DOI: 10.5061/dryad.8w9ghx3pk
title: Paleolimnological assessment of a hyper-eutrophic lake (Nowlans Lake, N.S., Canada) Cladoceran communities

description: 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).
description: All data presented in this folder originate from sediment cores
 collected from the deepest basin of Nowlans Lake using a gravity corer in
 mid-May 2018. Cores were sectioned at 0.5-cm intervals using a vertical
 extruder. Chronology of the sediment core was established through standard
 <sup>210</sup>Pb dating techniques (See cited Manuscript
 Methodology, and Table 1 for reported dates). Trends in sedimentary chl-a
 concentrations were inferred by visible reflectance spectroscopy (VRS)
 using a FOSS NIRSystems model 6500 rapid content analyzer. The
 concentration of VRS chl-a and its major degradation products was
 calculated from the resulting reflectance spectra between 650–700 nm using
 a linear regression equation. Twenty-eight sediment
 samples were processed for Cladocera subfossil remains. Approximately 1–2g
 of wet sediment per interval was deflocculated in 5% KOH solution and
 heated. After digestion, the sample was sieved on a 38-µm mesh and rinsed
 with deionized water. Materials were put into labelled glass scintillation
 vials with 1% safranin staining solution and 95% ethanol. Next, sample
 were pipetted onto glass coverslips, and contents were evaporated. Glass
 coverslips were permanently mounted onto slides using Entellan®.
 Sedimentary remains were identified to genus or species level using
 bright-field microscopy at 200× or 400× magnification. Coverslips were
 scanned in entirety for all identifiable remains. Identifications were
 performed using subfossil taxonomic guides for eastern North America (See
 cited Manuscript Methodology). Non-fragmented remains of bosminid
 carapaces were measured using Zeiss Zen imaging software.