~ Pergamon Waz. Sci. Tech. Vol 40. No.7. pp. 117-12.5. 199901999

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PHYTOPLANKTON ACTIVITIES INHYPERSALINE, ANOXIC CONDITIONS.I-DYNAMICS OF PHYTOPLANKTONSUCCESSION IN THE SOLAR LAKE(TABA, EGYPT)

Gamila H. Ali

Water Pollution Colltrol Department, National Research Cellter Dokki. Cairo, Egypt

ABSTRACT

The seasonal and vertical distribution of planktonic algae in the Solar Lake (Taba-Egypt) and their relationto some aquatic environmental factors were discussed through the period (Scp. 1996-Aug. 1997). Surfacewater analysis showed that no remarkable changes were observed in nitrate, silicate and iron. while turbidity.salinity and chloride were changed according to the season. In water column profile. HIS. temperature andsalinity showed clear variations between stratification and holomi~is. Max.imum salinity (199%0) wasrecorded during stratification at 3-4 m depth. Stratification (Oct-June) appears clearly with changes intemperature (surface 16°C. thermocline up to 53.3·C and the bottom temperature around 47.7°C).Cyanobacterial mats of the Solar Lake are classified into two layers. the upper layer was dominated bycoccoide forms while the lower was dominated by filamentous forms. During the period of study. 39 algalspecies were Identified among which were 17 species of Cyanobacteria. 18 species of Bacillariophyta and 2species of either Chlorophyta or Dinoflagellates. © 1999 Published by Elsevier Science Ltd on behalf of theIAWQ. All rights reserved.

KEYWORDS

Cyanobacterial mat; holomixis; hypersaline; phytoplankton; solar lake; stratification.

INTRODUCTION

The primary constituents of the majority of microbial mats in saline lakes are built and dominated bycyanobacteria which are primary producers at the basis of the microbial foodweb in microbial mats (Burke,1995; Stal, 1995). However, eukaryotic algae e.g. diatoms and green algae are often present and sometimeseven abundant (Ehrlich 1978, Borowitzka, 1981). These ecosystems are characterized by steep andfluctuating physicochemical gradients of which those of light, oxygen and sulphide are the mostconspicuous. The organic matter produced by cyanobacterial photosynthesis is decomposed by the microbialcommunity. Sulphate reducing bacteria are important in the end-oxidation of the organic matter. Theseorganisms are obligate anaerobes and produce sulphide. Cyanobacteria, therefore, are sometimes exposed tolarge concentrations of the extremely toxic sulphide. Some species are capable of sulphide-dependentanoxygenic photosynthesis. Other species show increased rates of oxygenic photosynthesis in the presenceof sulphide and have mechanisms to oxidize sulphide while avoiding sulphide toxicity (Sial, 1995).

117

118 G. H. ALI

Solar Lake is a small pond (140 x 150 m) on the Sinai coast of the Gulf of Aqaba (Taba - Egypt). It is 4-6 mdeep depending on the time of the year. A mountain ridge protects it from the winds. The lake is separatedfrom the sea by a 60-m wide gravel bar and is fed by seawater seeping through the bar. It has a period ofholomixis in summer where temperature, salinity and oxygen distribution are homogenous. Stratificationbuilds up during winter with an inverse temperature profile ranging from 16°C above to 60°C below thethennocline. The stratification period lasts from 9-11 months (Cohen et aI., 1977a; Krumbein and Cohen,1984). In a seasonal study on the lake Hoyward, which is a hypersaline lake, Burke (1995) found thatstratification extended for 6 months each year. These extreme conditions limit the variety of organisms thatcan live in the Solar Lake. Different types of cyanobacterial and bacterial mats carpet the entire bottom ofthe lake and a few species of invertebrate also are present. The general features of the Solar Lake have beendescribed by Pore, 1969; Cohen et aI., 1977a; Cohen, 1984.

The main objectives of this research are monitoring the flora of the Solar Lake (Taba-Egypt) during theperiod of study (Sep. 1996 - Aug. 1997). Also, the relation between some aquatic environmental factors andphytoplankton distribution was discussed.

MATERIALS AND METHODS

Site of study

Figure I. The Solar Litke in Sinai (Taba- Egypt).

The site of the Solar Lake was illustrated in the Fig. (1).

Sample collection and preparation

Water samples were collected from the Solar Lake surface as well as different depths of the water columnduring the period of study (Sep. 1996-Aug. 1997). Water samples were collected in polyethylene bottles (ILcapacity) at every 25 or 50 cm depth at the mid point from the surface up to the bottom of the lake by usingwater sampler and peristaltic pump. For microscopical examination, water samples were concentrated eitherby centrifugation or via 0.45 11m membrane filters.

Algal blooms

Algal blooms are characterized by several predominant colours, mainly orange, brownish yellow and blue•green colour. Random samples representing different colours were collected in plastic bags and thenexamined microscopically for identification, isolation and purification purposes.

Algal identification

The classification of algae in algal bloom and in water column was based on Geitler (1932); Desikachary(1959); StrebIe and Krauter, (1978).

Chemical analysis of water

Phytoplankton activities in hypersaline-I. 119

PhysiclH:hemical characteristics for surface water samples were analyzed by the following methods: pHwas measured by using pH-meter, electric conductivity by conductivity meter and turbidity by turbidimeter.Also, alkalinity, hardness, chloride, sulphate, silica, iron, manganese, nitrite and hydrogen sulfide weremeasured according to APHA (1995). Nitrate was analyzed by sodium salicylate colourimetric method(DEV, 1984), while phosphate was measured by stannous chloride colourimetric method (Gales et al.,1966). Field measurements for water column characteristics at different depths, such as salinity were madeby hand refractometer, temperature by thermometer and density by densiometer.

RESULTS AND DISCUSSION

PhysiclH:hemical characteristics of surface water

The data for physico-chemical analysis of surface water was represented in Table 1. Seasonal variationsindicate that pH values were slightly alkaline throughout the period of study (annual mean is 8.28).Turbidity, conductivity and salinity were increased during summer (salinity 158%0, indicating higherevaporation rate). Total alkalinity was decreased in a predictable manner where its value recorded insummer reached 0.21 gr t CaC03. The observed increase in alkalinity values in winter and spring in thisstudy was also recorded by Ferris et al. (1994) in their microcosm experiments where they reported thatphototrophic cyanobacteria increased alkalinity. Chloride measurements recorded its maximum values insummer, while maximum sulphates were recorded in autumn. Silicates, nitrates and iron showed no obviouschanges during the four seasons under investigation. It is interesting to note that total phosphorus recordedhigher values in fall (0.8 mgr l

).

Table 1. Physico-chemical characteristics of the Solar Lake surface water (Sep. 1996 to August 1997)

ParameleT Season aMual Absolute value

Aununn Winter Spring Summer mean Mal<imum Minimum

-PH 8.• 8,5 8.1 8.1 8.38 8.S 8.1- Temperalure ·C 23.2 17.3 23.1 36.2 26.9 36.2 17.3

-Turbidity NTU 2 1.5 I.S 3.5 2.1 3.5 J.S- Dens,ty kgr' 1.07 1.05 1.06 1.13 LOS 1.13 1.05-Elmric oonducIivity mI mohscm" 110 90 110 180 261 3M 200-Salinity "" 90 70 82 158 100 158 70- Total Alkalinity Cac~ gml" 0.8 1.2 1.2 0.21 0.9 1.2 0.21

- TOIaI Hardness CaC~ gml" 2•.0 21.6 22.0 36.0 25.9 36.0 21.6

- Calcium Hardness caC~ gml" 4.0 3.4 4.0 3.2 3.7 4 3.2

- Magne:Wm HadnessCaCO.J gml" 20.0 18.2 18 32.8 22.3 32.8 18.0

-Chloride gml"CL 54.0 80.0 80.0 105.8 80.0 105.8 540

- SUlphate gml" SO. 40.0 16.5 17.0 20.0 23.4 40.0 16.5

- S,lica gml"Si~ 0.60 0.18 0.24 0.18 0.30 0.60 0.18

- Nibite mgrlN N.D N.D N.D N.D

- Nitrate mgr'N 0.06 0.08 0.078 0.09 OOS 0.09 0.06- Total Phosphorus mgr'P 0.82 0.11 0.12 0.124 0.29 0.82 0.11-Iron mg)"' Fe 0.55 0.30 0.35 0.55 0.44 0.55 0.30- Manganese mgr'Mn ND. ND. ND. N.D.

Each reading is the mean of three replicates.

PhysiclH:hemical characteristics of water column

Seasonal variations in water column profile showed clearly that, maximum salinity profiles (199%0) wereobserved from 3 to 4.5 m depth in December 1996 (at winter season) (Fig. 2). There were no obvious changes

~ QR~

between day and night salinity measWl:ments. In this connection, Cohen el al. (1977c) in their work on the SolarLake, recorded the highest salinity measurements (180%0) at 3 to 4 m depth in October 1970.

Regarding temperature values. solar heating causes increase in temperature degrees at different depths incomparison with surface water temperature values (Fig. 2). Maximum temperature degree recorded in thisinvestigation was 53.3°C at 3m depth in June 1997 (at spring season). Temperature tends to decreasetowards the bottom, but it is still very high if compared with surface temperature degree. Generallyspeaking, stratification which extended from October to June appears clearly with changes in temperatureprofile (Surface 17°C, thermocline up to 53.3°C and the bottom degree around 47.rC). Burke (1995)recorded the stratification in Hoyward hypersaline lake where it extended for 6 months each year. Duringholomixis which began at June the temperature was 31°C throughout the water column. A maximumtemperature of 60°C was recorded in the Solar Lake during 1970 by Cohen el al. (1977c).

Finally. one can say that. salinity and temperature are correlated with the stratification and holomixis in theSolar Lake. Gowen et al. (1995) in their research in the NW Irish Sea reported that stratification resultedfrom vertical gradients in temperature and salinity during the early stages of stratification.

pH measurements of the SOlar Lake water column showed that highest values were recorded in the surface,while decrease was noticed with increase in depth both in day and night. Throughout the period of study, pHvalues ranged from 7.35 at the bottom to 8.29 at the surface (Fig. 2). Cohen el al. (1977c), recorded pHrange from 6.9 at the bottom to 8.0 at the surface in fall during 1970.

Water density measurements revealed the relation between salinity and density where it increases withincrease in salinity of the water column. The density measurement of the surface record 1.051 gm.kg'l(Salinity 70%0) while density measurements at 1.5 m depth record 1.190 gm. kg'l (Salinity 190%0).

Hydrogen sulfide concentrations showed remarkable variations between stratification and holomixis wherethe maximum value recorded was 13.46 mgr l (Fig. 3). These data are in agreement with Cohen et al.(1975). who stated that an annual cycle is present between holomixis (low H2S concentration) and high H2Sduring stratification. During holomixis there was no H2S at the different depths of the water column. whileclear variations were observed in stratification, increase in H2S concentrations were recorded with increasein depth (Fig. 3). No obvious changes were detected between day and night H2S concentrations duringstratification. Cohen et aI. (1977a) stated that maximum H2S concentration in the hypoliminion variedbetween 5 and 39 ppm during 1968-1974.

ALGAL COMMUNITY STRUCTURE

Algal bloom

The vertical distribution of algal blooms, which covered the entire sides of the lake, showed that it consistedmainly of several species of cyanobacteria and some species of diatoms (Table 2). The cyanobacteria bloomconstituted a predominant microbial biomass in the lake. Cyanobacteria consists of two main communities,the upper one which was characterized by a deep orange colour and the lower one which was characterizedby the blue-green colour. The upper community was represented by coccoid species among them mainlyAphanotheca stagnina and Synechococcus aeruginosus which are dominant in autumn and winter while theywere high in spring and summer. Glocolhece transsylvanica was low in autumn and winter but it wasdetectable in spring and summer. Gomphospheria naegeliana and Cyanodictyon reticulatum disappeared inthe summer season. which indicates temperature sensivity of both species. Oscillalaria limnelica is alsorepresented but in lower amounts. The second (lower layer) community was represented by filamentousspecies and composed mainly of Oscillatoria limnelica. Oscillatoria salina. Spirulina subsalsa. SpirulinatenissifTUl and Phormidium fragile. Also. Microcoleus chlhonoplastes showed detectable distribution inspring and summer seasons.

Phytoplankton activities in hypersaline-I. 121

a·ae OayTUDe 11- ae Niabl

I!!~!!!~!!!~!!!~!l:~!

..I.

• i~~::-:-!~.'~.~~~!~r~.~:~~..a~...·~.~:-a-'-'-'-I-,-•.- .- .. ~ ...... "' ..... '"

••

•U

It

If11>-..... _

I=·,·=·r.~.'.:.r •••••••• _ ••••• N •• ~ •••••••

... 1-- ..;:::.-

P!~!:!!~!:!B!:!~!:!~!

Doplb (m)

....

.."t~--_

....

Figure 2. Water Profile oftbe Solar Lake during Sep. 1996 to Aug. 1997.

b-HolomiJ:i.

Dtplb(m)

during stratification andDr:plh(",

Mean Concenuation of hydrogen sulphidebolomixis (Sep. 1996.Aug. 1997).

....~ .... a·StraelflCatloa i'·.! I""

g:Ji&AI.. .. .. ...

.2 ei! .... i

a i:: .,. t:l us..0

III

(J •• :: uofi) f :R ! ~ ! 3 ! ~ ! :R ! ~ I i~

. .. ...

;::;Table 2: Phytoplankton Community Structure of Algal Bloom in the Solar Lake (Scp. 1996 to Aug J991). '"

SeasonsAlgacTaxa Autumm Winter Spring Summer

Upperl.ye! Lower layer Upper I.yer Lower layer Upperb):er Lower I.yer Upper I.yer Lower/.yerCy.nophyta·OscllfatoriD b""le/ica ++ ++++ ++ ++++ + +++ ++ ++++- Oscil/alOria salina ++ ++ + ++- Oscll/alOria ler'IlU + + ± ±• Gscil/alorla margarllifera + + ± ±- Spinl/ina absalsa ++ ++ ± +- Spiru/lna nlliSillma ++ ++ ± ±-PhormldilUlfjragt/e ++ ++ ± +- Lyr,gbyawztuarll + + ± ±• Mic/'OCoWus cIIt"-ottplaslc. ++ +++ + +- ChrOOCOCCll$ It"""tlC113 ± ± ± ±- ChrOOCOCCU$ turgtdus ± ± ± ± p-~aervgi_ +++ ++++ +++ +++ ;t:• Aphanothcea IIGpllItI ++++ ++++ +++ +++ ~• Gloeo/he« InJnfsylvanictl ++ + + +• GJlllplttlMphlritl_gli_ + + + +- ~ctyorl rw/IaJlIItI'" ± ± ± ±No. ofspeices 6 11 6 11 6 11 4 16Bedlbriop~

- NtlDcltitllJltCarl:r ++++ + ++++ + ++ ± ++ ±-NilUchlafilifDrml6 +++ + +++ + + + + +- NI/%$chltllanccoltlfa ± ± ± ±• Nltzlcmapal,tI ± ± ± ±• Amphora cojfrMjunllsl6 + + +++ ++- AMphoraprot'lIS Gngory ± ± + +- Amphora Irolstlliea HII:JL ± ±- Amphora ovalil + + ++ +- No. OIlpeCiet 8 Z 8 2 7 2 7 2To'" No. .hpeclet 14 13 14 13 13 13 II 18

Domin.nt:- ++++ Hip;. +++ Low:- ++ Detect.ble:- + Rare:- ±

Table 3: Phtoplankton community sturcutre of samples collected from the Solar Lake water column (Sep. 1996 to Aug. 1997).

Algae taxa Depth.(m)C,.opbyta 0.0 O.IS 0.5 0.75 10 1.50 1.75 1.0 1.15 1.50 2.75 l.O l.2S 3.5 40 •.S 5.0 S.S 60Dactyloeo«oprlr1tl1li". ++++ ++++ ++++ ++++ ++++ +++ ++ :t ± ± ± ± :t :t

O#fllatorall,,,,.,.tlcor ± :t :t :t ± ± :t + + +++ ++++ ++++ ~ ++++ ++++ ++++ ++++ ++++ ++++Spirllli"tI tmsissi",tI :t: ±Apl"IfIothICtI $ItJg1fi"tI +S)m«'-«.....-.- :t:OI/"OOCOCCId IlIrgIdID :t:

~No. o"pedu 2 3 ] 4 3 2 2 2 2 2 2 1 1 1 1 1 I I 1 ':r.BllCiDoriophyto 0

'0

Nitucltla ",,'lIriI + + .. + + + + + + ± ± ± .."Nilzschl.Jilifomtl6 ± ± :t: ± ± ± :t,..5

Nilzch/a IdItC1Ilata :t: "..M,losirtl vat'1I1Q/a ± 0c:.C)IClot~lIt1 Ct1Iffttl :t ± ++ + + + :t: :t: ± ± ± <

;:"

CJ""~IIt1turgtdu :I: :t ifDiatomtl ~IOI'IIatlllfl :t + + + + orSyrtrdra Ill". :t: + + + + :T

'<A",plrortl COJJftXl/omtS/6 :t: ± :t: Ipjrrnularla 81MII :t:G)o"OSilllltllltlmllatlllll :t: 1Navicula III"tlca :t:

No.oI.peda I .. .. 7 7 7 6 , 2 1 2 2 .DiaoflacdlatePerldl,,/uM tahlut_ + + +e:;y,,-Ji"....-._.. + + +

No.oItpedet 2 2 2Ollorop'yto

Duanli.llllltlli"a + + +PtmdarllftlltHWl'llf :t: :t: :t:

reo. of.peeles - - . - - - - 2 2 2TotIl No." spedn. ] 7 7 II 10 9 • II • • 4 4 3 I I

Dominant:- ++++ High:-+++ Low:-++ Detectable:- + Rare:- ±

N...

rn QK~

The classification of cyanobacterial mats according to the coloured layers was noticed by Oren et al. (1995).Their study on a hypersaline saltern pond found that two main layers are represented. the upper one isinhabited by carotenoid-rich unicellular cyanobacteria (Aphanotheca sp. and others) imparting an orange•brown colour. Under the brown layer, a green one dominated by Synechococcus is formed with filamentousPhormidium type as a minor component. Also the same observation was detected by Mir et aJ. (1991); well•developed mats were vertically stratified into three distinct pigmented layers. In the uppermost yellow•brown layer, diatoms and coccoid cyanobacteria were dominant. The second layer (green in colour) wascomposed mostly of Microcoleus sp. and a few filamentous Lyngbya sp. and coccoid cyanobacteria.

On the other hand, Campell and Golubic (1983) studied the lonal distribution and species composition ofbenthic cyanophyta mats in the hypersaline Solar Lake (Sinai) during the onset of the late annual holomixis.Eleven species of cyanophytes dominated the mats during the time of study, six of these are described asnew to science.

Members of Bacillariophyta make a very thin brownish- yellow layer near the shore (especially in winterduring December 1996) and also it appeared mixed with the upper community of cyanobacteria. This groupwas dominated mainly by some Nitzschia sp. where Nitzschia linearis and Nitzschiafiliformis were highlyrepresented in all seasons. Also. Amphora cojJeoajormis was presented in high amounts in June (Spring)1997 (Table 2). These data are in agreement with that obtained by Cohen et al., 1977a; Veres et al.. 1995.Also Lassen et al. 1992 found that marine microbial mats along the coast of Limfjorden, Denmark, weredominated by cyanobacteria with a surface layer populated by pennate diatoms.

Water column

Water column was dominated by a dense population of Dactylococcopsis salina at depths between 0.5 mand up to 2.5 m. It is the only cyanobacterial species which was identified in the water column while it wasnot represented in the cyanobacterial bloom. Oscillatoria limnetica predominated at 3 m depth up to thebottom of the lake (about 4-6 m) (Table 3) where salinity was 199%c.

The dominance of Dactylococcopsis and Oscillatoria was detected during stratification, while they partiallydisappeared during holomixis. In this connection Walsby et al. (1983), Spira and Rijn (1982) stated thatDactylococcopsis dominated the Solar Lake plankton between depths of I and 4 m dUring December 1979 toApril 1980, but disappeared during summer holomixis.

Bacillariophyta in the water column are composed of 12 species which may be detectable or of rarepresentation. These species are Nitzschia linearis. Nitzschia acicularis. Nitzschiafiliformis. Nitzschia sigma,Melosira granulata. Diatoma elongatum. Synedra ulna. Navicula mutica. Navicula pgymia. Naviculacryprocephala. Navicula virdula and Cyclotella cornIa.

Chlorophyta are represented only by Dunaliella salina and Pandorina morum which were represented inrare amounts. Also, Dinoflagellates are in rare or detectable amounts during the four seasons of the study.Where represented by two species Peridinium tabulutum and Gymnodinium aeruginosum.

Generally speaking, during the period of this study (Sep. 1996 - Aug. 1997) 39 algal species were identifiedof them 17 species of Cyanobacteria, 18 species of Bacillariophyta and 2 species of either Chlorophyta orDinoflagellate.

ACKNOWLEDGEMENT

This work has been funded by the Red Sea Programme. The author wishes to express her appreciation to theRed Sea Programme. project E under the supervision of Prof. Dr. Khayria Nagib, the Egyptian principalinvestigator of the project. The author was very grateful to Prof. Dr. Effat F. Shabana. Faculty of Science,Botany Department, Cairo Uni versity for her help in the preparation of the manuscript.

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Phytoplankton activities in hypersaline-I. 125

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