WATER TABLE AND REDOX CONDITIONS IN DEEP TROPICAL PEAT WATER TABLE AND REDOX CONDITIONS IN DEEP TROPICAL PEAT

WATER TABLE AND REDOX CONDITIONS IN DEEP TROPICAL PEAT

  • 期刊名字:湿地科学
  • 文件大小:577kb
  • 论文作者:Hajah Dulima Jali
  • 作者单位:Department of Geography
  • 更新时间:2020-07-08
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论文简介

第5卷第1期湿地科学Vol. 5 No. 12007年3月WETLAND SCIENCEMar.,2007WATER TABLE AND REDOX CONDITIONS IN DEEPTROPICAL PEATHajah Dulima Jali( Department of Geography , Faculty of Arts and Social Science , University Brunei Darssalamn , Tungku Link , BE1410 , Brunei )ABSTRACT :Redox potential in the well developed tropical peat swamp in Brunei was studied for a year. Generally theredox potential measurements showed a large variation , ranging from -234 mV to 727 mV. The expected rise in redoxvalues did not take place following the drop of water table during the dry months of June to September. The redox valueat 100 cm depth indicated that the soil remained reduced throughout the year in spite of the lowering of water table below150 cm in all sites during dry period. Similarly the redox values did not decrease rapidly following flooding when the wa-ter table rose to the surface. This phenomenon could be atributed to the topography of the peat dome which facilitatedthe fast lateral movement of water and thus promoted oxygen supply down the peat profile , though not great enough toreach the 100 cm depth. The rapid lateral flow of water in the outer Alan batu site facilitated aeration , but in the innersites remained which was reduced because of the slower water movement. The slower initiation of the reducing conditionwas likely due to the presence of nitrate which has accumulated as a result of ammonium oxidation during the relativelylong aerobic period. Differences in the distribution of redox potential with depth are possibly explained by the differentpermeability of peat affecting flow patterns and residence time of water. The nature and compactibility of the peat mighthave slowed the diffusion rates of O2 into the lower layer. Though the bulk density of the peat was low , the compositionof the peat might influence the peat permeability and hydraulic conductivity. The tree trunks are not decomposed or largebranches must have lowered permeability compared to the other peat material.KEY WORDS :water table ; redox potential ; peat swamp ; Brunei DarussalamCLC number :P941.78 S153Document code :A Article ID :1672 - 5948( 2007 )01 -013 -07Changes in redox potential( RP ) are the resultted to investigate the RP of the deep tropical peat andof the combined effects between many chemical ,to determine the relationship between water table andphysical and biological processes in the soil. Soil oxi-redox potential( Eh ).dation and reduction depend on soil respiration , diffu-1 MATERIALS AND METHODSsion of oxygen and carbon dioxide in soil and onchanges in biochemistry of the system.W aterlogged1.1Study Site .condition decreased the rate and amount of O2 diffu-The study was conducted in a well developed peatsing into the soil resulted in anaerobic condition( Bai-swamp of Belait ( 950 km2 ),in the a small Sultanateley , Beuchamp , 1973 ;Savant , Ellis ,1964 ). In an-(5 280 km2 ) of Brunei Darussalam , located in theaerobic soils RP was shown to be negatively correlatednorthwest coast of the Borneo Island , between the lati-with microbial activity( Kralova ,et al , 1992 ). Lowtude 4°N to 5°N and longitude 114°04'E to 115*35' E.RP developed with increased soil moisture content be-The Badas peatland is part of the extensive Baramcause of the partial or complete displacement of oxy-Peatland of Miri , Serawak and situated in between agen from soil and rapid consumption of oxygen by soil中国煤化工the lttoral fringe alongmicrobes ( Savant , Ellis,1964 ). RP in anaerobictheTMYHne sea. The study wassoils was also shown to be pH dependent ( DragunconCNMH Go2 1o December 2003.1993 ; Van Breemen , 1987 ). This study was conduc-The redox potential( Eh ) determined was conductedReceived date :12 - 09 - 2006 ; Revised date :23 - 02 - 2007Corresponding author : Hajah Dulima Jal( 1961 - ) , Male , Ph. D,senior lecturer. Main interesting fields :wetland ecology and menagement ,soil science , biogeography and environnental science. E-mail : dulina@ fass. ubd. edu. bn14湿地科学5卷for 12 months from October 2002 to September 2003.pose of large quantity of relatively un - decomposedData collection was done in fortnightly.woody material. Soil bulk is very low , less than 0. 1The climatic condition is hot and wet throughoutg /cm’,ranging from0.05 g /cm2 to0. 14 g /cm2whole year with mean temperature of 30 C and an-with the mean of 0.097 g/cm*. The peat of Badas isnual rainfall of 3 000 mm. The study sites were se-extremely acidic with the pH values ranging from 2.8lected across the topographical range of the peatto3.9 ,and the mean of 3.3.dome , from the edge to the centre ,about 1 m to2 m ..2 Methodsabove sea level. 4 sites were selected to represent1.2.1 Probe constructiondifferent peat forest communities. Site A was locatedThe redox potential in the peat profile was deter-in the Alan batu community , site B represent the Al-mined by using methods of Faulkner et al ( 1989,an bunga community , site C situated in the Alan pa-1992 ) and Coggeret al( 1992 ). Redox probes weredang padang Transition Communities and site D wasconstructed from 18 gauge platinum wires and 2. 5placed in the Alan padang community. In each sitemm copper wire of 25 cm ,50 cm , 100 cm length.the transact of 500 m long was constructed and 5The platinum was first cut into 1. 5 cm segments.sampling stations were install ed at 100 m interval.The segments were allowed to stand in 1: 1 mixture ofThe peat is heterogeneous , with the peat depthsconcentrated Nitric and Hydrochloric Acid for at leastrange from 9 m to 15 m. The surface layer consists of4 h to remove surface contamination of metal thatloose freshly fallen ltter up to 15 cm thick. The up-could occur during cutting or handling. The cut wireper layer( 20 - 40 cm ) contained well and partiallysegments were soaked in distilled water overnight.decomposed peat , followed by slightly , or partiallyThe platinum was soldered directly to the copper wiredecomposed peat ,containing well preserved treeand the junction was sealed with waterproof shrink-trunks , branches , twigs , leaves and roots among theable plastic insulation to protect it from moisturedecomposed debris. The deep layers( >1 m) com- ( Fig. 1 ).12 gauge copper wireWaterproof epoxyInsulationWaterproof epoxy一T←- 18 gauge platinum wire(1 cm long)Fig.1 Schematic diagram of the redox probePrior to use all electrodes were soaked in dis-was used to make a hole in the peat. The rod wastilled water for several days and tested for precision inslightly larger than the diameter of the wire and a fewpH buffered quin - hydrone solution ( Bohn , 1971 ).centimeters short of the desired depth. The electrodeAny electrode differing more than 10 mV from thwas中国煤化工the platinum end wasproper value( + 430 mV ) were cleaned and testedpus:HCNMHGurbed peat ,to the de-again and discarded if cleaning failed to correct thesirea uepur( 2J CIi ,Ju cim and 100 cm ). This pro-problem.vided a good soil - platinum contact. The top of the1.2.2 Installation of redox probeshole was closed around the copper wire. 3 replicatedProbes were installed on the flat surface , avoi-electrodes for each depth were installed in each sta-ding the mound and hummock. A sharpenedmetal rodtion. The electrodes were left in the field for the en-1期Hajah Dulima Jali :W ATER TABLE AND REDOX CONDITIONS IN DEEP TROPICAL PEAT15tire study period.eters were tested by using the Pearson Product - mo-1.2.3 Measurement of redox potentialment correlation coefficient( r ) analysis. Unless oth-Redox potential measurements were made in theerwise indicated , all tests were made at the 0. 05 sig-field by using a portable millivolt meter( ELE micro-nificant level.processor ). The mV meter was connected to the plati-2 RESULTS AND DISCUSSIONnum electrode by an insulated alligator clip soldieredto an insulated lead which ftted the metre jack.2.1 W ater Table FluctuationMeasurements were taken fortnightly. For every meas-The water table fluctuated with the rainfall re-urement , the meter was allowed to stabilise for 10 mingime , but they are not significantly correlated at abefore readings were taken.0.05 probability level ( r= 0.062,p= 0.21 ,1.3 Water Table Measurementn= 260 ,2 tailed ). The observed deviations fromA dip well was constructed by using a 1.5 msimple relationship between the rainfall and water ta-PVC pipe( 7 cm diameter ) to prevent the wall fromble suggested the importance of other internal sitescollapsing. The pipe was closed with a rubber stop-factors particularly the topography and peat character-per. On each sampling date the water table was meas-istics. The degree of water fluctuation depended onured by lowering a tape measure , with a tip paintedthe location of each site on the peat dome. Because ofwith thermoplastic paint , for easier detection of waterthe irregularity of the surface , raised mound and hum-level. The sampling interval was fortnightly.mocks , were not affected by the rising water , whereas1.4 Statistical Analysis .shallow depression , especially the craters created byData was organised by using sofware of Microsoftuprooted trees , formed small pools. The exact rangeExcel ( version 97 ) and statistically analysed by usingof water table fluctuation was not certain because thethe SPSS package( version9.5 ). One - way analysisdip wells were constructed only down to 150 cm , butof variance ( ANOVA ) of means was used to deter-observations indicated that the water table fluctuationmine significant differences in values obtained be-in Badas peat swamp was more than 1 m.tween sampling sites and times. Scheffe' s test was2.2 Redox Seasonal Patternused to analyse data with equal variance and Tam-The redox potentials showed a large degree ofhane' s test was use to analyse data with unequal vari-variation( Fig. 2 and Fig. 3 ) , with the range of 270ance( SPSS Inc. , 1992 ). Unless otherwise indica-mVto727mVat25cmdeep,53mVto629mVatted , all statistical tests were made at the 0. 05 signifi-50cmdeepand-234mVto350mVat100cm.cant level. Relationships between all measures param-deep.700 n-+25cm60-一50cm500+十100 cm且400i 300爱20100-200-中国煤化工LYHCNMHG*心心的Sampling datosFig.2 Seasonal pattern of mean redox potential at 25 cm ,50 cm and 100 cm deep in the study site at eachsampling date( each point is the mean value 5 subsampling station in each site )5回|包Redox potential (mV)岩旨宫。莒营营营电宫宫,3口多|告|中|↓富告粪|C悱的各乙匠了|和|司工|。|9°吕古88总g|管°吕古88莒g°吕台38ggWatertable (cm)un啡1期Hajah Dulima Jali :WATER TABLE AND REDOX CONDITIONS IN DEEP TROPICAL PEAT17At 25 cm deep ,the peat profile in all sites ap-all sites.peared to be oxidised throughout most time of theAt 100 cm deep , the peat was in a reduced toyear , as indicated by the redox reading of more thanvery reduced condition throughout the year ,in all400 mV , except in the months of November to Febru-sites especially during the first half of the study peri-ary , where the redox readings ranged from 250 mV tood ,( October to April ) where the redox readings400 mV , which suggested a moderately reduced con-ranged from - 250 mV to0 mV. A steady increase indition. There were larger discrepancies of redox val-the redox values to 300 mV was recorded during theues between sites in the wet months of January tosecond half of the study period , from April to Septem-March compared to readings during the dry months ofber. The mean redox reading were 114. 7 mV ,26. 1April to August. The mean redox value at 25 cm deepmV,32.3mV,and125.5mVforsiteA,B,C,D,of the peat site A ,B ,C ,D respectively were 573. 3respectively.mV ,455.1 mV ,465.3 mV and 461.8 mV.At all depths , the redox values recorded differedAt 50 cm deep , electrode reading indicated asignificantly between sites. The redox potential of themoderately oxidized to reduced condition in all sites ,Alan batu and the Alan bunga sites were significantlywith the values ranging from 53.3 mV to 629.5 mV.higher than the other sites. At 25 cm deep ,FThe values of redox readings at this depth showed a28.1,p<0.001,n=300.At50cmdeep,much higher variation between sites. The mean redoxF (3296)=18.9 p<0.001 ,n=300 . And at 100 cm .values measured in the Alan batu , Alan bunga , Alandeep F (3296)=18.4 p<0. 001 ,n= 300.padang transition , and Alan padang sites , respective-Measured redox potential values were significantlyly were419.6 mV ,336.7 mV ,369.3 mV and 303.8.correlated with peat pH and peat moisture ,at allmV. The condition was generally more reduced (

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