Although northern peatlands represent a globally significant reservoir for carbon, considerable uncertainty exists concerning solute transport systems within large (>1000 km2) peat deposits. We therefore delineated geochemical gradients linked to groundwater recharge and discharge along a 6 km transect within the 1200 km2 Red Lake Peatland of northwestern Minnesota. We used ratios of Ca/Mg and 87Sr/86Sr to distinguish discharge of calcareous groundwater (∼1.4 and 0.7155, respectively) to the peatland from the mineral substratum along a topographic gradient from a bog crest downslope to an internal fen water track and bog islands. In contrast, the stable isotopes of the porewaters (δ18O from −12.8 ‰ to −7.8 ‰) show that the active pore-spaces in these peat profiles have been flushed by recharge from the near-surface peat. We hypothesize that back-diffusion of groundwater-derived solutes from the peat matrix to active pore-spaces has allowed the geochemical signal from paleo-hydrogeologic discharge to persist into the current regime of dilute recharge. This effect has not been observed previously on the landform-scale and has important implications for carbon cycling in peatlands.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation (Award 0628611 ) and Syracuse University . We would like to thank Melody Scalfone and Xiangyu Mu for assistance in the field, and helpful comments on this manuscript by Don Rosenberry. We also thank the Minnesota Department of Natural Resources for use of near-site staging facilities and Lee Andrew and Will Cowen of Brainerd Helicopter Company for helicopter access to field sites. This paper benefitted from the comments of three anonymous reviewers.
- Matrix diffusion