Paleolimnology of a fluvial lake downstream of Lake Superior and the industrialized region of Sault Saint Marie

Abstract

A paleolimnological study was undertaken to describe the past environment of the St. Mary's River downstream of Lake Superior. Two sediment cores were obtained from the deepest part of Lake George, a fluvial lake in the river system. Rigorous analyses of radionuclides (210Pb, 226Ra, and 137Cs) and chemical properties provided an accurate sediment chronology. More than 450 diatom species from 47 genera were identified. Diatom and geochemical data indicated gradual environmental change in response to anthropogenic activities, including logging, hydrologic manipulation, and steel, leather, and paper industries. A decline in water quality occurred gradually from the late 1800s through the 20th century in response to human activities, as was apparent from an increase in eutrophic–planktonic diatom taxa. A decline in benthic taxa and an increase in contaminant metals were also contemporaneous with impacts during the 20th century. Subfossil diatoms were similar to those recorded in paleolimnological investigations from the Great Lakes. However, diatom profiles indicate that the algal supply from upstream Lake Superior has been minimal and that the cores mainly reflect environmental characteristics of the near-upstream environment. Despite stochastic sedimentary regimes and complex habitats in the lotic system, this study reinforces the value of river paleolimnology at carefully selected sites.

Laurentian Great Lakes Phytoplankton and Their Water Quality Characteristics, Including a Diatom-Based Model for Paleoreconstruction of Phosphorus

“…That the unique TP effect is lower than total is due to redundancies, such as correlation to variables like chlorophyll a and turbidity (Figure 1). While it is difficult to confirm the relative importance of these variance partitioning values, the unique variance explained by TP surpasses that observed for TP training sets developed in Europe [46] and Minnesota [47], [48]; 3.9% and 2.5% respectively, as presented by Juggins et al [22]. Of the selected variables, TP independently explained the most variation in the assemblage data, in contrast to alkalinity and chloride which had more than 70% reduction from total to uniquely explained variance.…”

Multiple mining impacts induce widespread changes in ecosystem dynamics in a boreal lake

“…It has been demonstrated that in sites with lower contamination, other perturbations (e.g. eutrophication) can override the signal of the effects of the metal/s 52 , 53 . However, within the post-mining period, the most significant changes in the diatom community were caused by the mine-derived salinity increase rather than the increase in toxic metal concentrations per se .…”

Peer Review #1 of "Metallic elements and oxides and their relevance to Laurentian Great Lakes geochemistry (v0.1)"

“…In their core of western Lake Superior, they found stable concentrations of Na up to 1955 ending with an increase in concentration likely resulting from urban inputs in the vicinity of Duluth, Minnesota. Reavie et al (2005) found that Na concentrations gradually increased in the 1800s with European settlement in their core from Lake George, just downgradient from Lake Superior. Sgro and Reavie (2017) attributed Na in their cores in Lake Erie to road salt impacts and found the highest concentrations in surface sediments.…”

“…The majority of 137 Cs in surface waters in North America, including the Great Lakes, is due to nuclear weapons testing, which began in 1952 and ended in 1963 with the Limited Test Ban Treaty. In the Great Lakes, the maximum deposition of 137 Cs was in the spring of 1963, though peaks in the sediment may be as much as two years later (ASTDR, 2004a;Reavie et al, 2005). The radionuclide is strongly bound to expandable lattice clay minerals such as illite in the Great Lakes, so it tends to be a reliable temporal indicator in sediment profiles.…”