Évaluation de la capacité de rétention des métaux dissous d'un marais artificiel en utilisant le périphyton et le gastéropode Helisoma trivolvis

Abstract

SUMMARYUrban and agricultural development has had a significant impact on the water quality of rivers and lakes around the world. In the last few décades, constructed wetlands hâve been designed as wastewater treatment Systems to prevent water quality détérioration in natural receiving waters. Constructed wetlands are built because they are considered sinks for many pollutants thereby protecting the water quality of downstream ecosystems. The treatment performance of thèse wetlands is generally assessed using mass balance calculations. However, the rétention of metals by constructed wetlands is highly variable and the factors involved are still poorly understood. If wetlands are sinks for metals, the métal content of organisms should be lower downstream than upstream. In this context, organisms can be useful to assess the réten-tion or transformation of metals by wetlands.The objective of this study was to détermine whether periphyton and the gastropod Helisoma trivolvis Say could be used to evaluate the rétention of dissolved metals in a constructed wetland. H. trivolvis is a freshwater pulmonate snail widespread in ponds across North America. It feeds mostly on periphyton and is more or less sedentary. Snails hâve been used as biomonitors because several species are métal tolérant. However, compared to snails, periphytic microorganisms may track more closely dissolved métal concentrations as they take up metals principally from the water column.This study was conducted at the Monahan Pond in Kanata, Ontario (Canada). This wetland was built in 1995 to treat run-off from an agricultural and residential watershed. Water chemistry samples, snails and periphyton grown on artificial substrata were collected at both the inlet and the Simonyi-Poirier et al. outlet of the wetland in the fall of 1999. Tissue samples were digested with concentrated nitric acid and métal analyses were done by ICP-MS (Inductively Coupled Plasma Mass Spectrometry). During the experiment several chemical parameters differed between the inlet and the outlet. Alkalinity was signifîcantly higher at the inlet and ail major cation concentrations were higher at the inlet. The température was on average 3 °C higher at the outlet. Mass balance calculations showed that the wetland was a sink for most dissolved metals. Snails and periphyton tissue métal concentrations were higher at the inlet than at the outlet for Cd and Ni. However, no significant diffé-rences were observed between inlet and outlet tissue concentrations for Cr and Al, whereas Mn was actually significantly higher at the outlet. As a resuit, the métal content of the organisms did not consistently reflect the dissolved métal concentrations in water. For ail metals except Cd and Zn, periphyton concentrations were on average higher than snail métal concentrations. Periphyton analyses can provide a more conservative measure of métal contamination and, when artificial substrates are used, correspond to defined and known periods of exposure.Rev. Sci. Eau, 16(2), 2003 M.This study demon...

Importance and Difficulties of Research on Metal Speciation in the Aquatic Ecosystem: an Ecologist's Viewpoint

“…5). The same conclusion was drawn by Simonyí-Poírier et al 32 from a study of the accumulation of 8 metals in the soft tissues of a freshwater snail (Helisoma trivolvis).…”