Paleolimnological assessment of long-term changes in a boreal recreational lake of the Fermont mining region (subarctic Quebec, Canada)

Figures & data

Figure 1. Map of the study area in eastern subarctic Quebec and bathymetric contours (in meters) of the northern basin of Lac Carheil (modified from MRN 1977).

Table 1. Modern and historical limnological data from Lac Carheil’s waters.

Parameter	August 1976 (Verrette et al. 1976)	July 2011 (OBVD 2011)	October 2011 (OBVD 2011)	July 2012 (Winegardner A, McGill University, unpubl.data)	June 2015
Tempsurface (C)	13.0	17.4	—	13.6	6.3
DOsurface (mg)	11.5	8.3	—	10.8	12.6
DOsurface (%)	∼100	—	—	115.5	102.2
pHsurface	7.2	7.8	—	7.5	7.5
Condsurface (µS/cm)	38	40	—	—	38
TPsurface (µg/L)	—	7.1	4.9	2.0	—
Secchi (m)	—	—	—	—	4.0
Mixing depth (m)	—	∼6	—	∼4	∼4

Note: OBVD, Organisme de bassins versants Duplessis; Temp, temperature; DO, dissolved oxygen; Cond, conductivity; TP, total phosphorus; Secchi, Secchi disk transparency.

Figure 2. Optical photographs of the sediment cores retrieved from the bottom of Lac Carheil with the resulting composite core.

Figure 3. (A) Unsupported ²¹⁰Pb decay curve and ¹³⁷Cs activity in the upper part of the composite core (CAR-1; 0–34.5 cm); (B) resulting age–depth curve of the uppermost section (0–12 cm) based on the application of the CRS model; and (C) estimated chronological curve for the entire composite core (CAR-1 + CAR-2; 0–60.5 cm) based on ²¹⁰Pb and ¹⁴C dating.

Table 2. Samples dated using ¹⁴C AMS in the composite core with their respective radiocarbon and calendar ages.

Depth (cm)	Material	Lab number	Conventional radiocarbon age (^14C year BP)	Calibrated 2σ age range (cal. year BP)	Calibrated median probability age (cal. year AD)
13.0–13.5	Wood	ULA-6379 UCIAMS-179132	130 ± 15	12–269	1840
21.5–22.0	Bulk sediment	ULA-6012 UCIAMS-172979	1865 ± 20	1732–1868	140*
26.5–27.0	Wood	ULA-6011 UCIAMS-172978	635 ± 20	557–661	1360
60.0–60.5	Bulk sediment	ULA-6013 UCIAMS-173542	10,055 ± 35	11,364–11,765	–9630*

Note: 2σ = 95.4%; calibrated median probability ages are rounded to the nearest decade.

*Date not considered.

Figure 4. Microradiographs (radio) and relative concentration stratigraphic profiles of the selected elements obtained from the μ-XRF analyses. The gray shaded area corresponds to the period of modern settlement in the catchment (i.e., 1971–2015).

Figure 5. Stratigraphic variation profiles of water (% water), organic matter (% OM), carbon (% C) and nitrogen (% N) concentrations, carbon to nitrogen ratio (C/N), and mean grain size within the composite core. The gray shaded area corresponds to the period of modern settlement in the catchment (i.e., 1971–2015).

Figure 6. Stratigraphic relative abundance variation profiles of the most common diatoms (≥2.5% in at least one level, except for Stephanodiscus minutulus) preserved in the composite core along with the profile of the PCA axis 1 sample scores summarizing the stratigraphic variations in the composition of the whole diatom assemblages. The black line (1840 AD) delimits the 2 statistically distinct diatom zones, whereas the gray shaded area marks the period of modern settlement in the catchment (i.e., 1971–2015). Note. The Staurosirella pinnata complex includes S. pinnata (mainly), S. pinnata var. acuminata, and S. pinnata var. intercedens; the Pseudostaurosira brevistriata complex includes P. brevistriata (mainly), P. brevistriata var. papillosa, and P. brevistriata var. elliptica; and the Achnanthidium minutissimum complex includes capitate and noncapitate forms of A. minutissimum.

Figure 7. Stratigraphic variation profiles of the diatom absolute concentration and diatom-inferred total phosphorus (DI-TP) concentrations in the composite core. The black line (1840 AD) delimits the 2 statistically distinct diatom zones, whereas the gray shaded area marks the period of modern settlement in the catchment (i.e., 1971–2015).

Ministère des Richesses naturelles (MRN). 1977. Courbes bathymétriques du lac Carheil. Map C-8412, 1/42 353. Québec (Qc).

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Verrette JL, Barbeau C, Moreau G. 1976. Ecological study of Carheil River – 1976. Québec (QC): Centre de recherches sur l'eau, Université Laval.

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Organisme de bassins versants Duplessis (OBVD). 2011. Cyanobactéries aux lacs Daviault, Sans Nom et Carheil. Volet I: hydrodynamique et physico-chimie. Étude partielle. Sept-Îles (QC).

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