Microbial dynamics in a High-Arctic glacier forefield: a combined field, laboratory, and modelling approach

Abstract

<p><strong>Abstract.</strong> Modelling the development of soils in glacier forefields is necessary in order to assess how microbial and geochemical processes interact and shape soil development in response to glacier retreat. Furthermore, such models can help us predict microbial growth and the fate of Arctic soils in an increasingly ice-free future. Here, for the first time, we combined field sampling with laboratory analyses and numerical modelling to investigate microbial community dynamics in oligotrophic proglacial soils in Svalbard. We measured low bacterial growth rates and growth efficiencies (relative to estimates from Alpine glacier forefields), and high sensitivity to soil temperature (relative to temperate soils). We used these laboratory measurements to inform parameter values in a new numerical model and significantly refined predictions of microbial and biogeochemical dynamics of soil development over a period of roughly 120 years. The model predicted the observed accumulation of autotrophic and heterotrophic biomass. Genomic data indicated that initial microbial communities were dominated by bacteria derived from the subglacial environment, whereas older soils hosted a mixed community of autotrophic and heterotrophic bacteria. This finding was validated by the numerical model, which showed that active microbial communities play key roles in fixing and recycling carbon and nutrients. We also demonstrated the role of allochthonous carbon and microbial necromass in sustaining a pool of organic material, despite high heterotrophic activity in older soils. This combined field, laboratory and modelling approach demonstrates the value of integrated model-data studies to understand and quantify the functioning of the microbial community in an emerging High-Arctic soil ecosystem.</p>

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

“…In contrast to model simulations by Bradley and others (2016) which showed that inorganic N accumulates at a relatively constant rate within Midtre Lovénbreen forefield, we observed that concentrations of inorganic N remain largely stable at 3–4 µg g −1 between the 0- and 113-year-old soils (Figs 3b and c). As NO 3 -N was found to constitute 100% of inorganic N in the silt loam-textured soils (ice-free for 0–50 years), it may be reasoned that inputs of NH 4 -N are rapidly immobilised by the soil microbial biomass (Bradley and others, 2016). Indeed, a study of the Loch Vale Watershed in the Colorado Rocky Mountains, USA, by Baron and others (1995) showed that NH 4 -N, which comprised ~50% of received inorganic N deposition, was incorporated directly into biomass or oxidised to NO 3 -N in soil, as well as snow pack and surface waters.…”

“…Conversely, the increase in NH 4 -N in the 113- and 2000-year-old soils (Fig. 3b) suggests that mineralisation processes are sufficient to facilitate the accumulation of inorganic N in the clay-textured soils (Bradley and others, 2016). This is supported by studies of the Damma glacier (Switzerland; Töwe and others, 2010), and Ödenwinkelkees and Rotmoosferner glaciers (Austria; Tscherko and others, 2003) which showed that functional genes ( chiA and aprA ) and rates of N mineralisation increase with soil age, respectively.…”

“…Soil ages had previously been determined by Bradley and others (2016) and Hodkinson and others (2003) using satellite imagery (Landsat TM 7), photographic records and carbon-14 dating techniques. As described by Bradley and others (2016), the fine earth fraction (≤2000 µm) of the soil samples was separated from coarser material in the field, transferred to high-density polyethylene bags (Whirl-Pak ® ; Lactun, Australia) and immediately frozen at −20°C. Representative aliquots of frozen sample were freeze-dried for elemental analysis, whereas aliquots for the determination soil texture, soil nutrient concentrations and nitrogenase activity were thawed in the dark at 4°C prior to analysis.…”

Disparity in soil bacterial community succession along a short time-scale deglaciation chronosequence on the Tibetan Plateau

“…The clear separation of early bacterial succession from transitional and late stages could be due to various reasons. Such as the early stage soil was exactly collected from the glacier tongue, and that the bacterial community could be derived from subglacial and/or glacial environment as observed by a previous study (Bradley et al, 2016). While the discrimination in the transitional and late stages for more or less could be due to soil physicochemical factors and among microbial interaction.…”

Organic carbon fluxes of a glacier surface: A case study of Foxfonna, a small Arctic glacier

“…A clear change in runoff amplitudes after 28th July 2012 coincided with the supraglacial catchment losing most of its snow cover, exposing supraglacial stores of OC. Future studies should test this hypothesis because this will impact estimates of OC release from glaciers with consequences for downstream extraglacial ecosystems (Fellman et al ., ; Hood et al ., ; Bradley et al ., ).…”