The Role of Water Speedwell in the Distribution and Rates of Metal Removal from Pinal Creek, Near Globe, Arizona

Abstract

Aquatic plants can be significant sinks for dissolved metals in metal contaminated streams. This study found water speedwell (Veronica anagallis aquatica) growing in Pinal Creek both bio-accumulates metals (Mn, Zn, Ni, and Co) and provides surfaces for metal precipitation. Analysis of plant tissue found that roots accumulate up to 80 g Mn/kg dry root, with the majority of metals associated with the external plant surface. Fine sediments around water speedwell colonies have 2-10 times higher metal concentrations than surrounding sediments. SEM photos of the plant surface show clumps of manganese oxides associated with what appear to be manganese-oxidizing bacteria. First order metal removal rates by water speedwell of 1 x 10^-3, 2 x 10^-3, and 5 x 10^-3 per hour for manganese, nickel, and cobalt, respectively were estimated by laboratory experiments. Water speedwell enhances metal removal in streams by providing surfaces conducive for metal oxyhydroxides precipitation.