ABSTRACT
This chapter examines considerations relevant to the reduction of selected trace metals in treatment marshes. For many of the trace metals, information is very scarce or absent. The spectrum of commonly measured trace metals is represented by the databases for urban runoff systems. A number of trace metals are essential micronutrients at low concentrations, but some trace metals may occur in source waters at concentrations that are toxic to sensitive organisms. Depositing sediments are capable of adsorbing significant quantities of trace metals directly, or indirectly through the accumulation of coatings such as organic matter, iron, and manganese oxyhydroxides, which will in turn act as trace element collectors. Wetland plants have trace amounts of nickel in their tissues, which are the lowest of those for the heavy metals. Wetland plants have trace amounts of cadmium in their tissues, typically with higher values for roots and rhizomes than for aboveground plant parts.
