Oil contamination of sediments by freeze-drying versus air-drying for organic geochemical analysis.

Freeze-drying is widely used in geochemical laboratories for preparing wet solid environmental samples such as sediments and soils before being analyzed for their contents and states of various metal elements and labile organic components that may be temperature- and/or redox-sensitive. Screening bulk geochemical analysis of two Artic lake sediment samples prepared by freeze-drying displayed unexpectedly high contents of labile organic matter (OM) represented by the Rock-Eval S1 peaks (e.g., 8.12 and 4.84 mg HC/g sediment). The amount of labile OM was reduced greatly for the freeze-dried sediment samples after a thorough cleaning of the freeze-drier sample chamber (e.g., 2.75 and 1.46 mg HC/g sediment), but was still significantly higher than that of the equivalent air-dried samples (e.g., 0.76 and 0.23 mg HC/g sediment). Compositional analysis of the labile OM fractions by gas chromatography (GC) of both freeze-dried and air-dried aliquots of the same sediments indicates the presence of unresolved complex mixture (UCM) humps of C10-C23 hydrocarbons in the freeze-dried samples. In contrast, air-dried samples, either real sediments or blank laboratory materials represented by clean sand and thermally spent shale, do not show the C10-C23 hydrocarbon UCM humps on their GC traces. The hydrocarbon UCM humps persist in the freeze-dried samples even they further went through air-drying at ambient conditions. Both bulk and compositional analytical results in this work appear to indicate the potential risk of introduction of external hydrocarbons to the prepared materials during freeze-drying process, especially if an aged freeze-drier was used without being thoroughly cleaned and if pump oil and cooling fluids were components of the device.

Lacustrine Arcellinina (Testate Amoebae) as Bioindicators of Arsenic Contamination.

Arcellininids (testate amoebae) were examined from 61 surface sediment samples collected from 59 lakes in the vicinity of former gold mines, notably Giant Mine, near Yellowknife, Northwest Territories, Canada to determine their utility as bioindicators of arsenic (As), which occurs both as a byproduct of gold extraction at mines in the area and ore-bearing outcrops. Cluster analysis (Q-R-mode) and detrended correspondence analysis (DCA) reveal five arcellininid assemblages, three of which are related to varying As concentrations in the sediment samples. Redundancy analysis (RDA) showed that 14 statistically significant environmental parameters explained 57 % of the variation in faunal distribution, while partial RDA indicated that As had the greatest influence on assemblage variance (10.7 %; p < 0.10). Stress-indicating species (primarily centropyxids) characterized the faunas of samples with high As concentrations (median = 121.7 ppm, max > 10000 ppm, min = 16.1 ppm, n = 32), while difflugiid dominated assemblages were prevalent in substrates with relatively low As concentrations (median = 30.2 ppm, max = 905.2 ppm, min = 6.3 ppm, n = 20). Most of the lakes with very high As levels are located downwind (N and W) of the former Giant Mine roaster stack where refractory ore was roasted and substantial quantities of As were released (as As2O3) to the atmosphere in the first decade of mining. This spatial pattern suggests that a significant proportion of the observed As, in at least these lakes, are industrially derived. The results of this study highlight the sensitivity of Arcellinina to As and confirm that the group has considerable potential for assessing the impact of As contamination on lakes.

Arcellacea (testate lobose amoebae) as pH indicators in a pyrite mine-acidified lake, Northeastern Ontario, Canada.

Arcellacea (testate lobose amoebae) were examined in 24 sediment-water interface samples collected over two late August field seasons in 2010 and 2011, from James and Granite lakes, Temagami Region, Northeastern Ontario. The work was carried out to quantitatively test species-environment relationships in a lake system known to be characterized by a significant pH gradient, partially the result of contamination from the early twentieth century Northland Pyrite Mine Co., located on the shoreline in the southern basin of James Lake. Redundancy analysis confirmed that arcellacean assemblage structure was most strongly controlled by pH, explaining 14.06 % (p < 0.002) of the total variance. Q- and R-mode cluster analysis supported by detrended correspondence analysis yielded two major faunal assemblages. The Oligotrophic Assemblage (1) had a Shannon Diversity Index (SDI) ranging up to 2.45, typical of healthy boreal lakes. This assemblage characterized samples collected from higher pH stations within James and Granite lakes away from the immediate area of the mine site, while the Low pH Assemblage 2010 (2a) and Low pH Assemblage 2011 (2b) groupings were from the very low pH environments of James Lake adjacent to the former mine site. Both low diversity assemblages (SDI ranging from 0.62 to 1.22) were characterized by Arcella vulgaris, a species known to thrive in hostile lacustrine environments. Differing depositional conditions during August 2010, a probable result of different prevailing wind patterns that summer, led to allochthonous specimens of the seasonally planktic Cucurbitella tricuspis dominating the Low pH Assemblage 2010 (2a) fauna.

Limited freshwater cap in the Eocene Arctic Ocean.

Remains of the freshwater fern Azolla, found in Eocene (~50 Ma ago) sediments in the modern central Arctic Ocean, have been used to suggest that seasonal freshwater caps covered the entire Arctic Ocean during that time, with significant impact on global ocean circulation and climate. However, these records are located on the Lomonosov Ridge, which during the Eocene was a continental fragment barely rifted from Eurasia, separating the smaller Eurasian Basin from the much larger Amerasian Basin to the west. As such, the Lomonosov Ridge does not necessarily record environmental conditions of the broader Arctic Ocean. We tested the hypothesis of freshwater caps by examining sediment records from the western Amerasian Basin. Here we show that in the larger Amerasian Basin the Azolla event is associated with marine microfauna along with allochthonous (terrestrially sourced) organic matter. We propose that Azolla events are related to an increased hydrologic cycle washing terrestrially sourced Azolla, and other organics, into the Arctic Ocean. If freshwater caps did occur, then they were at best restricted to the small Eurasian Basin and would have had a limited impact on Eocene global climate, contrary to current models.

Autoecological approaches to resolve subjective taxonomic divisions within arcellacea.

Arcellacea (testate lobose amoebae) are important lacustrine environmental indicators that have been used in paleoclimatic reconstructions, assessing the effectiveness of mine tailings pond reclamation projects and for studying the effects of land use change in rural, industrial and urban settings. Recognition of ecophenotypically significant infra-specific 'strains' within arcellacean assemblages has the potential to enhance the utility of the group in characterizing contemporary and paleoenvironments. We present a novel approach which employs statistical tools to investigate the environmental and taxonomic significance of proposed strains. We test this approach on two identified strains: Difflugia protaeiformis Lamarck strain 'acuminata' (DPA), characterized by fine grained agglutination, and Difflugia protaeiformis Lamarck strain 'claviformis' (DPC), characterized by coarse grained agglutination. Redundancy analysis indicated that both organisms are associated with similar environmental variables. No relationship was observed between substrate particle size and abundance of DPC, indicating that DPC has a size preference for xenosomes during test construction. Thus DPC should not be designated as a distinct strain but rather form a species complex with DPA. This study elucidates the need to justify the designation of strains based on their autecology in addition to morphological stability.