This study was to evaluate the lichen flora of St. Croix National Riverway (SACN) with respect to the air quality. Part of SACN is along the border of Minnesota and Wisconsin and the headwaters are entirely within Wisconsin. Parts of the lower SACN are downwind and near several pollution sources,
including the metropolitan area of Minneapolis and St. Paul.
Lichens are good indicators of air quality and this project uses lichens as air quality indicators.
Field work was done in 1988 and 1990 when 2327 collections were made at 77 localities. At some localities additional material of Parmelia rudecta was collected for chemical analysis. While collecting at each locality observations were made about the general health of the lichens.
The species list includes 265 species collected for this study and an additional 20 species reported by Fink but not
found by me. There were 72 species collected only once in the study. This large number of rare species is probably due to the long length of the park. There were 18 species species with a distinctly northern distribution (from Grantsburg north). Another group of 16 species were found from just south of Taylors Falls north to the upper end of the park. A group of 10 species had a southern distribution extending from about Taylors Falls south to Prescott. There were also a number of species found only on the basaltic rocks around Taylors Falls.
Most of the species were found the whole length of the park in suitable habitats.
Some lichens were found in this study that are of special significance. Parmelia stuppea, a species on the Minnesota
Threatened & Endangered list, was thought to have been eliminated from the region but was found in Minnesota at the locality four miles south of Taylors Falls. This is the first modern record for this species in Minnesota. Sticta weigelei, another rare species was found at Norway Point Landing in the cedar swamp. This species was previously known from northern Minnesota and is probably a new record for Wisconsin.
Parmelia rudecta was collected at ten localities for elemental analysis. The sulfur levels range from 620 ppm to 1580 ppm for all samples with the higher levels at the
southern end of the park and also at Namekagon Dam (at the most northern end). There are no known sulfur sources near the
northern end of the park and no explanation is available for this high sulfur level. The higher levels of sulfur at the southern end (Hudson to Kinnickinnic SP) might be due to
industrial activity around Minneapolis/St. Paul or the King Power plant near Hudson. From Taylors Falls north sulfur levels are normal and there are no obvious trends.
Wetmore CM. Lichens and air quality in St. Croix National Scenic Riverway. Final Report. 1991:1-40.
1 PDF computer file (38 pages; 2 pages of tabulated data, 19 pages of maps; 2 pages of graphs)
National Park Service
Wetmore, Clifford M..
Lichens and air quality in St. Croix National Scenic Riverway: Final Report..
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