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Laurie Stockmeier Photos by Terre and Laurie
A calcareous fen is an alkaline peatland nourished by groundwater seepages and springs rich in calcium and magnesium bicarbonates that are sometimes commingled with calcium and magnesium sulfates. These compounds precipitate out as the groundwaters rise to the surface and warm, resulting in a calcareous fen substrate that is mineral-rich and alkaline. The calcareous fen is one of the rarest wetland types in North America. However, thanks to an optimal confluence of dolomitic bedrock, climate, and recent glaciation, a number of calcareous fens occur in southeastern Wisconsin. The Bluff Creek and Clover Valley Fen State Natural Areas support several pristine calcareous fens.
Bluff Creek State Natural Area is located in Walworth
County on Highway P, 2.1 miles South of Highway 12. Calcareous
fens and springs are found in 6 areas of the site and represent
18 of the total 296 acres. |
The
Calcareous Fens of Bluff Creek and Clover Valley 
Calcareous
fen flora must tolerate harsh, cold, wet, alkaline, high-calcium
conditions. Nonetheless, calcareous fen flora is typically diverse.
Calcareous fen denizens include shrubby cinquefoil (Pentaphylloides
floribunda), fen grass-of-Parnassus (Parnassia glauca), fen star
sedge (Carex sterilis), and marsh muhly (Muhlenbergia glomerata).
Among other plants, the Bluff Creek calcareous fens harbor the
small white lady's slipper (Cypripedium candidum) currently listed
as threatened in Wisconsin. At the Clover Valley fens you can
find the low nutrush (Scleria verticillata), a state species of
special concern. Also found in both sites are the state threatened
beaked spike rush (Eleocharis rostellata), false asphodel (Tofieldia
glutinosa), tussock bulrush (Scirpus cespitosis), and several
species of special concern. When compared to other plant communities
of the midwest, calcareous fen communities support a disproportionately
high number of endangered, threatened and rare species.