Small natural wetland ameliorating zinc-contaminated water

This small wetland measured approximately 11.5 x 3.5 x 0.2 m. It had only one source of water, located on the right in the foreground, and one discharge point, in the background. The water entering this wetland had zinc concentrations measuring 3.2 ppm (mg/L). The water exiting the wetland measured 0.3 ppm zinc. The pH along the water flow path ranged from 6.4 to 6.6.

Image of a small natural wetland

Several other metals were retained by this small wetland. Their concentrations in sediments and in plants (aboveground) are presented in the table below.

Metal concentrations (ppm) in plant tissues and sediments of wetland receiving mine drainage.
Metal
Plants
Sediments
Cadmium
0.50
66
Copper
2.81
110
Lead
<2.5
98
Zinc
102
10,345

In a natural wetland with the same vegetation, but unimpacted by mine drainage, metal concentrations were as follows:

Metal concentrations (ppm) in plant tissues and sediments of wetland unimpacted by mine drainage.
Metal
Plants
Sediments
Cadmium
<0.50
23
Copper
4.27
46
Lead
4.7
<50
Zinc
132
1,114

Note that despite the higher metal levels in sediments of the wetland receiving mine drainage, zinc being present at ten times higher concentrations, plant tissues in both wetlands have essentially the same metal concentrations. Clearly, metal uptake did not occur. This could be because the metals were biologically unavailable, or because the plants were actively regulating their uptake.

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Last modified Sunday, November 03, 1996 3:58:48 PM