HYDROCHEMICAL CHARACTERISTICS OF A RECLAIMED SUBURBAN WETLAND, MENASHA, WISCONSIN

The Heckrodt Wetland Reserve, on the north shore of Lake Winnebago near Appleton WI consists of a natural wetland and a reclaimed industrial landfill. The area is bordered on three sides by developed land, and is the last vestige of an extensive natural wetland system that once bordered the lake.

Since March of 1999, shallow (1 to 2 m) ground water samples have been collected and analyzed to determine chemical trends associated with hydrologic events. Four automated wells and four sand point wells provided access to groundwater samples and continuous hydrologic monitoring. The wells form an 800 m transect from the beach on the south end to an adjacent property on the north end. Hydrologic data show that from May through February, ground water flows from the adjacent lake into the wetland. After the spring thaw in early March, melt water input to the wetland, along with an artificially lowered lake level, causes a reversal in flow direction. Water flows out of the wetland until late April when the lake level returns to its normal elevation.

At all four wells, calcium, magnesium, and sodium concentrations are independent of water level. The concentration of trace metals, including copper and iron, responds inversely to water level fluctuation.

Ground water conductivity in the two northerly wells ranged from 1165 to 1654 µS. The other two wells, one of which is located on the lakeshore, yielded conductivity values between 335 and 787 µS. The anomalously high conductivity in the northern wells is possibly related to sulfate (up to 380 mg/L) from alum sludge deposited in the industrial landfill.

Continuing research will investigate in more detail the source of the sulfate contamination and its lateral distribution. A better understanding of the wetland’s hydrology and groundwater chemistry will assist in determining the necessity and direction of the ongoing rehabilitation effort.