Sudbury Sediments Revisited: Evaluating Limnological Recovery in a Multiple-Stressor Environment

Abstract

Paleolimnological techniques were utilized to determine whether diatom and scaled chrysophyte assemblages in Daisy, Swan, and Tilton lakes (Sudbury, Ontario) have recovered toward their preimpact conditions as a result of reduced inputs of anthropogenic pollutants (SO 4 2− and metals) or whether other environmental stressors have affected recovery trajectories. In addition, geochemical analysis was used to track trends in sedimentary nickel and copper concentrations through time. Preindustrial algal assemblages were primarily dominated by circumneutral to alkaline and pH-indifferent taxa. However, with the onset of open-pit roasting and smelting operations, there was a stratigraphic shift toward acid-tolerant species. With wide-scale smelter emission reductions commencing in the 1970s, scaled chrysophyte assemblages in Swan and Daisy lakes have started to show signs of biological recovery in ∼1984 and ∼1991, respectively. Although the scaled chrysophyte assemblage in Tilton Lake has not recovered toward the predisturbance assemblage, the decline in acidophilic taxa and increase in circumneutral taxa in recently deposited lake sediments indicate that the community is responding to increased lake water pH. Conversely, diatom assemblages within each of the study lakes have not begun to recover, despite well-documented chemical recovery. It is suspected that biological recovery in Sudbury area lakes may be impeded by other environmental stressors such as climate warming. Copper and nickel concentrations in lake sediments increased with the onset of mining activities and subsequently declined with emission controls. However, metal concentrations in lake sediments remain elevated compared to preindustrial concentrations. Together, biological and geochemical evidence demonstrates the clear environmental benefits associated with smelter emission controls.

Diatoms as indicators of long-term nutrient enrichment in metal-contaminated urban lakes from Sudbury, Ontario

“…Further efforts are needed to quantify the relative sources of phosphorus to these lakes and, where possible, to recommend management options for controlling inputs. This is critical because new evidence (e.g., Rühland et al 2008, Tropea et al 2010 suggests that algal communities in northern Ontario are also sensitive to rising air temperatures. The combined effects of nutrient enrichment and climatic change may increase the severity and seasonal duration of algal blooms.…”

“…Paleolimnological studies have been widely used to assess the timing, rate and extent of acidification and metal contamination in the Sudbury region (Dixit et al 1987, Tropea et al 2010; however, only one paleolimnological investigation has focused on the long-term water quality changes related to cultural eutrophication in this region (Dixit et al 1996). This is likely because Sudbury is situated in a nutrient-poor landscape, and advanced cultural eutrophication has not been designated as a major threat to freshwater resources in the area.…”

Response of Bosmina size structure to the acidification and recovery of lakes near Sudbury, Canada

“…The lakes were heavily acidified by the 1970s (to pH <5; and have aqueous Cu and Ni concentrations that continue to exceed provincial water quality guidelines (Cooperative Freshwater Ecology Unit, Laurentian University, 2013). Each of the three Sudbury study lakes has undergone prior diatom-based reconstructions of pH (Dixit et al, 1987(Dixit et al, , 1990(Dixit et al, , 1996, analyses of sedimentary metals (Snetsinger, 1993;Tropea, 2008;Tropea et al, 2010), cladoceran assemblages and sedimentary chlorophyll-a (Labaj et al, 2015), and regular water chemistry monitoring since 1973 (Middle, Clearwater) or 1991 (Daisy; Cooperative Freshwater Ecology Unit, Laurentian University, 2013).…”

“…Sediments were stored in a cooler with cold packs until transportation to the laboratory. Only the surface (0-0.25 cm) sediments of the 2012 Daisy Lake core were analysed (representing the year 2012), with the remainder of the sediments sourced from a dated core previously analysed for sedimentary metals (Tropea, 2008;Tropea et al, 2010). The 2012 surface sediments allowed the most recent cladoceran assemblage of Daisy Lake to be assessed (Labaj et al, 2015), without the need to establish a 210 Pbbased chronology from a second core from the lake.…”

PALEOLIMNOLOGY | Lake Chemistry

“…Isotopic measurements of sulfur in these studies may additionally allow the source of sulfur pollution to be pinpointed (Nriagu and Coker, 1983). More recently, measurements of sediment copper and nickel, in addition to biological proxy indicators, have been used to track the recovery of industrially acidified lakes toward preimpact conditions (Tropea et al, 2010). Another promising geochemical technique that has recently been applied to paleolimnological problems, including acidification, is near-infrared spectroscopy (NIRS).…”