The relationship between metal concentration and organic matter in sediments and metal concentration in the aquatic macrophyte Eriocaulon septangulare

Sediment cores and samples of the submerged and rooted isoetid Eriocaulon septangulare (With.) were used to examine the relationships between the concentrations of Hg, Pb, Cd and Fe in plants, and metal concentrations and organic matter (OM) content of sediments. Thirteen sites in the littoral zone of Bentshoe Lake, a software lake of the Muskoka-Haliburton region of south-central Ontario were included in the study design. Metal concentrations in sediments ranged from 0.007 to 0.247 μg g−1 for Hg, 2.8 to 167.6 μg g−1 for Pb, 0.06 to 2.53 μg g−1 for Cd and 2.55 to 34.77 mg g−1 for Fe. There were significant positive correlations between metal concentrations in sediment and OM content. Metal concentrations measured in Eriocaulon septangulare were generally comparable to or higher than those in sediments, and for each respective metal, were consistently higher in the roots than in the shoots. Concentrations of metals in E. septangulare ranged (dry weight, leaf concentration listed first and roots second for each metal) from 0.03 to 0.22 μg g−1 for Hg, from 2.6 to 62.8 μg g−1 for Pb, from 0.58 to 13.33 μg g−1 for Cd and from 0.61 to 156.20 mg g−1 for Fe. Metal concentrations in the roots and in the leaves were significantly positively correlated for Hg, Cd and Fe. Metal concentrations in the roots were not correlated with metal concentrations in the sediments. The presence of high concentrations of organic matter (OM) in sediments is shown to decrease the availability of metals to E. septangulare. However, when the total metal concentrations in sediments were normalized for organic content, there was a significant correlation with metal in the plant for Hg, but not for the other metals under consideration.