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. Michaëlis-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 Michaëlis-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 Michaëlis-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.