Paleolimnological assessment of a hyper-eutrophic lake (Nowlans Lake, N.S., Canada) Cladoceran communities

Mink fur farming was once a widespread agricultural activity in
southwestern Nova Scotia. Some freshwaters near mink fur farm operations
now show severe water quality issues. Notably, the watershed of Nowlans
Lake (southwestern Nova Scotia, Canada) once contained six mink farms as
well as a fish meal feed processing plant. It is now one of the most
productive lakes in Atlantic Canada, with exceedingly high measured Total
Phosphorus concentrations. Here, we provide data from a paleolimnological
investigation on the long-term environmental changes that occurred in
Nowlans Lake, and how these changes have impacted cladoceran communities.
First, we identify abundances of cladoceran taxa throughout the sediment
core, corresponding to assemblages from the ~1900s to present day
(determined by 210Pb dating analyses – see Table 1 of cited manuscript),
and provide raw counts. We detected shifts in the dominant pelagic
cladoceran taxa beginning in the early 1900s, with decreases in
small-bodied bosminids, while taxa such as Chydorus brevilabris and
Daphnia pulex spp. increased. We identified assemblage “zones” using a
constrained hierarchal clustering analysis, denoting three distinct
assemblage groups (Script 03). We then provide empirical measures of the
body sizes of bosminids in each sediment interval, as body sizes of
cladocerans are good proxies of shifts in predation. We identified
bottom-up ecological factors as the likely drivers of these assemblage
shifts, as body sizes were found to be consistent through time with a Mann
Kendall Monotonic Trend Analysis (Script 02). Finally, we reconstructed
and provide data on trends in sedimentary chl-a concentrations using
visible reflectance spectroscopy (VRS). After conducting a PCA on
cladoceran assemblages and extracting PC1 scores, we observed a strong
relationship by VRS chl-a and PC1 scores, suggesting similar timing
between increases in lake productivity and major cladoceran changes
(Script 01).