations of 8±10 mg/l at the swamp outlets were similar to stream and groundwater inputs. During periods of low ¯ow, concentrations of SO 4 at the swamp outlets declined to less than 3 mg/l. At this time lower water table elevations resulted in increased interaction of input water with anoxic peats, and therefore, SO 4 reduction. Contrasts in till depth and the nature of groundwater ¯ow between catchments resulted in dierences in SO 4 dynamics between years and swamps. In dry summers the absence of groundwater inputs to the swamp in the catchment with thin till resulted in a large water table drawdown and re-oxidation of accumulated S, which contributed to maximum SO 4 concentrations (up to 35 mg/l) during storm runo. Continuous groundwater input to the swamp in the catchment with deeper till was critical to maintaining saturated surfaces and ecient SO 4 retention during both dry and wet summers. A conceptual model of wetland SO 4 retention and export, based on catchment hydrogeology, is developed to generalize the SO 4 dynamics of valley bottom wetlands at the landscape scale.