Abiotic and biotic variables of lakes
There were significant differences in average total length and weight
among lake trout collected throughout 2017 annual sampling from L260,
L223, L224, and L373 (ANOVA, p ≤ 0.05) (Table 1b; Figure S4).
Average total length and weight of lake trout in Lake 260 were
significantly greater than average total length and weight of lake trout
in L223, L224, and L373 (Tukey HSD, adj-p ≤ 0.0001 for all
comparisons). Furthermore, average total length and weight of lake trout
in Lake 223 were greater than average total length and weight of lake
trout in L224 (Tukey HSD, adj-p ≤ 0.002 for both comparisons).
There were no significant differences in average total length and weight
among L224 and L373 and among L223 and L373 (Tukey HSD, adj-p> 0.05 for all comparisons). Although there were
differences in length and weight, average condition factors did not
significantly differ among populations (ANOVA, p = 0.1) (Table
1b; Figure S4).
Total zooplankton abundance ranked from highest to lowest was as
follows: L223 > L260 > L224 >
L373 (Table 1c). L223 and L260 also had the highest zooplankton species
richness (38 species), whereas species richness was lower in L224 (29
species) and L373 (26 species) (Table 1c). The most abundant zooplankton
within all lakes were rotifers (e.g. Keratella cochlearis ,Kellicottia bostoniensis , Polyarthra remata ,Polyarthra vulgaris , Kellicottia longspina ) and copepods
(e.g. cyclopoida nauplii ) (Figure S5). L373 had the highest H’
index of 2.50, followed by L260 with 2.08, then L223 with 1.93, and
finally L224 with 1.67 (Table 1c). L373 and L260 also had the greatest
evenness of zooplankton species with equitability index values of 0.77,
followed by L223 and L224 with equitability values of 0.53 and 0.50,
respectively. Thus, L373 and L260 contain the most diverse,
evenly-distributed zooplankton communities. Abundance of all species
across all lakes can be found in Additional File 1: Table S7.
Average water quality parameters are presented in Table 1d and
visualized in Figure S6. There were no significant differences in
average suspended phosphorus, suspended nitrogen, suspended carbon, and
total dissolved phosphorus among lakes (Tukey HSD, adj-p> 0.05 for all comparisons). However, L223 and L260 had
significantly higher levels of total dissolved nitrogen than L224 and
L373 (Tukey HSD, adj-p ≤ 0.0001 for both comparisons).
Chlorophyll-a levels were significantly lower in L224 compared to Lakes
223 and 260 (Tukey HSD, adj-p > 0.03 for both
comparisons), while chlorophyll-a levels did not significantly differ
among L223, L260, and L373 (Tukey HSD, adj-p > 0.05
for all comparisons). However, there was a visible trend of increased
chlorophyll-a in L223 and L260 (Figure S6). Average dissolved oxygen
levels in L260 were significantly lower compared to all other lakes
(Tukey HSD, adj-p ≤ 0.0001 for all comparisons). Average
alkalinity was significantly higher in L373 compared to all other lakes
(Tukey HSD, adj-p ≤ 0.0001 for all comparisons), whereas
alkalinity was significantly lower in L224 compared to all other lakes
(Tukey HSD, adj-p ≤ 0.0001 for all comparisons). Furthermore,
average pH was significantly higher in L373 as compared to L224 and L260
(Tukey HSD, adj-p ≤ 0.01 for all comparisons ) but pH did not
significantly differ among L223, L224 and L260 (Tukey HSD, adj-p> 0.05 for all comparisons). Average temperature was
comparable among the lakes; however, water temperature of L373 was
significantly lower than in L223 and L224 (Tukey HSD, adj-p ≤
0.03 for all comparisons) whereas temperature did not significantly
differ among L223, L224, and L260 (Tukey HSD, adj-p> 0.05 for all comparisons). Finally, average conductivity
was significantly lower in L224 compared to all other lakes (Tukey HSD,
adj-p ≤ 0.02 for all comparisons).
PCA of 11 variables for the four lakes was used to identify variation in
water quality characteristics. Proportions of variance explained by PC1,
PC2, and PC3 were 50.39%, 29.53%, and 20.08%, respectively. PC1 and
PC2 explained the maximum amount of total variance (79.92%). Variable
loadings on each PC are presented in Additional File 1: Table S8 and are
graphically represented in a PCA biplot (Figure 6). PC1 had strong
positive loadings from suspended nitrogen (0.42), suspended carbon
(0.38), conductivity (0.38), and chlorophyll a (0.36) (Figure 2;
Additional File 1: Table S8). The highest scoring lakes for PC1 were
L223 (1.18) and L260 (1.68), while the PC1 score was weakest for L373
(0.61) and was strongly negative for L224 (-3.47). Furthermore, the
strong negative PC1 score of L224 and strong negative PC1 loading of
total dissolved phosphorus (-0.39) suggest that L224 had high total
dissolved phosphorus relative to lakes scoring positively on PC1 and
that total dissolved phosphorus likely drove the variation of L224 from
other lakes.
PC2 had strong positive loadings from pH (0.55), alkalinity (0.42), and
dissolved oxygen (0.34) as well as negative loading from chlorophyll-a
(-0.24) (Figure 6; Additional File 1: Table S8). L223 was the only lake
with a positive PC2 score (2.49) out of the lakes of interest (Figure
6). Overall, PCA suggested that L260 and L223 were most similar in terms
of water quality characteristics while L224 and L373 varied from all
other lakes (Figure 6). Hierarchical clustering analysis confirmed that
L223 and L260 were most closely related based on water quality
characteristics whereas L224 and L373 clustered apart from L223 and L260
(Figure S7).