Paradigms of metal accumulation in rooted aquatic vascular plants

This paper reviews paradigms of metal accumulation in rooted aquatic vascular plants. Radio-tracer studies have demonstrated that root uptake from sediments with subsequent translocation to above-ground tissues is the principal pathway for metal movement. The metal concentration of rooted macrophytes is generally proportional to metal concentrations in the underlying sediments, excluding crystal lattice-bound metals. Deviations from 1:1 predictions between sediment and macrophyte metal concentrations have been shown to be correlated to variation in sediment geochemistry. Sediment pH, redox potential and organic content are three particularly important sediment variables that affect phase partitioning of metals, and their bioavailability. Metals contained within macrophyte tissues can participate in cycling within the littoral zone, or at senescence, lost to the surrounding water in a dissolved form or exported out of the lake bound to shoot fragments. Relatively little is known about the trophic transfer of macrophyte-bound metals to herbivores or algae. A better understanding of the role of rooted aquatic macrophytes in ecosystem processes is likely to be advanced by considering the fate of plant metals leaked during the summer, and those dissolved forms lost to the water column during senescence. Modeling metal accumulation in aquatic vascular plants has been restricted to empirical models that provide descriptions of general patterns.