Uptake of bromide by two wetland plants (Typha latifolia L. and Phragmites australis (Cav.) Trin. ex Steud).

The successful use of bromide (Br-) as a conservative tracer for hydrological tests in wetland systems requires minimal Br- loss due to plant uptake. The uptake of Br- by two wetland plants, cattail (Typha latifolia L.) and reed grass (Phragmites australis (Cav.) Trin. ex Steud), was investigated in greenhouse flow-through microcosms. Concentrations of Br- and other pertinent constituents in sediment pore water were measured at 2 cm depth increments in the sediment column. The vertical Br- concentration profiles in the sediments clearly revealed Br- uptake by T. latifolia and by P. australis. X-ray spectroscopy studies of bromine in plant samples revealed the accumulation of Br- in root and leaf tissues. Plant transpiration was found to significantly concentrate dissolved species in sediments and was accounted for in the calculations of Br uptake rates. Michaelis-Menten kinetics satisfactorily describe Br- uptake by T. latifolia. The uptake of Br- by P. australis, however, showed unique features that could not be described using Michaelis-Menten kinetics. The addition of chloride (Cl-) effectively inhibited Br- uptake, and the uptake of Cl- and Br- by T. latifolia was shown to follow dual-substrate Michaelis-Menten kinetics. Results of this study indicate that the use of Br- for tracer experiments in vegetated wetland systems should be evaluated with great caution.