344 Chiang Mai J. Sci. 2013; 40(3)

Chiang Mai J. Sci. 2013; 40(3) : 344-355http://it.science.cmu.ac.th/ejournal/Contributed Paper

Phytoplankton as a Bio-indicator of Water Quality inthe Freshwater Fishing Area of Pak Phanang RiverBasin (Southern Thailand)Amphorn Sakset [a] and Wanninee Chankaew [b][a] Surat Thani Inland Fisheries Development and Research Center, Thakham Sub-district, Punpin District,

Surat Thani 84130, Thailand.[b] Department of Fishery, Faculty of Agriculture, Rajamangala University of Technology Srivijaya, Nakhon Si Thammarat 80110, Thailand.Author for correspondence; e-mail: phornfresh@hotmail.com, wannaneeja@yahoo.com

Received: 27 February 2012Accepted: 7 November 2012

ABSTRACTPhytoplankton in the freshwater fishing area of Pak Phanang River Basin (PPRB),

Nakhon Si Thammarat Province in southern Thailand was monitored at three differenthabitat sites over three different seasons in 2006, in order to assess water quality conditionand suggest any fishery management measures. The water quality parameters still remainedsuitability for inland fisheries. A total of 62 genera and an average density of 10,020units L-1 of phytoplankton belonging to six divisions were identified. The third-mostabundant genera were Peridinium sp, Protoperidinium sp which most related to velocityand Trachelomonas sp. which most related to ammonia nitrogen. Shannon-Wienerdiversity index showing that phytoplankton diversity was generally in medium leveland implied that water quality condition was moderately-polluted. Also, the AARL-PPscore assessed that the water quality condition in the area was considered meso-eutrophicand moderately-polluted, but it was still suitable for aquatic animal growth and survival.Furthermore, fishery management through water monitoring should be regularlyconducted. Restocking aquatic animals/fishes should be implemented at sites and timeswith the best condition for survival.

Keywords: phytoplankton, bio-indicator, water quality, freshwater, Pak Phanang riverbasin

1. INTRODUCTIONPhytoplankton has been long used as an

effective water bio-indicator [1-2] that issensitive to environmental changes [1]. Somespecies thrive in highly eutrophic waters,whereas some species are very sensitive toenvironmental changes [1]. Rivers withweak water currents always contain

phytoplankton in division Chlorophyta,such as Pandorina and Eudorina, and indivision Euglenoplyta, such as Euglena andTrachelomonas [3]. Melosira and Cyclotellaare usually found in clean water, whereasNitzschia, Microcystis and Aphanizomenonare usually found in polluted waters [1].

Chiang Mai J. Sci. 2013; 40(3) 345

Chlamydomonas, Euglena, Scenedesmus [4]and Microcystis [4-5] are indicators ofeutrophic waters. Aphanizomenon,Microcystis and Ceratium are usually foundin high phosphate waters, while Anabaenais found in waters with slight nitrogencontent [6]. Palmer [2] listed sixty generaof plankton which are the most organicpollution-tolerant. Euglena, Oscillatoria,Chlamydomonas, Scenedesmus, Chlorella,Nitzschia, Navicula, and Stigeoclonium arethe top eight genera which can indicateorganic pollution in the waters. Rott et al.[7] used the Shannon diversity and evennessindices of phytoplankton to assess waterconditions in tropical Asian water bodies.They were classified as eutrophic level inThailand. Moreover, Peerapornpisal et al.[8] developed a method to assess the waterquality in water bodies by using dominantphytoplankton scoring system, i.e. AARL-PP score which is a simple evaluationmethod without chemical requirement.The results were more than 90% consistentwith physical and chemical parameters.

Pak Phanang River Basin (PPRB) islocated along the southeastern seashore ofThailand. Its area covers around 3,183 km2.In 1995, the Uthokvibhajaprasid Sluice gate wasconstructed on Pak Phanang River at Hu LongSub-District (about 6 km from the seashore),Pak Phanang District, Nakhon Si ThammaratProvince as a Royal Initiative Project in aneffort to provide freshwater for agricultureand household purposes, and to preventsaltwater intrusion into agricultural areas [9].However, the dam has affected fishing areasof the Pak Phanang River up to 100 kmupstream due to loss of tidal influences andassociated marine and brackish waters,which has caused a decrease in fisheryproduce and thus in income of local people[10]. Before the dam construction, peoplearound this river gained benefit from the

influence of the tide in terms of brackishand marine fishery production. However,the tidal area has become a semi-loticfreshwater area since the dam beganoperating in 1999. Aquatic biodiversity andfish production have been reduced. Somefish species have disappeared, particularlybrackish and marine species. The dam hasreduced biodiversity and disturbed fishbreeding [11]. Water quality is also low asthe consequence of agricultural residueaccumulation [11]. So, direct and indirectimpacts of the dam have been affecting theway of living of local people, especiallyfishermen [12].

This paper illustrates the use ofphytoplankton as a bio-indicator to assesswater quality conditions and imply any fisherymanagement measures in the freshwaterfishing area of the Pak Phanang River Basinwhich was seriously affected by the damconstruction.

2. MATERIALS AND METHODSThe study was conducted over three

seasons in three different ecosystems in thefreshwater fishing area, about 100 kmupstream of the dam site in 2006. The seasonswere covered dry season (February andMarch), early rainy season (June and July), andheavy rainy season (October and December).During the study period, the sluice gates werenormally closed during the dry and rainyseasons, and opened during the heavy rainyseason. The ecosystems were divided intodownstream site (nearby the dam), middle-stream site (main tributary), and upstreamsite (peat swamp) (Figure 1).

In each study site, water samples werecollected for measurements based onAPHA, AWWA and WPCP [1] at thesurface and 0.5-1 m above the ground withthree replications (left, middle, and rightside of the river). Water temperature was

346 Chiang Mai J. Sci. 2013; 40(3)

Figure 1. Survey sites of phytoplankton in the freshwater fishing area, PPRB, 2006(S1 = Downstream site, S2 = Middle-stream site, and S3 = Upstream site).

measured with a thermometer. Watertransparency was measured with a black-white 20 cm diameter Secchi disk. Salinitywas measured with a salinometer.Dissolved oxygen (DO) was measured byDO meter. Ammonia nitrogen wasmeasured by Nessler Method. Nitrate(NO-

3-N) was measured by the CadmiumReduction Method. Orthophosphate (PO+

4-P) was measured by the Ascorbic Acid.Velocity was measured by flow meter. Waterdept was measured by depth gauge.

Phytoplankton samples were collectedalong with the water quality measurementsusing by the Kemmerer water sampler. Watersamples were filtered through a plankton netwith pore size of 20 micron. Filtered sampleswere preserved in 95% alcohol (equal volumesof alcohol and water sample) with theaddition of 1 ml L-1 saturated copper sulfatesolution (CuSO4) to retain color [1]. Thesamples were then transported to thelaboratory for identification of genera andcounting the number of phytoplankton unitsof each genus by using a Sedgwick-Raftercounting chamber under a compoundmicroscope following the methods in APHA,AWWA and WPCP [1], Wongrat [13], and

Prescott [4].Univariate analysis; mean and standard

deviation (SD) was applied to describe andevaluate the variations of the water qualityparameters among sampling sites and seasons,and derived values were compared withstandard values for fisheries in Thailand [15-16], and compared with previous studiesbefore the dam construction (1996-1999) [17];diversity indices including number of genera,abundance, richness index, evenness index andShannon-Wiener’s diversity index (loge) wereused to assess diversity level of phytoplanktonand to see trends of change along with thesections of the river and seasons, as well ascompared with previous studies before thedam operation (1996-1999) [17]; one-wayanalysis of variance (ANOVA) was performedto determine significant differences in waterquality parameters and phytoplanktonabundance among sites and seasons. Multiplecomparisons using LSD test were performedto identify significantly different means amongsites and seasons at the 0.05 level.

Multivariate indices analysis; clusterand Ordination Multi-Dimensional Scaling(MDS) analyses were used to classifysimilarity of water quality parameters and

Chiang Mai J. Sci. 2013; 40(3) 347

phytoplankton communities amongseasons and sites. The cluster and MDSanalyses aimed to find groupings ofsimilarities of samples among different sitesand seasons such that samples within agroup are more similar to each other thansamples in different groups. The resultingcluster was shown in a tree-like diagramcalled dendrogram and MDS was shownas a map. Both the dendrogram and mapwere constructed based on standardizedEuclidean distances matrix for the watervariables and Bray-Curtis similarity matrix(fourth root transformation) forphytoplankton communities; a similaritypercentage-species contribution (SIMPER)analysis was applied to test the waterparameters and genus affecting groupsimilarity, with Primer program Version5 for Windows, based on Clark andWarwick [14]; Canonical Correspondenceanalysis (CCA) was carried out to assess therelationship between 10 dominant genera(96% of total abundance) and water qualityparameters by CANOCO version 4.5. Theresult was showed by CCA map. Inaddition, AARL-PP score was also used toassess the mass of water quality based onPeerapornpisal et al. [8].

3. RESULTS AND DISCUSSIONThe water quality variables relating to

phytoplankton, i.e. water temperature, watertransparency, DO, ammonia and NO-3-N, hadaverage values that were still in the standardrange for class 2 [16] and inland fisheries [15-16], excepted PO+4-P, which was less than thestandard range. The salinity value was generallysuitable for freshwater phytoplankton genera.Velocity was generally very slow, and waterdept of study area was shallow (Table 1).After the dam began operating, the salinityof upper dam area had decreased, and thewater became freshwater condition because

the dam blocked seawater moving up the river(tidal water). The salinity decreasing related toincrease of phytoplankton density which alsoled to transparency decrease. Also, ammoniawas higher than before the dam operation [17](Table 1) caused to phytoplankton increment.The higher ammonia might be a result ofmore sedimentation and nutrient loading[18] in the area. However, the result ofANOVA test showed that there was nosignificant difference among sites (P>0.05)in temperature, transparency, ammonia,NO-3-N, PO+4-P, DO and velocity. In contrast,salinity and water dept showed significantdifference (P<0.05) among sites. The resultof LSD test showed that the salinity had thehighest value at the down and middle streamsites (P<0.05) where were occasionallyaffected by sea water when opening the sluice.The water dept had higher value at theupstream (Table 1). In terms of season,ANOVA showed that water depth was similar(P>0.05) among seasons but there weresignificant differences among seasons (P<0.01)in temperature, transparency, ammonia,NO-3-N, PO+4-P, DO, velocity, and salinity.The LSD test (P<0.05) showed that velocityhad the highest values during the early rainyseason, while ammonia, NO-3-N and PO+4-Pshowed highest concentration during the dryseason. The salinity, temperature andtransparency showed highest concentrationduring the dry and early rainy seasons. DOhad the highest value during the early rainyseason which related to phytoplanktonabundance.

The results of cluster and MDS analysesto test similarity of the water qualityparameters variations among seasons and sitesshowed two groups by season over all sites;1) dry season and early rainy seasons, and 2)heavy rainy season (Figure 2). This suggeststhe changes that they might be related toprecipitation and drainage of water gate. The

348 Chiang Mai J. Sci. 2013; 40(3)

gate was normally closed during the dryseason and early rainy season to storefreshwater for irrigation and water supply, andwas opened in the heavy rainy season tocontrol flooding [9]. Also, the SIMPER

analysis showed that the transparency andDO indicated similarity within the eachgroup at contributing greater than 5% ofthe similarity. However, their values in firstgroup were higher than another.

Table 1. Variations of water quality in freshwater fishing area, PPRB, 2006 and comparisonof variables before damming and comparison with standard values for fisheries (* <0.5 ppt= freshwater, 0.5-25 ppt = Brackish water; different superscripts in a column indicated significantdifference at P<0.05).

Parameters Sites/seasons Dry seasonEarly rainyseason

Heavy rainyseason Mean + SD

Before thedamoperation[17]

Standardforfisheries

Temperature( )

Transparency(cm.)

Ammonianitrogen(mg L-1)

NO-3-N

(mg L-1)

PO+4-P

(mg L-1)

Salinity (ppt)

DO(mg L-1)

Water depth(m)

Watervelocity(m s-1)

DownstreamMiddle-streamUpstreamMean + SDDownstreamMiddle-streamUpstreamMean + SDDownstreamMiddle-streamUpstreamMean + SDDownstreamMiddle-streamUpstreamMean + SDDownstreamMiddle-streamUpstreamMean + SDDownstreamMiddle-streamUpstreamMean + SDDownstreamMiddle-streamUpstreamMean + SDDownstreamMiddle-streamUpstreamMean + SDDownstreamMiddle-streamUpstreamMean + SD

29.70+0.3730.41+0.9329.90+0.5930.00+0.71a

71.50+28.7568.38+29.5261.88+20.3467.25+24.36a

0.31+0.130.36+0.160.51+0.240.39+0.20a

0.21+0.160.20+0.160.22+0.180.21+0.16a

0.022+0.0030.018+0.0040.022+0.0120.021+0.007a

1.00+1.070.63+0.520.00+0.000.54+0.78a

8.56+4.938.00+4.265.29+2.057.28+4.04ab

2.9+0.62.2+0.93.5+0.52.9+0.80.01+0.010.06+0.040.01+0.000.03+0.03a

29.62+0.4930.47+0.5030.24+0.5130.11+0.61a

72.90+34.5474.30+36.2363.40+9.8570.20+27.73a

0.12+0.030.08+0.020.22+0.330.14+0.20b

0.03+0.030.13+0.150.08+0.070.08+0.10b

0.002+0.0010.002+0.0010.002+0.0000.002+0.001b

0.50+0.530.40+0.520.00+0.000.30+0.47a

9.93+2.078.09+4.566.35+1.298.12+3.24 a

3.1+0.71.8+0.73.9+3.42.9+2.10.18+0.070.17+0.070.03+0.030.14+0.09b

28.62+0.5129.15+1.0228.52+1.4228.76+1.06b

37.25+14.6333.83+19.0233.75+7.2834.94+13.70b

0.32+0.160.27+0.100.23+0.060.27+0.12c

0.14+0.060.13+0.040.10+0.030.12+0.05b

0.002+0.0000.002+0.0000.002+0.0000.002+0.000b

0.00+0.000.00+0.000.00+0.000.00+0.00b

5.83+1.345.75+2.117.81+2.036.46+2.05b

2.1+0.51.5+0.43.0+1.62.2+1.10.04+0.030.08+0.060.11+0.050.07+0.05a

29.24+0.6929.93+1.0529.46+1.2529.54+1.0558.27+30.1756.53+32.6351.13+18.7555.31+27.380.25+0.150.23+0.150.30+0.260.26+0.190.12+0.110.15+0.120.12+0.110.13+0.110.009+0.0020.007+0.0020.009+0.0050.008+0.0040.40+0.70a

0.30+0.47a

0.00+0.00b

0.25+0.537.92+3.357.13+3.726.65+2.057.23+3.132.7+0.6ab

1.8+0.7b

3.5+1.8a

2.7+1.30.08+0.040.10+0.060.05+0.030.08+0.06

30.22+1.44

84.40+46.20

0.10+0.12

0.23+0.18

0.018+0.010

4.90+5.86

--

-

25-32 [15]

30-60 [15]

0.5 [16]

5.0 [16]

0.1-0.2[23]

<0.5* [23]

> 6.0 [16]-

-

Chiang Mai J. Sci. 2013; 40(3) 349

Figure 2. Normalized Euclidean cluster diagram and MDS of environmental similarity in thefreshwater fishing area, PPRB, 2006 (T1 = Dry season, T2 = Early rainy season, T3 = Heavyrainy season, S1 = Downstream site, S2 = Middle-stream site, and S3 = Upstream site).

Sixty-two genera of the phytoplanktonbelonging to six divisions were found,having an average density of 10,020 unitsL-1. The third-most abundant genera werePeridinium, Protoperidinium andTrachelomonas (Table 2). These generausually dominate in nutrient rich waters[19]. As of this study, all of them werepresent at the midstream site during theearly rainy season (closed period). Thedominant genera seem changed beforedamming in 1996-1999 which wereChaetoceros, Peridinium andTrichodesmium [17]. The number of generawas high at the upstream site during earlyrainy season (42) whereas the number ofindividuals was high at the midstream siteduring early rainy season (55,021individuals L-1) (Table 2) because of the

abundance of some genera, especiallyPeridinium sp. and Protoperidinium sp.However, the ANOVA showed that therewas no significant difference in abundanceof phytoplankton among sites at P>0.05,but there were significant differences inabundance among seasons at P < 0.05, andLSD test showed that the highestabundance were during the early rainyseason (P<0.05) (Table 2). The evennessand Shannon-Wiener diversity indices inTable 2 were high during almost all seasonsand sites except for the early rainy seasonat the downstream site where a lowernumber of genera (21) were observed, alsodominated by a few genera i.e. Peridiniumsp., Protoperidinium sp. and Trachelomonassp. (Table 2).

350 Chiang Mai J. Sci. 2013; 40(3)

Table 2. Divisions, genera and average density (units L-1) of phytoplankton in the freshwaterfishing area, PPRB, 2006 (T1 = Dry season, T2 = Early rainy season, T3 = Heavy rainy season,S1 = Downstream site, S2 = Middle-stream site, and S3 = Upstream site).

Genera T1S1 T1S2 T2S1 T2S2 T2S3 T3S1 T3S2 T3S3 Average

BacillariophytaChaetoceros sp.Cyclotella sp.Diatoma sp.Fragilaria sp.Navicula sp.Nitzschia sp.Pinnularia sp.Surirella sp.Tabellaria sp.AbundanceNo. of genera (total)ChlorophytaActinastrum sp.Ankistrodesmus sp.Bambusina sp.Closterium sp.Coelastrum sp.Cosmarium sp.Crucigenia sp.Desmidium sp.Euastrum sp.Eudorina sp.Dictyosphaerium sp.Gonatozygon sp.Gonium sp.Hyalotheca sp.Kirchneriella sp.Micrasterias sp.Mougeotia sp.Nephrocytium sp.Oocystis sp.Pandorina sp.Pediastrum sp.Pleodorina sp.Pleurotaenium sp.Scenedesmus sp.Selenastrum sp.Spondylosium sp.Staurastrum sp.Staurodesmus sp.Tetraedron sp.Triploceras sp.Volvox sp.Xanthidium sp.Zygnema sp.AbundanceNo. of genera (total)

00000500272

26110004280032000100000182012014509060010

18714

2200006000283

92103028130292010000001221002310300600270

21416

0300026000292

050663

181303811034030001060646012010031

31420

00000000000

1035003902300100000002023500

229000000000

4399

T1S3

00000101022

18180240059001800000006064400

4590020001610

84213

01000501073

54928

132262012420009121032076702675017281020

51924

00102211296

80024310090000000006231149002120000

11214

00100302175

300451100600001001171100320021003108016

013218015217

23011210214140102313117140414017120120

11426

031006011129

3711042583511211002210508271199209130240

31125

Chiang Mai J. Sci. 2013; 40(3) 351

ChrysophytaDinobryon sp.AbundanceNo. of genera (total)CyanophytaAnabaena sp.Chroococcus sp.Dimorphococcus sp.Merismopedia sp.Microcystis sp.Oscillatoria sp.Spirulina sp.AbundanceNo. of genera (total)EuglenophytaEuglena sp.Euglepha sp.Lepocinclis sp.Phacus sp.Strombomonas sp.Trachelomonas sp.AbundanceNo. of genera (total)PhyrrophytaCeratium sp.Dinophysis sp.Noctiluca sp.Peridinium sp.Prorocentrum sp.Protoperidinium sp.No.of abundanceNo. of genera (total)Grand total ofabundanceGrand total ofgenera (total)Species richness indexEvenness indexShannon-Wienerdiversity index

Phytoplankton abundance was at 4,464individuals L-1 in 1996-1999 [17] and 10,020individuals L-1 in this study. The speciesrichness index was 3.99 in 1996-1999 [17]and 3.89 in this study. The evenness indexwas 0.42 in 1996-1999 [17] and 0.47 in ourstudy. The Shannon-Wiener diversityindex was 1.47 in 1996-1999 [17] and 1.63in this study, showing tends to increaseafter dam construction. Considering the

diversity levels in the water bodies, Begonet al. [20] stated that the evenness indexranges between 0.0 and 1.0, with 1.0representing a situation in which all speciesare equally abundant, and the Shannon-Wiener’s diversity index value was generallybetween 1.5 and 3.5, where a high valueindicates high species diversity. So, in thisstudy, the diversity indices indicated thatthe phytoplankton had medium

Genera T1S1 T1S2 T2S1 T2S2 T2S3 T3S1 T3S2 T3S3 AverageT1S3Table 2. Continued

551

10710040391244

31100

1894

1,3921,896

4

340

127120

3765494

2,765

29

3.530.541.82

661

14240024012744

16500925

9941,256

4

70

164250

4446404

2,217

33

4.150.571.98

000

14700060543

4900610

7438533

50

85335800

1,2163

2,464

31

3.840.531.82

000

6000307791109254

2800300

1,0941,152

3

3800

12,7960

1,14013,974

316,492

21

2.060.300.92

12121

0140046

1,574728

2,3624

20700

5150

10,29711,019

3

27620

21,9200

18,58440,782

455,021

27

2.380.421.39

14141

06601981855

98289241720

1,2972,519

5

400

89500

8992

4,041

42

4.940.542.00

661

000053414533

83110

1652

1,0741,335

5

10700

59700

7042

2,210

31

3.900.461.58

551

030001723433

419100

3750

1,8832,687

4

5400

71500

7692

3,583

30

3.540.421.43

10101

2410064175

111272614

8241,029

6

900

1621352074

1,386

49

6.640.441.72

661

42500132691034145

1638

1031842

2,1772,637

6

590

1274,164

02,2876,637

610,020

62

3.830.471.63

352 Chiang Mai J. Sci. 2013; 40(3)

distribution and diversity. Also, based onthe diversity index implied that the waterquality condition in the area wasmoderately-polluted [21], and still suitablefor aquatic animal growth and survival [22].

The cluster and MDS analyses dividedthe phytoplankton distribution into threegroups by season. The first was during thedry season at all sites. The second was duringthe early rainy season at the upstream site andduring the heavy rainy season at all sites. Thethird group was during the early season at thedownstream and the middle-stream sites(Figure 3). The genera that indicated thesimilarity within each group at contributinggreater than 5% of the similarity wereTrachelomonas (Tra.), Noctiluca (Noc.), Euglena(Eug.), Phacus (Pha.), Chroococcus (Chro.) andEudorina (Eudo.) in the first group; Trachelomonas,Euglena, Phacus, Peridinium (Per.) and Scenedesmus

(Sce.) in the second group; andTrachelomonas, Peridinium, Scenedesmus,Protpperidinium (Protoper.), Oscillatoria(Oscil.), Spirulina (Spiru) and Actinastrum(Acti.) in the third group (Figure 3).According to the result, some genera, suchas Noctiluca, which can live in saltwaterdisappeared during the rainy seasons. Thedensity of other genera such as Trachelomonassp., Peridinium and Protoperidinium increasedduring rainy seasons (Table 2). The changemight be a result of rainfall and nutrient loadsmore suitable for these genera. Trachelomonassp. thrives in waters rich in nitrogenousnutrients while Peridinium sp. and Protoperidiniumsp. prefer waters rich in organic nutrients [13].Also, the result of AARL-PP score showedthat Peridinium was predominant in this area(42% of total density), indicating that thetrophic level in freshwater fishing area of

Figure 3. Bray-Curtis cluster diagram and MDS of phytoplankton similarity in the freshwaterfishing area, PPRB, 2006 (T1 = Dry season, T2 = Early rainy season, T3 = Heavy rainy season,S1 = Downstream site, S2 = Middle-stream site, and S3 = Upstream site).

Chiang Mai J. Sci. 2013; 40(3) 353

PPRB was meso-eutrophic and the waterquality condition was moderately-polluted.

The triplot of 10 dominant genera andwater quality parameters provided by CCAis shown in Figure 4. Genera are expressed asarrows. The length of an arrow indicates theimportance of this factor. Each arrowdetermines a direction or axis in the diagram,obtained by extending the arrow in bothdirections. The projection of a genus on thisaxis shows its preference for high or lowvalues of this factor [25]. Thus, the resultsindicated that change in water dept andnutrients were an important characteristicdriving genus composition. Lepocinclis sp wasdominated by deepest water dept at T2S3.Phacus sp, Euglena sp, Trachelomonas sp andScenedesmus sp were dominated by shallowerwater dept and higher ammonia at T1S1,T3S1, T3S2 and T3S3. Genus compositionat T2S1 and T2S2, which the study area

were characterized by higher temperature,transparency, DO and velocity with slightlysalt water, was dominated by Peridinium sp,Protoperidinium sp, Oscillatoria sp and Spirulinasp. At the T1S2 and T1S3 which the nutrientswere higher, dominant genus was Noctiluca sp.

Furthermore, in terms of fisherymanagements in order to maintainenvironment and stocks, regular monitoringof pollution should be conducted around theyear. Restocking of native species should betaken at sites and seasonal times most criticalfor the survival of ecosystems. For example,restocking of Macrobrachium. rosenbergii whichprefers slightly saline water should be done atdownstream sites, regardless of the season,since these areas are frequently affected by seawater influx, and this species favors theresulting slightly brackish water. Restocking ofherbivorous species such as Barbodes gonionotuswhich is a freshwater species and feeds on

Figure 4. Relationship between 10 dominant genera and water quality parameters in thein the freshwater fishing area, PPRB, 2006 (T1 = Dry season, T2 = Early rainy season,T3 = Heavy rainy season, S1 = lower part of the river sampling site, S2 = middle partof the river sampling site and S3 = upper part of the river sampling site).

354 Chiang Mai J. Sci. 2013; 40(3)

phytoplankton would be best conductedat middle stream sites during the earlyrainy season which offers plenty ofphytoplankton serving as natural food.

In conclusion, phytoplankton diversityin the freshwater fishing area of PPRBcould be considered at medium level. Thewater condition was meso-eutrophic andmoderately-polluted, but is still suitable foraquatic animal growth and survival.However, water quality/environmentshould be continuously monitored. Finally,restocking aquatic animals/fishes should beconducted in appropriate sites/times ofeach species for better survival.

ACKNOWLEDGEMENTSThis research proposal was been

recommended by a special committee of TheResearch and Development Project of PakPhanang River Basin. Funding for the fieldresearch was provided by the ThailandResearch Fund (TRF). Special thanks go tothe all people from the Pak Phanang RiverBasin who shared their ideas, experienceand knowledge.

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