Postglacial wetland succession, carbon accumulation, and forest dynamics on the east coast of Vancouver Island, British Columbia, Canada

Abstract

Peatland development and carbon accumulation on the Pacific coast of Canada have received little attention in paleoecological studies, despite wetlands being common landscape features. Here, we present a multi–proxy paleoenvironmental study of an ombrotrophic bog in coastal British Columbia. Following decreases in relative sea level, the wetland was isolated from marine waters by 13,300 cal yr BP. Peat composition, non-pollen palynomorph, and C and N analyses demonstrate terrestrialization from an oligotrophic lake to a marsh by 11,600 cal yr BP, followed by development of a poor fen, and then a drier ombrotrophic bog by 8700 cal yr BP. Maximum carbon accumulation occurred during the early Holocene fen stage, when seasonal differences in insolation were amplified. This highlights the importance of seasonality in constraining peatland carbon sequestration by enhancing productivity during summer and reducing decomposition during winter. Pollen analysis shows that Pinus contorta dominated regional forests by 14,000 cal yr BP. Warm and relatively dry summers in the early Holocene allowed Pseudotsuga menziesii to dominate lowland forests 11,200–7000 cal yr BP. Tsuga heterophylla and P. menziesii formed coniferous forest in the mid- and late Holocene. Tephra matching the mid-Holocene Glacier Peak–Dusty Creek assemblage provides evidence of its most northwesterly occurrence to date.

A comparison of Holocene testate amoeba assemblages and paleohydrological records from pollen slides and wet-sieved peat

“…Testate amoeba analyses were conducted on Holocene peat cores obtained from two bogs located 160 km apart on Vancouver Island in British Columbia, Canada. Both peatlands were the focus of previous multi-proxy paleoecological studies that included analyses of pollen, macrofossils, carbon, and nitrogen, and identification of testate amoebae, among other non-pollen palynomorphs (Lacourse and Davies, 2015; Lacourse et al, 2019). Port McNeill Bog (PMB) is a small (20 ha) ombrotrophic bog dominated by Sphagnum and ericaceous shrubs, with an average summer water table depth of 20 cm.…”

“…Both peatlands formed in the early Holocene following lake infilling and both are characterized by substantial changes in peat type and accumulation rates over the Holocene. Details on the two peatlands, sampling methods, paleoenvironmental reconstructions and chronologies are provided in Lacourse and Davies (2015) and Lacourse et al (2019).…”

“…In this study, new testate amoeba records were produced for both study sites using the conventional wet-sieving method and then compared to testate amoeba data previously obtained from standard palynological analyses. Lacourse and Davies (2015) and Lacourse et al (2019) prepared peat samples (1–2 cm 3 ) for pollen and non-pollen palynomorph analyses (including testate amoebae) using 150 µm sieving, 10% KOH for 8 min, and acetolysis for 2.5 min. Samples were not treated with hydrofluoric (HF) and hydrochloric (HCl) acids, although 10% HCl was used to dissolve tablets of Lycopodium spores for estimating microfossil concentrations.…”

“…The tests identified on pollen slides are typically included among non-pollen palynomorphs and have been used as additional indicators of past surface wetness variability in peatlands while reconstructing local and regional vegetation dynamics (e.g. Garneau, 1998; Kuhry, 1997; Lacourse et al, 2019; Lavoie and Richard, 2000; van Geel, 1978; van Geel et al, 1981). It is generally assumed that testate amoeba analyses from pollen slides provide poor paleohydrological records compared to those obtained using the conventional wet-sieving preparation method (Hendon and Charman, 1997).…”

“…Hence, the potential of testate amoebae as paleohydrological indicators in palynological studies needs to be better investigated in order to improve their use in further studies. In this study, we compare new testate amoeba records produced by the conventional wet-sieving method to testate amoebae data from previous palynological studies on the same two Holocene peat profiles (Lacourse and Davies, 2015; Lacourse et al, 2019). The main objectives are to (1) compare the composition of testate amoeba assemblages based on taxa concentrations and relative abundances, (2) determine the differences in taxa diversity and richness, and (3) evaluate the potential of palynological testate amoeba assemblages as quantitative proxies of paleohydrological changes in peatlands.…”