Abiotic and Seasonal Factors Influencing Trace Metal Levels (Cd, Cu, Ni, Pb, and Zn) in the Freshwater AmphipodGammarus fasciatusin Two Fluvial Lakes of the St. Lawrence River

Abstract

The potential use of the freshwater amphipod Gammarus fasciatus as a biomonitor of metal pollution has been assessed in two fluvial lakes of the St. Lawrence River. Metal (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) concentrations were measured twice at 22 sites in Lakes St. Pierre and St. Louis, both in oxic sediments and in amphipods. Concentrations of free-metal ions at the sediment–water interface were estimated from lake water pH and sediment/water sorption equilibria. Multiple linear regression models forecasting trace metal (Cd, Cu, Ni, Pb, and Zn) levels in amphipods were developed, using abiotic variables (sediment-bound metals, sediment organic carbon, free-metal ions, hydrogen ions, dissolved calcium, and dissolved organic carbon) and biotic (size class) variables. These models explained 73–81% of the observed variation, except in the case of Zn (68%) and Cu (61%), indicating that G. fasciatus is a promising biomonitor for Cd, Ni, and Pb in littoral environments. Seasonal patterns of amphipod contamination were identified for Fe, Ni, and Pb, summer concentrations being higher than those measured during the fall. Size-dependent variation in amphipod metal levels was found, smaller organisms being more contaminated than larger ones.