Abstract
Contemporary measurements of carbon (C) accumulation rates in peatlands around the world often show the C sink to be stronger on average than at times in the past. Alteration of global nutrient cycles could be contributing to elevated carbon accumulation in the present day. Here we examine the effect of volcanic inputs of nutrients on peatland C accumulation in Moanatuatua Bog, New Zealand, by examining a high-resolution Late Holocene C accumulation record during which powerful volcanic eruptions occurred, depositing two visible rhyolitic tephra layers (Taupo, 232 ± 10 CE; Kaharoa, 1314 ± 12 CE). Carbon accumulation rates since c. 50 CE, well before any human presence, increased from a background rate of 23 g C m−2 yr−1 up to 110 g C m−2 yr−1 following the deposition of the Taupo Tephra, and 84 g C m−2 yr−1 following the deposition of the Kaharoa Tephra. Smaller but nevertheless marked increases in C accumulation additionally occurred in association with the deposition of three andesitic-dacitic cryptotephras (each ≤ ∼1 mm thick) of the Tufa Trig Formation between the Taupo and Kaharoa events. These five periods of elevated C uptake, especially those associated with the relatively thick Taupo and Kaharoa tephras, were accompanied by shifts in nutrient stoichiometry, indicating that there was greater availability of phosphorus (P) relative to nitrogen (N) and C during the period of high C uptake. Such P was almost certainly derived from volcanic sources, with P being present in the volcanic glass at Moanatuatua, and many of the eruptions described being associated with the local deposition of the P rich mineral apatite. We found peatland C accumulation to be tightly coupled to N and P accumulation, suggesting nutrient inputs exert a strong control on rates of peat accumulation. Nutrient stoichiometry indicated a strong ability to recover P within the ecosystem, with C:P ratios being higher than most other peatlands in the literature. We conclude that nutrient inputs, deriving from volcanic eruptions, have been very important for C accumulation rates in the past. Therefore, the elevated nutrient inputs occurring in the present day could offer a more plausible explanation, as opposed to a climatic component, for observed high contemporary C accumulation in New Zealand peatlands.
Highlights
The global peatland carbon (C) sink is vast, 644 GT by the most recent estimates (Yu, 2011; Dargie et al, 2017), and greater than all the C content of fossil fuels burnt since 1870 (~435 GT C, as cited in Le Quere et al, 2018)
We find that nutrient inputs, derived directly and indirectly from volcanic eruptions, have affected C cycling in the past, and increased nutrient inputs could be primarily responsible for observed rapid C accumulation in peatlands where climatic limitations to growth are weak
Volcanoes can deliver phosphorus to ecosystems through a variety of mechanisms, and the presence of the phosphate-rich mineral apatite and the presence of phosphorus within easilyweatherable volcanic glass support the contention that volcanic eruptions have been a source of elevated phosphorus inputs into Moanatuatua Bog
Summary
The global peatland carbon (C) sink is vast, 644 GT by the most recent estimates (Yu, 2011; Dargie et al, 2017), and greater than all the C content of fossil fuels burnt since 1870 (~435 GT C, as cited in Le Quere et al, 2018). Peatlands are very important for the global carbon cycle, and there is much interest in the controls of their C uptake and loss. Modern carbon sequestration in peatlands, measured over the past quarter-century or so, is often much higher than measurements of C accumulation rates (CAR) obtained from in peat cores representing longer time periods (Ratcliffe et al, 2018; Liu et al, 2019). In contrast to modern C flux measurements, longterm measurements of CAR, derived from peat cores, typically span several millennia or more and are heavily weighted towards the period before industrialisation began (~1750 CE). Ratcliffe et al / Quaternary Science Reviews 246 (2020) 106505 nitrogen (N) (Stevens et al, 2015) and phosphorus (P) deposition (Brahney et al, 2015; Wang et al, 2015b), and nutrient-mediated effects have been cited as hypothetical explanations for the discrepancy between long-term and modern records of peatland C uptake (Turunen et al, 2004; Yu, 2012; Ratcliffe et al, 2018)
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