Elevated Heavy Metal Contents in Marsh Soils Affected by Seasonal Saline Run-off from Adjacent Roadways.

Urban wild lands are often unintentional receptacles of waste materials originating from anthropogenically altered landscapes and human activities around them.  The University of Wisconsin Arboretum is renowned as one of the world’s earliest ecological restoration sites, hosting the Curtis Prairie, a tall grass mixed native forb wild land in the center of an expanding urban area in Madison, Wisconsin.  The UW Arboretum also hosts extensive areas of wetlands interfacing Lake Wingra and connected to detention ponds that buffer the natural areas from effects of road run-off from heavily traveled streets and highways that bound the Arboretum on nearly all sides.  A study undertaken to evaluate edaphic conditions favoring expansion of invasive Phalaris arundinacea (reed canary grass) revealed elevated levels of heavy metals (Cu and Zn) in the Curtis Prairie subsoils.  In further evaluations of a large marsh area to the east of Curtis Prairie, highly elevated heavy metals levels were attributed to the exacerbating effects of seasonal saline waters from heavily salted roadways adjacent to that marsh.  Here, total Cu, Cr, Pb, and Zn maxima ranged from 3 to 15 times greater than background levels.  Lead levels in at least one location approached the USEPA “level of concern” for exposure to children (300 ppm).   The relatively high concentrations of metals in this marsh probably originate from local sources, including road debris, old industrial waste materials and buried Cu cables for a broadcasting antenna that used the sub-saline conditions of the marsh to boost its output signal.  Since many broadcasting antenna facilities are located in or near wetlands, which are considered marginal use areas, the presence of aging buried cable fields associated with these facilities may be overlooked as sources of localized point contamination, especially when salt influxes can create conductive electrolyte solutions that facilitate metal solubilization.