Ecology of peatland testate amoebae in Svalbard and the development of transfer functions for reconstructing past water-table depth and pH

Paul J Morris,Dan J Charman,Graeme T Swindles,Alex Channon,Angela V Gallego-Sala,Dave Beilman,Matthew J Amesbury,Thomas G Sim,Andy J Baird

doi:10.1016/j.ecolind.2021.108122

Abstract

Peatlands are valuable archives of information about past environmental conditions and represent a globally-important carbon store. Robust proxy methods are required to reconstruct past ecohydrological dynamics in high-latitude peatlands to improve our understanding of change in these carbon-rich ecosystems. The High Arctic peatlands in Svalbard are at the northern limit of current peatland distribution and have experienced rapidly rising temperatures of 0.81 °C per decade since 1958. We examine the ecology of peatland testate amoebae in surface vegetation samples from permafrost peatlands on Spitsbergen, the largest island of the Svalbard archipelago, and develop new transfer functions to reconstruct water-table depth (WTD) and pH that can be applied to understand past peatland ecosystem dynamics in response to climate change. These transfer functions are the first of their kind for peatlands in Svalbard and the northernmost developed to date. Multivariate statistical analysis shows that WTD and pore water pH are the dominant controls on testate amoeba species distribution. This finding is consistent with results from peatlands in lower latitudes with regard to WTD and supports work showing that when samples are taken across a long enough trophic gradient, peatland trophic status is an important control on the distribution of testate amoebae. No differences were found between transfer functions including and excluding the taxa with weak idiosomic tests (WISTs) that are most susceptible to decay. The final models for application to fossil samples therefore excluded these taxa. The WTD transfer function demonstrates the best performance (R2LOO = 0.719, RMSEPLOO = 3.2 cm), but the pH transfer function also performs well (R2LOO = 0.690, RMSEPLOO = 0.320). The transfer functions were applied to a core from western Spitsbergen and suggest drying conditions ~1750 CE, followed by a trend of recent wetting and increasing pH from ~1920 CE. These new transfer functions allow the reconstruction of past peatland WTD and pH in Svalbard, thereby enabling a greater understanding of long-term ecohydrological dynamics in these rapidly changing ecosystems.

Highlights

Peatlands and wetlands are widespread across the non-glaciated areas of the High Artic (Walker et al, 2005) and represent a substan tial carbon store, with soils holding an estimated 34 ± 16 Pg C (Hugelius et al, 2014)
We examine the ecology of peatland testate amoebae in surface vegetation samples from permafrost peatlands on Spitsbergen, the largest island of the Svalbard archi pelago, and develop new transfer functions to reconstruct water-table depth (WTD) and pH that can be applied to understand past peatland ecosystem dynamics in response to climate change
This finding is consistent with results from peatlands in lower latitudes with regard to WTD and supports work showing that when samples are taken across a long enough trophic gradient, peatland trophic status is an important control on the distribution of testate amoebae

Summary

Introduction

Peatlands and wetlands are widespread across the non-glaciated areas of the High Artic (Walker et al, 2005) and represent a substan tial carbon store, with soils holding an estimated 34 ± 16 Pg C (Hugelius et al, 2014). There are growing concerns that warming temperatures will expose greater amounts of soil carbon to decomposition via deeper permafrost thaw and that warming will in crease rates of microbial decomposition, leading to a positive feedback with climate (Koven et al, 2015; Schuur et al, 2015). In creases in productivity associated with longer and warmer growing seasons may result in greater carbon accumulation in peatlands at midlatitudes and in particular at high-latitudes (Gallego-Sala et al, 2018). Improved understanding of autogenic factors relating to permafrost thaw, hydrological change, productivity and decomposition are crucial for better quantifying future peatland carbon dynamics (Sim et al, 2021; Waddington et al, 2015). It is important that proxy methods for reconstructing past ecohydrological dynamics in High Arctic peat lands are developed and rigorously tested to increase understanding of ecosystem change and to inform future predictions

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