Influence Factors Analysis to Chlorophyll a of Spring Algal Bloom in Xiangxi Bay of Three Gorges Reservoir

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1 J. Water Resource and Protecton, 2009, 3, do: /jwarp Publshed Onlne September 2009 ( Influence Factors Analyss to Chlorophyll a of Sprng Algal Bloom n Xangx Bay of Three Gorges Reservor Abstract Huajun LUO 1, 3, Defu LIU 2, Daobn JI 1, Yulng HUAG 3, Yngpng HUAG 3 1 College of Water Resources and Hydropower Engneerng, Wuhan Unversty, Wuhan, Chna 2 College of Hydroelectrc & Cvl Engneerng, Three Gorges Unversty, Ychang, Chna 3 College of Chemstry & Lfe Scence, Three Gorges Unversty, Ychang, Chna E-mal: luohuajun@21cn.com Receved June 25, 2009; revsed July 13, 2009; accepted July 17, 2009 To study the relatonshp between envronmental varables and chlorophyll a of sprng algal bloom n Xangx Bay of Three Gorges Reservor, stepwse multple bnomal regresson and grey relatve analyss methods were adopted. In surveys, 13 statons have been nvestgated and 143 samples were collected weekly from March 4 to May 13 n The study shows envronmental varables (turbdty, total ntrogen, dssolved oxygen, total phosphates and slcate) are key factors durng algal bloom. The grey relatve values and ther permutaton ndcated that turbdty was the most mportant factor and had comprehensve effect on chlorophyll a. The more number of nteractve varables s found to be an ndcaton of bochemcal actvty durng sprng algal bloom n Xangx Bay such as DO T, Turb TP and so on. There was good lnear relatonshp between chlorophyll a and the nteracton of DO wth T ( R , P ).The nteracton of nutrents (TP T, TP SO 4, T SO 4 ) had sgnfcant nfluence to chlorophyll a and probably determned the nter-specfc competton at dfferent nutrent concentratons. Keywords: Stepwse Multple Bnomal Regresson, Grey Relatve Analyss, Chlorophyll a, Envronment Varables, Algal Bloom, Xangx Bay 1. Introducton Bomass of phytoplankton n terms of the concentraton of chlorophyll a s one of the most wdely accepted methods n the study of bologcal producton as t ndcates total plant materal avalable n the water at prmary level of food chan [1]. Hence the growng and declnng condton of algal bloom can be descrbed by the spatal and temporal varaton of chlorophyll a. There are many study methods to the relatonshp between chlorophyll a and physcochemcal factors such as stepwse multple regresson analyss [2], grey relatve analyss [3] and artfcal neural network [4]. Chlorophyll a can be related to the envronmental parameters by means of lnear regresson, though t provdes only the predcton effcency of a sngle factor at a tme [5 7]. But the algal bloom s the multvarate nteracton and nonlnear process. So a number of factors jontly controllng the boactvtes are to be consdered. Grey theory can reflect the dynamc state of data and has been broadly appled n the last decade snce Deng Julong suggested the dvson of systems nformaton to whte, grey and black [8]. The systematc analytcal method of grey theory was used to study the relatonshp between bomass of octluca scentllans Macartney or Prorocentrum sgmodes Bohm (two red tde organsms) and varous physcochemcal factors of seawater [9,10]. Recently the relatonshp between chlorophyll a and envronmental factors n Xangx Bay of Three Gorges Reservor form March to Aprl n 2005 were reported [6]. They showed that ecologcal factors (ncludng total ntrogen, total phosphorus, water temperature, transparency and dssolved oxygen) had sgnfcant mpact on the concentraton of chlorophyll a usng correlaton analyss and lnear regresson method. But the multvarate nteracton and nonlnear process n the algal bloom were not consdered n the prevous work. So ths present paper ams to study: (1) controllng and nteractve factors of chlorophyll a, (2) nonlnear nterrelatonshp between

2 H. J. LUO ET AL. 189 physcochemcal parameters and chlorophyll a of sprng algal bloom n Xangx Bay. In order to acheve ths, stepwse multple bnomal regresson method and grey relatve analyss are adopted. 2. Materals and Methods 2.1. Area Descrpton The Three-Gorge Dam (TGD) n Chna s the world s largest dam, measurng 2335 m long and 185 m hgh, and the reservor created by t wll have an area of 1080 km 2 n 2009 [11]. The Xangx Rver, whch les 38 km upstream from the Dam, s the largest trbutary n the Hube porton of Three-Gorge Reservor (TGR). Ths rver s 94 km long wth a watershed of 3099 km 2 (between and E long., and lat.) [12]. Wth mpoundment of TGR, the downrver stretch of Xangx Rver was nundated and Xangx Bay was formed. The water level n the Xangx Rver has ncreased 40 m and the water flow velocty has dropped from the orgnal m/s [13] to m/s [14]. So when water temperature ncreased n sprng, there were algal blooms wth prolonged retenton tme and hgh nutrent concentratons n Xangx Bay. A. Formosa, C. acuta and C. ovata were the domnant speces Samplng and Analyss Water samples were collected at 13 statons n Xangx Bay (Fgure 1). Statons X0-X11 are on the Xangx Rver. Staton GL s located at the downstream of Gaolan Rver, whch s the largest trbutary of the Xangx Rver. Samplngs were performed weekly from March 4 to May 13, Water samples were collected at 0.5 m depth from surface n the mddle of the rver usng a 5-L skn sampler (Hydrobos-Kel). Water temperature (WT), dssolved oxygen (DO), ph, turbdty (Turb) were recorded n stu usng mult-parameter water qualty analyzer (Hydrolab DS5). Total phosphates (TP), phosphate (PO 4 ), total ntrogen (T), ammonum ntrogen (H 4 ), ntrate (O 3 ), slcate (SO 4 ) were determned n the laboratory usng State Envronmental Protecton Admnstraton (SEPA) standard methods [15]. For chlorophyll a (Chl.a) analyss, samples fltered through Whatman GF/F flters were extracted wth cold 90% acetone and estmated by spectrophotometer [16]. Fgure 1. Samplng statons n Xangx Bay.

3 190 H. J. LUO ET AL Statstcal Analyss Usng Stepwse Multple Regresson Method of choosng the mnmal set of envronmental varables that can explan the varaton n the affected parameter [17] was adopted earler. A modern approach to explore the possble nfluence of varous envronmental varables on phytoplankton dynamcs s the applcaton of a multvarate statstcal analyss [18]. These methods are wdely used n ecologcal studes and have proved to be useful for understandng nteractons between ecologcal factors that nfluence phytoplankton producton. In ths study, an attempt s made to nclude the ndvdual factors, second order and nteracton effects of the envronmental parameters vz: WT ( ), DO (mg/l), ph, Turb (TU), TP (mg/l), PO 4 (mg/l), T (mg/l), H 4 (mg/l), O 3 (mg/l) and SO 4 (mg/l) to relate chlorophyll a concentraton (mg/m 3 ) n the predctve model. A stepwse multple regresson analyss s appled usng phytoplankton (Chl.a) as the dependent varable, whle ndvdual, second order and nteracton effects of the above lsted envronmental parameters as the ndependent varables, to examne the controllng role of any partcular parameter or group of parameters on phytoplankton bomass Grey Relatve Analyss Based on the above nvestgaton, chlorophyll a concentraton (mg/m 3 ) n Xangx Bay was used as the analyzed sequence { X 0 ( k) k 1,2,, }, samplng number 143, and 10 factors ncludng WT ( ), DO (mg/l), ph, Turb (TU), TP (mg/l), PO 4 (mg/l), T (mg/l), H 4 (mg/l), O 3 (mg/l) and SO 4 (mg/l) were to be regarded as comparatve sequences or subsequences { X j ( k) k 1,2,, } ( j 1,2,,10). The calculaton method [19] of grey system relatve degree s as follows: All the sequences are ntated for makng them comparable. Let the analyzed sequence be: { 0 Y0 ( k) k 1,2,, } { Y0 (1), Y0 (2),, Y ( )} X 0 (1) X 0(2) X 0( ),,, (1) M 0 M 0 M 0 M 1 0 X 0( k) k 1 So the comparatve sequences are: { Y j ( k) k 1,2,, } { X j ( k) / M j k 1,2,, }( j 1,2,,10) (2) M j 1 k 1 X ( k) j and the comparatve sequence { ( t)}, whch s called Let { ( k) k 1,2,, }( 1,2,,10) be a rela- tve coeffcent between the analyzed sequence { Y 0 ( t)} the grey relatve coeffcents. Then Y j Mn ( k) Max( k) k k ( k) ( k) Max ( k) k ( 1,2,,10; k 1,2,, ) (3) ( k) Y0 ( k) Y ( k) and ( 0 1) s a dstngushed coeffcent. Here we take t as Let k ( k) ( 1,2,,10) (4) 1 s a relatve degree between the analyzed se- quence { Y ( )} and the comparatve sequence { Y j ( t)}. 0 t 3. Results Usng stepwse multple bnomal regresson method, the optmal emprcal mode of multple bnomal regresson to chlorophyll a of sprng algal bloom n Xangx Bay s obtaned as follows: 2 Chl. a DO ( DO) DOT TurbTP TP T TPSO T SO 4 4 ( R , S , F , P , n 143 ) (5) 7,135 Partal correlaton coeffcent, t test value and p-value of ndependent varables n Equaton (5) are presented n Table 1. All p-value of ndependent varables are less than The grey relatve values between the analyzed sequence and subsequences for samples of 13 statons were calculated. The results of relatve values are lsted n Table 2, and the results of ther permutaton are n Table Dscusson The stepwse multple regresson and grey relatve analyss show the envronmental varables (Turb, T, DO, TP, SO 4 ) are more mportant and can reflect the

4 H. J. LUO ET AL. 191 Table 1. Partal correlaton coeffcent, t test value and p-value of ndependent varables n Equaton 5. ndependent varables partal correlaton coeffcent t test value p-value DO (DO) DO T T urb TP TP T TP SO T SO Table 2. Grey relatve values between chlorophyll a and physcoc hemcal factors. Staton WT DO ph Turb TP PO 4 T H 4 O 3 SO 4 X X X X X X GL X X X X X X Average Perm utaton Table 3. Averages and permutaton of the gr ey relatve values from 13 statons. WT DO ph Turb TP PO 4 T H 4 O3 SO change of chlorophyl l a concentraton of sprng algal bloom n Xangx Bay. Based on grey relatve analyss, Turbdty was the most mportant factor n the algal bloom and had comprehensve effect on chlorophyll a. As the low turbdty value chlorophyll a was n hgh level (Fgure 2) because lght llumnance under clear water was hgh and benefcal to phytoplankton photosynthess [20]. When t raned from Aprl 15 to Aprl 22 n Xangx Bay, turbdty and slt ncreased, lght llumnance under water decreased. Meanwhle, nutrents such as phosphates were adsorbed by slt n the rver (nteractve factor Turb TP was ncluded n Equaton 5). So algal bloom declned. trogen enterng aquatc systems arses from a varety of sources that nclude pont and non pont source polluton, bologcal fxaton of gaseous ntrogen and the deposton of ntrogen oxdes and ammonum [21]. Mean T of sprng algal bloom n Xangx Bay was mg/l wth a mnmum and maxmum concentraton of and mg/l respectvely. Chlorophyll a of sprng algal bloom had sgnfcant negatve correlaton wth T (Spearman r 0. 18, n 143, p ), O 3 (Spearman r 0. 28, n 143, p ). Meanwhle T had sgnfcant negatve correlaton wth DO (Spearman r 0. 32, n 143, p 0. 01) and there was good lnear relaton- shp between chlorophyll a and the nteracton of DO wth T (DO T) (Fgure 3): Chl.a ( DOT) ( R , S , P , n 143 ) (6) These data ndcate ntrogen transformaton by DO

5 192 H. J. LUO ET AL. Fgure 2. Temporal and spatal change of turbdty and Chl.a n dfferent samplng statons of Xangx Bay. Fgure 3. The relatonshp between chlorophyll a and DO T n Xangx Bay.

6 H. J. LUO ET AL. 193 Fgure 4. The relatonshp between chlorophyll a and dssolved oxygen n Xangx Bay. plays an mportant role n phytoplankton growth and the soluble nutrents may be effectvely uptake by phytoplankton. The relatonshp between chlorophyll a and dssolved oxygen was nonlnear (Fgure 4), whch regresson model was as follows: Chl. a exp(0.2166do) ( R , S , P , n 143 ) (7) It was due to the ncrease of oxygen whch was released durng phytoplankton photosynthess [22] and the decrease of oxygen whch was consumed by organc matter [23]. Total phosphate and slcate were also mportant factors to chlorophyll a. Mean values of TP and SO 4 n Xangx Bay were mg/l and mg /L respectvely durng sprng algal bloom. The phosphate load was hgh and ncreased from downstream to upstream because there were phosphate mnes and phosphate plants n the upstream of Xangx Rver [24]. Datoms were the domnant speces durng the later stage of algal bloom and slcate was necessary to datoms growth. The cooperate nteracton of nutrents (TP T, TP SO 4, T SO 4 ) had sgnfcant nfluence to chlorophyll a durng sprng algal bloom based on stepwse multple bnomal regresson and probably determned the nter-specfc competton at dfferent nutrent concentratons, because ther ntakes were speces specfc [25]. So the relatonshp between dfferent algal speces denstes and dfferent nutrent concentratons would be studed n the futu re work. 5. Conclusons The study usng stepwse multple regresson and grey relatve analyss method shows the sgnfcant nfluence of envronmental varables (turbdty, total ntrogen, dssolved oxygen, total phosphates and slcate) and ther nteractons on the producton of chlorophyll a. The grey relatve values and ther permutaton ndcated that turbdty was the most mportant factor and had comprehensve effect on chlorophyll a. The more number of nteractve varables s found to be an ndcaton of bochemcal actvty durng sprng algal bloom n Xangx Bay such as DO T, Turb TP and so on. There was good lnear relatonshp between chlorophyll a and the nteracton of DO wth T (DO T). The nteracton of nutrents (TP T, TP SO 4, T SO 4 ) had sgnfcant nfluence to chlorophyll a and probably determned the nter-specfc competton at dfferent nutrent concentratons. 6. Acknowledgements Ths work was funded by atonal atural Scence Foundaton of Chna (o ). We thank Yu We, Yang Zhengjan and Su Yanme for ther assstance n the feld and lab. 7. References [1] G. A. Weyhenmeyer, T. Blenckner, and K. Pettersson, Changes of the plankton sprng outburst related to the

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