Microbial and Biogeochemical Dynamics in Glacier Forefields Are Sensitive to Century-Scale Climate and Anthropogenic Change

Abstract

The recent retreat of glaciers and ice sheets as a result of global warming exposes forefield soils that are rapidly colonized by microbes. These ecosystems are dominant in high-latitude carbon and nutrient cycles as microbial activity drives biogeochemical transformations within these newly exposed soils. Despite this, little is known about the response of these emerging ecosystems and associated biogeochemical cycles to projected changes in environmental factors due to human impacts. Here, we applied the model SHIMMER to quantitatively explore the sensitivity of biogeochemical dynamics in the forefield of Midtre Lovénbreen, Svalbard, to future changes in climate and anthropogenic forcings including soil temperature, snow cover, and nutrient and organic substrate deposition. Model results indicated that the rapid warming of the Arctic, as well as an increased deposition of organic carbon and nutrients, may impact primary microbial colonizers in Arctic soils. Warming and increased snow-free conditions resulted in enhanced bacterial production and an accumulation of biomass that was sustained throughout 200 years of soil development. Nitrogen deposition stimulated growth during the first 50 years of soil development following exposure. Increased deposition of organic carbon sustained higher rates of bacterial production and heterotrophic respiration leading to decreases in net ecosystem production and thus net CO 2 efflux from soils. Pioneer microbial communities were particularly susceptible to future changes. All future climate simulations encouraged a switch from allochthonously-dominated young soils (<40 years) to microbially-dominated older soils, due to enhanced heterotrophic degradation of organic matter. Critically, this drove remineralisation and increased nutrient availability. Overall, we show that human activity, especially the burning of fossil fuels and the enhanced deposition of nitrogen and organic carbon, has the potential to considerably affect the biogeochemical development of recently exposed Arctic soils in the present day and for centuries into the future. These effects must be acknowledged when attempting to make accurate predictions of the future fate of Arctic soils that are exposed over large expanses of presently ice-covered regions.

Plant colonization mediates the microbial community dynamics in glacier forelands of the Tibetan Plateau

“…(3) The spatial distribution of glaciers can also affect climate and microbial communities [90,91]. (4) The climate factors (temperature and precipitation) can influence soil physicochemical properties and microbial community [92,93]. The temperature and precipitation data used in the SEM were derived from the National Tibetan Plateau Data Center [94,95].…”

Distribution of soil nitrogen and nitrogenase activity in the forefield of a High Arctic receding glacier

“…Uniform incubation parameters were used to achieve linear rates of C 2 H 2 reduction over a 24-h period, where parameters were chosen to reflect mean summer growth/melt season conditions. As the soil microbial community in the Midtre Lovénbreen forefield is dominated by autotrophic organisms (Hodkinson and others, 2003; Bradley and others, 2017; Nash and others, 2018), it was reasoned that nitrogenase activity, which is positively correlated with the soil moisture content (Chapin and others, 1991), would be restricted to a period when water is available to the biota (Logan, 1968). However, despite low temporal variability in the soil N pool during the short summer season in Svalbard (Bardgett and others, 2007), it may be argued that N inputs released to the soil solution through snowmelt and rainfall may influence potential rates of asymbiotic BNF.…”

Five decades of terrestrial and freshwater research at Ny-Ålesund, Svalbard

“…On glacier surfaces in Svalbard, autumn snow onset has been delayed by two days/decade between 1961 and 2012 (van Pelt et al 2016). Local glaciers are consistently retreating, opening up forelands for biological colonization (Bradley et al 2017;Schuler et al 2020). Sea-ice formation has become restricted to the northern part of Kongsfjorden (Pavlova et al 2019) and tidewater glacier melting patterns have also changed (Sundfjord et al 2017).…”