The lacustrine sedimentary records of coal-burning atmospheric pollution

1740Science in China ser. d earth Sciences 2005 Vol 48 No. 101740--1746The lacustrine sedimentary records of coal-burningatmospheric pollutionWANG Yunfei, HU Shouyun ',2, ZHU Yuxin, YIN Yu, ZHOU Wangping'E. Appel& V Hoffmann1. Nanjing Institute of Geography Limnology, Chinese Academy of Sciences, Nanjing 210008, China2 Department of Geography, Shanghai Normal University, Shanghai 200234, China3. Institut fur Geowissenschaften, Universitat Tubingen, 72076 Tubingen, GermanyCorrespondenceshouldbeaddressedtoHuShouyun(email:hu_shouyun@hotmail.com)Received june 3. 2004: revised december 3. 2004Abstract Based on the studies on diatom, ostracods and magnetism on a core acquired fromlacustrine sediments, as well as correlation analysis between concentration of acid diatom andthe instantaneous lowest pH value, the processes of environment evolution in Lake yangzonghawere reconstructed. The lacustrine environment was favorable in the 1950s, and began to bepolluted by a coal-burning power plant since 1960. During 1965-1980, the instantaneous lowestpH value of lake water decreased to 5-6 when heavily polluted. There was a decrease trend inthe pollution from 1983 to 1999, but coal-burning atmospheric pollution was still a main problemfor environmental retrieving. As acid precipitated, acid-tolerant species overspread, and shellfishdisappeared, as well as ferromagnetic particulates dissolved because of the consequent changeof pH-Eh values in the interface of water and soil, which results in the change of environmentalproxies versus depth Thus, the environmental evolution of Lake Yangzonghai is reconstructed inthis paper based on the inferences mentioned aboveKeywords: atmospheric pollution, proxies, environmental reconstruction, lacustrine sediment, Lake YangzonghaDOⅠ:10.1360/02vd0322With the acceleration of industrialization, coal- pollution in catchments. Thus, by establishing chronburning atmospheric pollution is getting more and ological frame, measuring environmental proxies andmore serious in many regions in China. However, interpreting its mechanism with lacustrine sediments,there are only about ten odd years literature records the history of coal-burning atmospheric pollution canabout pollution in some large and mid-sized cities, be reconstructedwhere the atmosphere has perhaps been polluted forseveral decades. and therefore it is difficult to knowLake Yangzonghai (24051-240 58 N, 102 58the process and characteristic of pollution, and diffi- 10301 E)is located about 30 km southeast of Kuncult to evaluate its damage to environment. Lacustrine ming City, Yunnan Province. It is a typical faultsediment, a natural record with high resolution and downthrown中国煤化工 t of Xiaojianggood continuity, is widely distributed on the earth. It fracture zoneCNMHGIts average warecorded the changes of aquatic, ecosystematic and ter depth is 1y. 5 m with a maximum depth of 30.0 msedimentary environments resulting from atmospheric Environmental investigation carried out in May ofCopyright by Science in China Press 2005Lacustrine sedimentary records of coal-burning atmospheric pollution1999 revealed that pH value of the lake water was 8. 18: 5 cm, made in Austria) in the northern part of the lake,dissociative CO, concentration of bottom water was where the depth of water was 21.7 m. The sediments1.77 mg/L; and the degree of mineralization was 327 were gray lacustrine clay. The color of topmost 12 cmmg/L, while the concentration of So4 came up to was not as dark as the lower part because of burned58.5 mg/L. The biomass of phytoplankton was 1.51 coal ash inside Subsamples of YZH-I for magneticmg/L. Chlorophyta and Bacillariophyta were the biological and geochemical analysis as well as fordominant species, while Cyanophyta was occasional. dating by Cs and Pb isotopes were taken at interThe biomass of zooplankton was 0.14 mg/L and the vals of 0.5 cm for the topmost 10 cm, and at intervalsdominant species was Rotatoria. Gastropoda, Lamelli- of I cm in the rest of the core in situ, then frozen inbrachia, and Ostracoda were rare species in shellfish. laboratory under 4C. Isotopes for Cs and 2IpELocal fishes died out. The lake had characteristics of dating were measured using a and y power spectrumacidified water and differentiated obviously with other meter Magnetic measurements were carried out usinlakes in Yunnan Plateau.2a Bartington MS2 susceptibilityThe basin of Yangzonghai stretches along the N-s superconducting magnetometer in the paleomagneticdirection, surrounded by hills and mountains withlab, University of California, Davis. In each case, 2 gof sediment was taken for diatom analyses, 5g forelative heights among 400-1000 m. Thus, dispersion ostracods analyzes. Geochemical samples wereof airborne pollutants produced by the local industry treated by HNO3-HF-HClO4 solution, and then measwithin the catchment is likely limited to the basin area. ured by a Jarrel-Ash 110 ICP-AES (Inductively Cou-During the 1950s, the water quality of Lake Yang- pled Plasma Atomic Emission Spectrometer, made inzonghai was still fairly good, and the environment was America). All non-magnetic measurements mentionedfavorable, with multiplex hydrobiology and a lotspecial species However, atmospheric pollution was ography Limnology, Chinese Academy of Sciencesafter power plant, cement plant, fertilizeraluminium company, that combusts fossil2 Results and discussionsfuel. were built in the earlier 1960s. but there is noDating by Pb(using a model of constant supplystation to monitor and evaluate the atmosphere in this rate)indicates an age of 1823 A.C. at the depth of 22basin up till now. In this paper, we report the history cm and the average sedimentation rate of 1. 25 mm/areconstruction of coal-burning atmospheric pollution Results of Cs indicate three nuclear events(nucleardimentblast tests at 1954 and 1963, and the Tschernobyl nu1 Sampling and analyzingclear power plant disaster in Russia in 1986)at thedepths of 13 cm, 11.5 cm and 4 cm5, respectivelyThree short sediment cores(44--47 cm in depth) Thus we established the accurate time sequence ofyere recovered by a piston corer (inner diameter of core sediment in Lake Yangzonghai(see Table 1)Table 1 Distribution of sample ages versus depthDepth/cmAge/ADAge/AD1611181882121960201871940TH中国煤化工1838CNMHG*k The age frame is basedCs dating1742Science in china ser d earth sciences2.1 Diatom records and its changesalgae community competes intensely for light, nutriAccording to the concentration of diatom(thenumber of diatom in per gram sample), two parts areents and living space, it is very sensitive to thedivided at 12 cm of the core. The concentration of dia- changes of the lacustrine environment. The studies ontom is low below 12 cm, among 1-33 grains/g, with algae acidifying control in lab showed that cyanobacan average 5.5 grains/g. However, there are abundant teria and most chlorophyte could not adapt to acidifiedspecies, such as Cyclotella bodanica, Navicula rhyn- surface water, and would reduce rapidly and die outchocephala, Cocconeis placentula, Surirella robusta,when the lake was affected by acid precipitation. InCymbella gracilis and so on. This kind of diatocontrast, some diatom and dinoflagellate could endurethe acid well, and then they would become the domipopulation and low biomass of this kind indicate nant community in acid waterfindlayunpolluted water within a low nutritional level before fied diatom by acid tolerance in his quantificationalthe 1960s 31. The concentration quickly increases to research of transfer function between diatom commu-387 grains/g at 12 cm, and even 2738 grains/g at 8 cm, nity and lake water chemistry. He argued that manythe maximum within this core. above 8 cm, diatom genera and species of Coscinodiscaceae, Fragilariaceae and tabellariaceae had a better acid tolerancewas sharply reduced, but still higher than 50 grains/g. Cyclotella bodanica, one pelagic species of familyThe average concentration above 12 cm is 838Coscinodiscaceae, is popularly distributed within lakesgrains/g. Diatom species within this interval is not asrivers and pools in high-latitudes or nearby mountainabundant as the lower part, and the dominant species areas. It is a familiar species of diatom in acid wateris Cyclotella bodanica, which is more than 95% of preferring to live in the acid water with pH 7-4.5diatom population, even reaches 99% at 6.5--9.5 cm. best of ph 5. So, we can deduce that the water ofObviously, it is Cyclotella botanica that results in the lake Yangzonghai has been acidified by coal-burningsharp increasing of concentration above 12 cm(Fig. 1)atmosphere pollution since 1960. Afterwards, the localalgae communities were destroyed, while acid-tolerarCyclotella bodanica boomed and become the preThe planktonic algae are lower plants, and alsodominant species of plankton. That is why the concen-portant primary productivity in lacustrine biota. Sincetration of acid-tolerant diatom increased sharply at the(o+m kg) A m mgeg' (pieces)B(grans (grains Age.frame§8宫古0了19981990-1986l98125中国煤化工CNMHGig. 1. Magnetic, biological and geochemical changeLacustrine sedimentary records of coal-burning atmospheric pollutiondepth of 12 cmtakes sessile algae in the bottom of lake as food. The2.2 Ostracods recordsdisappearance of Limnocythere inopinata at 9.5 cm idue to the gradual death of sessile algae in shallowOstracods are abundant below 18 cm, with an av- water zone since 1970. There are scattered Limnoage abundance of 9.8 pieces/g(number of shellThichgram sample), among which, Candona neglectareveals its good adaptability to the environment andmost plentiful, approximately 40% of all ostracods, indicates the change of atmospheric pollution intensityhile Limnocythere sp. and Limnocythere inopinata Limnocythere inopinata may survive and multiplyapproximately 25%-30%. There is only a few Cypria nearby river outfall again 3ophthalmica with abundance of 1-2 pleces/g in this 2.3 Vertical changes of K and ARMinterval. Ostracods reduces to 3. 4 pieces/g at 17-13cm, where Limnocythere inopinata is the dominantMagnetic susceptibility(K)and anhysterisis remaspecies probably due to its good adaptability, whilnent magnetization(ARM) of the core are shown inLimnocythere sp. and Cypria ophthalmica are occa- Fig. I. Below 12 cm, k is relatively strong and consional. Candona neglecta is absent at depths over 16 stant, with an average value of 433X10-mkg"cm in the core. Above 12 cm, Limnocythere sp and which indicates that the source of ferromagnetic minCypria ophthalmica disappear and most samples are eral and the sedimentary environment are relativelyshort of ostracods. However, the average abundance of stable. Above 12 cm, k decreases sharply withostracods has a little increase to 0. 41 pieces/g above 4 some dramatic fluctuations. Its average value de-cm, where only Limnocythere inopinata is foundcreased to 280x10-m' ke- and two minimum exOrganism impoverishment is widely reported as themes are 263X10-m kg" and 131X10-m kgater acidification intensified During the acidification at 8.5 cm and 5 cm respectively. There is an increaseprocess, high concentrations of H, active Al and trend in up most 4 cm, with a relatively high value ofabundant CO2 were released, which could cause ex300×10°mkgat the top arm almost has thtinction of mostms and only a few acid-tolersame pattern as K. It reveals that ferrimagnetic mineralant and pollutant-tolerant species survived 10) During Is the main magnetic carrier. Detailed rock magnetismforming its shell, Ostracoda, Gastropoda and Lamelliresearch was carried out in Universitat Tubingenbrachia species need a large amount of calcium car- Germany. Thermomagnetic curves(K-T)on two mag-bonate, and therefore they will disappear early in theacidification process, when their absorbability of calletic extracts indicate that magnetite is the main macium are destroyed by acid water 1.2.Furthermorenetic component J-T curves also demonstrate it. Alldestroyed living conditions and evolution of biotic magnetic results mentioned above have been pub-community in acidified water also relate to the graduallished already 4, so no further details are given heredisappearance of ostracods at 12 cm. Candona ne-Grainsize analysis on burned coal ash of power plantglecta, which survives only in clean deep water, isshows that grainsize is quite inhomogeneous, rangingvery sensitive to environmental changes, and then i t from 0.02 to 2000 um, with a mean of 90 um. Somewill die out firstly when organic pollutant increases researchesargued that dramatic increase of k could befrom intense anthropogenic activitiesl3l. Cypria oph- the response towards human activities. Meanwhile, thethalmica, one kind of nekton, needs to stop on sub- change of material source, the transform and dissolu-merged plants to look for foodsubstratum stion of ferromagnetic mineral and the forming othe disappearance of Cypria ophthalmica at 11 cm authigenic中国煤化工 the magneticcould reflect that submerged plants became absentfluctuatirectly from theCNMHgradually around 1965. Limnocythere inopinatapower plantsamnan,w and the k value ofwhich prefers to live in coastwise or shallow water, 6128X10 mkg, which is rather stronger than theScience in china ser d earth sciencesbackground of lacustrine sediment, and should pro- 2.4 Reconstruction of the history of atmosphericduce an enhanced signal of magnetic concentrationpollution by environmental proxiesthe sediments when it is discharged into the lakeThe sediment below 12 cm was deposited beforeAnalysis of total Fe content on the sediment shows 1960. Environmental proxies show that Lake Yang-that the average Fe content is 43. 8 mg/g above 12 cmand46.9mg/gbelow12cm(fig.1).comparEdwithZonghaiwaswithinafavourableenvironmentandnotaffected by atmospheric pollution at that time. abovethe total Fe content of burned coal ash (59.9 mg/g),w12 cm, all the proxies reveal the lacustrine sedimededuce that the disappearance of ferromagnetic min- tary responses towards atmospheric pollution and acideral in sediment causes the abnormal low k in the up- precipitation. However, the responses of surface waterper part of the coreto atmospheric pollution are complex. LakAround the interface of water and soil, pH and Eh have a very strong capacity to buffer and neutralize thevalues are the most important factors that affect the acid precipitation. Acid rain and dry deposition of somigration and deposition of Fe element. k is relatively cannot be revealed by such obvious index as pH whenstrong and stable below 12 cm. It reveals that the replaced by Ca, Mg, K, Na and so on in soil andsedimentary environment was under a neutral and al- rock. Acid percipitation spoiled former mass balkaline oxidation condition, favorite to preserve Fe ance of ecological system and the relationship betweenelement"), which is similar to the deep water zone of all the factors, while the competion of species andLake Fuxianhu, a lake on the south of Lake Yang- evolution of aquatic ecosystem were still in processzonghai. The sharp decrease of K at the upper part in- Rare character record"said that groups of fruiter anddicates the change of pH and Eh around interface. crop on the north of lake were ever died many timesPrecipitation of acid rain or SO2 can directly increase when atmospheric pollution was in most serious statethe concentration of H, while H has a negative cor- These kinds of short-term pollutions with high intenrelation with Eh. Consequently, the value of pH and sity could also cause the decrease of lake waters in-Eh values decrease sharply. Thus, Eh decreases in the stantaneous pH, death of aquatic organism and drainterface. which offers the favorable conditions for matic change of environment,. all these character-activation and migration of Fe element. In addition, istics make it possible to quantitatively analyze theIth the help of anaerobic vibrio of desulfurization, continuous change of the instantaneous lowest pH andthe sulfurate oxysalt is reduced to H2S, which often to reconstruct environment after 1960changes the interface to a strong reducing environmentIn order to quantitatively analyze the change trendwhich enables Fe to lower valenic ion as the following of lake water's instantaneous PH value, according toequation/7Ithe ecological characteristic of Cyclotella bodanicaFe(oh)3 +e-Fe(oh2 +OHwe set the lowest average concentration of 98 grains/In the uppe3-5 cm as an instantaneous ph value ofFe7, and the highest average concentration of 1520Because ferromagnetic particulates which contrib- grains/g in the upper 10.5-6 cm as an instantaneousute to K are finer, they will be moved out first during ph value of 5. Moreover, according to the change ofthe migration of Fe element. At the same time, plenti- ostracods, we set the depth of Il cm where Cypriful quincunx pyrite is found in this part, which con- ophthalmica disappeared and submerged plants almostfirms that there was in redox condition indeed. and died out as a mark where the instantaneous pH valuethat the geochemical process mentioned above cer-enth nf 9 5 cm where limnotainly happened.18)cythere inop中国煤化士 essile algae inCNMHG1)Local Water Conservancy Writing Group of Yiliang County, The chronicles of Lake Yangzonghai in Yiliang County(second version), 1987.Lacustrine sedimentary records of coal-burning atmospheric pollutionshallow water zone almost died out around 1970 as ack where the instantaneous ph value was 5.5-6est instantaneous pH at ll cm and9 cm respectively令入The median of ph values is used to represent the loAfter verifying the concentration of Cyclotelladanica, we have four pairs data of lowest instantane-ous ph value and diatom concentration in upper core197019801990The correlation curve of pH value and Cyclotella bedanica concentration are shown in Fig. 2. Further pa- Fig 3. The changes of the instantaneous lowest ph value calculatedrameter calculating and curve fitting reveal a linear by the concentration of Cyclotella bodanica and the linear equationnegative correlation between pH value and Cyclotella acid precipitation. K and ARM reveal the geochemicalbodanica concentration(r >0.9). According to the fol- process that acid precipitation changed the pH-Eh enlowing linear equationvironment around interface of water and soil. whichF=-0.001424×X+7.155,further resulted in the disappearance of ferromagneticparticulates. Those magnetic proxies are the most senwhere X is the concentration of Cyclotella bodanica at sitive proxies for coal-burning atmospheric pollutionany depth, r is the lowest instantaneous ph value, we and good natural record for environment reconstruccan calculate the instantaneous lowest pH value at anytiondepth above 12 cm. Then the continuous trend curve(2)Based on the environmental proxies, the polluhai is drawn in Fig 3. This figure reconstructs the histion process in Lake Yangzonghai is reconstructedtory of atmosphere pollution in Lake YangzonghaThe natural lacustrine environment was favorable be-since the 1960sfore 1960. It began to be affected by atmospheric pollution and acid precipitation in 1960, and the instanta3 Conclusionsneous ph value reached 6.63. The serious pollution(1)The vertical distributions of diatom and os- decreased the lowest instantaneous pH value to 5-6tracods record the spread process of acid-tolerant spe- from 1965 to 1980. Afterwards, the intensity of pollucies and the disappearance of shellfish resulting from tion decreased from 1984 to 1999, no more reports7.5F=-0001424×H+7.155taneous pH value of lake water reached to 6.5-7, alr=09993870+▲though the polluted environment is hard to be rediableThe reason for decreasing intensity of pollution after1983 is that local plants and companies replaced thelocal Pliocene coal with high sulphur content by high6.0quality coal with lower sulphur content from otherplacesal the cl5.0nd the process of atmospheric pollution,dll as its80012001600damage towards the lacustrine environment, which isDiatom concentrationconsistent with the literature records. ItFig. 2. Linear correlation analysis between the concentration of that coal-brCyclotella bodanica and the instantaneous lowest pH value of lake中国煤化工in is thewater(thick line is smooth curve)tant factorCNMH Gof biodiversity,1746Science in china ser d earth sciencesspread of acid-tolerant species and the worsening of 10. 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