SOIL PEDOLOGY- Article Review Nilovna Chatterjee

Overview of selected Article  Title: Genesis of Spodic Materials underneath Peat Bogs in a Danish Wetland  Authors: Soren M. Kristiansen, Kristian dalsgaard, Ingrid K. Thomsen, Heike knicker, Ankel Laubel, Dennis Schneider & Bent V. Odgaard.  Journal: Soil Science Society of America Journal - Pedology Division.

Overview of selected Article  Year: 2010 (July-August) (Published online on 2 nd June, 2010)  Volume: 74 (Number – 4)  Pages: 1284 – 1292

Justification Of Research  The underlying spodic horizon could be a possible indication of commonly occurring depth to the water table.  It could also indicate fluctuation in water table according to different pedologic factors causing different drying and wetness condition in soil in different parts of worlds.

Theories suggested: Theory 1: Spodic materials in a wet soil form directly as an illuvial horizon under a fluctuating water table. Theory 2: Spodic materials originates from upland soils which is Fe-rich Spodosol developed in a well drained substrate. A slow rising water table could have ripped off the Fe but more C may be stored due to OM precipitation underneath the peat bog.

Existence of the two proposed Theories: Coexisting as continuum in nature

Objectives:  To determine spatial and temporal relationship between spodic material underneath wetland and in overlying peaty material.  To determine the time of formation of peat bog i.e to check if it was formed before, simultaneous or after the primary OM accumulation in the illuvial subsoil horizon.

Methodology  1. Field Soil Sampling (Detailed Soil Survey map, augered soil up to 2 m depth per hectare)  2. Wet chemical Analyses (Soil Characteristics)  3. Micromorphology (using Kubiena boxes)  4. Pollen Analysis (using HF treatment)

Methodology (continued)  C NMR spectroscopy of precipitated OM (using HF treatment)  6. Radiocarbon Dating of soil organic matter (SOM) fractions (separated SOM into four compartment).

Soil Maps: Figure 1: Maps of study site in Stadsborg, Denmark ( L ): Land use cadastral map around 1800 before drainage. ( R ): USDA present day soil map.

Soil and Pollen Analyses: Soil samples were analyzed and tested for color, texture, bulk density, OC, pH, C:N Pollen was concentrated from stratigraphical subsamples from Kubiena boxes using HF pre- treatment to remove minerals. The pollen was mounted on silicone oil and grains were counted at a magnification of 400x.

C-13 NMR : Solid state NMR spectra were obtained from air dried and sieved material from 2Bhsm and 2Bs horizon. Treatment with HF to remove minerals. NMR spectroscopy obtained on a Bruker DSX 200, operating at a frequency of 50.3 MhZ Fourier transformation was applied.

Radio Carbon Dating Spodic materials were analyzed both as bulk soil samples and OM. Fractionation procedure separated OM into four compartments: acid extractable OM, humic acid, fulvic acid & humin. Soil washed with 2% HCl to yield acid extractable fraction. Selected soil samples from B horizons were radio carbon dated and analyzed for total C.

Results and Findings:  Soil classified as Medisaprist.  However, Strong illuvial features were noted in 2Bs horizon at 25 to 40 cm depth of mineral soil, qualifying this as spodic with ortstein properties.

 Soil and profile study suggested that OM illuviation in 2Bs horizon is mainly dominated by Al-OM complexation with an insignificant pedogenic alluminosilicate and lower extractable Fe and no Fe-related redox feature in the profile.  NMR study confirmed the presence of oxidized organic residues in 2Bs and 2Bsm horizon that might be related to the lateral transport DOM..

findings  Pollen data revealed that vegetation on the study site might have undergone podzolization before peat growth with a younger spodic horizon and formation of perched water table by sphagnum peat bogs.  Both pollen and radiocarbon dating data confirmed that a strong illuvial complexation of Al-OM for spodic materials where alkyl C structure were bounded by Al (from macromolecular structure) in wet sites that was possible near the period of peat bog covering the area compared to weak OM illuvial process in upland well- drained soil

What is Medisaprist soil (An example)  The soil is extremely poorly drained, being saturated to the soil surface throughout the year. Naturally, the soil supports very dense stands of silver pine forest but once cleared supports only swamp vegetation (sphagnum moss, rushes, ferns)  cm: Very fluid highly decomposed brownish black forest peat with abundant tree roots.  cm: Very fluid to moderately fluid dark brown silty peat with abundant tree roots.  cm: Dark greyish yellow moderately firm silt loam, massive.  cm+: Compact iron and organic-coated outwash gravels

Comprehension  The theory of formation of spodosol under wet condition as used by Harris and Hollien, 2000 acted as a backbone for this study and helped a lot for the critical review of this article.  Build up of spodic horizon were well discussed in our course with special reference to Al-Fe-OM complexation process which is really appreciable.

Conclusion  Applied methods for this study suggested that wet spodosol under Danish peat bog were formed by a strong in-situ Al-OM illuvial complexation on a recent time or just before the covering of peat bog into the wetland rather than Fe-rich well-drained upland spodic materials stayed there over a long period of time

Thank you!