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The Effects of pH, Flow Rate, and Carbon Supplementation on Manganese Retention in Mesocosm Wetlands

Dep. of Biology, Pennsylvania State Univ., University Park, PA 16802;

William R. Wenerick

13 Castlevale Circle, Irmo, SC 29063-2600;

Frederick M. Williams

Dep. of Biology, 208 Mueller Lab, Pennsylvania State Univ., University Park, PA 16802;

Paul J. Wuest

Dep. of Plant Pathology, 310 Buckhout Lab, Pennsylvania State Univ., University Park, PA 16802.

^* Corresponding author (lrs{at}nevada.edu).

ABSTRACT

In an effort to obtain design parameters, a wetland mesocosm experiment was conducted to determine the effects on Mn retention of flow rate, inlet pH, and C supplementation. Sustained Mn retention was not achieved under reducing conditions when spent mushroom substrate was used as a substrate irrespective of flow rate, inlet pH, and C supplementation regimes. However, a lowered flow rate resulted in many significant effects on outlet water chemistry, including lower outlet Mn concentrations, higher outlet pH, lower outlet acidity, higher outlet alkalinity, higher outlet sulfide, lower outlet sulfate, and lower outlet redox potential. Supplementation of the wetlands with dairy whey resulted in marginally lower outlet Mn concentrations and marginally higher outlet sulfide levels. Wetlands receiving a neutral pH had lower outlet acidity, higher outlet alkalinity, lower outlet sulfate, but equivalent outlet Mn concentrations to wetlands receiving an acidic pH. Sulfate reduction was stimulated by reducing flow rates and metal loads. Metal extractions indicated that most of the Mn was retained as exchangeable Mn (37%), carbonate-bound Mn (30%), and oxide-bound Mn (21%), with most (64%) of the Mn retained at the surface of the wetland. The dominant form of Mn found in the subsurface substrate samples was exchangeable Mn (44%), indicating that stable forms of Mn did not form under reducing conditions.

currently at Dep. of Biological Sciences, Univ. of Nevada, Box 454004, Las Vegas, NV 89154-4004

Received for publication April 11, 1994.