Predicting Metal Release from Peatlands in Sudbury, Ontario, in Response to Drought
2015
Watmough, Shaun A. | Orlovskaya, Liana
Peatlands are often regarded as metal repositories, but under drought conditions may switch from sinks to sources of metals and contaminate downstream ecosystems. To evaluate whether the release of metals into soil solution in peatlands is predictable using simple, widely available soil parameters, six peatlands, with varying levels of metal contamination, including a previously limed peatland, were sampled around the Sudbury, Ontario, region, and were subjected to simulated drought. The simulated drought lowered soil water pH and dissolved organic carbon (DOC) concentrations, which is consistent with field observations. Metal partitioning (K d) values for Co, Mn, Ni, and Zn, with just one exception at one peatland, could be significantly predicted by just the pH of the soil water, although the strength of the relationship varied considerably among sites. The metal speciation model WHAM VII predicted that the free metal ion concentration of all metals tested, including Cu and Al, increased significantly with decreasing pH. At the same time, DOC-bound metal concentrations were predicted to decrease as DOC levels were lower, which for metals with strong organic matter affinities (Cu and Al) offset the increase in free metal ion concentration in soil solution following summer drought. Climate change forecasts for more frequent and sustained droughts may promote metal release from peatlands and increased mobilization to surface waters, and importantly, for some metals, the potential toxicity of the metals released from peatlands may increase to a greater extent than expected from increases in total metal concentrations because of decreased DOC following drought.
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