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

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 (62.5090°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 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.

Late-Holocene diatom community response to climate driven chemical changes in a small, subarctic lake, Northwest Territories, Canada

“…The observed WRAe deposit (<5 mm), derived from the Plinian-style Mount Churchill Eruption (White River Ash, ~1100 cal BP; Patterson et al, 2017) had a short-term impact on sediment size fractionation, and metals but resulted in no immediate change in the diatom community (Hutchinson et al, 2019). However, after the event there were increases in Stauroneis spp., Sellaphora spp., Pinnularia spp., Neidium spp., and Encyonopsis spp.…”

“…2200 cal BP) an r-strategist, also supports the observation that a period of stability persisted in the lake during this time. The reduction of EM2 and EM3 at 55–56 cm is the result of the White River Ash tephra deposit 1100 years ago cal BP (Hutchinson et al, 2019; Patterson et al, 2017). After the eruption and deposition of tephra, there is a shift in grain size to EM4 during the MWA (53–40 cm; ca.…”

Power, security, and exchange: Impacts of a Late Holocene volcanic eruption in Subarctic North America

“…A decrease in spruce would have reduced riverside vegetation and woody debris that harbored salmon fry and regulated water temperatures crucial to successful incubation (Martin et al., 1986). Resident lake fish were harmed by changes in silica and pH levels in water that altered phytoplankton, algae, chironomid, amphipod, and diatom communities (Abella, 1988; Hutchinson et al., 2019; Kurenkov, 1966). However, we predict that anadromous fish recovered within ten years thanks to salmonid life cycles (roughly five years) and plankton blooms associated with ash input (Bisson et al., 1988, 2005; Parsons and Whitney, 2012).…”

Responses of testate amoebae assemblages (Amoebozoa: Arcellinida) to recent volcanic eruptions, inferred from the sediment record in Laguna Verde, southern Patagonia, Argentina

“…Volcanic events can be significant triggers of ecological change in lakes. Depending on tephra composition and limnological characteristics, dissolution of tephra can alter water chemistry, modify the lake ecosystem, and change the sediment composition (Hutchinson et al 2019;Massaferro and Corley 1998;Telford et al 2004). In many cases, ashfall increases turbidity in lakes, reduces light penetration and modifies biotic communities (Barker et al 2000;Hutchinson et al 2019;Lotter and Birks 1993;Mayr et al 2019).…”

“…Other studies, however, argued that the response of diatom assemblages to volcanic ash also depends on other factors such as lake morphology (e.g. lake surface area, water volume), water chemistry, sedimentology, and thickness of the tephra (Hutchinson et al 2019;Telford et al 2004). Serra et al (2016) found that even though diatoms and chironomids decrease in abundance associated with deposition of tephra layers, chironomids do not seem to decline as much as diatoms, which almost disappear after a tephra layer is deposited.…”