| Title | Diatom ecological response to deposition of the 833-850 CE White River Ash (east lobe) ashfall in a small subarctic Canadian lake |
| Author | Hutchinson, S J; Hamilton, P B; Patterson, R T; Galloway, J M; Nasser, N A; Spence, C; Falck, H |
| Source | PeerJ 7, 6269, 2019 p. 1-21, https://doi.org/10.7717/peerj.6269 (Open Access) |
| Year | 2019 |
| Alt Series | Natural Resources Canada, Contribution Series 20180371 |
| Publisher | PeerJ |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html |
| Province | Northwest Territories |
| NTS | 85J/09SW |
| Area | Pocket Lake; Yellowknife |
| Lat/Long WENS | -114.3833 -114.3667 62.5167 62.5000 |
| Subjects | environmental geology; surficial geology/geomorphology; paleontology; geochronology; stratigraphy; Recent; paleoecology; surface waters; lakes; biota; microfossils; algae; diatoms; fossil assemblages;
lake sediment cores; tectonic history; volcanism; volcanic ash; depositional history; depositional environment; lacustrine environments; radiometric dating; radiocarbon dating; fossil distribution, strata; stratigraphic analyses; biostratigraphy;
biological communities; ecosystems; environmental impacts; acidity; paleoclimates; White River Ash; Mount Churchill Volcano; ashfalls; lacustrine sediments; tephra; subarctic; resilience; environmental adaptation; Phanerozoic; Cenozoic;
Quaternary |
| Illustrations | location maps; geoscientific sketch maps; tables; models; photographs; profiles; graphs; biostratigraphic charts |
| Program | Environmental Geoscience, Metal Mining:
northern baselines |
| Released | 2019 01 25 |
| Abstract | 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 (62.5090ºN, -114.3719ºW), 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 deposition. Non-metric Multidimensional Scaling (NMDS) and Stratigraphically Constrained Incremental Sum of Squares (CONISS) analyses were carried out and three distinct diatom assemblages were identified throughout the
interval. The lowermost 'Pre-WRAe Assemblage (Pre-WRAeA)' was indicative of slightly acidic and eutrophic lacustrine conditions. Winter deposition of the tephra layer drove a subsequent diatom flora shift to the 'WRAe Assemblage (WRAeA)' the
following spring. The WRAeA contained elevated abundances of taxa associated with oligotrophic, nutrient depleted and slightly more alkaline lake waters. These changes were only apparent in samples within the WRAe containing interval indicating that
they were short lived and only sustained for a single year of deposition. Immediately above the WRAe horizon, a third, 'Post-WRAe Assemblage (Post-WRAeA)' was observed. This assemblage was initially similar to that of the Pre-WRAeA but gradually
became more distinct upwards, likely due to climatic patterns independent of the WRAe event. These results suggest that lacustrine environments are sensitive to perturbations such as deposition of ash fall, but that ecological communities in
subarctic systems can also have high resilience and can recover rapidly. If subsampling of the freeze cores was carried out at a more standard resolution (0.5-1 cm) these subtle diatom ecological responses to perturbation associated with the WRAe
depositional event would not have been observed. This research illustrates the importance of high-resolution subsampling when studying the environmental impact of geologically 'near instantaneous' events such as episodic deposition of
ashfalls. |
| Summary | (Plain Language Summary, not published)
This study examines the response of lacustrine algae to deposition of an ash layer associated with a volcanic eruption. The study provides new insight to
recovery rates of algae to disturbance in a subarctic lake. |
| GEOSCAN ID | 313554 |
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