Effects of retrogressive permafrost thaw slumping on sediment chemistry and submerged macrophytes in Arctic tundra lakes

Abstract

1. Global warming is predicted to cause changes in permafrost cover and stability in the Arctic. Zones of high ion concentration in regions of ice-rich permafrost are a reservoir of chemicals that can potentially be transferred to fresh waters during thawing. Consequently, input of enriched runoff from the thaw and sediment and vegetation from the landscape could alter lakes by affecting their geochemistry and biological production. 2. Three undisturbed lakes and five lakes disturbed by retrogressive permafrost thaw slumps were sampled during late summer of 2006 to assess the potential effects of thermokarst shoreline slumping on water and sediment chemistry, the underwater light regime, and benthic macrophyte biomass and community structure. 3. Undisturbed lakes had sediments rich in organic material and selected micronutrients, while disturbed lakes had sediments richer in calcium, magnesium and strontium, greater transparency of the water column, and a well-developed submerged macrophyte community. 4. It is postulated that enriched runoff chemistry may alter nutrient availability at the sediment-water interface and also the degradation of organic material, thus affecting lake transparency and submerged macrophytes. The results suggest that retrogressive permafrost slumping can significantly affect food webs in arctic tundra lakes through an increase in macrophyte biomass and development of a more complex benthic habitat.

Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

“…In lakes that remain turbid following thermokarst disturbances, total phosphorus concentrations can be high, following phosphorus adsorption onto clays that are transported into aquatic systems (sub-Arctic Québec, Breton et al, 2009). Similarly, slumping can also increase sediment nutrient concentrations (Mackenzie Delta uplands, Mesquita et al, 2010), while shoreline expansion of thermokarst lakes in yedoma regions can enable nutrientrich yedoma soils, and the nutrient-rich plants that these soils support, to enter lakes (Siberia, Walter Anthony et al, 2014).…”

“…In regions where thaw increases both nutrients and DOM we may expect stimulation of total primary production in clear and shallow lakes but suppression of primary production in more coloured or deeper lakes (Sweden and Alaska, Seekell et al, 2015). In regions where retrogressive thaw slumping delivers mineral-rich sediments to lakes (Mackenzie Delta uplands, Thompson et al, 2008 andMesquita et al, 2010), permafrost degradation has led to significantly greater dissolved ion content, lower DOC concentrations following mineral adsorption, and increased water transparency. This has led to enhanced macrophyte development and higher abundance of benthic macroinvertebrates (Mackenzie Delta uplands, Mesquita et al, 2010 andMoquin et al, 2014) and higher abundance and diversity of periphytic diatoms (Mackenzie Delta uplands, Thienpont et al, 2013).…”

Paleolimnology of thermokarst lakes: a window into permafrost landscape evolution

“…The mechanism for this diatom floristic response is likely due to the rapid increase in water clarity, resulting in colonization of open-water and periphytic habitats. Aquatic macrophyte biomass and production are known to be greater in lakes impacted by slumping (Mesquita et al 2010). This paleolimnological change was found to be a strong indicator of the onset and (or) reinitiation of slump activity when compared to indirectly inferred methods (Thienpont et al 2013b).…”

Impacts of active retrogressive thaw slumps on vegetation, soil, and net ecosystem exchange of carbon dioxide in the Canadian High Arctic

“…In aquatic ecosystems, physical and chemical changes of sediment and water following slumping impact invertebrates, macrophytes, and diatoms, altering composition and abundance (Mesquita et al 2010;Thienpont et al 2013;Moquin and Wrona 2015;Chin et al 2016). The ecological impacts of ALDS have been analyzed at few sites in the High Arctic and changes to the physical environment following a disturbance event have been shown to influence vegetation recovery (Desforges 2000;Cannone et al 2010;Bosquet 2011;Cassidy 2011).…”