Wpływ pożaru na wartości wskaźników przeobrażenia utworów organicznych

http://www.degruyter.com/view/j/ssa (Read content)

Vol. 64 No 3/2013: 88–92

*email: adam.bogacz@up.wroc.pl

DOI: 10.2478/ssa-2013-0013

INTRODUCTION

In the process of transformation of organic for-mations, wettability is an important property, highly differentiated particularly in layers with variable hu-midity (Morley et al., 2005), rich in organic matter (Wallis and Horne, 1992). The moorsh process re-sults in organic formations becoming more hydropho-bic. This is of significance to environmental issues (Berglund and Person, 1996). Fires on soil organic matters, occurring increasingly frequently througho-ut the world, modify the water-absorbing properties of soils by increasing their temperature (Doerr et al., 2004). This effect is among others related to the de-hydration of soil colloids (Bauters et al., 2000).

Surface and ground fires affect the structure (Hallet and Young, 1999), fibre content (Bogacz et al., 2011), degree of decomposition of organic matter (De Bando et al., 1970; De Bando et al., 1976; Raison et al., 1986), and erosion of soils (Shakesby and Doerr, 2006).

The objective of this research was to determine the degree of organic matter transformation in stron-gly dried post-fire soils of the Lower Silesia region with the application of various research methods.

STUDY OBJECTS

The study objects were soils of forest areas: Cho-cianów – object Gromadka (GR),

Wo³ów-Mikorzy-ce-Górowo (MG), and meadow soils from Lubsko (LU) and Sobin-Jêdrzychów (SJ). Organic soil fires in the aforementioned forest areas occurred between 1986 and 1992. Meadow soil fires occurred in 2006 and 2008. Before the fires, the soils were composed of strongly dried moorsh layers at a medium or strong moorsh degree. The soils were classified as moorsh soils and peat-moorsh soils, hemic or sapric (Komi-sja V Genezy, Klasyfikacji i Kartografii Gleb PTG, 2011). Organic matter peat accumulated on sand or sand and gravel formations in fluvial valleys. Such sand formations sometimes contain silty insertions. Low peat horizons were represented by the following genera: Carex sp. and Alnus sp. (Bogacz et al., 2010). Under the moorsh layer, medium deep peats were deposited (MtIIb1 and MtIIIc1). After the soil fires, shallow moorsh-peat soils with visible horizons or ash admixture were frequently encountered.

On strongly burnt surfaces, soils categorised as organic-mineral soils (Me11 or Mmr11) were also recorded. According to the currently binding Classi-fication of Polish Soils (Komisja V Genezy, Klasyfi-kacji i Kartografii Gleb PTG, 2011), these soils may be classified as gley, peat, or peat-gley soils (Bogacz et al., 2011). Post-fire forest communities were re-presented by alder swamp forests (Alnus sp.), mar-shy coniferous forests, and birch swamp forests. Me-adow communities were only represented by Carex sp. and post-fire substitute communities most frequ-ADAM BOGACZ*, BEATA £ABAZ, PRZEMYS£AW WONICZKA

Institute of Soil Science and Environmental Protection, University of Life Sciences, 50-357 Wroc³aw, ul. Grunwaldzka 53

Impact of fire on values of organic material transformation

indicators

Abstract: The article discusses organic and organic-mineral soil transformations induced by fire. The research covered 24 soil profiles. It was primarily focused on water properties of post-fire soils, such as the hydrophobic degree, analysed by means of percent alcohol (MED) and WDPT test, and soil water capacity indicator (W1). The above indicators determine the degree of intensification

of the moorsh process in post-fire organic soil horizons. Total carbon content was also determined by means of a gas method analyzer by CS – MAT 5500, as well as the level of organic material decomposition by means of the half syringe method. The achieved result suggests that the moorsh process and low temperature fires led to an increase in the hydrophobic property of soil organic matter, whereas in high fire temperature, the soil included more ash, and the hydrophilic properties were higher. The significant degree of transformation was also confirmed by the water capacity indicator (W1). It primarily concerned the upper horizons of the investigated

soil profiles. The majority of the 76 analysed soil samples showed signs of secondary transformation.

ently classified as Molinio Arrhenatheretea, with high dominance of grass, nettles, and alder seedlings (Bo-gacz et al., 2006; Bo(Bo-gacz et al., 2010; Bo(Bo-gacz et al., 2011). The following is an example morphological de-scription of post-fire soil profile Mikorzyce-Górowo:

stant fibre – unrubbed (B), and on the absorbency measurement method in soil extractions in 1mol NaOH dcm–3 _{following Sapek and Sapek (1997).} Re-sults regarding the degree of decomposition are

pre-fl O 0–2cm mulltypeorgancihorzion,we,twtihAlnussp.andBetulasp. elaves rfagment,smosi,tabruptdsiitnctnessand s n o zi r o h f o s ei r a d n u o b y h p a r g o p o t h t o o m s t M 2–10cm moorshhorzion, ifnegrainsrtucture,7.5YR3/3gra,ymosi,tabruptdsiitnctness andsmoothtopography s n o zi r o h f o s ei r a d n u o b 1 a O 10–28cm lowpeathorzion,smoldered, rfagmenstofsmolderedwoodandpea,tcolourofpeat10YR2/1balck,colour t p u r b a ,t e w , e r u t c u rt s y k c o l b -s u o h p r o m a , 3 R t a e p d e s o p m o c e d y l g n o rt s , k c al b 0 / 2 N st n e m g a rf d e r e d l o m s f o s n o zi r o h f o s ei r a d n u o b y h p a r g o p o t h t o o m s d n a s s e n t c n it si d 2 a O 28–48cm rtansiitonalpeathorzion,srtonglydecomposedpeatR3,10YR2/1balck,amorphous-blockysrtucture,some s s e n t c n it si d t p u r b a ,s el tt o m n o ri e n if – s e r u t a e f ci h p r o m y x o d e r e m o s ,t e w ,t a e p d e r e d l o m s n i d o o w d e r e d l o m s s n o zi r o h f o s ei r a d n u o b y h p a r g o p o t y v a w d n a i O 48–67cm rtansiitonalpeathorzion,lowdecomposedpeatR1,10YR5/6yellowsihbrown,we,t ifbresrtucture,presence H f o 2S,abruptdsiitnctnessandsmoothtopography boundareisofhorzions e O 67–92cm rtansiitonalpeathorzion,lowdecomposedpeatR1,10YR4/3darkgra,ywe,tamorphous-blockysrtucture, H f o e c n e s e r p 2S,thinsandy alyer,sabruptdsiitnctnessandsmoothtopographyboundareisofhorzions C +92cm mineralhorzion,sandy– ifnegravelmaterai,l5GY5/1greensihgra,yverywe,tgelypropetreis ,s s e c o r p h s r o o m f o y ti s n e t n i w o l ,li o s h s r o o m :) 1 1 0 2 G T P , b el G ii f a r g o tr a K i ij c a k if y s al K ,y z e n e G V a j si m o K ( n o it i n if e d li o S .) 1 b It M ( d n a s n o s r e y al y d n a s n i h t h ti w ,t a e p d e s o p m o c e d 1 R w o l d n a 2 R m u i d e m n o 3 R t a e p d e s o p m o c e d y l g n o rt s m o rf d e p o l e v e d ) ci v u l F ci n i e r D ci rt u E ( sl o s o t si H ci m e H – 6 0 0 2 B R W e e rt t n a n i m o D . e g al b m e s s a t s e r o f p m a w s d ei r d , e c a rr e t d o o lf a n o y el l a v r e v ir a f o tr a p l a n i g r a m e h t n i d e t a c o l sl i o s : st n e m m o C : s ei c e p s AlnusincanawtihsingelBetulapendulaandAbiesalba.

STUDY METHODS

The study on the degree of transformation of post-fire organic soils covered a total of 24 soil profiles, described in detail in terms of morphology. The de-scribed profiles were represented by 98 soil samples. The soil samples were divided into groups covering: organic-mineral formations, containing between 5 and 20% of organic matter (7 samples), ashes remaining after peat burning (7 samples), moorsh (25 samples), peats (44 samples), and humus layers (10 samples). Values of the following transformation degree indi-cators were determined: organic soil formation water capacity indicator (W₁) by Gawlik (1996) and poten-tial wettability. The indicator values were determi-ned by means of the following tests: water drop pe-netration time (WDPT) (Vant'Woudt, 1959) and ethanol drop penetration time in soil formations (MED) (Letey et al., 2000). The measurements were conducted at a temperature of 20o_{C. Mean test} re-sults based on 10 tests are presented in Table 1, Table 2 and Figs. 1–5. The study also covered organic car-bon content (OC) following removal of carcar-bonates, determined by means of the gas analysis method in a CS-MAT 5500 device, as well as degree of decompo-sition of organic matter, measured by means of the half syringe method (Lynn et al., 1974) based the con-tent of so-called rubbed fibre or decomposition

resi-sented in Table 1 and Fig. 4 and Fig. 5. For statistical calculation, Statistica 9.0. software was used.

RESULTS AND DISCUSSION

Genetic horizons of post-fire transformed soils are primarily distinguished by a strong diversification of organic carbon content (OC) resulting from different intensity of fires and time of their occurrence (For-bes et al., 2006). The study showed higher mean OC contents in moorshes than in peats. This phenome-non might be caused by low temperature fires, frequ-ently occurring in deep moorsh. At low oxygen ava-ilability, a process similar to pyrolysis results in an increase in carbon content in analysed samples. Low temperature fires often increase carbon content by as much as 30–50% before a fire incident (Ponomarien-ko and Anderson, 2001; Forbes et al., 2006). Such a possibility is described by Efremova and Efremov (2006), who studied fires of large areas of Siberian peats. Peat or moorsh burning also results in a decre-ase in the volume of decomposition-resistant fibre (B). Results presented in Table 1 classify organic matters as sapric ones, and only in some cases as hemic ones. One of the physical indicators used to evaluate transformation of secondary organic formations is W₁ – absorbing capacity by Gawlik (1996). It is applica-ble to the diagnosis of moorsh horizons in different

decession phases, distinguished earlier during field works. The threshold value for the W1 indi-cator is 0.35 for low ash forma-tions, and 0.41 for high ash for-mations. It distinguishes peats showing no secondary transfor-mation symptoms from moorsh (Gawlik, 1996). For the majori-ty of genetic horizons of organic soils and organic-mineral soils, the study results were equivalent to field observations. GR soils were distinguished by an initial (I) or low (II) degree of secon-dary transformation only in

cer-tain surface or subsurface horizons. A higher degree of transformation occurred in horizons with ashes. Soils of the second forest object (MG) were much stronger transformed than GR soils, and were distin-guished by an initial (I), weak (II), or medium (III) degree of secondary transformation. Peat

transforma-tion sometimes covered the entire soil profiles. A si-gnificant degree of transformation in the analysed organic formations of meadow areas LU SJ was ob-served in all of the organic horizons of the second meadow object (SJ). Surface horizons were frequen-tly determined as subject to strong secondary

trans-. D E M s s al c Nameofcalss C[%2H]5OH _<W₅DPT ₅[s_–]_{60 60–180 180–600 600–3600 3600–18000 >18000} 7 6 5 4 3 2 1 ci b o h p o r d y h y l e m e rt x e ci b o h p o r d y h y l g n o rt s y r e v ci b o h p o r d y h y l g n o rt s ci b o h p o r d y h y l e t a r e d o m ci b o h p o r d y h y t h g il s ci l y h p o r d y h ci li h p o r d y h y r e v 6 3 4 2 3 1 5 . 8 5 3 0 – – – – – – 1 1 – – – 1 1 2 4 – – 5 2 – – – – 2 4 – – – – 1 5 1 5 1 – – – 4 2 1 1 – – – – 1 2 5 1 – – – – TABLE 2. Summary of results of MED and WDPT tests in the scope of analysis of hydrophobic properties

FIGURE 1. Number of soil samples within water absorption classes in post-fire areas based on the MED test TABLE 1. Coefficients of the degree of transformation of soil formations

n o it a m r o f f o e p y T OC g k g m –1 B_{% o}T_ry_gp_ae_no_cif l ai r e t e m W1 WDPT ] s [ cMalEssD r e tt i L 139–466 6 4 3 4–2323 shaepmrcici – 4–418962060 2–67 t a e P 127–511 6 2 3 2–1450 shaepmrcici 0.100.–304.87 3–1336248050 16–7 h s r o o M 253–497 8 5 3 1–1389 shaepmrcici 0.100.–409.96 16154–33312320 2–67 h s A 25.5–112 4 . 7 6 – – – 11–3007571 14–5 l a r e n i m -ci n a g r O 55.5–109 1 . 7 8 – – – 3–939204300 14–6

Explanation: W1– water absorption coefficient, WDPT – water drop penetration time, MED –

dary transformation. The initial stage of transforma-tion (I) was represented by 14% of samples, low de-gree of transformation (II) – by 12%, medium dede-gree of transformation (III) – by 14%, high degree of trans-formation (IV) – by 7%, and the degraded stage (V) – by 4%. The latter group involved surface horizons of burnt moorsh. The study results show a substan-tially higher degree of transformation of organic me-adow formations in relation to the forest soils (Fig. 1, Fig. 2 and Fig. 3).

Based on wettability tests WDPT and MED, more than 60% of the analysed soil samples were classi-fied to the 6th and 7th class, i.e. as strongly or extre-mely hydrophobic, and only 10% to the 1st, 2nd, and 3rd class, i.e. as very hydrophilic, hydrophilic, or low hydrophilic. Ash horizons accumulated as a result of peat burning, as well as horizons with burnt fragments of vegetal remains and silted horizons, showed a hy-drophobic capacity lower than that of peat horizons or duffs unaffected by fire (Fig. 1). The water drop penetration time (WDPT) test applied revealed re-sults similar to those of the MED test, as presented in details in Table 2, and in the calculation of the corre-lation coefficient r=0.64, n=98, p>0.05, as well as the chart of this correlation in Fig. 4. An increase in OC content in soil samples affected wettability indi-cator values (WDPT). This phenomenon is also con-firmed by a high correlation coefficient for the sam-ples studied: r=0.53, n=98, p<0.05 (Fig. 5). A similar correlation was also observed in studies by Roy et al. (2000) and £achacz et al. (2009). According to £achacz et al. (2009), the observed phenomenon is particularly visible when OC > 120 g kg–1 _{of soil,} when soil samples become significantly hydropho-bic. This is also confirmed by the studies the results of which are presented in Fig. 4 and Fig. 5. Such be-haviour of organic matter is also determined by the possibility of alternate humidification and drying (Bisdom et al., 1993). The potential water capacity of organic soils is closely related to temperature, type of burnt organic matter, and oxygen availability du-FIGURE 2. Secondary transformation of pyrogenic (forest) soils

based on the water absorption coefficient W₁ (Gawlik, 1996) FIGURE 3. Secondary transformation of pyrogenic (meadow)soils based on the water absorption coefficient W₁ (Gawlik, 1996)

FIGURE 4. Correlation between the values of the WDPT indicator, and MED test

FIGURE 5. Correlation between the values of the WDPT indicator and organic matter content (OC)

            1 – no change 2 – initially secondary

3 – weakly secondary transformed

4 – medium secondary transformed 5 – strong secondary transformed 6 – completely degraded

1 – no change 2 – initially secondary

3 – weakly secondary transformed

4 – medium secondary transformed 5 – strong secondary transformed 6 – completely degraded            

formations (IV), or even degradation (V). A higher degree of secondary transformation was particularly observed in organic surface horizons. Among the ho-rizons analysed, 46% showed no symptoms of

secon-ring a fire incident (Doerr et al., 2004). Based on mean WDPT values calculated for the described post-fire soils, potential water repellent capacity of peats hi-gher than that of moorsh is not confirmed.

CONCLUSIONS

1. Fires resulted in a decrease in potential hydropho-bic capacity of organic horizons. A higher degree of secondary transformation was usually observed in surface horizons, and concerned horizons with ashes. 2. Organic matter burning or burnout significantly

modified its hydrophobic capacities.

3. Values of the W₁ parameter indicated a degree of transformation of organic horizons of meadow so-ils higher than that of forest soso-ils.

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Received: July 26, 2012 Accepted: October 9, 2013

Wp³yw po¿aru na wartoœci wskaŸników przeobra¿enia utworów organicznych

Strzeszczenie: Artyku³ dotyczy stopnia przeobra¿enia gleb organicznych i organiczno-mineralnych wywo³anego pod wp³ywem po¿arów. Badania przeprowadzono na 20 profilach glebowych. G³ównie skoncentrowano siê na w³aœciwoœciach wodnych gleb popo¿arowych, takich jak: ich stopieñ hydrofobowoœci, bazuj¹c na teœcie alkoholowym (MED) i (WDPT) oraz wskaŸnik pojemnoœci wodnej (W1). Powy¿sze wskaŸniki œwiadczy³y o stopniu intensyfikacji procesu murszowego w popo¿arowych poziomach

organicz-nych gleb. Dodatkowo okreœlono zawartoœæ wêgla ca³kowitego metod¹ Tiurina aparatem CS – MAT 5500 oraz stopieñ rozk³adu materii organicznej metod¹ pó³strzykawki. Otrzymane wyniki wskazuj¹ na proces murszowy oraz po¿ary niskotemperaturowe – jako czynniki prowadz¹ce do wzrostu cech hydrofobowych materii organicznej, jednak przy wysokiej temperaturze po¿arów gleba wyka-zuje wy¿sz¹ zawartoœæ popio³u oraz wy¿sz¹ hydrofilowoœæ. Znacz¹cy stopieñ przeobra¿enia materii organicznej w glebach popo¿a-rowych jest równie¿ charakteryzowany przez wskaŸnik pojemnoœci wodnej (W1). Dotyczy to g³ównie powierzchniowych poziomów

badanych profili. Wiêkszoœæ z badanych 76 próbek glebowych wykazuje cechy przeobra¿enia wtórnego.