Fig 1.
Map showing beaches and approximate sites sampled for benthic invertebrates in Lake Superior near the Keweenaw Peninsula, Michigan, 2021. Samples were collected to assess the association between stamp sands (SS, a byproduct of copper mining) and invertebrate communities.
At each site, a petite Ponar was used to collect sediment, which was analyzed for benthic invertebrates, metal concentrations and SS percentage. The beach most highly contaminated with SS is near Buffalo Reef (BUR-H; white circles). Another beach in Grand Traverse Bay that has been protected by a pier south of BUR-H is known to have some SS contamination (GTB-M; grey triangles). Further south and around a bend in the shoreline is another bay, where we did not expect to observe SS, but we did observe low concentrations of SS ((Little Traverse Bay; LTB-L; white triangles). A control beach with was located ~ 58 km away (Big Bay; BIG-C; white triangles). In addition, we sampled some sites previously sampled by Kerfoot et al. ( [5]; Resample stations; yellow triangles). Base map data from OpenStreetMap (openstreetmap.org/copyright), and imagery is from the U.S. Geological Survey (https://www.usgs.gov/tools/national-map-viewer).
Table 1.
Aggregated physical and water quality characteristics of sampling areas where benthic invertebrates (all sites) and zooplankton (beach sites) were collected in 2021 to assess the impact of stamp sands (in Lake Superior near the Keweenaw Peninsula, Michigan). Means are reported with standard deviation.
Fig 2.
Graphical comparisons of (A) stamp sand content (percent) and total recoverable concentrations (mg/kg dry weight, DW) of (B) As, arsenic; (C) Cd, cadmium; (D) Co, cobalt; (E) Cr, chromium; (F) Cu, copper; (G) Fe, iron; (H) Mn, manganese; (I) Ni, nickel; (J) Pb, lead; (K) Se, selenium; and (L) Zn, zinc; in the sediments collected by petite Ponar from beach sites at Buffalo Reef (BUR-H), Grand Traverse Bay south of Traverse River (GTB-M), Little Traverse Bay (LTB-L) and Big Bay (BIG-C), Michigan in 2021.
Letters in individual panels refer to beaches that were not clearly different using the non-parametric Peto-Peto test. In all panels, boxes encompass the first and third quartiles. The lines (whiskers) show the largest or smallest observation that falls within 1.5 times the box size. Observations that fall outside the lines are shown individually.
Fig 3.
Probable effects quotients (PEQs) for total recoverable (A) copper and (B) sum of 7 metals (as
ΣPEQs) in the sediments collected bypetite Ponar from study sites in Lake Superior near the Keweenaw Peninsula, Michigan, 2021. The ΣPEQ calculations in panel B include the PEQ for copper, arsenic, chromium, lead, nickel, zinc, and cobalt; the horizontal dotted lines in panels A and B are PEQ = 1, above which increased rates of adverse biological effects are expected. In panels A and B, boxes encompass the first and third quartiles. The thick black line is the median. The lines (whiskers) show the largest or smallest observation that falls within 1.5 times the box size. Observations that fall outside the lines are shown individually. (C) The bivariate relationship between stamp sands (as % of sediment) and copper concentration; the horizontal dotted line shows the probable effects concentration (PEC) for copper (149 mg/kg dw, equivalent to a PEQ of 1), above which biological effects are considered likely. The solid line (panel C) is the Cu concentration predicted from a model relating stamp sands to the log of the copper concentration (dashed lines indicate 95% confidence interval on the prediction). BUR-H – beach near Buffalo Reef that has been heavily impacted by stamp sands (SS); GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS); RES – samples from sites resampled from Kerfoot et al. [5].
Fig 4.
Particle size distribution in sediments collected by petite Ponar at each beach in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
Top of bars are means and vertical lines are standard errors. BUR-H – beach near Buffalo Reef that has been heavily impacted by stamp sands (SS); GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS); RES – samples from sites resampled from Kerfoot et al. [5].
Table 2.
Benthic taxa observed at benthic sampling locations in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
Fig 5.
Graphical comparisons of abundance (as number, n, per square meter, m2) and number of taxa for benthic invertebrates collected by petite Ponar from beach sites in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
BUR-H – beach near Buffalo Reef that has been heavily impacted by stamp sands (SS); GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS). Boxes encompass the first and third quartiles. The thick black line is the median. The lines (whiskers) show the largest or smallest observation that falls within 1.5 times the box size. Observations that fall outside the lines are shown individually.
Table 3.
Differences in benthic invertebrate density (log count per m3) among beaches, estimated using a generalized linear model at sites in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
Fig 6.
Non-metric, multi-dimensional scaling (NMDS) plot of benthic invertebrate community composition at four beaches) in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
The four beaches varied by stamp sands (SS) impact: BUR-H – beach near Buffalo Reef that has been heavily impacted by SS; GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS). Solid ellipses enclose the centroid of the group within 1 standard deviation, and dashed ellipses enclose the centroid of the group with 95% confidence interval. Individual species are plotted at the point where their distribution is at a theoretical maximum. The two-dimensional stress of the NMDS ordination is 0.14 and the distance matrix was generated using the Bray-Curtis dissimilarity index.
Table 4.
Zooplankton taxa observed at the benthic sampling locations in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
Fig 7.
Zooplankton density (count per cubic meter, m3) (A) and diversity (B) by beach in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
The beaches varied by impact of stamp sands (SS): BUR-H – beach near Buffalo Reef that has been heavily impacted by stamp sands (SS); GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS). Boxes encompass the first and third quartiles. The thick black line is the median. The lines (whiskers) show the largest or smallest observation that falls within 1.5 times the box size.
Fig 8.
Non-metric, multi-dimensional scaling (NMDS) plot of benthic invertebrate community composition at four beaches) in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
The four beaches varied by stamp sands (SS) impact: BUR-H – beach near Buffalo Reef that has been heavily impacted by SS; GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS). Solid ellipses enclose the centroid of the group within 1 standard deviation, and dashed ellipses enclose the centroid of the group with 95% confidence interval. Individual species are plotted at the point where their distribution is at a theoretical maximum.. The order Cyclopoida and the family Cyclopidae (within the same order) appear in the exact same space on this NMDS plot (which obscured the labeling); therefore, only Cyclopoida is labeled. The two-dimensional stress of the NMDS ordination is 0.17 and the distance matrix was generated using the Bray-Curtis dissimilarity index.
Table 5.
Differences in zooplankton density (log count per m3) among beaches, estimated using a generalized linear model in Lake Superior near the Keweenaw Peninsula, Michigan, 2021.
Table 6.
Models relating stamp sand (SS) content, copper concentration in the sediment (Cu), the sum of the probable effects quotients (ΣPEQ) for 7 metals in the sediment, and water depth (Depth) to the density and taxonomic richness of the benthic invertebrate community in the Keweenaw Peninsula, Michigan, 2021. BUR-H – beach near Buffalo Reef that has been heavily impacted by SS; GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS); RES – samples from sites resampled from Kerfoot et al. [5].
Table 7.
Comparison of models relating stamp sand (SS) content, copper concentration in the sediment (Cu), the sum of the probable effects quotients (ΣPEQ) for 7 metals in the sediment, and water depth (Depth) to the presence of benthic invertebrate community sampled from beaches in Lake Superior, Michigan, 2021. Models are ranked using Akaike’s information criterion, corrected for small sample size (ΔAICC). Models were generalized multi-level models that used a negative binomial distribution to estimate the number of individuals in a petite Ponar grab. Standardized coefficients and intercept are reported for the best model. Unstandardized coefficients by taxa are reported in Table 8.
Table 8.
Results of multi-level model (MLM) showing unscaled effect sizes of stamp sands (SS, as a percentage; %) and depth (in meters) on the benthic invertebrate community composition at several beaches in Lake Superior, Michigan. The inferred SS percentage at the maximum likelihood of presence for each taxa was calculated by solving for the SS percentage at the vertex of the parabola defined by the SS and SS2 effect sizes. At several beaches, the maximum %SS never occurred. BUR-H – beach near Buffalo Reef that has been heavily impacted by SS; GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS); RES – samples from sites resampled from Kerfoot et al. [5]. The strongest standardized effect for each taxa is highlighted in bold.
Fig 9.
Count per petite Ponar grab sample for seven individual taxa versus copper (Cu) concentration (mg/kg dry weight; DW) in samples collected from Grand Traverse Bay, Little Traverse Bay and Big Bay, Lake Superior, Michigan, 2021.
Additional taxa shown in Fig 10. Points are data and dashed lines are the predictions from a multi-level mixed effects models using a negative binomial distribution to predict abundance (Table 8). Predictions are conditional on the taxa and the beach that was sampled, as a result predictions over cover the portion of the gradient in Cu concentration that was present in that beach. As a result, prediction lines for Little Traverse Bay (LTB-L) beach and Big Bay (BIG-C) beach are very short, as these beaches have very low Cu concentrations compared to the other beach categories. BUR-H – beach near Buffalo Reef that has been heavily impacted by stamp sands (SS); GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS); RES – samples from sites resampled from Kerfoot et al. [5].
Fig 10.
Count per petite Ponar grab sample for seven individual taxa versus copper (Cu) concentration (mg/kg dry weight; DW) in samples collected from Grand Traverse Bay, Little Traverse Bay and Big Bay, Lake Superior, Michigan, 2021.
Additional taxa shown in Fig 9. Points are data and dashed lines are the predictions from a multi-level mixed effects models using a negative binomial distribution to predict abundance (Table 8). Predictions are conditional on the taxa and the beach that was sampled, as a result predictions over cover the portion of the gradient in Cu concentration that was present in that beach. As a result, prediction lines for Little Traverse Bay (LTB-L) beach and Big Bay (BIG-C) beach are very short, as these beaches have very low Cu concentrations compared to the other beach categories. BUR-H – beach near Buffalo Reef that has been heavily impacted by stamp sands (SS); GTB-M – beach in Grand Traverse Bay south of the Traverse River with some SS contamination; LTB-L – beach in Little Traverse Bay with very little SS; BIG-C- beach in Big Bay (a control site with no SS); RES – samples from sites resampled from Kerfoot et al. [5].