Accumulation and distribution of metals in Bolboschoenus maritimus (Cyperaceae), from a South African river

Abstract

The Diep River is a major freshwater ecosystem in the Western Cape, South Africa. Although it is surrounded by many sources of metal pollution, the actual metal levels in this river system are unknown. Wetland plants are known to accumulate metals and may possibly be used as biomonitors of metal contamination in a river system. One such species, the sedge Bolboschoenus maritimus, is found in abundance along the banks of this river. The aim of this study was to investigate and monitor the degree of metal contamination in the water and sediments of the lower Diep River, as well as to study the seasonal accumulation and distribution of metals in B. maritimus, and the use thereof as biomonitor species. Two sampling sites were used: one site above the wetland section of the river, receiving runoff mainly from agricultural lands (site 1), and one site close to the river mouth (site 2), exposed to several possible pollution sources. Water, sediment, and plant (root, leaf and stem) samples were collected seasonally for 1 year and analyzed for Al, Zn, Cu, and Fe. There was greater bioaccumulation of metals by plants at site 2, due to greater bioavailability of metals. B. maritimus was shown to be a root accumulator of metals. Seasonal fluctuations in root, stem, and leaf metal concentrations did not follow seasonal sediment concentration patterns. However, using B. maritimus as test species did provide valuable additional information to sediment and water analyses. More extensive research is needed to conclude whether this species is an effective biomonitor in the lower Diep River environment.