Amazon Basin Forest Pyrogenic Carbon Stocks First
Total Page：16
File Type：pdf, Size：1020Kb
Geoderma 306 (2017) 237–243 Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma Amazon Basin forest pyrogenic carbon stocks: First estimate of deep storage MARK ⁎ Nina Koelea, , Michael Birdb, Jordahna Haigb, Ben Hur Marimon-Juniora, Beatriz Schwantes Marimona, Oliver L. Phillipsc, Edmar A. de Oliveiraa, C.A. Quesadad, ⁎⁎ Ted R. Feldpauscha,e, a Laboratório de Ecología Vegetal, Universidade do Estado de Mato Grosso (UNEMAT), Caixa Postal 08, CEP 78.690-000 Nova Xavantina, MT, Brazil b College of Science, Technology and Engineering and Centre for Tropical Environmental and Sustainability Science, James Cook University, Cairns, Queensland 4870, Australia c School of Geography, University of Leeds, Leeds LS29JT, UK d National Institute for Research in Amazonia (INPA), C.P. 2223, 69080-971 Manaus, Amazonas, Brazil e Geography, College of Life and Environmental Sciences, University of Exeter, Rennes Drive, Exeter EX4 4RJ, UK ARTICLE INFO ABSTRACT Keywords: Amazon Basin forest soils contain considerable soil organic carbon stocks; however, the contribution of soil Deep mineral soil horizons pyrogenic carbon (PyC) to the total is unknown. PyC is derived from local fires (historical and modern) and Soil organic carbon external inputs via aeolian deposition. To establish an initial estimate of PyC stocks in non-terra preta forest with Pyrogenic carbon stability no known history of fire, to assess site and vertical variability, as well as to determine optimal sampling design, we sampled 37 one hectare forest plots in the Amazon Basin and analysed PyC via hydrogen pyrolysis of three individual samples per plot and of bulked samples to 200 cm depth. Using our data and published total organic carbon stocks, we present the first field-based estimate of total PyC stock for the Amazon Basin of 1.10 Pg over 0–30 cm soil depth, and 2.76 Pg over 0–100 cm soil depth. This is up to 20 times higher than previously as- sumed. Three individual samples per 1 ha are sufficient to capture the site variability of PyC in our plots. PyC showed significant, large-scale variability among plots. To capture 50% of the PyC in 200 cm soil profiles, soil must be sampled to a depth of at least 71 cm. PyC represents a significant (11%) portion of total organic carbon in soil profiles 0–200 cm depth. This finding highlights the potentially important role that historical fire has played in modifying soil C stocks. Our data suggest that PyC is an important carbon pool for long-term storage, involved in millennial scale biogeochemical cycling, particularly in the subsurface soil. 1. Introduction biochar (pyrolysed biomass used as soil amendment) receives much interest as a C sink and soil conditioner globally (e.g. Mao et al., 2012; Amazon forest soils represent a large soil carbon pool, containing Turcios et al., 2016). Anthropogenic Amazon Dark Earths, also referred approximately 36.1 Pg C in the upper 30 cm and 66.9 Pg C in the upper to as Terra Preta de Índio, show significantly increased fertility through 1m (Batjes and Dijkshoorn, 1999). A substantial part of this carbon PyC additions (Glaser 2007); however, it is unknown if PyC in natural pool may exist as pyrogenic carbon (PyC) resulting from biomass forest soils in the Amazon Basin affects biomass and vegetation dy- burning. Following biomass burning, a fraction of PyC can quickly be namics. Knowledge on PyC in global carbon stocks and cycling is also lost from the soil through erosion in steep slopes (Rumpel et al., 2006, needed for monitoring and management of soil organic carbon under 2009) and decomposition (Kuzyakov et al. 2009; Bird et al., 2015). The land-use change and climate change (e.g. Cerri et al., 2007). Evaluating remaining PyC is highly resistant to degradation through its chemical the impact of PyC on natural forest soil dynamics, requires first quan- structure and through environmental conditions unfavourable to de- tifying PyC stocks in ecosystems globally. composition such as low oxygen and protection of PyC in organo-mi- The pools and fluxes of PyC in forest soils remain largely unknown neral complexes (Knicker, 2011). Therefore, PyC may reside in soils and poorly quantified (Santín et al., 2015), although Rodionov et al. from decades to millennia (Gouveia and Pessenda, 2000; Pessenda (2010) has estimated PyC stocks in grasslands around the world. For et al., 1996, 2001; Knicker, 2011). Given its stability, PyC in the form of example, Forbes et al. (2006) estimated that anywhere between 1 and ⁎ Corresponding author. ⁎⁎ Corresponding author at: Geography, College of Life and Environmental Sciences, University of Exeter, Rennes Drive, Exeter EX4 4RJ, UK. E-mail addresses: [email protected] (N. Koele), [email protected] (T.R. Feldpausch). http://dx.doi.org/10.1016/j.geoderma.2017.07.029 Received 3 April 2017; Received in revised form 24 July 2017; Accepted 24 July 2017 Available online 08 August 2017 0016-7061/ © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/). N. Koele et al. Geoderma 306 (2017) 237–243 35% of soil organic carbon (SOC) in soil is PyC. Estimates of soil PyC firme tropical forest with no known history of recent fire or recent stocks are scarce for many areas worldwide (Bird et al., 2015). For the anthropogenic disturbance. Within each plot, one soil pit and five humid tropical forest soils, Bird et al. (2015) assumed 1% PyC/SOC, but within-plot individual auger samples (undisturbed soil sampler, Eij- it remains to be tested whether this is an accurate estimate. In the kelkamp, Agrisearch Equipment BV, Giesbeek, the Netherlands) were Amazon Basin, the amounts and spatial distribution of PyC in forest taken from the following depths of mineral soil: 0–5, 5–10, 10–20, soils can be linked to the historical occurrence of fire, due to drier 20–30, 30–50, 50–100, 100–150, 150–200 cm. Within-plot individual climatic periods in the past or through human disturbance in the last samples were taken throughout the whole 1 ha plots. Sampling proto- 9000 years (Pessenda et al., 2004). Filling the knowledge gaps con- cols for RAINFOR soils are described in detail by Quesada et al. (2010). cerning PyC stocks and distribution in tropical forest soils will allow Soils were classified according to the World Reference Base for Soil explicit incorporation of PyC dynamics into soil carbon models. Resources (IUSS Working Group WRB, 2006). Forest soil carbon exhibits significant spatial heterogeneity. Adequate sampling is needed to capture this heterogeneity, which can 2.2. Hydrogen pyrolysis quantification of pyrogenic carbon reveal patterns of both fire and above-ground biomass variation. Soil organic carbon in the topsoil can vary significantly over a lateral scale PyC was determined as stable polycyclic aromatic carbon analysed − of centimeters to meters, with coefficients of variation (CVs) larger than via hydrogen pyrolysis (HyPy) presented as an abundance (g kg 1) and 20% (Amador et al., 2000; Schöning et al., 2006; Metcalfe et al., 2008). as a ratio to TOC. TOC was determined by elemental analysis using a Lateral and horizontal PyC in soil content is probably even more vari- Costech ECS-4010 elemental analyser fitted with a zero blank auto- able than SOC, as PyC distribution is controlled by the spatial variation sampler. The PyC fraction of TOC was determined by elemental analysis of modern and past fire, biomass and post-fire erosion processes following hydrogen pyrolysis, which quantifies the Stable Polycyclic (Preston and Schmidt, 2006). Adequate sampling to capture hetero- Aromatic Carbon component of total PyC in a sample as defined by geneity of SOC in terra firme Amazon forest soils may require between (Wurster et al., 2012). The HyPy analysis technique used in this study 2 and 102 samples within 0.6 to 1 ha plots, depending on sampling follows the procedure described by Meredith et al. (2012). Briefly, solid depth and other physical and biological soil parameters (Metcalfe et al., ~10–50 mg samples were loaded with a Mo catalyst, pressurized to 2008). 150 bar of hydrogen gas in the HyPy reactor and heated at − − Past research suggests that bulking 25 samples from 5 transects into 300 °C min 1 to 250 °C, then 8 °C min 1 until a final hold temperature one bulk sample sufficiently captures the site distribution over several of 550 °C which was maintained for 2 min. The carbon content of the kilometers of SOC in woodlands, savanna, and deserts (Bird et al., sample before and after HyPy was used to calculate PyC content as a 2004). Similarly, the site and vertical distribution of charcoal may be fraction of TOC. We used the following soil bulking scheme to assess adequately described by taking between 2 and 10 samples per ca. 3 ha variability by depth and lateral variability within plots. Depth varia- (McMichael et al., 2012). Establishing a robust and adequate sampling bility: in a subset of 11 of the 37 sampled plots, chosen to represent as design for PyC determination would facilitate the integration of PyC in much as possible Amazon Basin forest soils, samples were analysed for standard soil sampling and surveys, thereby improving estimates for all depths to 200 cm. In three plots, samples were analysed to 150 cm, PyC stocks globally. Furthermore, while soil sampling is usually re- and for the remaining 23 plots samples were analysed to 30 cm depth. stricted to the upper soil layers, a large body of evidence now suggests Lateral variability: in 16 of the 37 sampled plots, three out of five in- that deeper C and nutrient pools contribute significantly to ecosystem dividual samples were analysed for depths 0–5, 5–10, 10–20, 20–30 cm, biogeochemical cycling (e.g.