DOI: 10.5061/dryad.tmpg4f502
title: Data for: Andic soil properties and tephra layers hamper C turnover in Icelandic peatlands - selective dissolution of Al, Fe, Si and decomposition proxies

description: Due to frequent volcanic activity and erosion of dryland soils, peatlands
 in Iceland receive regular additions of mineral aeolian deposits
 (tephra and eroded material). Therefore, their soils may develop not only
 histic, but also andic characteristics. Here we present data sets
 of a study that elucidates interactions between carbon characteristics and
 andic soil properties in Histosols of three Icelandic peatlands. The data
 sets contain information about the soil carbon structure derived by 13C
 NMR spectroscopy, andic soil properties based on selective
 dissolution of Al, Fe and Si, decomposition proxies C/N, δ13C and δ15N,
 information on total carbon and nitrogen content, dry bulk density, soil
 organic matter content and pH measured in deionised water and
 NaF solution.
description: 1. Description of methods used for collection/generation of
 data: <br><em>1.1 Soil Sampling
 Approach</em><br>The research area is in Austur Húnavatnssýsla
 in northwest Iceland. Soil samples were collected from three peatlands
 along a north-south transect from the coast (Torfdalsmýri - TDM), via the
 lowlands (Tindar - TIN) to the highland fringe (Hrafnabjörg - HRAFN). At
 each peatland, one soil profile was excavated. Each profile contains well
 preserved tephra deposits from the Hekla 3 and Hekla 4 eruption. Pooled
 bulk soil samples were collected at 10 cm intervals down to a depth of 20
 cm below the Hekla 4 tephra layer. Above and below the tephra layers,
 the sampling interval was reduced to 2 x 5 cm. 
 <em>1.2 Laboratory analyses</em>
 <em>1.2.1 Solid state 13C NMR
 spectroscopy </em><br>Solid state <sup>13</sup>C
 NMR spectroscopy was used to determine the chemical composition or
 structure of soil organic carbon (see e.g. Kögel-Knabner,
 1997).  <em>1.2.2 Dry Bulk Density, Soil Organic
 Matter, %C and %N, stable isotope ratios δ<sup>13</sup>C and
 δ<sup>15</sup>N </em><br>The dry bulk density of
 the soils (DBD) was determined by weighing after the drying of a known
 volume of soil. Soil organic matter content (SOM) and %Ash was measured by
 loss on ignition at 550 °C (e.g. Heiri et al., 2001). Determination of
 total carbon (%C) and nitrogen (%N) by dry combustion and of the stable
 isotope ratios δ<sup>13</sup>C and δ<sup>15</sup>N
 was conducted by the Cornell Isotope Laboratory, USA.  
 <em>1.2.3 Phosphate retention and pH in DiH2O and
 NaF</em><br>Phosphate retention was measured by
 spectrophotometrical absorbance at 466 nm after color reaction with nitric
 vanadomolybdate acid reagent (Blakemore et al., 1987). The pH in 1N NaF
 solution (pHNaF) was determined following Blakemore et al. (1987) and Soil
 Survey Staff (2014). Soil acidity (pH<sub>H2O</sub>) was
 measured in deionised water (DiH<sub>2</sub>O), using a
 soil:water ratio of 1:10 (Blakemore et al., 1987; Rayment & Lyons,
 2011). <br> <br><em>1.2.4 Selective dissolution of Al,
 Fe and Si</em><br>Extraction of Al, Fe and Si with ammonium
 oxalate (0.2 M, pH 3.0) followed Soil Survey Staff (2014; method 4G2). The
 sum of Al<sub>o</sub> + ½Fe<sub>o</sub> was
 calculated, which is a diagnostic criterion of andic soil properties (≥
 2%; IUSS Working Group WRB, 2015). Ferrihydrite was estimated as
 %ferrihydrite = %Fe<sub>o</sub> x 1.7 (Childs, 1985).
 Extraction of Al and Fe with sodium pyrophosphate followed Soil Survey
 Staff (2014; method 4G3). Allophane or allophane-like constituents were
 estimated by the equation proposed by <br>Mizota and van Reeuwijk
 (1989), based on Parfitt and Wilson (1985).  A more
 detailed description of the sampling approach and laboratory analyses is
 provided in the following manuscript: Möckel, S. C.,
 Erlendsson, E., & Gísladóttir, G. (2021). Andic Soil Properties
 and Tephra Layers Hamper C Turnover in Icelandic
 Peatlands. <br>Submitted to the Journal of JGR - Biogeosciences.
 https://doi.10.1002/essoar.10506826.1.
 References Blakemore, L. C., Searle, P. L.,
 & Daly, B. K. (1987). Methods for Chemical Analysis of
 Soils. Lower Hutt, NZ: NZ Soil Bureau, Department of Scientific and
 Industrial Research.  Childs, C. W. (1985). Towards
 understanding soil mineralogy II. Notes on ferrihydrite. N.Z. Soil Bureau
 Laboratory Report CM7. Lower Hutt, New Zealand: N.Z. Soil
 Bureau.  Heiri, O., Lotter, A. F., & Lemcke, G.
 (2001). Loss on ignition as a method for estimating organic and carbonate
 content in sediments: reproducibility and comparability of results.
 Journal of Paleolimnology, 25(1),
 101-110. https://doi.org/10.1023/A:1008119611481 IUSS
 Working Group WRB. (2015). World Reference Base for Soil Resources 2014,
 update 2015. International soil classification system for naming soils and
 creating legends for soil maps. World Soil Resources Reports No. 106. FAO,
 Rome. Kögel-Knabner, I. (1997). 13C and 15N NMR
 spectroscopy as a tool in soil organic matter studies. Geoderma, 80(3),
 243-270. https://doi.org/10.1016/S0016-7061(97)00055-4
 Mizota, C., & van Reeuwijk, L. P. (1989). Clay Mineralogy
 and Chemistry of Soils Formed in Volcanic Material in Diverse Climatic
 Regions. Soil Monograph 2. Wageningen: ISRIC.  Parfitt,
 R. L., & Wilson, A. D. (1985). Estimation of allophane and
 halloysite in three sequences of volcanic soils, New Zealand. Volcanic
 Soils Catena Supplement, 7, 1-8.  Rayment, G. E.,
 & Lyons, D. J. (2011). Soil Chemical Methods - Australasia.
 Australia: CSIRO Publishing.<br> <br>Soil Survey Staff.
 (2014). Soil Survey laboratory Methods manual: soil Survey investigations
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description: DATA-SPECIFIC INFORMATION FOR: Moeckel et al 2021_andic soil
 properties_decomposition proxies.xlsx 1. Number of
 variables: 20 2. Number of observations: 45 soil
 samples 3. Variable List: <br>The table shows raw
 data of:<br>- Selective extraction of aluminum (Al), silicon (Si)
 and iron (Fe) with ammonium oxalate (Al<sub>o</sub>,
 Fe<sub>o</sub>, Si<sub>o</sub>) reported in g
 kg<sup>-1</sup>. <br>- Selective extraction of Al and Fe
 with sodium pyrophosphate (Al<sub>p</sub>,
 Fe<sub>p</sub>) reported in g
 kg<sup>-1</sup>.<br>-
 Al<sub>o</sub>+0.5*Fe<sub><sup>o</sup></sub>, allophane and ferrihydrite reported in %.<br>- Al<sub>p</sub>/Al<sub>o</sub> and Fe<sub>p</sub>/Fe<sub>o</sub> ratios.<br>- Phosphate retention (P-ret.) reported in %.<br>- Total carbon (C) and nitrogen (N), reported in %.<br>- C/N ratio.<br>- Stable isotope ratios δ<sup>15</sup>N and δ<sup>13</sup>C, reported in ‰.<br>- Dry bulk density (DBD) reported in g cm<sup>-3</sup>.<br>- Soil organic matter content (SOM) reported in %.<br>- pH measured in deionised water (pH<sub>H2O</sub>) and in 1N NaF solution (pH<sub>NaF</sub>) DATA-SPECIFIC INFORMATION FOR: Moeckel et al 2021_13C NMR.xlsx 1. Number of variables: 2 2. Number of observations: 45 soil samples 3. Variable description: <br>The data tables show results of <sup>13</sup>C NMR spectroscopy of 45 soil samples, i.e. the chemical shift (ppm) and the according relative intensity (%).