Testate amoebae as a proxy for reconstructing Holocene water table dynamics in southern Patagonian peat bogs

Simon Van Bellen,Verónica A Pancotto,Richard J Payne,Thomas P Roland,Neil J Loader,Emma M Rice,Tim J Daley,F Alayne Street‐Perrott,Dmitri Mauquoy,Paul D M Hughes

doi:10.1002/jqs.2719

Abstract

ABSTRACTTestate amoebae are abundant and diverse in Sphagnum peat bogs and have been used extensively as indicators of past water table depths. Although these unicellular protists are widely dispersed with globally similar hydrological preferences, regional variations in communities demand region‐specific transfer functions. Here we present the first transfer function for southern Patagonian bogs, based on 154 surface samples obtained from transects in five bogs sampled in 2012 and 2013. Significant variance was explained by pH, electrical conductivity and, in particular, water table depth. Transfer functions for water table were constructed using weighted averaging and evaluated by cross‐validation and independent test sets. The optimal transfer function has predictive ability, but relatively high prediction errors given the wide range in sampled water tables. The use of independent test sets, as well as cross‐validation, allows a more rigorous assessment of model performance than most previous studies. For a subset of locations we compare surface and subsurface samples to demonstrate significant differences in community composition, possibly due to vertical zonation. Our results provide the first quantification of hydrological optima and tolerances for several rare species, which may include Southern Hemisphere endemics and pave the way for palaeohydrological reconstructions in southern Patagonian bogs.

Highlights

Peatland palaeoecology has been widely used to reconstruct environmental and climate change at centennial to millennial timescales (Barber, 1981; Barber et al, 1994; Mauquoy et al, 2002; Yu et al, 2003; De Vleeschouwer et al, 2009)
The aim of this study is to (i) examine the composition and biogeography of testate amoebae in southern Patagonia; (ii) quantify the relationship between amoeba assemblages and key environmental variables; (iii) construct and test a transfer function model to infer peat bog water table depth (WTD) from palaeoassemblages and (iv) assess the ecology of taxa that are abundant in fossil samples but infrequent in training sets
Taxonomic richness is negatively correlated with WTD in linear regression, i.e. richness is significantly lower for dry microenvironments for both the complete datasets and the sites individually (À0.75 < r < –0.33 and all P < 0.05), with the exception of PAR bog

Summary

Introduction

Peatland palaeoecology has been widely used to reconstruct environmental and climate change at centennial to millennial timescales (Barber, 1981; Barber et al, 1994; Mauquoy et al, 2002; Yu et al, 2003; De Vleeschouwer et al, 2009). Water table fluctuations, vegetation assemblages and microfaunal dynamics are closely linked to changes in precipitation and temperature regime (Aaby, 1976; Schouten et al, 1992; Charman et al, 2004; Mauquoy and Yeloff, 2007). Testate amoebae are characterized by high reproduction rates (in the order of 10–27 generations per annum, Charman, 2001) and can register rapid responses to variations in seasonal mire surface wetness, the final resolution of the temporal signal reflects the accumulation rate of the peat

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Conclusion