Impacts of Heavy Metals on Higher Aquatic Plant, Diatom and Benthic Invertebrate Communities in the Niagara River Watershed near Welland, Ontario

Abstract

Abstract Nickel, chromium, zinc and lead were 60 to 500 times more concentrated in the sediments downstream of the Atlas Specialty Steels Co. than they were in the sediments of the upper Welland River or in the nearby Lyon’s Creek. These metals reached concentrations of 4,900 mg kg−1 dry weight (ppm) of nickel versus 10 ppm upstream, 890 versus 5 ppm lead, 1,050 versus 30 ppm zinc and 5,120 verses 10 ppm chromium. Changes in higher aquatic plant species composition and relative abundance downstream of the Atlas Specialty Steels Co. were plotted as a function of the downstream distance (800 m) from the point source discharge of the company. Four zones in the distribution patterns of aquatic plants were recognized. In the first zone (0–10 m from the point source) benthic invertebrates and aquatic plants were absent. In zone 2 (10–15 m from the point source) pollution tolerant benthic invertebrates such as sludge worms and blood worms as well as pollution tolerant long stemmed emergent macrophytes such as bulrushes and cattails first appeared. Further downstream (15–120 m from the point source), short stemmed macrophytes became abundant and benthic invertebrate diversity and density began to increase (zone 3). Only in zone 4 (120–800 m from the point source) did submersed macrophytes first appear and benthic invertebrates such as isopods, snails and leeches became established. Sites where sediments displayed the highest levels of heavy metal contamination displayed low species richness and low benthic invertebrate densities. These same sites displayed the highest proportions of pollution tolerant chironomid genera such as Procladius cf. bellus and Phaenopsectra flavipes and the highest percentage of pollution tolerant diatoms such as Nitzschia hantzschia and N. palea. Chironomid density was significantly lower below the point source (19 individuals m−2 versus 162 individuals m−2 upstream) as was species richness (11 versus 20 species, P < 0.05). A similar pattern was evident for other benthic invertebrates as well as epipelic diatoms (15 vs. 34 species). In addition, the frequency of chironomid deformities was significantly higher at the downstream site than at the upstream “control” site (27% vs. 9%).