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Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia
Quaternary International xxx (2015) 1e10
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Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia ~ lli a, *, Endla Asi b, To ~ nu To ~ nutare a, Alar Astover a, Lech Szajdak c, Indrek Tamm a Raimo Ko a
Estonian University of Life Sciences, F.R. Kreutzwaldi Str. 1A, 51014 Tartu, Estonia €e Road 33, 10616 Tallinn, Estonia Estonian Environment Agency, Mustama c Institute of Agricultural and Forest Environment, Polish Academy of Sciences, ul. Bukowska 19, 60-809 Poznan, Poland b
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
The morphology and chemical characteristics of mineral soils underlying modern peaty (histic) and shallow peat soils (or histosols) are analyzed in pedoecological conditions of Estonia. The underlying shallow peat mantle gley soils have been formed on different geological origin (glaciolacustrine, glacial, glaciofluvial, marine) parent materials. The peat mantle overlying gley soils has accumulated in the process of landscape paludification during the post glacial period. Using the Estonian Soil Classification (ESC), the peat layer thickness of peaty soils is 10e30 cm and of shallow peat soils, 30e100 cm. The studied peaty soils may be characterized as polygenetic soils. Depending on parent material properties (calcareousness, acidity, texture) and feeding water the peaty soils are divided into two types specified by ESC as peaty gley soils and peaty podzols, and by WRB as Histic Gleysols and Histic Podzols. The mineral soils underlying peat soils may be defined as paleosols. The development of such soils has proceeded according to the chronosequence: gley soils or protosols / peaty soils / fen soils / transitional bog soils / bog soils, whereas mineral paleosols may be found under fen, transitional bog and bog soils. The peat soils studied in this research work, classified by ESC as drained shallow transitional (mesotrophic) bog soils and by WRB as Drainic Dystric Ombric Hemic Fibric Histosols, are located on the edges of bog areas and are fed mostly by mesotrophic surface seepage water. In comparative analysis of three soil groups (peaty gley soils, peaty podzols and shallow peat soils) (i) their location on the landscape, the geological origin of their parent materials and morphology of the mineral layers are characterized; (ii) the vertical distribution of organic carbon and total nitrogen contents, and different characteristics of soil acidity are analyzed, and (iii) their catenal position or associated soils are characterized. In the case of peaty soils, the three types of mineral soil profiles (eluvial, eluvio-accumulative and accumulative) which underlie the peat cover were elucidated. Under thicker peat layers, i.e. under shallow peat soils, mostly humus accumulative profiles were found. In all analyzed sites, in the course of progressive paludification (among this peatification) the peaty soils have been formed from gley soils. The formation of the peaty soil stage was followed by the fen soil stage. Depending on the feeding water, some of these soils developed in the direction of bog soils, with an intermediary transitional bog stage. Artificial drainage is of great importance in the development of peat cover, which influences first the decomposition of top layer peat. © 2015 Elsevier Ltd and INQUA.
Keywords: Drainage Forest soils Paleosols Peatification Peat mantle Pedoecological conditions
1. Introduction
* Corresponding author. ~ lli), [email protected] (E. Asi), tonu. E-mail addresses: [email protected] (R. Ko ~nutare), [email protected] (A. Astover), szajlech@man. [email protected] (T. To poznan.pl (L. Szajdak), [email protected] (I. Tamm).
The formation of peat mantle (organic layer) on the lowest, liberated from continental ice and sea water, areas of Estonia took place during the postglacial period in the process of landscape paludification (including peatification). As the process developed, the mineral soil cover of the lowest parts of the landscape was gradually isolated by peat mantle from biological turnover and circulation of its component substances; the influence of
http://dx.doi.org/10.1016/j.quaint.2015.08.045 1040-6182/© 2015 Elsevier Ltd and INQUA.
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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meteorological features on mineral part of the soil cover weakened as well. At a certain point in time, the mineral soils were buried under the peat mantle: therefore, they may be treated as paleosols. In this study, the morphology, geological origin, granulometric composition and some chemical characteristics of mineral soil layers located under thin (<100 cm) peat mantle are analyzed in the temperate zone of the Atlanticecontinental climatic conditions. For better understanding the developmental peculiarities of the mineral soil cover, the data on formation time, position on the landscape and association with adjacent soils are presented. At the present time, the development of these buried mineral soils is controlled or influenced to a great extent by the character of the peat mantle covering them, and therefore the composition and fabric of the peat mantle and peculiarities of its modern ecological relationships with plant cover and feeding water (including artificial drainage) are also treated. The forming of the soil cover on higher Estonian (Upland Estonia) areas was initiated approximately 11e12,500 years ago, but on lower areas (Lowland Estonia) much later (7e8000 years ago; Raukas, 1995). The peatification of mineral gley soils started very soon after their liberation from the ice and sea water. The forming of high bog peats began later, 6e7000 years ago. The dominating parent materials of mineral soils underlying a shallow peat mantle are glaciolacustrine, glacial, glaciofluvial and marine deposits, with variegated texture and fabric. It appears that the research on the development of soil cover under the peat mantle, from the aspect of soil science, has been modest.
2. Material and methods 2.1. Material For the research work, data from the soil survey ‘BioSoil’ conducted under the framework of EC regulation Forest Focus were used. Data regarding the humus status characteristics from the database ‘Pedon’ as baselines levels in the evaluation of buried and paleosols development stages in comparison with modern normally developed soils were used as Supplemental Data. The distribution of BioSoil research areas (RA) by Estonian counties is given in Fig. 1; their complete list (numbers and names), grouping and soil species may be found in Table 1. The general and pedoecological characterization of separated soil groups is shown in Tables 2 and 3. Soil names of RAs are given by Estonian Soil Classification (ESC) and the World Reference Base for Soil Resources (WRB) with their codes (Table 1), but soil texture in the same table ~lli et al., 2008; IUSS…, 2014). Names of soil groups only by WRB (Ko are given in Table 2 by ESC and in Table 3 by WRB; group II is subdivided by certain characteristics into two subgroups (IIa and IIb). Soils of group IIa have been formed in much more fertile edaphological conditions as compared with soil group IIb (Table 3). In the process, previously published research on soil genesis (Reintam, 1997) as well as geological, telmatological and other works conducted in Estonia (Valk, 1988; Orru, 1995; Raukas, 1995; €e, 1997) were used. Raukas, Teeduma
Table 1 Research areas (RA), their distribution by counties, soil species by ESC and WRB, and altitude above sea level. Groupsa of RA
No of RA
Site of RA
County
Location on landscape b
I (5)
43 59 88 117 121 29 64 195 27 102 188 7 26 63 109 130 154 159
IIa (3)
IIb (3)
III (7)
€etaguse Ma K€ aru Kaavere Sandra Meleski Mustanina K€ aina Rassiku Kalina €€ Ra aka Loone Vahastu €lja Aruva Remniku Aula-Vintri Kanaküla Taagepera ~e Mustjo
Ida-Viru €€ La ane-Viru ~geva Jo Viljandi Viljandi Ida-Viru Hiiu ~geva Jo Ida-Viru Viljandi Rapla Harju Ida-Viru Ida-Viru Saare P€ arnu Valga ~ lva Po
AASL , m
Group
48 96.5 76.5 21.5 34 28 15.5 54.5 70.5 36.5 57.5 46.5 54 32 32 32 105 90
Nll Nul Sul Sll Sll Nll Nll Nul Sul Sll Nul Nll Nul Nll Nll Sll Sul Sul
Code by ESCd
Code by WRB
Texture by WRB
S2e300 S200 S1e200 S1e200 0 S200 Go1 Go1 Go1 GI1 GI1 GI1 LG1 LG1 LG1 LG1 LG1 LG1 LG1n
HS-hm/sa/om/dy/dr HS-hm/om/dy/dr HS-hm/fi/om/dy/dr HS-hm/fi/om/dy/dr HS-hm/om/dy/dr GL-hi/rd/cc/eu-sl/dr GL-hi/rd/eu-dr GL-hi/rd/ca-lo/dr GL-hi/rd/dy-lu/dr GL-hi/rd/sp/dy-ar/dr GL-hi/rd/dy-ar/lu/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab/os-lo/dr
LS/SL SiL L S LS SiL/SiCL S/SCL L/SL LS/S/LS/CL S/S S/S S/S S/LS/S S/S S/S S/S S/LS SL/SiL/L
c
a
Characterization of soil groups is given in Tables 2 and 3. AASL e altitude above sea level. c Classifying of RA-s by their location on landscape: N e North Estonia, S e South Estonia, ll e lowland, ul e upland. d Soil codes by ESC: S00 e thin (S000 e thick) transitional bog soils, where the lower indexes indicate peat decomposition degrees (1 e slightly, 2 e moderately and 3 e well), Go1 e saturated peaty soils, GI1 e unsaturated peaty soils and LG1 e peaty podzols. b
Table 2 Research areas' groups, their names by ESC and general characterization. Soil group
No of RA
Position on landscape and type of feeding water
Composition of tree layerb
Fed mostly on rainfall and mesotrophic seepage surface water; mixotrophic bog plains edges Depressions bottoms (lowest areas) on landscape and transitional areas between mineral and organic soil covers; fed by minerotrophic surface water Depressions on poor sandy wet areas and between beach ridges; fed by minerotrophic acid surface water
Pn7-8Bt2(Pc)
a
No
Name
I
Transitional bog soils
43, 59, 88, 117, 121
IIa IIb
Peaty gley soils
29, 64, 195 27, 102, 188
III
Peaty podzols
7, 26, 63, 109, 130, 154, 159
a b
Bt5-6Pc1-4Pn1-3
Pn10(Bt)
By ESC. Tree species: Bt e Betula, Pn e Pinus, and Pc e Picea (number following the tree e share of ten).
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
~lli et al. / Quaternary International xxx (2015) 1e10 R. Ko
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Table 3 Pedoecological characterization of RA-s soil groups. Group
Soil group namea
Type of HCb
HC acidity, pHCaCl2
Forest site typec and quality classd
OLe, cm
I
Drainic Dystric Ombric Fibric Hemic Histosols (Abruptic) Eutric Reductic Histic Gleysols (Drainic, Loamic, Siltic) Spodic Dystric Reductic Histic Gleysols (Drainic, Arenic, Luvic) Carbic Albic Histic Podzols (Arenic, Drainic, Ortsteinic)
Mesotrophic peat Peaty mull
Very strongly acid, 2.6e3.5
50e100
Slightly acid, 5.5e6.4
Peaty moder
Strongly acid, 3.5e4.5
Peaty mor
Very strongly acid, 2.6e3.5
Mesotrophic transitional bog and Myrtillus drained bog forests; IVeV Rich paludified Dryoptris and Filipendula mixed forest; IIeIII Paludified Polytrichum-Myrtillus and Carex forests; IIIeIV Poor paludified Vaccinium ulginosum and Polytrichum-Myrtillus forests; IIIeV
IIa IIb III a b c d e
12e18 17e30 17e27
By WRB. ~lli (HC e humus cover). By Ko ~hmus (2006). By Lo For not drained forests. Total thickness of organic layers.
2.2. Methodological remarks Some terms widely used in the Estonian soil science literature need some additional explanation: (i) soil cover e a superficial earth layer that is influenced by the soil forming process and consists of humus cover and subsoil; (ii) humus cover e a superficial part of soil cover or topsoil characterized by active carbon cycling; (iii) soil species e the taxon of ESC identified by soil genesis, and (iv) soil association e an assemblage of two or more soil species within a designated geographical unit, recurring in different patterns across the landscape. Analogically to the mineral soil cover (formed on mineral deposits), the cover formed on peats (or on peatlands) is the peat soil cover, which consists of different species of peat soils or histosols. The transitional area between mineral and peat soils is characterised by two layered soil covers, the superficial horizons of which have organic origin; the lower one has a mineral origin (Fig. 2). The thickness of peaty soil humus cover depends on peat (Thorizon by ESC) thickness as well as on the presence/absence of organo-mineral horizons' (AT as transitional horizon between humus and peat horizons) thickness. For humus cover (or epipedon) ~ lli et al., 2009a) is thickness of peat soils, the conventional 30 cm (Ko taken.
The thickness of peaty soil cover depends on both the thickness of the peaty humus cover and the profile fabric of the mineral subsoil. The peat soil cover thickness is taken as 50 cm, whereas for the characterization of shallow peat soils (having mineral soil material starting <100 cm from the soil surface) by WRB, the supplementary qualifier ‘abruptic’ is used. The eluvial horizon (E) is divided after ESC into two different subhorizons, whereas Ea is albic or podzolic and El eluvic or lessivaged horizon. RAs soils were analyzed (i) as dominant, subdominant or associated pedons, and (ii) as a compartment of soil association. As all studied soil groups (IeIII) have been developed from gley soils, ~ lli et al., 2008) were taken for baseline modern gley soils (Ko comparative analysis. In our work, a pedocentric approach is used, i.e. the soils are considered as a main terrestrial ecosystem forming agent. The parent materials on which the mineral soils of RAs have been formed are presented in Table 4. The properties (texture, calcareousness) and geological origin of these deposits were for the geological base, not only for singular pedons, but also for surrounding soil associations. Distribution patterns of geological deposits (geodiversity) have been influenced with its direct and lateral interrelationships on the whole landscape soil cover diversity or pedodiversity. Only the most superficial part (to the
Fig. 1. ‘BioSoil’ research areas (RA) distribution by Estonian counties. Soil groups names by Estonian Soil Classification (ESC): I e transitional bog soils, II e peaty gley soils, and III e peaty podzols. For RA-s' name, soil type and grouping see Table 1 and for soil groups general and pedoecological characterization e Tables 2 and 3.
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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Fig. 2. Soils of peatlands and mineral wetlands. G e gley soils; G1 e peaty or histic soils; M00 and S00 e thin peat soils or histosols (accordingly: M e fen and S e transitional bog soils); R000 and S000 e thick peat soils (R e bog soils); T e peats (T1 e fibric, T2 e hemic and T3 e sapric).
depth 50e75 cm) of the Quaternary deposit has been influenced by soil forming processes and therefore was incorporated into the soil cover composition (Tables 1 and 4). The research on the development of landscapes during the Quaternary and on the liberation of the Estonian territory from ice and water bodies covering them, in concordance with our field researches on the fabric of soil profiles, enabled us to estimate the approximate initial time of different soil forming processes and the age of soils (Raukas, 1995; Reintam, 1997; GSE, 1999). One important index in those estimations was the altitude of the RA above sea level as determined during the field works for each RA.
Environmental Research Laboratory (Tartu). Organic carbon was determined by infrared (combustion at 1100 C) using a Primacs-sc TOC Analyzer/Skalar. Total nitrogen was assayed spectrometrically by a modified Kjeldahl method using the titrimetric Kjeldec system. Soil pH in CaCl2 and H2O were determined by electrochemical methods using a soil-liquid ratio 1:5 and a Jenway 3320 pH meter. Exchangeable (xch) and free Hþ (acidity) were analysed electrochemically by barium chloride extraction (titrated to pH 7.8). The levels of aqua regia-extractable (xtr) and exchangeable (from barium chloride extraction) cations (xch) Ca were assayed spectrometrically using inductively coupled plasma spectroscopy.
Table 4 Quaternary deposits as mineral base and/or parent material of RA-s' soils. Group of RA
No of RA
Mineral deposits code on geological mapa
Deposits' origin and texture
I
43 59 88 117 121 29 64 195 27 102 188 7 26 63 109 130 154 159
lgIIIvrb/gIIIvr lgIIIvr gIIIvr lgIIIvr lIV/lgIIIvr lgIIIvrb/gIIIvr mIVlm/mIVlt/lIVan gIIIvr lgIIIvr/gIIIvr lgIIIvrb/gIIIvr lgIIIvrb lgIIIvrb/fIIIvr lgIIIvr lgIIIvrb mIVlm/mIVlt/lIVan lgIIIvrb fIIIvr/gIIIvl fIIIvl/gIIIvl/gIIug3/gIIug1
Baltic ice lake (BIL) loamy sands on glacial sandy loams BIL silty loams Glacial (pebble) loams Glaciolacustrine fine sands and clays Lacustrine loamy sands on glaciolacustrine sands and sandy loams BIL silty loams and silty clay loams on glacial silty clay loams Limnea sea sands on Litorina sea and Ancylus lake sandy clay loams Glacial loams and sandy loams Glaciolacustrine loamy sands and sands on glacial deposits BIL sands BIL sands BIL sands or glacifluvial stratified sands Glaciolacustrine fine sands BIL fine sands Limnea sea fine sands on litorina lake gravelly sands BIL sands Glacifluvial fine sands and loamy sands on glacial loams Glacifluvial silty loams and sandy loams on glacial loams
IIa
IIb
III
a Some abbreviations used in codes of Quaternary deposits map (1:400,000) of Estonia (GSE, 1999): Group name by origin lg e glaciolacustrine, g e glacial, l e lacustrine, m ~rtsj€ ~ rtsja €rve subformations' BIL e marine, f e glacifluvial; Subseries: II e Middle Pleistocene, III e Upper Pleistocene, and IV e Holocene; Subformations vr e Vo arve, vrb e Vo deposits, vl e Valgj€ arve, lm e Limnea Sea, lt e Litorina Sea, an e Ancylus Lake, ug1 e Lower Ugandi, and ug3 e Upper Ugandi.
2.3. Methods of laboratory analyses The particle size distribution in mineral soil material was determined by ISO 11277 (by sieving and sedimentation) in the Soil Laboratory of the Estonian University of Life Sciences. Chemical characteristics of all other soil samples were analysed in the
Cation exchange capacity was calculated according to the sum of bases and extractable acidity. The stocks of humus per different layers were calculated on the basis of their thickness, humus content (concentration) and soil bulk density. A detailed description of the laboratory analyses is given in the ‘BioSoil’ project manual (Forest Focus, 2006).
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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3. Results The thickness of peat layers and their subdivisions are given in Table 5 for RA soils. In all sites, the peat layers have accumulated on mineral soil layers in a similar regular order. The first peat layer in contact with mineral soil layer is well decomposed or sapric peat. In the course of further paludification, it was covered by moderately decomposed or hemic peat and subsequently by thin, undecomposed falling debris, or in the course of bogging a high bog or fibric peat layer was formed (Fig. 2). In the case of peaty podzols, the thickness of peats with lower decomposition degree is increased due to higher acidity and poorer mineral composition of the feeding water.
5
specified as paleosols; they are peaty paleosols or histopaleosols (Faw, 2012). The studied peat soils, classified by ESC drained shallow transitional (mesothropic) bog soils and by WRB mostly ‘Drainic Dystric Ombric Fibric Hemic Histosols (Abruptic)’, are located on the edges of larger bog areas and are fed mostly by mesotrophic surface seepage water. Peat layer thickness does not depend on soil age, as there are no substantial differences between soil group ages. The age of a soil is directly dependent upon its location (altitude above sea level) and its liberation time from the ice and/or sea water. Depending on the character of the feeding water, the peat formation on mineral lowland areas proceeds with accumulation of fen peats and the formation of thick (>100 cm) ‘Eutric Rheic Sapric
Table 5 Thickness, subdivision and minimally needed time for peat layers forming; the thickness and age of modern soil covers. Groupa
No of RA
Thickness of OLb, cm
I (5)
43 59 88 117 121 29 64 195 27 102 188 7 26 63 109 130 154 159
50 80 100(80) 105(80) 65 12 15 18 17 30 21 27 17 19 17 24 19 17
IIa (3)
IIb (3)
III (7)
a b c d e
Subdivision of OLc, cm T1
T2
T3
5 8 10 29 7 1 1 1 1 1 1 1 1 1 1 1 6 1
18 26 5 31 26 2 4 0 0 6 4 2 10 6 4 5 5 10
27 46 85 45 32 9 10 17 16 24 16 24 6 12 12 18 8 6
Timed, yr
Thickness of SCe, cm
Age of SC, 103 yr
1250 2020 2970 2200 1550 340 410 550 540 910 610 850 380 510 480 660 390 380
50 50 50 50 50 40 30 36 59 75 58 72 72 65 60 74 70 68
8.2 8.1 8.0 7.9 8.0 8.1 5.5 8.0 8.2 7.9 8.0 7.0 8.1 7.9 5.5 8.3 8.3 8.0
For group characterization see Tables 2 and 3. OL e organic layers or organic part of profiles. OL-s' subdivisions T1 e slightly, T2 e moderately and T3 e well decomposed peat. Time needed as minimum for forming of OL. SC e soil cover.
The thickness of peaty soil covers includes both peat layers and mineral soil layers influenced by soil forming processes, where the total maximal Ra thickness is within 70e75 cm. The studied peaty soils (with peat mantle 10e30 cm) are transitional soils between peat soils and gley soils, whereas peaty soils' fabric depends on the ratio of peat formation and peat decomposition. Depending on parent material properties (calcareousness, acidity, texture, feeding water) the peaty soils were divided into peaty gley soils and peaty podzols. The peat soils studied are characterized mostly by a shallow (50e100 cm) peat layer, but the mineral soils under the peat layer may be specified as paleosols. Not only mineral soils may be defined as paleosols. When the conventional thickness of the peat soil cover is taken to be 50 cm, the peat layers beneath may also be
Histosols’ or proceeds in the direction of bog soils, forming ‘Dystric Ombric Fibric Histosols’. There exist sufficient possibilities for forming different transitional or intermediate species of peat soils. The thickness of the studied mineral soil layers and their resultant horizons are given in Table 6. Names and textures of these species may be found in Table 1. The character of dominance and association with other soil species are estimated using the large scale (1:10,000) soil map (Land Board, 2001). The comparison of the data about forest site types with soil cover classification units i.e. with soil species determined by ESC, demonstrates the mismatching of their classification units. For profound characterization of plant growing and ecosystem forming condition, the data on soil cover properties should be preferred and used.
Table 6 Thickness and fabric of mineral layers (ML), dominance, relation to forest site type and association with other soil species. Group
No of RA
ML, cm
Profile formula of MLa
Dominanceb
FSTc
Associated soilsd
I
43 59 88 117 121 29 64
35 40 20 20 40 28 15
BG-C1G-C2G BG-CG BG-CG BCG-C2G BCG-CG AT-BCG-CG-C2G AT-BCG-CG-C2G-C3G
a a sd sd d sd sd
ss mds ss ss ss tr-an tr
GI1-LG1-LG M000 -S000 -Go1 M00 -Go S000 -M00 -Go1-Go M00 -S000 Go-AG Go-Gk-LG1
IIa
(continued on next page)
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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6 Table 6 (continued ) Group IIb
III
No of RA
ML, cm
Profile formula of MLa
Dominanceb
FSTc
Associated soilsd
195 27 102 188 7 26 63 109 130 154 159
18 42 45 37 45 55 46 43 50 51 51
AT-BCG-CG AT(A)-ElB-BCG-C2G AT-ElB-B(s)G-CG AEl-BG-BC-C2G-C3G-C4G EaB-B(h)s-BCG-CG EaB-Bhs-BCG-CG EaB-BG-CG Ea-BhsG-BCG-C1G-C2G Ea-BhsG-BCG-CG Ea-BhsG-BCG-C2G EaB-EaBsG-C2G
d a a a sd d d a a sd a
an an kr-ms ms-an sn kr-ms kr kr tr kr-ms kr-ms
Go GI-M00 -Go1-LG1 R00 -S00 -GI-LG1-LG LkG-LG-LG1 LGn-LG-LkG-GI S00 -GI-Lg-Lkg LG-GI1-LkG LkG-GI-LG GI-GI1-LG-Lkg-M00 LG-Lg-Lkg LPg-S00 -LG-Lk
a
Horizons in soil profile formulas are given by WRB, for some exceptions see Methods. Dominance: d e dominant, sd e subdominant and a e associated soil. ~hmus (2006): ss e transitional bog, mds e Alder-birch fen, tr e Carex, an e Filipendula, kr e Polytrichum, ms e Myrtillus, sn e Vaccinium FST e forest site types by Lo ulginosum. d Soil species by ESC (see also Table 1): LG e Gley-podzol, M00 e thin (M000 e thick) fen soil, R00 e thin bog soil, Go e leached gley soil, AG e alluvial gley soil, Gk e pebble gley rendzina, GI e eluviated gley soil, LkG e podzolic gley soil, Lg e gleyed typical podzol, Lkg e gleyed podzolic soil, LPg e gleyed pseudopodzolic soil, Lk e podzolic soil. b c
The generalized complex formulas of soil profiles demonstrate the substantial differences between the four soil subgroups (Table 7). Differentiation of soil mineral part has taken place mostly before the soil peatification process. Formation of peat cover stops incorporation of carbon into the mineral part of the soil cover by biological processes. At the same time, some chemical processes (connected with podzolization and leaching of its products) continued after the cessation of biological processes.
Of great importance in the development of peat mantle is artificial drainage, which influences the decomposition rate of top layer peats. In the case of drainage, the decomposition degree of superficial peat layers is increased, which is accompanied by an increase of peat bulk density, decreasing thickness (by subsidence) of the peat mantle, and increased emission of carbon dioxide into the atmosphere, or a decrease of soil cover carbon storage (Fig. 3).
Table 7 Generalized soil groups and subgroups' profiles formula. Soilsa by ESC
Group
00
I IIa IIb III a b c d
S Go1 GI1 LG1
Generalized formula of profilesb
OLc, cm
MLd, cm
Soil cover thickness, cm
T1-T2-T3-BG(BCG)-CG(C2G) O1-(O2)-O3-AT-BCG-CG-C2G O1-(O2)-O3-AT-ElB(AEl)-BG(BCG)-CG-C2G O1-O2-O3-(Ea)EaB-BhsG(BG)-BCG-CG-C2G
50e105 12e18 17e30 17e27
20e40 15e28 37e45 43e55
50 30e40 58e75 60e74
Codes by ESC see Table 1; 2) T e peat layers, O e peaty forest floor layer, and numbers behind them indicate decomposition stage, whereas 1 e is slightly. Moderately and 3 e well decomposed. OL e organic layers or organic part thickness. ML e mineral layers' thickness.
In Table 8, the soils are characterized by soil groups, using the principal and supplemental qualifiers of the WRB. The factors influencing morphology and thickness of soil cover, properties and development of peat mantle and underlying soils are: (i) its location (catenal position) on the landscape (altitude above sea level, landforms), (ii) geological origin, texture and properties of soil parent material, (iii) the composition and character of the feeding water, (iv) the character of dominant and associated soils, and (v) drainage status of the area.
The data on vertical distribution of soil acidity and calcareousness characteristics are given for the mineral part of peaty soils in Table 9 and for peat soils in Table 10. The vertical distribution of soil organic carbon in the mineral layers of peaty gley soils and peaty podzols is different (Fig. 4). In the upper part of the mineral layers of peaty gley soils the concentration (g kg1) of organic carbon is higher as compared with peaty podzols. In the lower part, it is the opposite.
Table 8 Characterization of RA-s' soil groups by means of WRB-2014 qualifiers. Group
Soil by ESC
Qualifiers: Principal//supplemental
I IIa IIb III
S00 Go1 GI1 LG1
hemic, sapric, fibric, drainic, ombric, dystric//e histic, reductigleyic, calcic, calcaric, eutric//loamic, drainic histic, reductigleyic, spodic, dystric//luvic, arenic, loamic, drainic histic, albic, gleyic, ortsteinic//arenic, drainic
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
~lli et al. / Quaternary International xxx (2015) 1e10 R. Ko
7
Table 9 Vertical distribution of chemical characteristics in mineral part of peaty (histic) soils. Characteristica
Unit
Peaty gley soils 0e10 ne12
1
Corg Ntot pHCaCl2 pHH2 O Free Hþ Ca-xtr Ca-xch a b
49.2b 2.9b 5.1a 5.6a 4.0ab 4.0a 149b
g kg g kg1
mmol þ kg1 g kg1 mmol þ kg1
b
Peaty podzols 10e20 ne6
20e40 ne6
40e80 ne6
0e10 ne14
10e20 ne7
20e40 ne7
40e80 ne7
15.1a 0.5a 5.5a 6.0a 1.9a 4.0a 40a
7.0a 0.3a 5.8a 6.5a 1.1a 8.1ab 38a
3.3a 0.3a 6.2a 6.7a 0.7a 19.0b 48a
12.0ab 0.5b 3.5a 4.5a 7.7c 0.1a 2.3a
11.9ab 0.4ab 3.8ab 4.5a 4.9b 0.2ab 1.9a
13.2b 0.5b 4.1bc 4.7ab 3.1ab 0.4b 2.7a
6.8a 0.2a 4.4c 5.1b 2.0a 0.7c 4.1a
Ntot g kg1
Ntot Mg ha1
C:N
pHCaCl2
Ca-xch mmol kg1
BSa %
e e 11.2 1.6 5.6 e
e e 14.9 17.8 15.0 e
4.4 6.4 5.6 7.3 5.8 6.1
0.6 3.3 0.1 ND 7.6 1.6
80 79 99 100 99 98
Abbreviations: org e organic, tot e total, xtr e extractable, xch e exchangeable. The letters indicate significant difference at the p < 0.05 level.
Table 10 Chemical characteristics of mineral layers underlying shallow peat soils. No of RA
Depth cm
43 43 59 88 117 121 a b
Corg g kg1
Thickness cm
5085 85125 80120 100120 105125 65105
35 40 40 20 20 40
Corg Mg ha1
3.3 e 27.0 9.2 27.0 0.9
b
18 e 167 28 84 6
ND e 1.8 0.5 1.8 ND
BS e base saturation. ND e not determined.
In addition to the vertical distribution of Corg and Ntot concentrations (g kg1), data on vertical distributions of carbon and nitrogen stocks (Mg ha1) are presented in Table 11 for peaty soils and in Table 10 for peat soils. Table 12 includes the assembled data needed for comparative analysis of wet soil humus status.
4. Discussion 4.1. Peat mantle development Depending on the climatic zone and on local pedoecological conditions, the peat mantles upon mineral deposits may vary
Table 11 Vertical distribution of soil organic carbon and total nitrogen stocks (Mg ha1) in mineral layers of peaty soils. Soil group
Soil
Stock
Corg and Ntot by soil layers, Mg ha1
II
G1 ne8 LG1 ne6
Corg Ntot Corg Ntot
31.6 1.76 8.6 0.39
0e5
III a
5e10 ± ± ± ±
4.3a 0.37 1.8 0.09
16.9 0.88 5.9 0.28
± ± ± ±
C:N by soil layers
10e20 4.1 0.19 1.3 0.06
23.8 1.16 15.1 0.59
± ± ± ±
20e40 6.6 0.25 2.2 0.10
22.2 1.18 34.3 1.28
± ± ± ±
40e80 7.7 0.28 4.8 0.11
13.1 0.57 28.8 1.01
± ± ± ±
5.2 0.18 5.9 0.21
0e5
5e10
10e20
20e40
40e80
18.0
19.2
20.5
18.8
23.0
22.0
21.1
25.5
26.8
28.5
Mean ± SE.
Table 12 Comparison of wetland soils' organic and mineral layers by mean thicknesses (cm) and Corg stocks (Mg ha1). Soilsa
n
OLb, cm
MLc, cm
Corg OL Mg ha1
Corg ML Mg ha1
Total Corg Mg ha1
Corg of solum Mg ha1
Corg OLd Mg ha1 cm1
Corg ML Mg ha1 cm1
C:N OL/ML
Sourcee
S00 Go1 GI1 LG1 Go&GI LG LG1
5 3 3 6 8 6 15
71.0 15.0 22.7 18.8 3.0 9.4 15.4
31.0 20.3 41.3 49.3 62.0 67.6 59.6
481.7 53.6 104.9 99.0 9.8 30.4 45.3
60.6 74.5 139.7 92.6 140.5 83.1 71.8
542.3 128.1 244.6 191.6 150.3 113.5 117.1
348.1 114.3 223.1 143.4 150.3 113.5 117.1
6.8 3.6 4.6 5.3 3.3 3.2 2.9
2.0 3.7 3.4 1.9 2.3 1.2 1.2
32.0/15.2 17.2/12.0 28.2/24.4 29.5/26.1 21.9/13.6 36.9/16.1 38.7/19.4
BioSoil BioSoil BioSoil BioSoil Pedon Pedon Pedon
a b c d e
Soils e see Table 6. OL e organic layers. ML e mineral layers. Mg Corg per 1 ha and per 1 cm soil layer. ~lli et al., 2008). BioSoil i.e. from actual work and Pedon (Ko
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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Fig. 3. Development of peatification.
widely according to their fabric, properties and thickness (Valk, €kila €, Saarnito, 1988; Allikvee and Ilomets, 1995; Orru, 1995; Ma 2008; Gorham et al., 2012). Here, we will treat this from the position of soil science using ESC as a tool to explain the present status of landscape peatification (Figs. 2 and 3). Peat soils (peat thickness >30 cm) cover 23.7% of Estonian ter~ lli et al., 2009b). Of this, 2/3 has been formed by peatifiritory (Ko cation of mineral soils and 1/3 by terrestrialization of water bodies (Allikvee and Ilomets, 1995). By soil type, 59.0% of peat soils are typical fen, 21.7% bog, 14.7% transitional bog, 2.3% alluvial fen and ~lli et al., 2009a). By peat thickness, 2.3% technogenic peat soils (Ko 65.9% are thick (>100 cm), 21.5% shallow (50e100 cm) and 12.6% very shallow (30e50 cm). Only the superficial part (in ecological conditions of temperate zone e approximately 50 cm) of peatland peat is peat soil cover. The underlying parts should be treated as natural resources (or peat reserve). Analogously, soils or soil cover can form on oil shale, on brown coal or on other sediments of organic origin, which superficial part may be treated as particular soils' parent material. Theoretically, the underlying soil covers peats may qualify as paleosols or more precisely peaty paleosols i.e. histopaleosols (Faw, 2012). However, such an approximation may have only theoretical, rather than practical importance.
Fig. 4. Vertical distribution of soil organic carbon (g kg1) in peaty (histic) gley soils (G1) and in peaty podzols (LG1).
Peaty soils (with peat thickness 10e30 cm) form 6.3% of Estonian soil cover; 4.7% belongs to peaty gley soils (saturated, nonsaturated, alluvial, coastal) and 1.6% to peaty podzols. All peaty soils in our study may be characterized as polygenetic soils with very shallow peat layer. Peatification takes place as well on natural gley soils, which is indicated by the presence of a very thin (<10 cm) superficial peat layer. According to our estimates, the peatification which proceeds on wet mineral soils involves approximately 15% of the Estonian soil cover. There is not firm agreement in the determination of peat soil cover thicknesses or in separating peat soil cover from peat deposits as natural reserves. For Estonian or for temperate pedoecological conditions, it seems acceptable to us to take 50 cm as the thickness of peat soil cover, and 30 cm for more active topsoil cover thickness. Peat carbon storage in bog soils' superficial 30 cm layers is 40e47 Mg Corg ha1, and in the 50 cm superficial layer or in the peat soil cover it is 130e148 Mg Corg ha1. For the fen soils, the same characteristics are accordingly 168e180 and ~lli et al., 2009a). The soil organic carbon 320e347 Mg Corg ha1 (Ko stock per hectare in transitional bog soil cover depends on the character of paludification processes. Under bogging conditions, the carbon stocks are similar to bog soils, but artificial drainage produces stocks more similar to the fen soils. The formation of peat mantle upon mineral deposits on lowlands includes the following chronosequence: gley soils or protosols (some of them have also <10 cm layer of peat) / peaty soils (with peat layer thickness 10e30 cm) / fen soils (very shallow, shallow and thick) / transitional bog soils (mostly thick and shallow) / bog soils (mostly thick). In all analyzed sites the peat layers have accumulated in the course of progressive paludification in the following order: sapric well decomposed peat / hemic intermediately decomposed peat / fibric (bog) peats. Peat accumulation and type depends on (i) soil phytoproductivity and peat forming from fallen debris, and (ii) peat decomposition and subsidence. Depending on the feeding water character (i) the peat formation proceeds with further accumulation of fen peat and therefore the formation of thick (>100 cm) WRB ‘Eutric Rheic Hemic Sapric Histosols’ or (ii) proceeds to the direction of bog ‘Dystric Ombric Fibric Histosols’. The intermediate transitional bog stage, with fibri-hemic and later with fibric peat histosols, may be found as well. All peat soils in this research belong by ESC to transitional bog soils (Tables 2 and 3). Artificial drainage (Oleszczuk et al., 2008) plays a crucial role in the development of the peat mantle, influencing the decomposition of the top layer peats. The intensified decomposition of upper peat influences layers deep within peat deposits. During the peatification history, the conditions for peat formation have changed in €kila €, Saarnisto, 2008; Gorham connection with climatic change (Ma et al., 2012). General directions and possible lapses in peat formation on Estonian territory are explained in Fig. 5.
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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Fig. 5. Evolution of paleoecological conditions (A) during Quaternary on the territory of Estonia, as pre-requisite of its peatification and bogging (B). A e development of paleoecological conditions (climate periods and accumulation of Quaternary sediments) in relation to time scale from the past until nowadays, where the abbreviations cl e cool, wr e warm, ar e arid and hm e humid characterise the climate, and BIL e Baltic Ice Lake and LIL e Local Ice Lake kind of sediments. B e the most intensive periods of peatification and bogging are shown by fragmentary columns, where the abbreviations ll e lowland, ul e upland, N e North Estonia and S e South Estonia explain the geomorphologic situation. The part A of the figure is compiled by Raukas, but the part B by Ilomets.
4.2. Rationale about mineral layer development The wet mineral soils of Estonia have been developed on parent materials accumulated mainly during the Upper Pleistocene. Of the total area, the glacial deposits represent 47.7%, glaciolacustrine 6.8%, and glaciofluvial 3.1% (Raukas, 1995). Although marine and lacustrine deposits' area is relatively small, they are the dominating parent material for the wet peaty and peat soils (GSE, 1999). Distribution of soil parent materials by RA with characterization of their texture is given in Table 4. The most important factor in soil formation and properties is the texture and calcareousness of parent materials, along with the character of the feeding water. The mineral Quaternary deposits on lowlands have been gradually transformed in its surficial part into the soil cover. In the initial stage of development, the shallow gley soils or protosols with accumulation of semi-decomposed organic matter into thin AThorizon have been formed. It may be supposed that some initially had a very thin (<10 cm) peat layer, as is characteristic of the ~ lli et al., 2008). contemporary young coastal gley soils (Ko In further soil cover development, some gley soils were transformed into peaty gley soils. In conditions suitable for the podzolization process (areas with sandy texture and oligotrophic feeding water), gley-podzols rather than gley soils formed. A thicker (10e30 cm) fibric peat layer was formed on gley-podzols, or they have been transformed into peaty podzols. Some properties of the two peaty gley soil subgroups (IIa and IIb) are substantially different (Tables 1, 3 and 6). Comparison of saturated peaty soils (Go1) and unsaturated peaty soils (GI1) reveals that the latter have eluvic properties. Their profile thickness is greater due to eluvial and illuvial horizons. Therefore, they form a transitional group of soils between saturated peaty soils and peaty podzols. However, it is possible that there are various changes in soil forming processes in concordance with changing soil forming factors. More commonly, the peaty gley soils transform into various fen soils (very shallow, shallow and thick), and the peaty podzols become bog soils. Under a very shallow (10e30 cm) peat mantle, three (clearly different) types of mineral soil profiles (humus accumulative, clay
eluvio-accumulative and AleFe-humus eluvial) were elucidated. Under shallow peat soils or histosols (peat thickness 50e100 cm), mostly humus accumulative mineral profiles were found. In comparison with modern gley soils, in their mineral part organic carbon content and stocks, and distribution depth (RA 59 is an exception) are much lower (see Tables 10 and 12). Judging by the age of the soil cover (Table 5), which for most RA soils is 7.9e8.3 ka (with exceptions for RAs 7, 64 and 109) and probable initiation time of peatification (approximately 6000 years ago), there existed intermittent periods with substantial loss of peats. Supposedly, these losses have been caused by climate change (Fig. 5), or by wild fires (Kuhry, 1994). It does not seem that artificial drainage has substantial influence on mineral soil properties (i.e. to content of organic carbon and nitrogen, and to acidity) underlying shallow peat layers. The drainage of peatlands favours researcher access to mineral paleosols under peaty soils.
5. Concluding remarks The forming of peat mantle with thickness >10 cm slowed or stopped accumulation of organic carbon into the underlying mineral soil, whereas in wet, permanently reducing (anoxic) conditions the decomposition rate of soil organic matter falls to zero. Therefore the soil profiles of gley soils underlying the peat mantle have been preserved mostly in an unchanged state. Under a shallow peat mantle, three types of mineral soil profiles (humus accumulative, clay eluvio-accumulative, AleFe-humus eluvial) were elucidated. In comparison with modern gley soils, the humus content and mineral profile depth of the studied polygenetic and paleosols was much lower. The first peat layer on paludified peaty gley soils is well decomposed sapric peat, which has been later covered by moderately decomposed hemic peat and at the surface, formed from falling litter, by poorly decomposed fibric peat. A great influence on the top layers of peat mantles is artificial drainage, which intensifies decomposition by forming a hemic peat layer on the surface of bog soils. However, the drainage did not have
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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substantial influence on the underlying mineral soils' properties (Corg, Ntot, acidity), at least during the initial period of its functioning. From the pedogenetic and (paleo)ecological aspects, it is important that soils have been researched as a complex of genetic horizons. Characterization of soil profiles (including paleosols) in mutual relationships with soil forming factors is of pivotal importance for an ecosystem approach and for the understanding of soil cover functioning and development regularities on landscapes. Acknowledgements We wish to thank the European Commission and the Estonian Environmental Investment Centre for co-financing the project ‘BioSoil’ soil survey; the Soil Science Laboratory of Estonian University of Life Sciences and Environmental Research Laboratory in Tartu for chemical analyses, and the Estonian Academy of Sciences for the support to our Estonian-Polish scientific collaboration. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.quaint.2015.08.045. References Allikvee, H., Ilomets, M., 1995. Sood ja nende areng (Peatlands and their development). In: Raukas, A. (Ed.), Eesti. Loodus. Valgus, Tallinn, pp. 327e347 (in Estonian, with English summary). Faw, M., 2012. A Pedogenic Approach to the Classification of Paleohistosols (MS. Thesis). Bowling Green State University, USA. Forest Focus, 2006. Sampling and analysis of soil. In: Manual on Methods and Criteria for Harmonized Sampling, Assessment, Monitoring and Analysis of the Effects of Air Pollution on Forests. Part IIIa. Forest Soil Co-ordinating Centre, Brussels, Belgium.
€pp, R., Geological Survey of Estonia (GSE), 1999. In: Kajak, K., Raukas, A., Karuka Rattas, M. (Eds.), Quaternary Deposits of Estonia. Map in Scale 1:400,000. GSE, Tallinn. Gorham, E., Lehman, C., Dyke, A., Clymoc, D., Janssens, J., 2012. Long-term carbon sequestration in North American peatlands. Quaternary Science Reviews 58, 77e82. IUSS Working Group WRB, 2014. World Reference Base for Soil Resources 2014. International Soil Classification System for Naming Soils and Creating Legends for Soil Maps. World Soil Resources Reports No. 106. FAO, Rome. ~lli, R., Astover, A., Noormets, M., To ~nutare, T., Szajdak, L., 2009a. Histosol as an Ko ecologically active constituent of peatland: a case study from Estonia. Plant and Soil 317 (1e2), 3e17. ~lli, R., Ellerma €e, O., Ko €ster, T., Lemetti, I., Asi, E., Kauer, K., 2009b. Stocks of organic Ko carbon in Estonian soils. Estonian Journal of Earth Sciences 58, 95e108. ~lli, R., Ellerma €e, O., Teras, T., 2008. Digital Collection of Estonian Soils. EMÜ. (Cited Ko 2014 Oct 22). Available from: http://mullad.emu.ee. Kuhry, P., 1994. The role of fire in the development of Sphagnum-dominated peatlands in western Boreal Canada. Journal of Ecology 82, 899e910. Land Board, 2001. Soil Map. (Cited 2015 March 13). Available from: http:// geoportaal.maaamet.ee. ~ hmus, E., 2006. Eesti metsakasvukohatüübid (Estonian forest site types). Eesti Lo Loodusfoto, Tartu (in Estonian). €kila €, M., Saarnisto, M., 2008. Carbon accumulation in boreal peatlands during the Ma Holocene e impacts of climate variations. In: Strack, M. (Ed.), Peatlands and €skyla, Finland, pp. 24e43. Climate Change. International Peat Society, Jyva €per, H., Maryganova, V., 2008. Impacts of Oleszczuk, R., Regina, K., Szajdak, L., Ho agricultural utilization of peat soils on the greenhouse gas balance. In: Strack, M. (Ed.), Peatlands and Climate Change. International Peat Society, €skyla, Finland, pp. 70e97. Jyva Orru, M., 1995. Eesti Turbasood. Teatmik (Estonian mires. Handbook). Eesti Geoloogiakeskus, Tallinn (in Estonian, with English summary). Raukas, A. (Ed.), 1995. Eesti. Loodus. Valgus ja Eesti Entsüklopeediakirjastus, Tallinn (in Estonian, with English summary). Raukas, A., Teedum€ ae, A. (Eds.), 1997. Geology and Mineral Resources of Estonia. Estonian Academy Publishers, Tallinn. €e, A. (Eds.), Geology and Reintam, L., 1997. Soil formation. In: Raukas, A., Teeduma Mineral Resources of Estonia. Estonian Academy Publishers, Tallinn, pp. 298e306. Valk, U. (Ed.), 1988. Eesti sood [Estonian peatlands]. Valgus, Tallinn (in Estonian, with English summary).
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia ~ lli a, *, Endla Asi b, To ~ nu To ~ nutare a, Alar Astover a, Lech Szajdak c, Indrek Tamm a Raimo Ko a
Estonian University of Life Sciences, F.R. Kreutzwaldi Str. 1A, 51014 Tartu, Estonia €e Road 33, 10616 Tallinn, Estonia Estonian Environment Agency, Mustama c Institute of Agricultural and Forest Environment, Polish Academy of Sciences, ul. Bukowska 19, 60-809 Poznan, Poland b
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
The morphology and chemical characteristics of mineral soils underlying modern peaty (histic) and shallow peat soils (or histosols) are analyzed in pedoecological conditions of Estonia. The underlying shallow peat mantle gley soils have been formed on different geological origin (glaciolacustrine, glacial, glaciofluvial, marine) parent materials. The peat mantle overlying gley soils has accumulated in the process of landscape paludification during the post glacial period. Using the Estonian Soil Classification (ESC), the peat layer thickness of peaty soils is 10e30 cm and of shallow peat soils, 30e100 cm. The studied peaty soils may be characterized as polygenetic soils. Depending on parent material properties (calcareousness, acidity, texture) and feeding water the peaty soils are divided into two types specified by ESC as peaty gley soils and peaty podzols, and by WRB as Histic Gleysols and Histic Podzols. The mineral soils underlying peat soils may be defined as paleosols. The development of such soils has proceeded according to the chronosequence: gley soils or protosols / peaty soils / fen soils / transitional bog soils / bog soils, whereas mineral paleosols may be found under fen, transitional bog and bog soils. The peat soils studied in this research work, classified by ESC as drained shallow transitional (mesotrophic) bog soils and by WRB as Drainic Dystric Ombric Hemic Fibric Histosols, are located on the edges of bog areas and are fed mostly by mesotrophic surface seepage water. In comparative analysis of three soil groups (peaty gley soils, peaty podzols and shallow peat soils) (i) their location on the landscape, the geological origin of their parent materials and morphology of the mineral layers are characterized; (ii) the vertical distribution of organic carbon and total nitrogen contents, and different characteristics of soil acidity are analyzed, and (iii) their catenal position or associated soils are characterized. In the case of peaty soils, the three types of mineral soil profiles (eluvial, eluvio-accumulative and accumulative) which underlie the peat cover were elucidated. Under thicker peat layers, i.e. under shallow peat soils, mostly humus accumulative profiles were found. In all analyzed sites, in the course of progressive paludification (among this peatification) the peaty soils have been formed from gley soils. The formation of the peaty soil stage was followed by the fen soil stage. Depending on the feeding water, some of these soils developed in the direction of bog soils, with an intermediary transitional bog stage. Artificial drainage is of great importance in the development of peat cover, which influences first the decomposition of top layer peat. © 2015 Elsevier Ltd and INQUA.
Keywords: Drainage Forest soils Paleosols Peatification Peat mantle Pedoecological conditions
1. Introduction
* Corresponding author. ~ lli), [email protected] (E. Asi), tonu. E-mail addresses: [email protected] (R. Ko ~nutare), [email protected] (A. Astover), szajlech@man. [email protected] (T. To poznan.pl (L. Szajdak), [email protected] (I. Tamm).
The formation of peat mantle (organic layer) on the lowest, liberated from continental ice and sea water, areas of Estonia took place during the postglacial period in the process of landscape paludification (including peatification). As the process developed, the mineral soil cover of the lowest parts of the landscape was gradually isolated by peat mantle from biological turnover and circulation of its component substances; the influence of
http://dx.doi.org/10.1016/j.quaint.2015.08.045 1040-6182/© 2015 Elsevier Ltd and INQUA.
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2
meteorological features on mineral part of the soil cover weakened as well. At a certain point in time, the mineral soils were buried under the peat mantle: therefore, they may be treated as paleosols. In this study, the morphology, geological origin, granulometric composition and some chemical characteristics of mineral soil layers located under thin (<100 cm) peat mantle are analyzed in the temperate zone of the Atlanticecontinental climatic conditions. For better understanding the developmental peculiarities of the mineral soil cover, the data on formation time, position on the landscape and association with adjacent soils are presented. At the present time, the development of these buried mineral soils is controlled or influenced to a great extent by the character of the peat mantle covering them, and therefore the composition and fabric of the peat mantle and peculiarities of its modern ecological relationships with plant cover and feeding water (including artificial drainage) are also treated. The forming of the soil cover on higher Estonian (Upland Estonia) areas was initiated approximately 11e12,500 years ago, but on lower areas (Lowland Estonia) much later (7e8000 years ago; Raukas, 1995). The peatification of mineral gley soils started very soon after their liberation from the ice and sea water. The forming of high bog peats began later, 6e7000 years ago. The dominating parent materials of mineral soils underlying a shallow peat mantle are glaciolacustrine, glacial, glaciofluvial and marine deposits, with variegated texture and fabric. It appears that the research on the development of soil cover under the peat mantle, from the aspect of soil science, has been modest.
2. Material and methods 2.1. Material For the research work, data from the soil survey ‘BioSoil’ conducted under the framework of EC regulation Forest Focus were used. Data regarding the humus status characteristics from the database ‘Pedon’ as baselines levels in the evaluation of buried and paleosols development stages in comparison with modern normally developed soils were used as Supplemental Data. The distribution of BioSoil research areas (RA) by Estonian counties is given in Fig. 1; their complete list (numbers and names), grouping and soil species may be found in Table 1. The general and pedoecological characterization of separated soil groups is shown in Tables 2 and 3. Soil names of RAs are given by Estonian Soil Classification (ESC) and the World Reference Base for Soil Resources (WRB) with their codes (Table 1), but soil texture in the same table ~lli et al., 2008; IUSS…, 2014). Names of soil groups only by WRB (Ko are given in Table 2 by ESC and in Table 3 by WRB; group II is subdivided by certain characteristics into two subgroups (IIa and IIb). Soils of group IIa have been formed in much more fertile edaphological conditions as compared with soil group IIb (Table 3). In the process, previously published research on soil genesis (Reintam, 1997) as well as geological, telmatological and other works conducted in Estonia (Valk, 1988; Orru, 1995; Raukas, 1995; €e, 1997) were used. Raukas, Teeduma
Table 1 Research areas (RA), their distribution by counties, soil species by ESC and WRB, and altitude above sea level. Groupsa of RA
No of RA
Site of RA
County
Location on landscape b
I (5)
43 59 88 117 121 29 64 195 27 102 188 7 26 63 109 130 154 159
IIa (3)
IIb (3)
III (7)
€etaguse Ma K€ aru Kaavere Sandra Meleski Mustanina K€ aina Rassiku Kalina €€ Ra aka Loone Vahastu €lja Aruva Remniku Aula-Vintri Kanaküla Taagepera ~e Mustjo
Ida-Viru €€ La ane-Viru ~geva Jo Viljandi Viljandi Ida-Viru Hiiu ~geva Jo Ida-Viru Viljandi Rapla Harju Ida-Viru Ida-Viru Saare P€ arnu Valga ~ lva Po
AASL , m
Group
48 96.5 76.5 21.5 34 28 15.5 54.5 70.5 36.5 57.5 46.5 54 32 32 32 105 90
Nll Nul Sul Sll Sll Nll Nll Nul Sul Sll Nul Nll Nul Nll Nll Sll Sul Sul
Code by ESCd
Code by WRB
Texture by WRB
S2e300 S200 S1e200 S1e200 0 S200 Go1 Go1 Go1 GI1 GI1 GI1 LG1 LG1 LG1 LG1 LG1 LG1 LG1n
HS-hm/sa/om/dy/dr HS-hm/om/dy/dr HS-hm/fi/om/dy/dr HS-hm/fi/om/dy/dr HS-hm/om/dy/dr GL-hi/rd/cc/eu-sl/dr GL-hi/rd/eu-dr GL-hi/rd/ca-lo/dr GL-hi/rd/dy-lu/dr GL-hi/rd/sp/dy-ar/dr GL-hi/rd/dy-ar/lu/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab-ar/dr PZ-hi/ab/os-lo/dr
LS/SL SiL L S LS SiL/SiCL S/SCL L/SL LS/S/LS/CL S/S S/S S/S S/LS/S S/S S/S S/S S/LS SL/SiL/L
c
a
Characterization of soil groups is given in Tables 2 and 3. AASL e altitude above sea level. c Classifying of RA-s by their location on landscape: N e North Estonia, S e South Estonia, ll e lowland, ul e upland. d Soil codes by ESC: S00 e thin (S000 e thick) transitional bog soils, where the lower indexes indicate peat decomposition degrees (1 e slightly, 2 e moderately and 3 e well), Go1 e saturated peaty soils, GI1 e unsaturated peaty soils and LG1 e peaty podzols. b
Table 2 Research areas' groups, their names by ESC and general characterization. Soil group
No of RA
Position on landscape and type of feeding water
Composition of tree layerb
Fed mostly on rainfall and mesotrophic seepage surface water; mixotrophic bog plains edges Depressions bottoms (lowest areas) on landscape and transitional areas between mineral and organic soil covers; fed by minerotrophic surface water Depressions on poor sandy wet areas and between beach ridges; fed by minerotrophic acid surface water
Pn7-8Bt2(Pc)
a
No
Name
I
Transitional bog soils
43, 59, 88, 117, 121
IIa IIb
Peaty gley soils
29, 64, 195 27, 102, 188
III
Peaty podzols
7, 26, 63, 109, 130, 154, 159
a b
Bt5-6Pc1-4Pn1-3
Pn10(Bt)
By ESC. Tree species: Bt e Betula, Pn e Pinus, and Pc e Picea (number following the tree e share of ten).
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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3
Table 3 Pedoecological characterization of RA-s soil groups. Group
Soil group namea
Type of HCb
HC acidity, pHCaCl2
Forest site typec and quality classd
OLe, cm
I
Drainic Dystric Ombric Fibric Hemic Histosols (Abruptic) Eutric Reductic Histic Gleysols (Drainic, Loamic, Siltic) Spodic Dystric Reductic Histic Gleysols (Drainic, Arenic, Luvic) Carbic Albic Histic Podzols (Arenic, Drainic, Ortsteinic)
Mesotrophic peat Peaty mull
Very strongly acid, 2.6e3.5
50e100
Slightly acid, 5.5e6.4
Peaty moder
Strongly acid, 3.5e4.5
Peaty mor
Very strongly acid, 2.6e3.5
Mesotrophic transitional bog and Myrtillus drained bog forests; IVeV Rich paludified Dryoptris and Filipendula mixed forest; IIeIII Paludified Polytrichum-Myrtillus and Carex forests; IIIeIV Poor paludified Vaccinium ulginosum and Polytrichum-Myrtillus forests; IIIeV
IIa IIb III a b c d e
12e18 17e30 17e27
By WRB. ~lli (HC e humus cover). By Ko ~hmus (2006). By Lo For not drained forests. Total thickness of organic layers.
2.2. Methodological remarks Some terms widely used in the Estonian soil science literature need some additional explanation: (i) soil cover e a superficial earth layer that is influenced by the soil forming process and consists of humus cover and subsoil; (ii) humus cover e a superficial part of soil cover or topsoil characterized by active carbon cycling; (iii) soil species e the taxon of ESC identified by soil genesis, and (iv) soil association e an assemblage of two or more soil species within a designated geographical unit, recurring in different patterns across the landscape. Analogically to the mineral soil cover (formed on mineral deposits), the cover formed on peats (or on peatlands) is the peat soil cover, which consists of different species of peat soils or histosols. The transitional area between mineral and peat soils is characterised by two layered soil covers, the superficial horizons of which have organic origin; the lower one has a mineral origin (Fig. 2). The thickness of peaty soil humus cover depends on peat (Thorizon by ESC) thickness as well as on the presence/absence of organo-mineral horizons' (AT as transitional horizon between humus and peat horizons) thickness. For humus cover (or epipedon) ~ lli et al., 2009a) is thickness of peat soils, the conventional 30 cm (Ko taken.
The thickness of peaty soil cover depends on both the thickness of the peaty humus cover and the profile fabric of the mineral subsoil. The peat soil cover thickness is taken as 50 cm, whereas for the characterization of shallow peat soils (having mineral soil material starting <100 cm from the soil surface) by WRB, the supplementary qualifier ‘abruptic’ is used. The eluvial horizon (E) is divided after ESC into two different subhorizons, whereas Ea is albic or podzolic and El eluvic or lessivaged horizon. RAs soils were analyzed (i) as dominant, subdominant or associated pedons, and (ii) as a compartment of soil association. As all studied soil groups (IeIII) have been developed from gley soils, ~ lli et al., 2008) were taken for baseline modern gley soils (Ko comparative analysis. In our work, a pedocentric approach is used, i.e. the soils are considered as a main terrestrial ecosystem forming agent. The parent materials on which the mineral soils of RAs have been formed are presented in Table 4. The properties (texture, calcareousness) and geological origin of these deposits were for the geological base, not only for singular pedons, but also for surrounding soil associations. Distribution patterns of geological deposits (geodiversity) have been influenced with its direct and lateral interrelationships on the whole landscape soil cover diversity or pedodiversity. Only the most superficial part (to the
Fig. 1. ‘BioSoil’ research areas (RA) distribution by Estonian counties. Soil groups names by Estonian Soil Classification (ESC): I e transitional bog soils, II e peaty gley soils, and III e peaty podzols. For RA-s' name, soil type and grouping see Table 1 and for soil groups general and pedoecological characterization e Tables 2 and 3.
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Fig. 2. Soils of peatlands and mineral wetlands. G e gley soils; G1 e peaty or histic soils; M00 and S00 e thin peat soils or histosols (accordingly: M e fen and S e transitional bog soils); R000 and S000 e thick peat soils (R e bog soils); T e peats (T1 e fibric, T2 e hemic and T3 e sapric).
depth 50e75 cm) of the Quaternary deposit has been influenced by soil forming processes and therefore was incorporated into the soil cover composition (Tables 1 and 4). The research on the development of landscapes during the Quaternary and on the liberation of the Estonian territory from ice and water bodies covering them, in concordance with our field researches on the fabric of soil profiles, enabled us to estimate the approximate initial time of different soil forming processes and the age of soils (Raukas, 1995; Reintam, 1997; GSE, 1999). One important index in those estimations was the altitude of the RA above sea level as determined during the field works for each RA.
Environmental Research Laboratory (Tartu). Organic carbon was determined by infrared (combustion at 1100 C) using a Primacs-sc TOC Analyzer/Skalar. Total nitrogen was assayed spectrometrically by a modified Kjeldahl method using the titrimetric Kjeldec system. Soil pH in CaCl2 and H2O were determined by electrochemical methods using a soil-liquid ratio 1:5 and a Jenway 3320 pH meter. Exchangeable (xch) and free Hþ (acidity) were analysed electrochemically by barium chloride extraction (titrated to pH 7.8). The levels of aqua regia-extractable (xtr) and exchangeable (from barium chloride extraction) cations (xch) Ca were assayed spectrometrically using inductively coupled plasma spectroscopy.
Table 4 Quaternary deposits as mineral base and/or parent material of RA-s' soils. Group of RA
No of RA
Mineral deposits code on geological mapa
Deposits' origin and texture
I
43 59 88 117 121 29 64 195 27 102 188 7 26 63 109 130 154 159
lgIIIvrb/gIIIvr lgIIIvr gIIIvr lgIIIvr lIV/lgIIIvr lgIIIvrb/gIIIvr mIVlm/mIVlt/lIVan gIIIvr lgIIIvr/gIIIvr lgIIIvrb/gIIIvr lgIIIvrb lgIIIvrb/fIIIvr lgIIIvr lgIIIvrb mIVlm/mIVlt/lIVan lgIIIvrb fIIIvr/gIIIvl fIIIvl/gIIIvl/gIIug3/gIIug1
Baltic ice lake (BIL) loamy sands on glacial sandy loams BIL silty loams Glacial (pebble) loams Glaciolacustrine fine sands and clays Lacustrine loamy sands on glaciolacustrine sands and sandy loams BIL silty loams and silty clay loams on glacial silty clay loams Limnea sea sands on Litorina sea and Ancylus lake sandy clay loams Glacial loams and sandy loams Glaciolacustrine loamy sands and sands on glacial deposits BIL sands BIL sands BIL sands or glacifluvial stratified sands Glaciolacustrine fine sands BIL fine sands Limnea sea fine sands on litorina lake gravelly sands BIL sands Glacifluvial fine sands and loamy sands on glacial loams Glacifluvial silty loams and sandy loams on glacial loams
IIa
IIb
III
a Some abbreviations used in codes of Quaternary deposits map (1:400,000) of Estonia (GSE, 1999): Group name by origin lg e glaciolacustrine, g e glacial, l e lacustrine, m ~rtsj€ ~ rtsja €rve subformations' BIL e marine, f e glacifluvial; Subseries: II e Middle Pleistocene, III e Upper Pleistocene, and IV e Holocene; Subformations vr e Vo arve, vrb e Vo deposits, vl e Valgj€ arve, lm e Limnea Sea, lt e Litorina Sea, an e Ancylus Lake, ug1 e Lower Ugandi, and ug3 e Upper Ugandi.
2.3. Methods of laboratory analyses The particle size distribution in mineral soil material was determined by ISO 11277 (by sieving and sedimentation) in the Soil Laboratory of the Estonian University of Life Sciences. Chemical characteristics of all other soil samples were analysed in the
Cation exchange capacity was calculated according to the sum of bases and extractable acidity. The stocks of humus per different layers were calculated on the basis of their thickness, humus content (concentration) and soil bulk density. A detailed description of the laboratory analyses is given in the ‘BioSoil’ project manual (Forest Focus, 2006).
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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3. Results The thickness of peat layers and their subdivisions are given in Table 5 for RA soils. In all sites, the peat layers have accumulated on mineral soil layers in a similar regular order. The first peat layer in contact with mineral soil layer is well decomposed or sapric peat. In the course of further paludification, it was covered by moderately decomposed or hemic peat and subsequently by thin, undecomposed falling debris, or in the course of bogging a high bog or fibric peat layer was formed (Fig. 2). In the case of peaty podzols, the thickness of peats with lower decomposition degree is increased due to higher acidity and poorer mineral composition of the feeding water.
5
specified as paleosols; they are peaty paleosols or histopaleosols (Faw, 2012). The studied peat soils, classified by ESC drained shallow transitional (mesothropic) bog soils and by WRB mostly ‘Drainic Dystric Ombric Fibric Hemic Histosols (Abruptic)’, are located on the edges of larger bog areas and are fed mostly by mesotrophic surface seepage water. Peat layer thickness does not depend on soil age, as there are no substantial differences between soil group ages. The age of a soil is directly dependent upon its location (altitude above sea level) and its liberation time from the ice and/or sea water. Depending on the character of the feeding water, the peat formation on mineral lowland areas proceeds with accumulation of fen peats and the formation of thick (>100 cm) ‘Eutric Rheic Sapric
Table 5 Thickness, subdivision and minimally needed time for peat layers forming; the thickness and age of modern soil covers. Groupa
No of RA
Thickness of OLb, cm
I (5)
43 59 88 117 121 29 64 195 27 102 188 7 26 63 109 130 154 159
50 80 100(80) 105(80) 65 12 15 18 17 30 21 27 17 19 17 24 19 17
IIa (3)
IIb (3)
III (7)
a b c d e
Subdivision of OLc, cm T1
T2
T3
5 8 10 29 7 1 1 1 1 1 1 1 1 1 1 1 6 1
18 26 5 31 26 2 4 0 0 6 4 2 10 6 4 5 5 10
27 46 85 45 32 9 10 17 16 24 16 24 6 12 12 18 8 6
Timed, yr
Thickness of SCe, cm
Age of SC, 103 yr
1250 2020 2970 2200 1550 340 410 550 540 910 610 850 380 510 480 660 390 380
50 50 50 50 50 40 30 36 59 75 58 72 72 65 60 74 70 68
8.2 8.1 8.0 7.9 8.0 8.1 5.5 8.0 8.2 7.9 8.0 7.0 8.1 7.9 5.5 8.3 8.3 8.0
For group characterization see Tables 2 and 3. OL e organic layers or organic part of profiles. OL-s' subdivisions T1 e slightly, T2 e moderately and T3 e well decomposed peat. Time needed as minimum for forming of OL. SC e soil cover.
The thickness of peaty soil covers includes both peat layers and mineral soil layers influenced by soil forming processes, where the total maximal Ra thickness is within 70e75 cm. The studied peaty soils (with peat mantle 10e30 cm) are transitional soils between peat soils and gley soils, whereas peaty soils' fabric depends on the ratio of peat formation and peat decomposition. Depending on parent material properties (calcareousness, acidity, texture, feeding water) the peaty soils were divided into peaty gley soils and peaty podzols. The peat soils studied are characterized mostly by a shallow (50e100 cm) peat layer, but the mineral soils under the peat layer may be specified as paleosols. Not only mineral soils may be defined as paleosols. When the conventional thickness of the peat soil cover is taken to be 50 cm, the peat layers beneath may also be
Histosols’ or proceeds in the direction of bog soils, forming ‘Dystric Ombric Fibric Histosols’. There exist sufficient possibilities for forming different transitional or intermediate species of peat soils. The thickness of the studied mineral soil layers and their resultant horizons are given in Table 6. Names and textures of these species may be found in Table 1. The character of dominance and association with other soil species are estimated using the large scale (1:10,000) soil map (Land Board, 2001). The comparison of the data about forest site types with soil cover classification units i.e. with soil species determined by ESC, demonstrates the mismatching of their classification units. For profound characterization of plant growing and ecosystem forming condition, the data on soil cover properties should be preferred and used.
Table 6 Thickness and fabric of mineral layers (ML), dominance, relation to forest site type and association with other soil species. Group
No of RA
ML, cm
Profile formula of MLa
Dominanceb
FSTc
Associated soilsd
I
43 59 88 117 121 29 64
35 40 20 20 40 28 15
BG-C1G-C2G BG-CG BG-CG BCG-C2G BCG-CG AT-BCG-CG-C2G AT-BCG-CG-C2G-C3G
a a sd sd d sd sd
ss mds ss ss ss tr-an tr
GI1-LG1-LG M000 -S000 -Go1 M00 -Go S000 -M00 -Go1-Go M00 -S000 Go-AG Go-Gk-LG1
IIa
(continued on next page)
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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6 Table 6 (continued ) Group IIb
III
No of RA
ML, cm
Profile formula of MLa
Dominanceb
FSTc
Associated soilsd
195 27 102 188 7 26 63 109 130 154 159
18 42 45 37 45 55 46 43 50 51 51
AT-BCG-CG AT(A)-ElB-BCG-C2G AT-ElB-B(s)G-CG AEl-BG-BC-C2G-C3G-C4G EaB-B(h)s-BCG-CG EaB-Bhs-BCG-CG EaB-BG-CG Ea-BhsG-BCG-C1G-C2G Ea-BhsG-BCG-CG Ea-BhsG-BCG-C2G EaB-EaBsG-C2G
d a a a sd d d a a sd a
an an kr-ms ms-an sn kr-ms kr kr tr kr-ms kr-ms
Go GI-M00 -Go1-LG1 R00 -S00 -GI-LG1-LG LkG-LG-LG1 LGn-LG-LkG-GI S00 -GI-Lg-Lkg LG-GI1-LkG LkG-GI-LG GI-GI1-LG-Lkg-M00 LG-Lg-Lkg LPg-S00 -LG-Lk
a
Horizons in soil profile formulas are given by WRB, for some exceptions see Methods. Dominance: d e dominant, sd e subdominant and a e associated soil. ~hmus (2006): ss e transitional bog, mds e Alder-birch fen, tr e Carex, an e Filipendula, kr e Polytrichum, ms e Myrtillus, sn e Vaccinium FST e forest site types by Lo ulginosum. d Soil species by ESC (see also Table 1): LG e Gley-podzol, M00 e thin (M000 e thick) fen soil, R00 e thin bog soil, Go e leached gley soil, AG e alluvial gley soil, Gk e pebble gley rendzina, GI e eluviated gley soil, LkG e podzolic gley soil, Lg e gleyed typical podzol, Lkg e gleyed podzolic soil, LPg e gleyed pseudopodzolic soil, Lk e podzolic soil. b c
The generalized complex formulas of soil profiles demonstrate the substantial differences between the four soil subgroups (Table 7). Differentiation of soil mineral part has taken place mostly before the soil peatification process. Formation of peat cover stops incorporation of carbon into the mineral part of the soil cover by biological processes. At the same time, some chemical processes (connected with podzolization and leaching of its products) continued after the cessation of biological processes.
Of great importance in the development of peat mantle is artificial drainage, which influences the decomposition rate of top layer peats. In the case of drainage, the decomposition degree of superficial peat layers is increased, which is accompanied by an increase of peat bulk density, decreasing thickness (by subsidence) of the peat mantle, and increased emission of carbon dioxide into the atmosphere, or a decrease of soil cover carbon storage (Fig. 3).
Table 7 Generalized soil groups and subgroups' profiles formula. Soilsa by ESC
Group
00
I IIa IIb III a b c d
S Go1 GI1 LG1
Generalized formula of profilesb
OLc, cm
MLd, cm
Soil cover thickness, cm
T1-T2-T3-BG(BCG)-CG(C2G) O1-(O2)-O3-AT-BCG-CG-C2G O1-(O2)-O3-AT-ElB(AEl)-BG(BCG)-CG-C2G O1-O2-O3-(Ea)EaB-BhsG(BG)-BCG-CG-C2G
50e105 12e18 17e30 17e27
20e40 15e28 37e45 43e55
50 30e40 58e75 60e74
Codes by ESC see Table 1; 2) T e peat layers, O e peaty forest floor layer, and numbers behind them indicate decomposition stage, whereas 1 e is slightly. Moderately and 3 e well decomposed. OL e organic layers or organic part thickness. ML e mineral layers' thickness.
In Table 8, the soils are characterized by soil groups, using the principal and supplemental qualifiers of the WRB. The factors influencing morphology and thickness of soil cover, properties and development of peat mantle and underlying soils are: (i) its location (catenal position) on the landscape (altitude above sea level, landforms), (ii) geological origin, texture and properties of soil parent material, (iii) the composition and character of the feeding water, (iv) the character of dominant and associated soils, and (v) drainage status of the area.
The data on vertical distribution of soil acidity and calcareousness characteristics are given for the mineral part of peaty soils in Table 9 and for peat soils in Table 10. The vertical distribution of soil organic carbon in the mineral layers of peaty gley soils and peaty podzols is different (Fig. 4). In the upper part of the mineral layers of peaty gley soils the concentration (g kg1) of organic carbon is higher as compared with peaty podzols. In the lower part, it is the opposite.
Table 8 Characterization of RA-s' soil groups by means of WRB-2014 qualifiers. Group
Soil by ESC
Qualifiers: Principal//supplemental
I IIa IIb III
S00 Go1 GI1 LG1
hemic, sapric, fibric, drainic, ombric, dystric//e histic, reductigleyic, calcic, calcaric, eutric//loamic, drainic histic, reductigleyic, spodic, dystric//luvic, arenic, loamic, drainic histic, albic, gleyic, ortsteinic//arenic, drainic
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Table 9 Vertical distribution of chemical characteristics in mineral part of peaty (histic) soils. Characteristica
Unit
Peaty gley soils 0e10 ne12
1
Corg Ntot pHCaCl2 pHH2 O Free Hþ Ca-xtr Ca-xch a b
49.2b 2.9b 5.1a 5.6a 4.0ab 4.0a 149b
g kg g kg1
mmol þ kg1 g kg1 mmol þ kg1
b
Peaty podzols 10e20 ne6
20e40 ne6
40e80 ne6
0e10 ne14
10e20 ne7
20e40 ne7
40e80 ne7
15.1a 0.5a 5.5a 6.0a 1.9a 4.0a 40a
7.0a 0.3a 5.8a 6.5a 1.1a 8.1ab 38a
3.3a 0.3a 6.2a 6.7a 0.7a 19.0b 48a
12.0ab 0.5b 3.5a 4.5a 7.7c 0.1a 2.3a
11.9ab 0.4ab 3.8ab 4.5a 4.9b 0.2ab 1.9a
13.2b 0.5b 4.1bc 4.7ab 3.1ab 0.4b 2.7a
6.8a 0.2a 4.4c 5.1b 2.0a 0.7c 4.1a
Ntot g kg1
Ntot Mg ha1
C:N
pHCaCl2
Ca-xch mmol kg1
BSa %
e e 11.2 1.6 5.6 e
e e 14.9 17.8 15.0 e
4.4 6.4 5.6 7.3 5.8 6.1
0.6 3.3 0.1 ND 7.6 1.6
80 79 99 100 99 98
Abbreviations: org e organic, tot e total, xtr e extractable, xch e exchangeable. The letters indicate significant difference at the p < 0.05 level.
Table 10 Chemical characteristics of mineral layers underlying shallow peat soils. No of RA
Depth cm
43 43 59 88 117 121 a b
Corg g kg1
Thickness cm
5085 85125 80120 100120 105125 65105
35 40 40 20 20 40
Corg Mg ha1
3.3 e 27.0 9.2 27.0 0.9
b
18 e 167 28 84 6
ND e 1.8 0.5 1.8 ND
BS e base saturation. ND e not determined.
In addition to the vertical distribution of Corg and Ntot concentrations (g kg1), data on vertical distributions of carbon and nitrogen stocks (Mg ha1) are presented in Table 11 for peaty soils and in Table 10 for peat soils. Table 12 includes the assembled data needed for comparative analysis of wet soil humus status.
4. Discussion 4.1. Peat mantle development Depending on the climatic zone and on local pedoecological conditions, the peat mantles upon mineral deposits may vary
Table 11 Vertical distribution of soil organic carbon and total nitrogen stocks (Mg ha1) in mineral layers of peaty soils. Soil group
Soil
Stock
Corg and Ntot by soil layers, Mg ha1
II
G1 ne8 LG1 ne6
Corg Ntot Corg Ntot
31.6 1.76 8.6 0.39
0e5
III a
5e10 ± ± ± ±
4.3a 0.37 1.8 0.09
16.9 0.88 5.9 0.28
± ± ± ±
C:N by soil layers
10e20 4.1 0.19 1.3 0.06
23.8 1.16 15.1 0.59
± ± ± ±
20e40 6.6 0.25 2.2 0.10
22.2 1.18 34.3 1.28
± ± ± ±
40e80 7.7 0.28 4.8 0.11
13.1 0.57 28.8 1.01
± ± ± ±
5.2 0.18 5.9 0.21
0e5
5e10
10e20
20e40
40e80
18.0
19.2
20.5
18.8
23.0
22.0
21.1
25.5
26.8
28.5
Mean ± SE.
Table 12 Comparison of wetland soils' organic and mineral layers by mean thicknesses (cm) and Corg stocks (Mg ha1). Soilsa
n
OLb, cm
MLc, cm
Corg OL Mg ha1
Corg ML Mg ha1
Total Corg Mg ha1
Corg of solum Mg ha1
Corg OLd Mg ha1 cm1
Corg ML Mg ha1 cm1
C:N OL/ML
Sourcee
S00 Go1 GI1 LG1 Go&GI LG LG1
5 3 3 6 8 6 15
71.0 15.0 22.7 18.8 3.0 9.4 15.4
31.0 20.3 41.3 49.3 62.0 67.6 59.6
481.7 53.6 104.9 99.0 9.8 30.4 45.3
60.6 74.5 139.7 92.6 140.5 83.1 71.8
542.3 128.1 244.6 191.6 150.3 113.5 117.1
348.1 114.3 223.1 143.4 150.3 113.5 117.1
6.8 3.6 4.6 5.3 3.3 3.2 2.9
2.0 3.7 3.4 1.9 2.3 1.2 1.2
32.0/15.2 17.2/12.0 28.2/24.4 29.5/26.1 21.9/13.6 36.9/16.1 38.7/19.4
BioSoil BioSoil BioSoil BioSoil Pedon Pedon Pedon
a b c d e
Soils e see Table 6. OL e organic layers. ML e mineral layers. Mg Corg per 1 ha and per 1 cm soil layer. ~lli et al., 2008). BioSoil i.e. from actual work and Pedon (Ko
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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~lli et al. / Quaternary International xxx (2015) 1e10 R. Ko
Fig. 3. Development of peatification.
widely according to their fabric, properties and thickness (Valk, €kila €, Saarnito, 1988; Allikvee and Ilomets, 1995; Orru, 1995; Ma 2008; Gorham et al., 2012). Here, we will treat this from the position of soil science using ESC as a tool to explain the present status of landscape peatification (Figs. 2 and 3). Peat soils (peat thickness >30 cm) cover 23.7% of Estonian ter~ lli et al., 2009b). Of this, 2/3 has been formed by peatifiritory (Ko cation of mineral soils and 1/3 by terrestrialization of water bodies (Allikvee and Ilomets, 1995). By soil type, 59.0% of peat soils are typical fen, 21.7% bog, 14.7% transitional bog, 2.3% alluvial fen and ~lli et al., 2009a). By peat thickness, 2.3% technogenic peat soils (Ko 65.9% are thick (>100 cm), 21.5% shallow (50e100 cm) and 12.6% very shallow (30e50 cm). Only the superficial part (in ecological conditions of temperate zone e approximately 50 cm) of peatland peat is peat soil cover. The underlying parts should be treated as natural resources (or peat reserve). Analogously, soils or soil cover can form on oil shale, on brown coal or on other sediments of organic origin, which superficial part may be treated as particular soils' parent material. Theoretically, the underlying soil covers peats may qualify as paleosols or more precisely peaty paleosols i.e. histopaleosols (Faw, 2012). However, such an approximation may have only theoretical, rather than practical importance.
Fig. 4. Vertical distribution of soil organic carbon (g kg1) in peaty (histic) gley soils (G1) and in peaty podzols (LG1).
Peaty soils (with peat thickness 10e30 cm) form 6.3% of Estonian soil cover; 4.7% belongs to peaty gley soils (saturated, nonsaturated, alluvial, coastal) and 1.6% to peaty podzols. All peaty soils in our study may be characterized as polygenetic soils with very shallow peat layer. Peatification takes place as well on natural gley soils, which is indicated by the presence of a very thin (<10 cm) superficial peat layer. According to our estimates, the peatification which proceeds on wet mineral soils involves approximately 15% of the Estonian soil cover. There is not firm agreement in the determination of peat soil cover thicknesses or in separating peat soil cover from peat deposits as natural reserves. For Estonian or for temperate pedoecological conditions, it seems acceptable to us to take 50 cm as the thickness of peat soil cover, and 30 cm for more active topsoil cover thickness. Peat carbon storage in bog soils' superficial 30 cm layers is 40e47 Mg Corg ha1, and in the 50 cm superficial layer or in the peat soil cover it is 130e148 Mg Corg ha1. For the fen soils, the same characteristics are accordingly 168e180 and ~lli et al., 2009a). The soil organic carbon 320e347 Mg Corg ha1 (Ko stock per hectare in transitional bog soil cover depends on the character of paludification processes. Under bogging conditions, the carbon stocks are similar to bog soils, but artificial drainage produces stocks more similar to the fen soils. The formation of peat mantle upon mineral deposits on lowlands includes the following chronosequence: gley soils or protosols (some of them have also <10 cm layer of peat) / peaty soils (with peat layer thickness 10e30 cm) / fen soils (very shallow, shallow and thick) / transitional bog soils (mostly thick and shallow) / bog soils (mostly thick). In all analyzed sites the peat layers have accumulated in the course of progressive paludification in the following order: sapric well decomposed peat / hemic intermediately decomposed peat / fibric (bog) peats. Peat accumulation and type depends on (i) soil phytoproductivity and peat forming from fallen debris, and (ii) peat decomposition and subsidence. Depending on the feeding water character (i) the peat formation proceeds with further accumulation of fen peat and therefore the formation of thick (>100 cm) WRB ‘Eutric Rheic Hemic Sapric Histosols’ or (ii) proceeds to the direction of bog ‘Dystric Ombric Fibric Histosols’. The intermediate transitional bog stage, with fibri-hemic and later with fibric peat histosols, may be found as well. All peat soils in this research belong by ESC to transitional bog soils (Tables 2 and 3). Artificial drainage (Oleszczuk et al., 2008) plays a crucial role in the development of the peat mantle, influencing the decomposition of the top layer peats. The intensified decomposition of upper peat influences layers deep within peat deposits. During the peatification history, the conditions for peat formation have changed in €kila €, Saarnisto, 2008; Gorham connection with climatic change (Ma et al., 2012). General directions and possible lapses in peat formation on Estonian territory are explained in Fig. 5.
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
~lli et al. / Quaternary International xxx (2015) 1e10 R. Ko
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Fig. 5. Evolution of paleoecological conditions (A) during Quaternary on the territory of Estonia, as pre-requisite of its peatification and bogging (B). A e development of paleoecological conditions (climate periods and accumulation of Quaternary sediments) in relation to time scale from the past until nowadays, where the abbreviations cl e cool, wr e warm, ar e arid and hm e humid characterise the climate, and BIL e Baltic Ice Lake and LIL e Local Ice Lake kind of sediments. B e the most intensive periods of peatification and bogging are shown by fragmentary columns, where the abbreviations ll e lowland, ul e upland, N e North Estonia and S e South Estonia explain the geomorphologic situation. The part A of the figure is compiled by Raukas, but the part B by Ilomets.
4.2. Rationale about mineral layer development The wet mineral soils of Estonia have been developed on parent materials accumulated mainly during the Upper Pleistocene. Of the total area, the glacial deposits represent 47.7%, glaciolacustrine 6.8%, and glaciofluvial 3.1% (Raukas, 1995). Although marine and lacustrine deposits' area is relatively small, they are the dominating parent material for the wet peaty and peat soils (GSE, 1999). Distribution of soil parent materials by RA with characterization of their texture is given in Table 4. The most important factor in soil formation and properties is the texture and calcareousness of parent materials, along with the character of the feeding water. The mineral Quaternary deposits on lowlands have been gradually transformed in its surficial part into the soil cover. In the initial stage of development, the shallow gley soils or protosols with accumulation of semi-decomposed organic matter into thin AThorizon have been formed. It may be supposed that some initially had a very thin (<10 cm) peat layer, as is characteristic of the ~ lli et al., 2008). contemporary young coastal gley soils (Ko In further soil cover development, some gley soils were transformed into peaty gley soils. In conditions suitable for the podzolization process (areas with sandy texture and oligotrophic feeding water), gley-podzols rather than gley soils formed. A thicker (10e30 cm) fibric peat layer was formed on gley-podzols, or they have been transformed into peaty podzols. Some properties of the two peaty gley soil subgroups (IIa and IIb) are substantially different (Tables 1, 3 and 6). Comparison of saturated peaty soils (Go1) and unsaturated peaty soils (GI1) reveals that the latter have eluvic properties. Their profile thickness is greater due to eluvial and illuvial horizons. Therefore, they form a transitional group of soils between saturated peaty soils and peaty podzols. However, it is possible that there are various changes in soil forming processes in concordance with changing soil forming factors. More commonly, the peaty gley soils transform into various fen soils (very shallow, shallow and thick), and the peaty podzols become bog soils. Under a very shallow (10e30 cm) peat mantle, three (clearly different) types of mineral soil profiles (humus accumulative, clay
eluvio-accumulative and AleFe-humus eluvial) were elucidated. Under shallow peat soils or histosols (peat thickness 50e100 cm), mostly humus accumulative mineral profiles were found. In comparison with modern gley soils, in their mineral part organic carbon content and stocks, and distribution depth (RA 59 is an exception) are much lower (see Tables 10 and 12). Judging by the age of the soil cover (Table 5), which for most RA soils is 7.9e8.3 ka (with exceptions for RAs 7, 64 and 109) and probable initiation time of peatification (approximately 6000 years ago), there existed intermittent periods with substantial loss of peats. Supposedly, these losses have been caused by climate change (Fig. 5), or by wild fires (Kuhry, 1994). It does not seem that artificial drainage has substantial influence on mineral soil properties (i.e. to content of organic carbon and nitrogen, and to acidity) underlying shallow peat layers. The drainage of peatlands favours researcher access to mineral paleosols under peaty soils.
5. Concluding remarks The forming of peat mantle with thickness >10 cm slowed or stopped accumulation of organic carbon into the underlying mineral soil, whereas in wet, permanently reducing (anoxic) conditions the decomposition rate of soil organic matter falls to zero. Therefore the soil profiles of gley soils underlying the peat mantle have been preserved mostly in an unchanged state. Under a shallow peat mantle, three types of mineral soil profiles (humus accumulative, clay eluvio-accumulative, AleFe-humus eluvial) were elucidated. In comparison with modern gley soils, the humus content and mineral profile depth of the studied polygenetic and paleosols was much lower. The first peat layer on paludified peaty gley soils is well decomposed sapric peat, which has been later covered by moderately decomposed hemic peat and at the surface, formed from falling litter, by poorly decomposed fibric peat. A great influence on the top layers of peat mantles is artificial drainage, which intensifies decomposition by forming a hemic peat layer on the surface of bog soils. However, the drainage did not have
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045
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substantial influence on the underlying mineral soils' properties (Corg, Ntot, acidity), at least during the initial period of its functioning. From the pedogenetic and (paleo)ecological aspects, it is important that soils have been researched as a complex of genetic horizons. Characterization of soil profiles (including paleosols) in mutual relationships with soil forming factors is of pivotal importance for an ecosystem approach and for the understanding of soil cover functioning and development regularities on landscapes. Acknowledgements We wish to thank the European Commission and the Estonian Environmental Investment Centre for co-financing the project ‘BioSoil’ soil survey; the Soil Science Laboratory of Estonian University of Life Sciences and Environmental Research Laboratory in Tartu for chemical analyses, and the Estonian Academy of Sciences for the support to our Estonian-Polish scientific collaboration. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.quaint.2015.08.045. References Allikvee, H., Ilomets, M., 1995. Sood ja nende areng (Peatlands and their development). In: Raukas, A. (Ed.), Eesti. Loodus. Valgus, Tallinn, pp. 327e347 (in Estonian, with English summary). Faw, M., 2012. A Pedogenic Approach to the Classification of Paleohistosols (MS. Thesis). Bowling Green State University, USA. Forest Focus, 2006. Sampling and analysis of soil. In: Manual on Methods and Criteria for Harmonized Sampling, Assessment, Monitoring and Analysis of the Effects of Air Pollution on Forests. Part IIIa. Forest Soil Co-ordinating Centre, Brussels, Belgium.
€pp, R., Geological Survey of Estonia (GSE), 1999. In: Kajak, K., Raukas, A., Karuka Rattas, M. (Eds.), Quaternary Deposits of Estonia. Map in Scale 1:400,000. GSE, Tallinn. Gorham, E., Lehman, C., Dyke, A., Clymoc, D., Janssens, J., 2012. Long-term carbon sequestration in North American peatlands. Quaternary Science Reviews 58, 77e82. IUSS Working Group WRB, 2014. World Reference Base for Soil Resources 2014. International Soil Classification System for Naming Soils and Creating Legends for Soil Maps. World Soil Resources Reports No. 106. FAO, Rome. ~lli, R., Astover, A., Noormets, M., To ~nutare, T., Szajdak, L., 2009a. Histosol as an Ko ecologically active constituent of peatland: a case study from Estonia. Plant and Soil 317 (1e2), 3e17. ~lli, R., Ellerma €e, O., Ko €ster, T., Lemetti, I., Asi, E., Kauer, K., 2009b. Stocks of organic Ko carbon in Estonian soils. Estonian Journal of Earth Sciences 58, 95e108. ~lli, R., Ellerma €e, O., Teras, T., 2008. Digital Collection of Estonian Soils. EMÜ. (Cited Ko 2014 Oct 22). Available from: http://mullad.emu.ee. Kuhry, P., 1994. The role of fire in the development of Sphagnum-dominated peatlands in western Boreal Canada. Journal of Ecology 82, 899e910. Land Board, 2001. Soil Map. (Cited 2015 March 13). Available from: http:// geoportaal.maaamet.ee. ~ hmus, E., 2006. Eesti metsakasvukohatüübid (Estonian forest site types). Eesti Lo Loodusfoto, Tartu (in Estonian). €kila €, M., Saarnisto, M., 2008. Carbon accumulation in boreal peatlands during the Ma Holocene e impacts of climate variations. In: Strack, M. (Ed.), Peatlands and €skyla, Finland, pp. 24e43. Climate Change. International Peat Society, Jyva €per, H., Maryganova, V., 2008. Impacts of Oleszczuk, R., Regina, K., Szajdak, L., Ho agricultural utilization of peat soils on the greenhouse gas balance. In: Strack, M. (Ed.), Peatlands and Climate Change. International Peat Society, €skyla, Finland, pp. 70e97. Jyva Orru, M., 1995. Eesti Turbasood. Teatmik (Estonian mires. Handbook). Eesti Geoloogiakeskus, Tallinn (in Estonian, with English summary). Raukas, A. (Ed.), 1995. Eesti. Loodus. Valgus ja Eesti Entsüklopeediakirjastus, Tallinn (in Estonian, with English summary). Raukas, A., Teedum€ ae, A. (Eds.), 1997. Geology and Mineral Resources of Estonia. Estonian Academy Publishers, Tallinn. €e, A. (Eds.), Geology and Reintam, L., 1997. Soil formation. In: Raukas, A., Teeduma Mineral Resources of Estonia. Estonian Academy Publishers, Tallinn, pp. 298e306. Valk, U. (Ed.), 1988. Eesti sood [Estonian peatlands]. Valgus, Tallinn (in Estonian, with English summary).
~ lli, R., et al., Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia, Quaternary Please cite this article in press as: Ko International (2015), http://dx.doi.org/10.1016/j.quaint.2015.08.045