Diatom ecological response to deposition of the 833-850 CE White River Ash (east lobe) ashfall in a small subarctic Canadian lake

A <5 mm thick volcanic ashfall layer associated with the White River Ash (east lobe [WRAe]) originating from the eruption of Mount Churchill, Alaska (833-850 CE; 1,117-1,100 cal BP) was observed in two freeze cores obtained from Pocket Lake (62.5090◦N, −114.3719◦W), a small subarctic lake located within the city limits of Yellowknife, Northwest Territories, Canada. Here we analyze changes in diatom assemblages to assess impact of tephra deposition on the aquatic biota of a subarctic lake. In a well-dated core constrained by 8 radiocarbon dates, diatom counts were carried out at 1-mm intervals through an interval spanning 1 cm above and below the tephra layer with each 1 mm sub-sample represented about 2 years of dep

What killed Frame Lake? A precautionary tale for urban planners

Frame Lake, located within the city of Yellowknife, Northwest Territories, Canada, has been identified as requiring significant remediation due to its steadily declining water quality and inability to support fish by the 1970s. Former gold mining operations and urbanization around the lake have been suspected as probable causes for the decline in water quality. While these land-use activities are well documented, li

Assessment of FlowCam technology as a potential tool for rapid semi-automatic analysis of lacustrine Arcellinida (testate lobose amoebae)

This study assessed the possibility of replacing conventional microscopic methods of species-level identification and quantification of Arcellinida with a more rapid method utilizing the FlowCam® with VisualSpreadsheet® (FCVS; Fluid Imaging Technologies, Inc.). Arcellinida are an established group of benthic bioindicators of water and sediment quality in lakes. The use of Arcellinida proxy analysis in lakes and peatlands has dramatically increased since the 1980s, but the labor-intensive nature of identifying and quantifying Arcellinida through microscopy limits the number of samples analyzed. A flow cytometer and microscope with machine learning software has been used to enhance the speed of micropaleontological analysis for some groups (e.g., diatoms), but the potential of using the instrument to analyze Arcellinida in lake sediments has not previously been assessed. The FCVS was assessed here as a method of rapidly analyzing Arcellinida by comparing the results obtained by FCVS with results previously obtained through conventional microscopy in a 2016 study, using the same 46 sediment-water interface samples collected from three quadrats (1–3) in Wightman Cove, Oromocto Lake, New Brunswick, Canada. The FCVS was found to be most suitable for categorizing taxa as morpho-groups rather than using conventional taxonomic species. Therefore, results of the 2016 study were reclassified at the morphological level to facilitate comparison. Results of cluster analysis and Bray–Curtis dissimilarity matrix (BCDM) analysis showed that arcellinidan assemblages obtained through conventional microscopy and FCVS were comparable. Analysis using FCVS reduced operator analysis time by approximately 45%. FCVS shows potential as a reliable method for more rapid analysis of lacustrine Arcellinida, particularly for very large sample data sets; however, FCVS technology can only resolve Arcellinida at the morphological level, meaning that conventional microscopy methods are required if finer species-level taxonomi

Behind the Organic Veil: Assessing the Impact of Chemical Deflocculation on Organic Content Reduction and Lacustrine Arcellinida (Testate Amoebae) Analysis

Arcellinida (testate lobose amoebae) are widely used as bio-indicators of lacustrine environmental change. Too much obscuring organic material in a gridded wet Petri dish preparation makes it difficult to observe all specimens present and slows quantification as the organic material has to be carefully worked through with a dissection probe. Chemical deflocculation using soda ash (Na2CO3·H2O), potassium hydroxide (KOH), or sodium hexametaphosphate ((NaPO3)6) has previously been shown to disaggregate and reduce organic content in lake sediments, but to date, no attempt has been made to comparatively evaluate the efficiency of these deflocculants in disaggregating organic content and their impact on Arcellinida analysis in lacustrine sediments. Here, we assess the effectiveness of soda ash, potassium hydroxide, and sodium hexametaphosphate treatments on removing organic content and the impact of those digestions on Arcellinida preservation in 126 sample aliquots subdivided from three sediment samples (YK-20, YK-25, and YK-57) collected from three lakes near Yellowknife, Northwest Territories, Canada. Following treatment, cluster analysis and Bray-Curtis dissimilarity matrix (BCDM) were utilized to determine whether treatments resulted in dissolution-driven changes in Arcellinida assemblage composition. Observed Arcellinida tests in aliquots increased drastically after treatment of organic-rich samples (47.5–452.7% in organic-rich aliquots and by 14.8% in aliquots with less organic matter). The BCDM results revealed that treatment with 5% KOH resulted in the highest reduction in observed organic content without significantly affecting Arcellinida assemblage structure, while soda ash and sodium hexametaphosphate treatments resulted in marginal organic matter reduction and caused severe damage to the arcellinidan tests

An Assessment of Sub-Meter Scale Spatial Variability of Arcellinida (Testate Lobose Amoebae) Assemblages in a Temperate Lake: Implications for Limnological Studies

Arcellinida (testate lobose amoebae), a group of benthic protists, were examined from 46 sediment-water interface samples collected from oligotrophic Oromocto Lake, New Brunswick, Canada. To assess (1) assemblage homogeneity at a sub-meter spatial scale and (2) the necessity for collecting samples from multiple stations during intra-lake surveys; multiple samples were collected from three stations (quadrats 1, 2, and 3) across the north basin of Oromocto Lake, with quadrat 1 (n = 16) being the furthest to the west, quadrat 2 (n = 15) situated closer to the center of the basin, and quadrat 3 (n = 15) positioned 300 m south of the mouth of Dead Brook, an inlet stream. Results from cluster analysis and non-metric multidimensional scaling (NMDS) analysis identified two major Arcellinida assemblages, A1 and A2, the latter containing two sub-assemblages (A2a and A2b). Redundancy analysis and variance partitioning results indicated that seven statistically significant environmental variables (K, S, Sb, Ti, Zn, Fe, and Mn) explained 41.5% of the total variation in the Arcellinida distribution. Iron, Ti and K, indicators of detrital runoff, had the greatest influence on assemblage variance. The results of this study reveal that closely spaced samples (~ 10 cm) in an open-water setting are comprised of homogenous arcellinidan assemblages, indicating that replicate sampling is not required. The results, however, must be tempered with respect to the various water properties and physical characteristics that comprise individual lakes as collection of several samples may likely be necessary when samplin

Sequential sample reservoirs for Itrax-XRF analysis of discrete samples

Geochemical analysis of sediment samples can be used to characterize between- and within-lake variability and provide insights into lake chemistry, depositional processes and contamination sources. The number of samples for geochemical studies is restricted by cost, sample volume required, and the destructive nature of inductively coupled plasma mass spectrometry, instrumental neutron activation analysis, or wavelength dispersive x-ray fluorescence. Core scanners that incorporate energy dispersive x-ray fluorescence spectrometry, such as the Cox Itrax-XRF core scanner, have high through-put and can be used to produce high-quality geochemical datasets at low cost without destroying sample material. Here we describe a new analysis vessel that enables rapid, non-destructive Itrax-XRF analysis of discrete sediment samples