Metals Associated with Suspended Sediments in Lakes Erie and Ontario, 2000–2002

Abstract

Sediment traps were deployed in the three major basins of Lake Erie, and the central (Mississauga) basin of Lake Ontario, and refurbished seasonally over the period 2000-2002. In Lake Ontario, sediment down-flux rates and corresponding contaminant down-flux rates were highest in winter during periods of unstratified thermal conditions, and generally increased with depth due to the influence of resuspended bottom sediments during all sampling periods. Lake Ontario suspended sediments exhibited the highest concentrations of metals; concentrations of mercury and lead frequently exceeded guideline values for bottom sediments. Contaminant levels in Lake Ontario suspended sediments were similar to concentrations in bottom sediments in the same area. There was a spatial trend toward higher suspended sediment metals concentrations from the eastern basin to the western basin of Lake Erie, which is similar to the trend in bottom sediment contamination. In the eastern basin of Lake Erie, which is the deepest area of the lake, there was no trend in down-flux rate with depth in 2001; however, down-flux rates increased with depth in 2002. Suspended sediments in the western basin of Lake Erie were determined to be largely resuspended bottom sediments; all western basin samples collected in the study exceeded the guideline value for mercury (0.486 microg/g).

Assessing the application of SeaWiFS ocean color algorithms to Lake Erie

“…The influence of atmospheric contamination, as gauged from the percentage of masked pixels in the SeaWiFS dataset, does not vary substantially among the three basins, suggesting that, while some of the residual scatter observed with the regional algorithms may be due to unresolved atmospheric effects, it is likely that most of the residual scatter in the central and western basins is due to other factors. The western basin is known to have high loads of suspended sediment (Kemp et al, 1977;Marvin et al, 2007), and to have relatively high concentrations of algae with multiple accessory pigments (Ghadouani and Smith, 2005). These can confound the satellite signal, making it difficult to separate chlorophyll a from other CPAs.…”

“…In addition to these variations in biological properties, most of the major rivers draining into Lake Erie empty into the western basin, where they deposit much of their accumulated sediment load (Kemp et al, 1977). This flux, and the resuspension of bottom sediments (Dusini et al, 2009;Marvin et al, 2007), contribute to the higher levels of turbidity observed in the shallow western basin as compared with other basins of the lake (Markarewiczl et al, 1999). Suspended sediments are a particular concern as they can be carriers of chemical contaminants (Marvin et al, 2002(Marvin et al, , 2004(Marvin et al, , 2007Painter et al, 2001).…”

“…Case 2 waters represent more complex optical settings, which may include phytoplankton, suspended sediments and other water-borne materials (see Mobley et al (2004) and Morel and Prieur (1977)). Within the relatively confined setting of Lake Erie, biological and sedimentological conditions can vary significantly (Kemp et al, 1977;Makarewicz, 1993;Marvin et al, 2007), resulting in potentially diverse optical conditions. While some regions of the lake may satisfy conditions for Case 1 waters, other regions may represent an extreme end member of Case 2 waters.…”

Heavy metals in sediments and uptake by burrowing mayflies in western Lake Erie basin

“…For example, Ankley et al (1996) showed bioturbation can cause oxidation of acid volatile sulfide, thereby altering the partitioning of sediment-associated metals like Cd and enhancing their bioavailability. In addition, Marvin et al (2007) noted that suspended sediments in the western Lake Erie basin were largely resuspended bottom sediments; hence, through bioturbation, mayfly nymphs may increase resuspended toxic contaminants (Bartsch et al, 1999;Bachteram et al, 2005), which increases Cd exposure for other aquatic organisms in the water column, including fish that may then take in Cd even without direct ingestion of mayflies. Based on the high Cd levels found in sediments in this study, the effect of mayflies on bioturbation is also of concern.…”

“…These contaminants also have the potential for resuspension into the water column. Marvin et al (2007) found that contaminated suspended sediments from the western basin of Lake Erie are heavily influenced by resuspended bottom sediments. Correspondingly, mayfly nymphs have the potential for facilitating resuspension of sediment-bound contaminants through bioturbation (Bartsch et al, 1999;Bachteram et al, 2005), particularly in spring during their emergence.…”