Geochemistry and hydrology of a calcareous fen within the Savage Fen wetlands complex, Minnesota, USA

Geochimica et Cosmochimica Acta



Savage Fen is a wetlands complex at the base of north-facing bluffs in the Minnesota River Valley. The complex includes 27.8 hectares of calcareous fen that host rare calciphile plants whose populations are declining in Minnesota. Water and sediment compositions in the calcareous fen were studied to gain a better understanding of the hydrologie System that sustains the rare vegetation. Groundwater in the fen is a calcium-magnesium-bicarbonate type with circumneutral pH values. The groundwater composition is the resuit of interactions among water, dissolved and gaseous carbon species, carbonates, and ion exchangers. Shallow groundwater is distinguished from deep groundwater by smaller concentrations of chloride, sulfate, magnesium, and sodium, and larger concentrations of calcium, bicarbonate, hydrogen sulfide, and ammonium. Magnesian calcite is the prevalent carbonate in unconsolidated sedimentary fill beneath the fen and is an important source and sink for dissolved calcium, magnesium, and inorganic carbon. Calcite concentrations just below the water table are small because aerobic and anaerobic oxidation of organic matter increase the partial pressure of carbon dioxide (PCO2), decrease pH, and cause calcite to dissolve. Thick calcite accumulations just above the water table, in the root zone of calciphile plants, result from water table fluctuations and attendant changes in PCO2. Groundwater beneath Savage Fen recharges in lakes and ponds south of the fen and upwells to the surface within the fen. Water at the water table is a mixture of upwelling groundwater and water near the surface that flows downslope from higher elevations in the fen. Changes in oxygen and hydrogen isotope compositions of shallow groundwater indicate that the proportion of upwelling groundwater in shallow groundwater decreases downgradient in the calcareous fen. Encroachment of reed grasses into the calcareous fen may reflect human-caused disturbances in the recharge area.

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Publication type Article
Publication Subtype Journal Article
Title Geochemistry and hydrology of a calcareous fen within the Savage Fen wetlands complex, Minnesota, USA
Series title Geochimica et Cosmochimica Acta
DOI 10.1016/0016-7037(94)90091-4
Volume 58
Issue 16
Year Published 1994
Language English
Publisher Geochemical Society
Publisher location Oxford
Contributing office(s) Minnesota Water Science Center
Description 15 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geochimica et Cosmochimica Acta
First page 3353
Last page 3367
Country United States
State Minnesota
Other Geospatial Savage Fen wetlands complex
Online Only (Y/N) N
Additional Online Files (Y/N) N
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