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The Characterization of the Arifiye peat.

Byline: MA1/4min Dizman, Ahmet Tutar and Ayhan Horuz

Summary: There is a fortune of the peat resources in Turkey, particularly around Lake Sapanca in Sakarya. There has been increasingly attention to peatlands in technological uses and agricultural applications. The Arifiye peat is a new resource. It needs to be elucidated by characterization of its chemical and physical properties. The objective of this study was to characterize a number of samples collected from fifteen different profiles of the peat (sapric) by measuring cation exchange capacity, water holding capacity, humic acid, fulvic acid, organic matter, organic carbon. In addition, the spectroscopic analysis suggested that the functional groups and molecular structure of the Arifiye peat resemble those of peatlands described previously in the literature.

Key words: peat; humic substances; characterization; UV-vis; FTIR, SEM.

Introduction

Peat as a term is described generally the layer of world's crust composed of organic materials in nature. Peat has been formed by plant residuals steeped in water or grown in humid environments at special conditions. Peat bog has distributed universally to lots of the temperate regions having cold and humid climates [1]. Peat deposits are also known as places collected or saturated with water and organic debris from earth surface of 30-40 cm to a depth of several meters [2], [3]. Deposits come into existence when there is a plenty of water during the year to preserve the organic substances from completely decomposition. As a result, they accumulate as sediments to form peat [4]. The peat extension of world has been estimated as a range of 2.39.5x1012 m2, giving a carbon pool to contain up to 570x1015 g. Peat age has been reported to vary between 1700 and 15000 years [5]. The Turkish peatlands are about 2.5x107 m2 [6].

The essence of these peatlands seems to have a fortune for Turkey so that they are less than 1/1000 of the total agricultural fields when compared with mineral fields [7]. The main properties of peatlands are low pH value, high organic matter, high cation exchange capacity (CEC) and low base saturation. Several researchers have studied the composition, structures and properties of peat species, using several chemical, physicochemical and biological methods. The objective of this study was to characterize Arifiye peat as a new resource used in Turkey as a soil regulator for indoor plants, vegetables and fruits.

Experimental

Analytical quality reagents (Merk Co., Sigma-Aldrich Co., Fluka, Germany) were used without purification. The solutions were prepared from high purity water (Millipore Elix 3, Millipore Co.), produced at 1015 S/cm. To obtain the E4/E6 ratio, the absorbance at 465 nm and 665 nm was measured using SHIMADZUUV2401 PC (UV VIS Recording Spectrometer) on solution of 3.0 mg of each HA in 10 mL of 0.05 mol/L NaHCO3. The structural information was investigated by Attenuated Total Reflectance Fourier Transform Infrared (ATR FTIR). To detect the heavy metals and other elements, Inductively Couple Plasma spectrophotometer (Perkin-Elmer, Optima 2100 DV, ICP/OES, Shelton, CT 064844794, USA) was used.

Peat sampling and characterization, isolation of humic substances

Peat profiles were obtained from Arifiye, located in Sakarya, Turkey (Figure 5 and 6). The location of the Arifiye peat is coordinated as close to 40 43' 2" N, 30 22' 31" E.

The Arifiye peat is typical sapric and has not been affected by direct pollution sources, either presently or historically. The accumulation of well- decomposed wood peat reflects strong drainage and dry conditions in the research area during the development of the respective layers. The homogeneous peat composition and decomposition reflect stable wet conditions during the development of the bog layer. Fifteen peat samples were collected from the horizon and dried in laboratory conditions with a minimum temperature of 50C and a maximum temperature of 75C. The samples were then ground and screened through a 2 mm (10 mesh) sieve.

The extraction was performed with 0.1 M NaOH. The precipitation was accomplished by 3035 mL of concn. HCl. The solutions were shared in two bottles each. The washing of the humic acids was performed in a first step via combining them into one bottle, which took about 30 mL of 1 M NaOH, refilling them up to 200 mL, and precipitating them with 5 mL of concn. HCl. The second step was to transfer them in 30 mL tubes with about 5 mL of 1 M NaOH, refill the solution to about 30 mL, and precipitate the humic acids with 1 mL of concn. HCl. The third step was the dissolution of the humic acids with 5mL of 1 M NaOH and their subsequent precipitation with 1 mL of conc. HCl. Finally, humic acids were elutriated in a solution of H2O with three drops of conc. HCl, centrifuged for 20 min, and the supernatant decanted and discarded. The extracted and washed humic acids were dried and stored [24].

The physical and chemical analysis of the Arifiye peat

After the Arifiye peat was saturated with distilled water, the reaction of medium was measured by Hanna Instruments pH 211 Microprocessor pH meter [9]. The electrical conductivities of the saturated peat samples were determined by Hanna DIST 3 Pocket Type Conductivity Meter. Organic carbon in the peat samples was measured by a method which all waited 46 hours in the kiln at 750C up to time that grey ash occurred. Total organic matter was calculated by multiplying organic carbon with 1,724 coefficients (by assuming that organic carbon is 58% of organic matter) [25]. The cation exchange capacities (CEC) of the Arifiye peat samples were determined by saturation method with sodium (NaOAC, pH=8.2) [26], [27]. The water holding capacities (WHC) of the samples were found by gravimetric method [28]. According to the method, firstly, samples were saturated by water. After that, excess water was drained by drawing.

Finally, the water holding capacity of the peat was determined by measuring gravimetrically its water content.

Results and Discussion

The pH values of the Arifiye peat samples were determined averagely as 5.3. These values indicated an acidic reaction as a result of dissociation of the acidic groups (carboxylic and phenolic acids) in the organic matter [8]. The electrical conductivity of the peat ranged in 0.30.4 dS/m. This range was accepted low because it was less than 0.9 dS/m [9].

The organic carbon and the organic matter of the peat were averagely found as 30% and 52% respectively (Figure 1). The deposits of organic matter at the SarigAll Region of Arifiye have increased because of the fact that the factors like less than 35C of medium temperature and low pH value decelerate dissociation of humus [10].

The yield of humic substances was averagely found as 47.5%, which humic acids were 36% and fulvic acids were 11.5% (Figure 2). This yield agreed with the value declared by Rydin and Jeglum [11]. Humic substances support CEC, WHC, hydrologic properties and carbon balance of the peat. The origin of the humic substances plays an important role to describe the humification. In addition, they comprise of the important part of the dissolved organic matter.

Table-1:-The ratio of E4/E5 of the Arifiye Peat to determine the aromaticity

Samples###465 nm###665 nm###E4/E6

1###0,14###0,0533###2,63

2###0,223###0,177###1,26

3###0,258###0,23###1,12

4###0,38###0,253###1,50

5###0,233###0,195###1,19

6###0,156###0,0963###1,62

7###0,166###0,0657###2,53

8###0,201###0,105###1,91

9###0,309###0,231###1,34

10###0,272###0,215###1,27

11###0,277###0,215###1,29

12###0,284###0,185###1,54

13###0,196###0,199###0,98

14###0,146###0,143###1,02

15###0,232###0,194###1,20

The UV/Vis spectra of the Arifiye peat were recorded in the range of 200800 nm (Table 1). The ratio E4/E6 of the diluted humic substances extracted from the peat were used in the characterization of humic (HA) and fulvic acids (FA). The E4/E6 ratio was much larger for the FA fractions than for the HA fractions. The larger E4/E6 values were associated with lower molecular weights [12]. This E4/E6 ratio is inversely related to the degree of condensation of the aromatic groups in humic substances [13], so that a high ratio would reflect a low degree of aromatic condensation and the presence of relatively large proportions of aliphatic structures. Although no samples indicated any sharp endpoint, they exhibited a slight projection characterizing humic substances at 450470 nm [14]. This projection reflects the unsaturated parts of humic substances or their absorbance with double bands (C=C, C=O and N=N) of aromatic groups [15].

The changes in the projection observed in the Arifiye peat were attributed to those in the concentration of aromatic compounds. In conclusion, these changes came from the structure of the characteristic differences in the humification process [16].

The CEC values of the Arifiye peat were determined averagely 167 meq/100 g (Figure 2).

The WHCs of the peat were averagely found 358% (Figure 2). WHC of some peat species like Sphagnum rise up to 1520 times of its dry weight [11].

Chromophores, responsible for the absorbance, include unbound electrons such as oxygen, sulfur, halogen atoms [17]. Absorbance is mainly formed due to the aromatic ring structures [18]. Moreover, the rotation of molecules and intermolecular interactions affect the spectra [19]. Absorbance increases with pH, aromaticity, total carbon content and molecular weight [20].

The measurements of FTIR spectroscopy were performed between the range of 600 and 4000 cm-1 for each sample. It was determined a similarity of FTIR spectrum for each other. All fractions exhibited absorption bands for a typical of humic substances [21]. Generally, it was observed wide and overlapped peaks in the region of 36002000 cm-1 (Figure 3). The most significant FTIR bands in terms of differences between the samples were found in the region of 1800900 cm-1. The FTIR spectra of the FAs showed a more pronounced adsorption band in the 1720 cm-1 region than those of the HAs, indicating a larger content of carboxyl groups. Evidence that this absorption band is mainly due to COOH groups was provided by the strong reduction in its intensity and the interdependent appearance of two new bands in the 1650 and 1350 cm-1 region. These ascribed to COO- ions resulting from the conversion of HAs and FAs to their salts.

In the 1300 and 900 cm-1 regions, the peak groups were accepted by ensuing of CO stretching. These peaks described generally aliphatic CH2, OH or CO groups. The peak groups in the region of 900-600 cm-1 indicated CO stretching belonging to carbohydrates and SiO belonging to silicates.

When the obtained spectra are compared with the each other, the quantity of aliphatic groups in the structure indicates a little bit difference. In this case, the formation of humic substances may be likely incomplete in some of the samples. In Figure 3, FTIR spectra of the fifteen different samples are similar to each other. Therefore, this means that the humification process of the samples was similar to each other.

The changes in the crystal structure of humic substances of the Arifiye peat were determined by the SEM study. As a result, the samples were observed whether they were crystal or not. The surface view of the Arifiye peat seems in Figure 4. According to this figure, it is understood that the Arifiye peat is not a crystal structure and it is a polymeric macromolecule. It was seen that humic substances formed by precipitation of molecules contained a nano-sized lumpy structure. This result was consistent with the proposed structure for peat [22].

As seen in Table 2, there is a wide range of the mineral contents between the peat samples. However, the main compounds are Si and Ca except for C, H, N and O. The Arifiye peat had a small amount of Si. The reason for this phenomenon could be the riverbed sediments brought by the mobility of the water or the soil flying with wind close to environment.

While Ca amount was higher than the value reported by Andriesse [23], Mg amount was found highest compared with peat species. The reason of this highest value may be that Mg in ionic form adheres strongly colloidal organic particles. Although Fe and Na amounts were higher than the suggested contents, Al was found low at the Arifiye peat [23]. In addition, because of the fact that there has not been a factor polluting the environment nearest the peat source, Cd and Pb were determined very low while the heavy metals and radionuclides such as Hg and As were not encountered. As a result of environmental changes, the various layers of peatlands indicate differences in the elemental composition. In general, the elemental contents of the Arifiye peat didn't indicate such differences compared with the others.

Experimental

Analytical quality reagents (Merk Co., Sigma-Aldrich Co., Fluka, Germany) were used without purification. The solutions were prepared from high purity water (Millipore Elix 3, Millipore Co.), produced at 1015 S/cm. To obtain the E4/E6 ratio, the absorbance at 465 nm and 665 nm was measured using SHIMADZUUV2401 PC (UV VIS Recording Spectrometer) on solution of 3.0 mg of each HA in 10 mL of 0.05 mol/L NaHCO3. The structural information was investigated by Attenuated Total Reflectance Fourier Transform Infrared (ATR FTIR). To detect the heavy metals and other elements, Inductively Couple Plasma spectrophotometer (Perkin-Elmer, Optima 2100 DV, ICP/OES, Shelton, CT 064844794, USA) was used.

Peat sampling and characterization, isolation of humic substances

Peat profiles were obtained from Arifiye, located in Sakarya, Turkey (Figure 5 and 6). The location of the Arifiye peat is coordinated as close to 40 43' 2" N, 30 22' 31" E.

Table-2: The elemental contents of the Arifiye Peat (as ppm).

Samples###Al###B###Ca###Cd###Cr###Cu###Fe###K###Mg###Mn###Na###Ni###P###Pb###Se###Si###Zn

###1###1,5###0###7995###0###0,1###1,2###2512###20,4###202###254###8,6###14###33###1###1###6280###53

###2###1,6###0###7330###0###0,1###1,2###2406###25,3###200###277###14###15###29###1###2###6105###47

###3###1,1###0###6670###0###0,1###1###2781###11,4###262###234###11###16###26###1###2###5371###55

###4###1,1###0###6905###0###0,1###1,4###2686###22###252###236###10###16###35###1###2###5741###60

###5###1###0###6935###0###0,1###1,7###2976###11,1###315###310###5###17###27###1###2###5786###65

###6###0,6###0###6920###0###0,1###2###2802###23,5###281###330###5,9###18###34###1###2###5777###50

###7###1###0###6820###0###0,1###1,5###2622###20,4###330###317###11###19###34###1###2###5683###61

###8###2,3###0###7045###0###0,1###1,3###2854###14,6###260###258###6###15###32###1###2###5987###50

###9###1,2###0###7005###0###0,1###1,6###2819###28,7###314###276###4###19###26###1###2###5927###76

###10###1###0###7030###0###0,1###1,1###2830###13,9###271###242###4,2###18###30###1###2###5945###67

###11###0,5###1###7995###0###0###0,1###2634###57,7###263###263###5,5###18###31###1###1###6280###62

###12###1,1###0###7025###0###0,1###1,3###2615###145###261###275###4,4###18###38###1###2###5945###89

###13###1###0###7015###0###0,1###1,5###2827###22,5###290###280###0,9###17###30###1###2###5938###62

###14###1,3###0###6865###0###0,1###1,7###3279###128###313###275###0,2###20###31###1###3###5652###72

###15###0,8###0###6990###0###0,1###1,7###2745###33,6###303###292###3,5###19###32###1###2###5821###53

The Arifiye peat is typical sapric and has not been affected by direct pollution sources, either presently or historically. The accumulation of well- decomposed wood peat reflects strong drainage and dry conditions in the research area during the development of the respective layers. The homogeneous peat composition and decomposition reflect stable wet conditions during the development of the bog layer. Fifteen peat samples were collected from the horizon and dried in laboratory conditions with a minimum temperature of 50C and a maximum temperature of 75C. The samples were then ground and screened through a 2 mm (10 mesh) sieve.

The extraction was performed with 0.1 M NaOH. The precipitation was accomplished by 3035 mL of concn. HCl. The solutions were shared in two bottles each. The washing of the humic acids was performed in a first step via combining them into one bottle, which took about 30 mL of 1 M NaOH, refilling them up to 200 mL, and precipitating them with 5 mL of concn. HCl. The second step was to transfer them in 30 mL tubes with about 5 mL of 1 M NaOH, refill the solution to about 30 mL, and precipitate the humic acids with 1 mL of concn. HCl. The third step was the dissolution of the humic acids with 5mL of 1 M NaOH and their subsequent precipitation with 1 mL of conc. HCl. Finally, humic acids were elutriated in a solution of H2O with three drops of conc. HCl, centrifuged for 20 min, and the supernatant decanted and discarded. The extracted and washed humic acids were dried and stored [24].

The physical and chemical analysis of the Arifiye peat

After the Arifiye peat was saturated with distilled water, the reaction of medium was measured by Hanna Instruments pH 211 Microprocessor pH meter [9]. The electrical conductivities of the saturated peat samples were determined by Hanna DIST 3 Pocket Type Conductivity Meter. Organic carbon in the peat samples was measured by a method which all waited 46 hours in the kiln at 750C up to time that grey ash occurred. Total organic matter was calculated by multiplying organic carbon with 1,724 coefficients (by assuming that organic carbon is 58% of organic matter) [25]. The cation exchange capacities (CEC) of the Arifiye peat samples were determined by saturation method with sodium (NaOAC, pH=8.2) [26], [27]. The water holding capacities (WHC) of the samples were found by gravimetric method [28]. According to the method, firstly, samples were saturated by water. After that, excess water was drained by drawing.

Finally, the water holding capacity of the peat was determined by measuring gravimetrically its water content.

Conclusion

In this study, the Arifiye peat as a new source was characterized with regard to its visible spectra, FTIR and SEM. According to the physical and chemical analysis of the Arifiye peat; pH, EC, CEC, WHC, OC, OM, HA and FA values of the samples reflected a kind of peat (sapric peat). Moreover, UV-vis spectra exhibited a slight projection characterizing humic substances at 450470 nm. This projection reflects the unsaturated parts of humic substances or their absorbance with double bands of aromatic groups. The measurements of the FTIR spectroscopy exhibited adsorption bands for a typical of humic substances. As a result, the peat samples were observed as non-crystalline structure by the SEM study.

Authors' Contributions

MD carried out all the analytical and instrumental analysis like FTIR and SEM. He participated in the sequence alignment and drafted the manuscript. He also prepared figures, tables and the result writings. AT helped the research protocol and conducted to field trial in Scientific Research Projects Unit of Sakarya University. AH performed manuscript revising and the final approval of the version to be published. All authors read and approved the final manuscript.

Acknowledgements

The authors would like to acknowledge Scientific Research Projects Unit of Sakarya University for providing the financial supply used in this study (project number: 20120204039).

Competing Interest

All of the authors declare that they have no competing interests.

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