Nawaf Nasser

Geochemistry of lakes across ecozones in the Northwest Territories and implications for the distribution of arsenic in the Yellowknife region. Part 1.

We obtained near total element geochemistry on 211 near-surface sediment samples from lakes along a transect across the Western Interior Platform to the central portion of the Slave Geological Province with a focus near the City of Yellowknife, Northwest Territories, to document regional concentrations of arsenic (As) and other elements in lake sediments. Concentrations of major and trace elements, including elements of potential human and ecological concern (As, Cd, Cr, Cu, Pb, Zn), were extracted from sediments using a modified aqua regia digestion. Concentrations of As exceed Canadian federal guidelines for the protection of aquatic life in most of the lakes sampled in the Slave Geological Province. Seventy one percent (n=149) of all sediment samples contain As concentrations higher than the Canadian Council of Ministers of the Environment (CCME) Interim Freshwater Sediment Quality Guideline of 5.9 mg/kg and 54% (n=114) of the samples contain As concentrations that exceed the CCME Probable Effect Level of 17 mg/kg. Sediments with the highest As concentrations are from lakes near the City of Yellowknife and likely reflect a combination of contamination associated with past industrial activity and geogenic input from mineralized bedrock and derived surficial materials (median As concentration 107.9 mg/kg, range 6.30->10,000+, n=95). Arsenic concentrations in lake sediments sampled elsewhere in the central Northwest Territories are lower (Ingraham Trail, median As concentration 10.6 mg/kg, range 1.9-101.6, n=27; Tibbitt to Contwoyto Winter Road, median As concentration 7.9 mg/kg, 0.3-101.4, n=52; Western Interior Platform, median As concentration 1.1 mg/kg, 0.1-7.1, n=37). Based on our data and a review of existing literature, background As concentration in lake sediments appear to ~25 mg/kg for the Yellowknife region, and lower for other regions in the central NWT. Other elements (Cr, Cu, Pb, Zn) are below sediment quality guidelines in the majority of lake sediments sampled.

Sequential sample reservoirs for Itrax-XRF analysis of discrete samples

AbstractGeochemical 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.

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, little information is available regarding their impact on the lake itself. For this reason, Arcellinida, a group of shelled protozoans known to be reliable bioindicators of land-use change, were used to develop a hydroecological history of the lake. The purpose of this study was to use Arcellinida to: (1) document the contamination history of the lake, particularly related to arsenic (As) associated with aerial deposition from mine roaster stacks; (2) track the progress of water quality deterioration in Frame Lake related to mining, urbanization and other activities; and (3) identify any evidence of natural remediation within the lake. Arcellinida assemblages were assessed at 1-cm intervals through the upper 30 cm of a freeze core obtained from Frame Lake. The assemblages were statistically compared to geochemical and loss-on-ignition results from the core to document the contamination and degradation of conditions in the lake. The chronology of limnological changes recorded in the lake sediments were derived from 210Pb, 14C dating and known stratigraphic events. The progress of urbanization near the lake was tracked using aerial photography. Using Spearman correlations, the five most significant environmental variables impacting Arcellinida distribution were identified as minerogenics, organics, As, iron and mercury (p < 0.05; n = 30). Based on CONISS and ANOSIM analysis, three Arcellinida assemblages are identified. These include the Baseline Limnological Conditions Assemblage (BLCA), ranging from 17–30 cm and deposited in the early Holocene >7,000 years before present; the As Contamination Assemblage (ACA), ranging from 7–16 cm, deposited after ∼1962 when sedimentation began in the lake again following a long hiatus that spanned to the early Holocene; and the Eutrophication Assemblage (EA), ranging from 1–6 cm, comprised of sediments deposited after 1990 following the cessation of As and other metal contaminations. The EA developed in response to nutrient-rich waters entering the lake derived from the urbanization of the lake catchment and a reduction in lake circulation associated with the development at the lake outlet of a major road, later replaced by a causeway with rarely open sluiceways. The eutrophic condition currently charactering the lake—as evidenced by a population explosion of eutrophication indicator taxa Cucurbitella tricuspis—likely led to a massive increase in macrophyte growth and winter fish-kills. This ecological shift ultimately led to a system dominated by Hirudinea (leeches) and cessation of the lake as a recreational area.

Conicocassis, a new genus of Arcellinina (testate lobose amoebae)

Superfamily Arcellinina (informally known as thecamoebians or testate lobose amoebae) are a group of shelled benthic protists common in most Quaternary lacustrine sediments. They are found worldwide, from the equator to the poles, living in a variety of fresh to brackish aquatic and terrestrial habitats. More than 130 arcellininid species and strains are ascribed to the genus Centropyxis Stein, 1857 within the family Centropyxidae Jung, 1942, which includes species that are distinguished by having a dorsoventral-oriented and flattened beret-like test (shell). Conicocassis, a new arcellininid genus of Centropyxidae differs from other genera of the family, specifically genus Centropyxis and its type species C. aculeata (Ehrenberg, 1932), by having a unique test comprised of two distinct components; a generally ovoid to subspherical, dorsoventral-oriented test body, with a pronounced asymmetrically positioned, funnellike flange extending from a small circular aperture. The type species of the new genus, Conicocassis pontigulasiformis (Beyens et al., 1986) has previously been reported from peatlands in Germany, the Netherlands and Austria, as well as very wet mosses and aquatic environments in High Arctic regions of Europe and North America. The occurrence of the species in lacustrine environments in the central Northwest Territories extends the known geographic distribution of the genus in North America considerably southward. Nawaf A. Nasser. Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada. Nawafnasser@cmail.carleton.ca R. Timothy Patterson. Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada. Tim.Patterson@carleton.ca