AN ABSTRACT OF THE THESIS OF. The Phytoplankton and Limnological Characteristics. Harry'. Phinney

Transcription

1 AN ABSTRACT OF THE THESIS OF Teesa G. Donoso fo the degee of Maste of Science in Botany and Plant Pathology pesented on Januay 9, Title: The Phytoplankton and Limnological Chaacteistics of Lago Rupanco, Osono, Chile Abstact appoved: Redacted fo Pivacy Hay'. Phinney Lago Rupanco is located in the cental plain of Chile (Bogel, 1964) at 40 50' S; 72 30' W. It lies at 117 m above sea level, and coesponds to type 28c of Hutchinson's (1967) classification. Lago Rupanco is a wam, monomictic lake, with winte ciculation and summe statification. Physical, chemical and biological paametes of this lake wee studied duing a cycle of 18 months fo the fist time in Lago Rupanco has a maimum depth of 160 m. The euphotic zone was sampled and the tempeatue anged fom 10 to 18 C with an oygen content between 9 and 11 mg/l. This lake had small amounts of nitatenitogen and phosphatephosphoous, as is chaacteistic of oligotophic lakes. The phytoplankton was analyzed qualitatively and quantitatively. A total of 84 taa was identified. Maimum and minimum values of phytoplankton elative abundance occued in sping and fall, espectively. The phytoplanktonic biomass was at its maimum in summe and at its

2 minimum in fall. Fou species wee the most abundant, Melosia ganulata, Sphaeocystis schoetei, Botyococcus baunii and Dinobyon divegens. Seasonal succession among the Bacillaiophyceae, Chloophyceae and Chysophyceae was obseved. The elationships between abiotic factos and the phytoplankton standing cop ae discussed.

3 THE PHYTOPLANKTON AND LIMNOLOGICAL CHARACTERISTICS OF LAGO RUPANCO, OSORNO, CHILE by Teesa G. Donoso A THESIS submitted to Oegon State Univesity in patial fulfillment of the equiements fo the degee of Maste of Science Completed: Januay 9, 1984 Commencement: June 1984

4 Appoved: Redacted fo Pivacy Pofesso Botany in of majo Redacted fo Pivacy Head of Depatment of Botany and Plant Pathology Redacted fo Pivacy Dean of Gadu School ( Date thesis is pesented Januay 9, 1984 Typed by LaVon Maue fo Teesa G. Donoso

5 DEDICATED TO My Husband Jose D. Nilliez and My Sons Felipe and Geado

6 ACKNOWLEDGEMENTS I would like to thank D. H.K. Phinney, my majo pofesso, fo his assistance and patience in helping me to complete the equiements of my gaduate pogam. Special thanks also go to D. R. Quatano fo his encouagement needed in making the decision to undetake a M.S. pogam. I would also like to epess my gatitude to D. R. Moita, D. C.D. McIntie, and D. M. Thompson, membes of my gaduate committee, fo thei assistance and citicism of this thesis. Thanks go to D. O. Paa fo his help in the identification of seveal phytoplanktonic species. Thanks also go to D. R. Tubb fo his assistance in the pepaation of this thesis and to D. H. Hoton fo gaciously facilitating my etun to Covallis to complete my thesis. I am indebted to my family and paticulaly to my husband Jose D. Nunez fo thei undestanding and suppot of my effots to complete this eseach. Thanks also go to J. Petes, R. Fuentealba, and R. Onate fo thei geneous help with my field and lab wok. This eseach was funded by the Instituto Pofesional de Osono, Chile.

7 TABLE OF CONTENTS Page INTRODUCTION 1 MATERIALS AND METHODS 3 Study Aea 3 Sampling 4 Mophomety 6 Physical and Chemical Measuements 7 Phytoplankton 9 RESULTS 12 Physical Factos 12 Chemical Factos 20 Phytoplankton 38 Species composition and abundance 38 Vetical distibution 46 Annual cycle and seasonal vaiations 55 DISCUSSION 67 BIBLIOGRAPHY 75

8 LIST OF FIGURES Figue 1. Bathymetic chat of Lago Rupanco, Osono, Chile. yage, 5 2. Hypsogaphic cuve of Lago Rupanco and its pecent distibution Depthvolume cuve of Lago Rupanco and its pecent distibution Secchi disk tanspaency in Lago Rupanco Isopleths of the pecentage tansmission of light undewate in Lago Rupanco Chonological distibution of isothems (C) in Lago Rupanco. 7. Chonological distibution of isopleths of dissolved oygen (mg/1) in Lago Rupanco. 8. Pecentage satuation of dissolved oygen concentation measued at diffeent depths in Lago Rupanco Chonological distibution of isopleths of hydogen ion concentation in Lago Rupanco Chonological distibution of isopleths of cabon dioide concentation in Lago Rupanco Chonological distibution of isopleths of total alkalinity (meq/1 CaCO3) in Lago Rupanco Chonological distibution of isopleths of total hadness (mg /1 CaCO3) in Lago Rupanco Chonological distibution of isopleths of ammonianitogen (4/1) in Lago Rupanco Chonological distibution of isopleths of nitatenitogen (pg/1) in Lago Rupanco Chonological distibution of isopleths of phosphatephosphoous (4/1) in Lago Rupanco. 32

9 Figue 16. Chonological distibution of isopleths of dissolved silica (mg/1) in Lago Rupanco. 17. Chonological distibution of isopleths of total dissolved solids (mg/1) in Lago Rupanco. Page, Chonological distibution of isopleths of total suspended solids (mg/1) in Lago Rupanco Relative abundance of each algal class by the month in Lago Rupanco Vetical distibution of some phytoplanktes duing winte 1981 in Lago Rupanco Vetical distibution of some phytoplanktes duing sping 1981 in Lago Rupanco Vetical distibution of some phytoplanktes duing summe 1982 in Lago Rupanco Vetical distibution of some phytoplanktes duing autumn 1982 in Lago Rupanco Vetical distibution of some phytoplanktes duing winte 1982 in Lago Rupanco Vetical distibution of some phytoplanktes duing sping 1982 in Lago Rupanco Relative biomass of each algal class by the month in Lago Rupanco Chonological distibution of biovolume of the (A and B) Bacillaiophyceae. (C) Melosia ganulata. 28. Chonological distibution of biovolume of the (A and B) Chloophyceae. (C) Stauastum tetaceum (D) Botyococcus baunii. 29. Chonological distibution of biovolume of the (A and B) Chysophyceae: Dinobyon divegens. 30. Chonological distibution of biovolume of the (A and B) Dinophyceae. (C) Peidinium cinctum

10 LIST OF TABLES Table 1. Mophometic values of Lago Rupanco, Osono, Chile. Page, List of monthly distibution in abundance of phytoplankton species collected in Lago Rupanco Calculated volumes of the most abundant species of Lago Rupanco. 56

11 THE PHYTOPLANKTON AND LIMNOLOGICAL CHARACTERISTICS OF LAGO RUPANCO, OSORNO, CHILE INTRODUCTION The southen glacial lakes of Chile and Agentina ae the only lage, deep oligotophic lakes in South Ameica that occu nea sea level. located between 39 and 42 The most chaacteistic zone is S latitude, and is efeed to in Chile as the Lagos Region. Despite the unique chaacte and economic impotance of these lakes, basic physical and chemical paametes of the lakes have not been measued and the study of annual cycles of phytoplankton and othe biota have not been attempted by investigatos. The pupose of this investigation was to measue basic chemical and physical paametes of one lake, Lago Rupanco, ove a yea and to elate these to phytoplankton populations measued ove the same time span. Limnological infomation on the Lagos Region of Chile is limited to the investigations of Loeffle (1960), Thomasson (1963), and Campos et al. (1974, 1977). The Agentine lakes east of the Andes in the same latitudes wee studied by Dago (1974) and Thomasson ( ). All of the investigations have been pimaily concened with physical and chemical studies, the biota, ecept fo fish, have been ignoed. Loeffle (1960) and Thomasson (1963) stated that

12 2 Lago Rupanco was dominated by Melosia, but used only one sample taken duing the summe months to each this conclusion. Clealy a time seies of phytoplankton samples combined with infomation concening the changing physical and chemical popeties is needed to chaacteize a lake and its phytoplankton populations. The southen egion of Chile has a apidly inceasing populations, and a gowing economy. These changes will pobably esult in an inceased eutophication of all lakes in the Lagos Region. It is impotant to descibe the limnological chaacteistics of at least a few of these lakes so that any geneal degadation of the lakes can be documented, and so that management of developments may be planned to educe the impact of man's activities on the conditions of the lakes. Fo these easons, the Instituto Pofessional de Osono established a Limnological Station on Lago Rupanco in The clea, deep lakes of the Lagos Region epesent one of the most valuable economic esouces of Chile, but without evidence of the conditions of the lakes and suounding watesheds, they may be uined unwittingly duing development. Phytoplankton populations espond quickly to eutophication. A time seies of quantitative and qualitative analyses defining the tophic status of Lago Rupanco can be used to establish the pistine conditions of the lake.

13 3 MATERIALS AND METHODS STUDY AREA Lago Rupanco is located at 40 50'S; 72 30'W at 117 m above sea level. This lake was fomed by glacial scouing of a valley that was late dammed with volcanic flows (Buggen 1946, 1950; Aguie and Levi, 1964; Mece, 1972). The last glaciation (19,400 yeas B.P.) coveed Lago Rupanco and the final lake fomation pobably occued less than 10,000 yeas B.P. The dainage into Lago Rupanco comes diectly fom 57 andean steams, and thee is only one outlet, the Rio Rahue. The wateshed is chaacteized by ganitic ocks low in calcium and steams of the egion have ph concentation anging fom 6.5 to 7.5 (Vila et al. 1978). The basin suounding Lago Rupanco is elatively undeveloped. The soil is thin and undelain by ganite. Small fams aise cattle and sheep and cultivate small plots of potatoes. Foesty povides the main income fo esidents aound the lake, small steam opeated saw mills ae found aound the lake. Despite a gowing population and some development, lage scale eosion is not in evidence. The weathe and climate chaacteistic of this zone coesponds to the type Csb of Koeppen (1958), with wam, dy summes and mild, moist wintes. Although duing the winte time the minimum tempeatues each the feezing

14 4 point, none of the lake feezes, due to the high heat budget of the lake and the stong wind action. Only small fam ponds show an ice cove, but the ice is not stong enough to suppot the weight of a peson. The winte ains and snowmelt in sping detemine the maimum flows of the steams coming into the lake. SAMPLING The studies of Lago Rupanco wee pefomed fom the Limnological Station of the Instituto Potesional de Osono, located on the nothen side of the lake appoimately 5 Km fom its outlet. The physical and chemical samples wee obtained monthly fom July 1981 to Decembe All the samples wee taken in the euphoic zone at an inde station located at the point of maimum depth on the westen side of the lake (Figue 1). A single station was consideed adequate because it had been detemined that thee wee not significant diffeences between measuements made at this station and at sites on the easten side of the Islote peninsula, whee the influence of the tibutaies wee epected to be consideable. The lage volume of the lake coupled with miing of the lake acts to educe localized vaiations in the wate column. The wate samples wee taken with Van Don bottles of 3 and 6 lites capacity. Chemical analyses wee pefomed in accodance with the Standad Methods (APHA, 1975). The inveted micoscope

15

16 6 technique of Lund et al. (1958) was used fo phytoplankton analysis. MORPHOMETRY The bathymetic chat was based on 20 paallel tansects selected to cove the lake suface unifomly. The tansects wee selected on the basis of infomation deived fom aeial photogammetic chats (1:50,000) fom the Instituto Geogafico Milita de Chile (1973). The depth along each tansect wee estimated fom Echosounde SimadEL stip ecoding made while tavesing the tansect at a constant low speed of ca. 7 Km/h. A magnetic compass and a telescope wee used fo navigation. The tansects wee oiented on a NothSouth ais, coecting fo magnetic deviation of 12 43'E. Depth pofiles wee egisteed in fathoms and conveted to metes. Consideing the egula featues of the vetical pofiles obseved on the echogams, contou intevals of 20 m wee judged to be adequate to chaacteize the goss mophology of the lake. The isobaths wee dawn by the pocedue ecommended by Welch (1948). Mophometic paametes wee calculated fom the bathymetic chat by following Hutchinson's (1957) methodology. The aea (A) and the shoeline (L) wee measued by using a pola planimete and a catomete, Wg, espectively. The hypsogaphic and volume cuves wee plotted by following the pocedue ecommended by Welch

17 7 (1948). The echange ate of the lake was calculated fom aveage outflow of m3/sec as estimated by Thomasson (1963) and Endesa (1981). PHYSICAL AND CHEMICAL MEASUREMENTS Light penetation in Lago Rupanco was measued with a standad sized (20 cm) Secchi disk. Additional light data wee obtained with a LICOR, LI185B, quantum senso, with a quantum esponse between nannometes. Light was measued as photosynthetically active adiation at the suface and undewate in micoeinsteins/m2 sec. Pecentages of the suface incident adiation tansmitted though the wate column wee gaphed at unifom intevals of 20% of attenuation (Wetzel and Likens, 1979). The main objective of measuing light attenuation was to be able to estimate the photosynthetically active photic zone at 1% level of iadiance. Tempeatue of the ai and suface wate wee measued with a mecuy themomete (20 to 100 C). A Kahlsico bathythemogaph was used to obtain the tempeatue pofiles of the wate column. Tempeatue data wee plotted at unifom intevals of 2 C (Wetzel and Likens, 1979). These measuements wee made to detemine the peiods of themal statification o ciculation of the lake. The oygen content was measued using the azide modification of the Winkle method. The pecentage of

18 8 oygen satuation was calculated fom Wetzel's (1975) nomogam. The ph was measued in the field with a potable Beckman phmete. Cabon dioide was estimated by titation with 0.005N NaOH and phenolphtalein indicato. The bicabonate alkalinity was estimated by titation with 0.01N HC1 and 0.1% W/V methyloange. Total hadness was measued by the EDTA titimetic method with the addition of the dye Eiochome black T. The calcium content was evaluated by the EDTA titation with mueide (ammonium pupuate) indicato. The concentation of magnesium was calculated fom the EDTA calcium hadness titation. The phenate method was used to estimate ammonianitogen. Nitate and nititenitogen wee measued by the cadmium eduction method. The nitate was educed in alkaline buffeed solution to nitite by passing the sample though a copeized cadmium metal fillings. This method is moe sensitive fo concentations less than 0.1 mg NO3N/1. The ascobic acid method was most appopiate fo phosphatephosphoous measuements. ange of 1500 pg PO4P/1. This method is applicable in a The molybdosilicate method was used to estimate dissolved silica. This method is accuate to at least ±0.02 mg/l. All the inoganic nutients aleady mentioned wee measued with a PYEUnicam digital spectophotomete. To evaluate total dissolved solids (TDS) and total suspended solids (TSS) the samples wee filteed. To

19 9 detemine TDS concentation, the filtate was evapoated at 105 C, and the esidue weighed (Boyd, 1979). Fo the concentation of TSS, the samples wee filteed though taed glass fibe filtes, died at 105 C and then the filte eweighed (Stickland and Pason, 1968). To detemine the oganic and inoganic factions of the total suspended solids, the filtes wee incineated in a muffle funace at 550 C fo 30 minutes. The weight loss epesented the oganic matte. PHYTOPLANKTON The phytoplankton was sampled with No 25 mesh nets (60pm diamete poe) and with Van Don wate bottles. Plankton nets wee towed hoizontally though the suface wate fo 10 minutes. Fo qualitative study, net plankton was analysed befoe being fied. Fo quantitative evaluation only the Van Don samples wee consideed. A subsample of 100 ml of the content of the watebottle was put into the appopiate plastic flask povided with a double lid. Sufficient Lugol's solution was added to each flask to equal 1% v/v fo fiation and pesevation of the samples (Vollenweide, 1974). Identification of the phytoplankton was accomplished pimaily with the aid of Bouelly, Les Algues d'eau douce ( ) and the Manual Taonomico del Fitoplancton de Aguas Continentales by Osca O. Paa et al. ( ).

20 10 The counting of the phytoplankton was caied out with a Leitz Inveted Micoscope. Compound sedimentation chambes of 25 mm diamete and 100 ml capacity wee used. The time allowed to ensue sedimentation of phytoplankton was 20 hous minimum (Lund et al., 1958). The chambes wee eamined at a magnification of 400X to 1000X depending on the size of the oganisms. As the time to count an entie chambe is ecessive, the count was esticted to a potion of the bottom suface of the chambe. Two stips pependicula to each othe, ove the middle of the bottom of the chambe wee always counted. It was consideed necessay to count ca. 100 individuals of each of the moe impotant species in the sample in ode to obtain a sufficient degee of statistical accuacy (Lund et al., 1958). By means of the mechanical stage of the micoscope othe stips located at an angle of 90 to one anothe wee counted. In the calculation of the numbe of cells pe unit volume, the volume of the chambe, its diamete and the aea counted wee consideed. These thee elements (volume, diamete and aea) detemined a facto which pemitted the epession of the numbe of cells pe lite. Assuming a nomal distibution of oganisms in the sample and hence in the lake, the abundance of the phytoplankton was epessed as numbe of cells pe lite (Schwoebel, 1970). To estimate the elative density of diffeent species the following citeia wee used: 10061% vey

21 11 abundant (VA), 6041% abundant (A), 4016% common (C), 151% ae (), if a taon was pesent only occasionally a single specimen (), o absent (). In detemining the biomass of the phytoplankton, the volume of each of the moe abundant species was calculated fom the mean dimensions of ten cells. It was assumed that the fom of the cells coesponded oughly to some simple geometic body (Vollenweide, 1974), and thei volume calculated. as unity. The specific gavity of the oganisms was taken Thus, the volume coesponded appoimately to the wet weight. The numbe of individuals of each species multiplied by the aveage cell volume was an estimate of the biomass of the phytoplankton pe unit volume. Spheical cuves wee used as a means of compaing the vetical distibution of phytoplankton. In ode to educe population numbes to a manageable size, the numbes of oganisms found at each depth wee not given in absolute numbes of cells pe lite but wee pesented as the cube oot of that numbe divided by 4.19 (R = k n/4.19), whee R = adius of spheical cuve, and k = scaling constant (Thomasson, 1963). Seasonal changes of the vetical distibution of the biovolume of populations wee epesented by using Nauweck's (1963) method.

22 12 RESULTS PHYSICAL FACTORS Fom the bathymetic chat, it should be noted that the long ais of Lago Rupanco lies in an appoimate SENW diection and the geatest depths occu along this ais (Figue 1). The basin has a elatively flat bottom that is inteupted in the cental pat by the Islote peninsula and 2 small islands (Cievos and Cabas). The esults of mophometic calculations fom the bathymetic chat (Table 1) yielded an hypsogaphic cuve (Figue 2) evealing a Ushaped pofile of the basin, with steep slopes, a flat bottom and poo development of the littoal zone. The volume cuve (Figue 3) ehibits a stong conveity, confiming the chaacteistics clealy shown in the aea cuve (Figue 2). The aveage of the echange ate in the lake was 7.5 yeas. The values fo tanspaency obtained with the Secchi disk wee between 10 and 20 m. The maimum tanspaency obseved was 20 m in Decembe 1981 and the minimum value was 10 m in August 1981 (Figue 4). Measuements of photosynthetically active adiation at the suface and undewate showed that the illumination had been educed to 1% of its suface value aound 2030 m, ecept fo the months of Novembe and Decembe when that depth was 10 and 60 m espectively. This statum of 060 m was consideed

23 13 Table 1. Mophometic values of Lago Rupanco, Osono, Chile. Paametes Symbols and Fomulas Results Length Km Beadth b Km Aea A Km2 Maimum depth Z m 160 m Mean depth 7= V/A 94 m Relative depth Z = 50 Zm 17 / % Depth of cypto depession Zc 43 m Volume V = h /3 (A1 + A2 + Al A2) Km3 Shoe line L Km Shoe line development DL = L/2/ Ratio of mean to maimum depth (Z:Zm) 0.59

24 km PERCENT AREA I00 Figue 2. Hypsogaphic cuve of Lago Rupanco and its pecent distibution.

25 km X 60 UJ CD PERCENT VOLUME 100 Figue 3. Depthvolume cuve of Lago Rupanco and its pecent distibution.

26 E i 0 n. 10 W 20 J A S 0 D j MAMJJASOND 198I 1982 Figue 4. Secchi disk tanspaency in Lago Rupanco.

27 17 the photic zone o the zone whee photosynthesis takes place and fom this zone the samples wee obtained (Figue 5). Duing the peiod analyzed, the tempeatues ecoded showed a vetical isothemy of 10 C (±0.2) duing the winte time (July to Sept.) down to the maimum depth measued of 100 m. In sping time (Oct. to Dec.) thee was an incease in the tempeatue of the suface layes of 2 to 4 degees. At the end of this peiod, themal statification was established (Figue 6). Statification continued though all the summe (Januay to Mach). The bathythemogaph ecod in Decembe 1981 showed the metalimnion lying between 20 and 50 m with the tempeatues of 15.8 C to 11.2 C, espectively. In Mach 1982, tempeatues went fom 16 C to 11 C between 22 to 33 m; and in Apil 1982, tempeatues wee between 14.5 and 11 C at 30 to 35 m, espectively. Afte May the metalimnion stated to disappea as the tempeatue of the wate deceased to 12 to 13 C, until it eached 10 C fom suface to the maimum depth measued in Septembe of both 1981 and 1982 (Figue 6). At the suface of the lake, the tempeatue anged fom 10 C in winte to 18 C in summe. The epilimniom inceased in depth fom Febuay to May and its tempeatue deceased fom 18 to 13 C, while the metalimnion went down 40 to 50 m deep. In the hypolimnion the tempeatue vaied between 11.2 and 9.8 C. This last tempeatue was the minimum egisteed in this zone at 100 m depth in Apil 1982.

28 18 I0 20 = J IIIIIIIIIII JFMAMJJAS 1982 ON 0 Figue 5. Isopleths of the pecentage tansmission of light undewate in Lago Rupanco.

29 19 IIIIIIIIIitliiiii ASONDJFMAMJJASOND Figue 6. Chonological distibution of isothems (C) in Lago Rupanco.

30 20 The isopleth of wate tempeatues at unifom intevals of 2 C, showed the tempeatues of the epilimnion fluctuating between 12 and 18 C, the metalimnion between 11 and 16 C and the hypolimnion between 10 and 11 C (Figue 6). The tempeatue vaiations at diffeent depths though the peiod studied showed that the uppe statum (020 m), the middle statum (2050 m) and the deepest one, had diffeent themal behavio. The suface layes inceased thei tempeatues fom the end of the winte to the summe time, eaching a maimum in Febuay and deceasing though the fall. The intemediate statum showed a constant incease in tempeatue fom the end of winte until the end of summe, with a decease in the fall. On the othe hand, the deepest statum was the most stable and unifom duing the cycle analysed. The pedominant winds in the egion ae fom the Noth in the winte time and the S.E. and S.W. fom Septembe though the summe time. These last 2 types of wind have a geat influence in the dynamics of the lake. Consideing the themal chaacteistics descibed, this lake coesponds to a wam monomictic lake with the peiod of ciculation duing the winte. CHEMICAL FACTORS The vetical distibution of dissolved oygen showed that pactically all the wate column had unifom

31 21 chaacteistics in elation to the concentation of this gas though all the yea. The concentations wee between 9.0 and 11.0 mg/1 (±0.2) (Figue 7). The lowest value was 8.81 mg/1 in Apil at 17 m. In summe the concentation of dissolved oygen was lowe in the suface layes than in the deepest ones. This situation was evesed duing the fall. In the winte thee was a concuent decease of the tempeatue of the wate and an incease in the dissolved oygen concentation. But the highe values wee found at the ealy sping, mg/l. In geneal, the esults gave an othogade oygen distibution with the pecentage of satuation always above 100% (Figue 8). The hydogen ion concentation anged fom 6.8 to 7.2 (Figue 9). A geat seasonal vaiation was not obseved although the highe values wee found mostly in sping. The cabon dioide concentation anged fom 1 to 8 mg/1 (Figue 10). The minimum value found was 0.77 mg/1 in Januay. The maimum was in sping, 8.4 mg/l. May also pesented high values anging fom 4 to 8 mg/l. Duing the winte time the concentation was lowe. The vetical distibution showed that cabon dioide was evenly distibuted fom the suface to the deepe layes duing most of the yea, ecept in May. The alkalinity consisted entiely of bicabonate. It anged fom 0.4 to 0.6 meq/1 (Figue 11). The lowest concentation occued in late sping and the highest duing

32 22 10 <9 20 /0 9 a_ 30 1%// (19 o a2 60 FMAMJJASON I I I I I I I I I I I 1982 Figue 7. Chonological distibution of isopleths of dissolved oygen (mg/1) in Lago Rupanco.

33 m.25m 50 m I t I I I I I I I I 1 I J F M A M J J A S 0 N D 1982 Figue 8. Pecentage satuation of dissolved oygen concentation measued at diffeent depths in Lago Rupanco.

34 j ' ? = I a 40 w o C9 / ) IIIIIIIIIIIii 6.9 t 1 O N D J F M A M J J AS OND Figue 9. Chonological distibution of isopleths of hydogen ion concentation in Lago Rupanco.

35 sdi.6 i si E II Ii IIIIIIIIIIII ONDJFMAMJ J ASOND Figue 10. Chonological distibution of isopleths of cabon dioide concentation in Lago Rupanco.

36 26 I 0 20 a. w cz ) 30 E 045 =40 I IIIIIII!lilt N D J J A S O N A SOND Figue 11. Chonological distibution of isopleths of total alkalinity (meq/1 CaCO3) in Lago Rupanco.

37 27 the winte ciculation peiod, with the vetical pofile almost unifom. The amount of hadness (Ca + Mg) was less than bicabonate alkalinity. Maimum concentations wee found in spingsumme, 20 to 29 mg/1 CaCO3, and the minimum in autumnwinte of 17 to 19 mg/1 CaCO3 (Figue 12). The vetical distibution was quite unifom with a slight decease in the deepe zone. These values accoding to Boyd (1979), ae chaacteistics of a soft wate. The concentation of ammonianitogen anged fom 0 to 21 pg/1 in The vetical distibution showed seasonal diffeences in concentation (Figue 13). The maimal values wee found in the spingsumme time, 10 to 20 pg/1, and the minimal ones wee obseved duing the fall. Results fo the winte of 1982 wee not ecoded. Besides these seasonal vaiations thee was also noticed a geat concentation in the suface and in the deepest layes duing the summe. This situation was evesed though the fall. Analysis of nititenitogen was negative. The concentation of nitatenitogen anged fom 2 to 48 pg/l. The isopleths demonstated that the peiod of lowe concentation of 2 to 15 pg/1 was duing late summe (Figue 14). Duing the autumn thee was an incease of nitates at the suface whee the maimum value of 48 pg/1 was ecoded. In the winte time, the nitate was almost unifomly distibuted in the wate column, with aveage levels of 20 to 25

38 V n 2 30 ' / 23 /9 /9 /7 A I 2/ 1 J / IIIIIIIIIIIIIII1 1 /9 O N D J F M A M J J AS OND Figue 12. Chonological distibution of isopleths of total hadness (mg /1 CaCO3) in Lago Rupanco.

39 an Figue al JFMA I 1 MJJ ASON II I 1 I I I I 1982 Chonological distibution of isopleths of ammonianitogen (pg/1) in Lago Rupanco.

40 i / ).7 20 I /0 /0 I W / MAMJJ ASO I 1982 Figue 14. Chonological distibution of isopleths of nitatenitogen (pg/1) in Lago Rupanco.

41 31 pg/l. In sping the values deceased and emained low until late summe (Mach). Thee was noted a diffeence in concentation between the suface and deepe stata. In autumn and winte the suface pesented the geate values. These concentations deceased though the sping until the ealy summe. On the othe hand, in the deepe layes the evese was tue. These seasonal and vetical vaiations of nitate concentations wee pesumeably associated with the ainfall duing autumn and winte, and with the main poduction of phytoplankton in sping and summe. The concentation of phosphatephosphoous anged fom 0 to 50 pg/l. This nutient showed a clea seasonal distibution (Figue 15). In the summe the concentations wee vaiable and anged fom 0 to 25 pg/1. Duing autumn the highest values, 30 to 50 ug/1, wee found mainly in the suface layes. In the winte, thee was a decease in the concentation of this nutient to below analytical detectability, 0 ug/1 in August. In the sping thee was a new incease in the concentation of phosphate. Pesumably these vaiations in nutient concentations wee elated to the ainfall and the agicultual activities on some aeas aound the lake. The vetical distibution was almost unifom ecept duing the peiod of statification. The diatoms ae the oganisms that ae fequently consideed in elation to the concentations of silica. Dissolved silica is assimilated in lage quantities by

42 MAMJJ I I L I A Figue 15. Chonological distibution of isopleths of phosphatephosphoous (pg/l) in Lago Rupanco.

43 33 diatoms in the synthesis of thei cell walls o fustules. Theefoe, utilization by diatoms can modify geatly the concentations and flu ates of dissolved silica in a lake. In Lago Rupanco the isopleths ehibited slight vaiations in seasonal and spatial distibution (Figue 16). The concentations of this nutient wee appoimately 10 mg/1 fom the end of summe until ealy sping. Duing late sping these values deceased and then they inceased to thei maimum concentations duing the summe time. At the same time it was also noted that the epilimnion and metalimnion had slightly highe concentations compaed with the hypolimnion. This situation could be eplained consideing that duing summe time, Lago Rupanco was statified. Silica concentations usually incease in the topholitic zones of lakes duing peiods of statification (Wetzel, 1975). The solids epesent the potion of a wate sample which is not lost upon evapoation. Solids include dissolved oganic matte, paticulate oganic matte, dissolved inoganic substances ecept gases and the CO 2 contained in bicabonate and paticulate inoganic substances (Boyd, 1979). Total dissolved solids (TDS) coesponds to the total esidue emaining afte evapoation of a wate sample which was fist filteed to emove suspended matte. The highe concentations of TDS in Lago Rupanco occued duing summe

44 // /0 20 E 30 /0 /0 a a 70 iv I Figue 16. JFMAMJJASOND 1982 I I i \I Chonological distibution of isopleths of dissolved silica (mg/1) in Lago Rupanco.

45 35 statification and in ealy fall (Figue 17). Duing winte though sping the values deceased until they eached minimal concentations in Octobe, and inceased a little by the end of sping. Also the distibution at diffeent levels showed that duing the time of highe values, they occued mainly in suface layes and in the season when the concentations wee lowe they occued in deepe layes. Total suspended solids (TSS) coesponds to total paticulate matte o dy weight of matte that is etained on a fine filte. This faction includes inoganic paticles and living and dead oganic matte. In Lago Rupanco the concentations of TSS wee vey low, fom Apil to Decembe, the monthly aveages anged fom 0.05 to 1.24 mg /i. Data fo summe time (Jan. to Mach) was not ecoded. The seasonal distibution obseved had highe values in ealy fall (Figue 18). The lowest concentations wee found in the ealy sping and they began to incease though Novembe and Decembe. Duing the winte the values wee moe o less stable between 0.2 and 0.3 mg/l. The spatial distibution of TSS showed that the highest values occued in deepe layes. This situation is opposite to that obseved fom the TDS. To detemine the oganic and inoganic factions of the total suspended solids, the filtes wee incineated in a muffle funace at 550 C fo 30 minutes. The weight loss

46 :14'50 2 /Ay" "1' 50 K , a \ E 30 = P.i.) } 0 40 / / 0 G5 2 O I lu /00 40n 6 UI 20 of / Figue 17. FMAMJJ A t t PO tit OND 1982 Chonological distibution of isopleths of total dissolved solids (mg/1) in Lago Rupanco.

47 37 Figue 18. nalf, L, '/ 0g /.5 1 I CL w e I L'576V J..1k i.h 0.3 U(1, 0/ AMJJ AS OND 1 1 i I It! 1982 Chonological distibution of isopleths of total suspended solids (mg /1) in Lago Rupanco.

48 38 epesented the oganic matte (Boyd, 1979). This faction was vey difficult to detemine in this study because the diffeences in weight wee vey slight ecept duing the winte time. Fom this it could be assumed that most of the paticulate matte of Lago Rupanco was oganic matte, ecept in the suface layes duing the winte. PHYTOPLANKTON, SPECIES COMPOSITION AND ABUNDANCE A total of eighty fou taa wee identified in samples taken fom Lago Rupanco. In Table 2, the geneal taonomic list is pesented togethe with the monthly distibution in abundance. Two classes wee best epesented, the Chloophyceae by 38 species and the Bacillaiophyceae by 29 species. Botyococcus baunii and Sphaeocystis schoetei wee the most abundant geen algae, followed by Stauastum tetaceum, Dictyosphaeium ehenbegianum and Monoaphidium contotum. The most abundant diatoms wee Melosia ganulata followed by Rhizosolenia eiensis, Syneda ulna and Cyclotella meneghiniana. The Chysophyceae was epesented by 2 species, Dinobyon divegens being the dominant one. Among the 3 species of Dinophyceae, Peidinium cinctum was the most fequent species. Eight species of Cyanophyceae, 1 Cyptophyceae and 3 Euglenophyceae wee pesent occasionally with a fequency equal to o less than 7%.

49 Table 2. List of monthly distibution in abundance of phytoplankton species collected in Lago Rupanco The elative density is given by the symbols: VA (Vey abundant, 61 to 100% fequency) A (Abundant, between 41 to 60%) C (Common, between 16 and 40%) (ae, between 1 and 15%) (pesent occassionally, single specimen) (absent) J A S 0 N D J F M A M J J A S 0 N D CYANOPHYCEAE Choococcus minutus Micocystis aeuginosa Rhabdodema lineae Anabaena sp. Rhaphidiopsis cuvata Oscillatoia cuviceps O. limosa Spiulina meneghiniana CRYPTOPHYCEAE Rhodomonas ovalis

50 Table 2. Continued J AS 0 N D J F M A M J J A S 0 N D CHRYSOPHYCEAE Dinobyon divegens Mallomonas A A VA A C C C DINOPHYCEAE Peidinium P. cinctum Gymnodinium fuscum X EUGLENOPRYCEAE Tachelomonas spinulosa X T. volvocina T. sydneyensis X BACILLARIOPHYCEAE Cyclotella meneghiniana Fs CD

51 Table 2. Continued... 1, J A S 0 N D J F M A M J J A S 0 N D Stephanodiscus astaea C A A C C C C A VA C C C Melosia ganulata M. italica M. hustedti M. pseudoganulata Rhizosolenia eiensis Asteionella fomosa Ceatoneis acus Diatoma hiemale Fagilaia constuens Fagilaia sp. Syneda ulna va. ulna S. ulna va oyhynchus Achnanthes sit

52 Table 2. Continued 1981 JFMAMJJASOND 1982 J A S 0 N D A. clevei Amphoa aff. fontinalis Cymbella cistula Diploneis aff. subovalis Gomphonema sp. Gyosigma sat Navicula sat 1 Navicula sp. 2 Pinnulaia sp. Nitzchia sp. Epithemia sp. Eunotiasa X X X X Stauoneis Pennatae indet.

53 Table 2. Continued J A S 0 N D J F M A M J J A S 0 N D CHLOROPHYCEAE Eudoina elegans Chlamydocapsa bacillus C. planctonica Tetaspoa sp. Gloeocystis sp. Paulschulzia tenea Tetaedon minimum Sphaeocystis sp. S. schoetei A Chloella sp. pocystis lacustis 0. pava Nephocytium al.p.. w

54 Table 2. Continued JASOND J F M A M J J A S 0 N D N. limneticum Kichneiella Ea K. lunais Ankistodesmus 2a Monoaphidium contoum C C C C C C Micactinium sp. Botyococcus baunii C C A A C C A Dictyosphaeium ehenbegianum D. pulchellum Coelastum cubicum Elakatothi gelatinosa Ancylonemasa Cosmaium sp. 1 C. leave va octangulae p.p.

55 Table 2. Continued 1981 JFMAMJJASOND 1982 J A S 0 N D Cosmaium sp. 2 Stauodesmus sat S. patens Stauastum tetaceum S. gacile S. otula S. muticum Closteium acutum va vaiabili Closteium sp. Radiofilum sp. Ulothi sp.

56 46 The geen algae had a high elative abundance thoughout the yea, anging between 8.63% in Januay, 56.80% in May and 93.31% in Septembe. The abundance of diatoms was also high, it anged between 5.35% in Decembe and 79.91% in August. The Chysophyceae had a minimum elative abundance of 0.09% in AugustSeptembe and maimum of 62.60% in Febuay. The elative abundance of Dinophyceae anged fom the minimal winte values of 0.0% to the highest of % duing the sping and summe time. The blue geens had a maimum elative abundance in Mach with 6.26%, % in JulyAugust, and wee absent in sping. The Cyptophyceae eached the elative abundance of 2.54% in Octobe, the othe values anged fom 0.3 to 1.5% to being absent in the winte. The elative abundance of Euglenophyceae was vey low, it did not each 0.5% (Figue 19). PHYTOPLANKTON, VERTICAL DISTRIBUTION The vaiation in vetical distibution of the moe abundant species of phytoplankton was ecoded monthly (Figue 2025). Duing the winte (JulySeptembe) of 1981, Dinobyon divegens showed slight diffeences in numbes between the suface and the deepe layes with a tendency to educed numbes below 20 m by the end of the season. The diatom, Rhizosolenia eiensis was moe abundant between 5 and 15 m and the geen algae Monoaphidium contotum and

57 Bac i I Iaiophyceae Chloophyceae Chysophyceae Cyanophyceae Dinophyceae Cyptophyceae Figue 19. Relative abundance of each algal class by the month in Lago Rupanco.

58 48 0 E 5 DMobyon divegens Rhizosotenio eiensis Monoophidium contotum Elotiococcus bounii w /19,635 \ c26,114 38,905 July ot 45,160 a zo 30 Aug. 6,545 57, X I , Sept Figue 20. Vetical distibution of some phytoplanktes duing winte 1981 in Lago Rupanco.

59 49 Dinobyon RhizosoMoo Me losing Monoaphidium 13stiococcus divegens eiensis ganulate contotum bounii , / 6,938 28, 471 Oct. ^ 20 a ,790 5, ,925 24,936 43, F a Figue 21. Vetical distibution of some phytoplanktes duing sping 1981 in Lago Rupanco.

60 50 Dinobyon Riniosolenio Melosio Monoaphidium S/auas /um divegens eiensis gand/ao con /o /um tetaceum 243,499 E 20 a O , ,370 Jan. 2 a ,572 35, Feb. 78, a_ Ma. Figue 22. Vetical distibution of some phytoplanktes duing summe 1982 in Lago Rupanco.

61 51 0 Dinobyon divegens Rhizosolenia eiensis Me los/a gonu/oto Botiococcus bounii Stouostum tetaceum 20 23, Apil E 0 10,407( 19,7391 f5563i 1_ 20 a 0 40 May E 19,032 (13, H 20 a O 40 June Figue 23. Vetical distibution of some phytoplanktes duing autumn 1982 in Lago Rupanco.

62 52 E 0 20 I a. w O 40 Dinobyon Rhizosokinia Melosie Dictyosphoeium 3/auas/um Monoaphidium ctivegens eiensis ganulate ehenbegianum letaceum con/o/um , ( ,731 ( I July ^ a. a. w , Aug. E w ,308 43,982k ,839 Sept. Figue 24. Vetical distibution of some 1982 in Lago Rupanco. phytoplanktes duing winte

63 53 0 Dinobyon Rhizosolenio Me/osio Monoophidium 8otiococcus Sphaeocystis divegens eiensis gonu /oto contotion bound schiletei E. 20 X a 40 8,954 14,923 7, ,197 Oct. 32,398 7,390 E 20 I a , ,069 Nov. Figue 25. Vetical distibution of some phytoplanktes duing sping 1982 in Lago Rupanco.

64 54 Botyococcus baunii wee distibuted fom 0 to 15 m (Figue 20). In the winte of 1982, the behavio of these 4 species was vey simila but besides these species anothe diatom and 2 additional geen algae eached high abundance levels: Melosia ganulata dominated with its geatest abundance fom 5 to 50 m, and Dictyosphaeium ehenbegianum with Stauastum tetaceum wee moe abundant in the statum fom 10 to 35 m (Figue 24). In the sping time (OctobeDecembe) of both yeas, Dinobyon divegens moved fom the suface layes to 10 and 35 m depth and inceased significantly in abundance in the deepe layes by the end of the season. Rhizosolenia eiensis deceased though this season and the highest concentations wee found below 30 m. Melosia ganulata dominated duing pat of this season with an abundance at and below 30 m geate than in the suface layes. Monoaphidium contotum, Botyococcus baunii and Sphaeocystis schoetei wee moe abundant fom 040 m (Figues 21 and 25). Duing the summe (JanuayMach), Dinobyon divegens dominated in the suface statum fom 0 to 25 m. Rhizosolenia eiensis showed a geate abundance below 40 m than above 40 m and Melosia ganulata had a peak at Januay and afte that was moe abundant below 30 m. 25 m in The geen algae at this time had a vey low abundance and also occued aound the 40 m depth (Figues 22).

65 55 In the fall (ApilJune), Dinobyon divegens deceased in numbes, its abundance being geate between 10 to 20 m depth. Diatoms also deceased in abundance in Apil and wee located at 50 m. But in May and June these algae wee found in the suface layes in inceasing abundance. The Chloophyceae inceased in abundance in the statum between 2030 m in Apil and May and became concentated in the suface layes with _Lowe abundance occuing by the end of the season (Figue 23). PHYTOPLANKTON, ANNUAL CYCLE AND SEASONAL VARIATIONS Cell numbes often ae not epesentative of tue biomass because of consideable vaiation in sizes of cells among algal species (Vollenweide, 1974). Theefoe, it was consideed appopiate to calculate the cell volume of the most abundant species as a means of estimating the biomass of each one (Table 3). The elative biomass of the main goups of the phytoplankton showed a geneal annual patten simila to that of the elative cell abundances (Figue 26). But this patten showed maked fluctuations in the less abundant goups. The Dinophyceae, fo eample, had a elatively high biomass compaed with the numbe of cells due to the lage volume of Peidinium cinctum. Duing the winte, the Bacillaiophyceae was the dominant goup with a biomass of pg/1 in 1981 and 1, pg/1 in These values coesponded to a

66 56 Table 3. Calculated mean volumes of the most abundant species of Lago Rupanco. Species Volume (mm3) Anabaena sp. 230 Oscillatoia cuviceps 427 Raphidiopsis cuvata 3250 Rhodomonas ovalis 150 Dinobyon divegens 960 Peidinium cinctum Gymnodinium fuscum 2160 Cyclotella meneghiniana 147 Melosia ganulata 6760 Rhizosolenia eiensis 1250 Syneda ulna va ulna 2055 Sphaeocystis schoetei 14 Monoaphidium contotum 40 Botyococcus baunii 500 Dictyosphaeium ehenbegianum 54 Stauastum tetaceum 1350

67 ASON D J F MAMJJ ASON OBacillaiophyceae Chloophyceae Chysophyceae Cyanophyceae Dinophyceae Cyptophyceae Figue 26. Relative biomass of each algal class by the month in Lago Rupanco.

68 58 elative biomass of %, espectively. At the end of this season in 1981, as diatoms deceased, the geen algae inceased eaching 79.52% of the total biomass. In 1982, diatoms dominated duing the whole winte. Consideing the biovolume of the 4 most abundant species, Melosia ganulata, Rhizosolenia eiensis, Syneda ulna and Cyclotella meneghiniana, a winte time bloom occued with a maimum biomass of 1.7 mm3/1 (Figue 27A). The highest concentations wee evenly distibuted in the wate column fom 060 m (Figue 27B). This bloom was pimaily composed of Melosia ganulata (Figue 27C). The maimum values fo the othe 3 species wee below 0.25 mm3/1. In 1982 the Chloophyceae showed low levels of elative biomass, between 0.1 and 1.5%. Consideing the 5 main species of this class: Botyococcus baunii, Stauastum tetaceum, Monoaphidium contotum, Sphaeocystis schoetei and Dictyosphaeium ehenbegianum, the biovolume anged fom 0.01 to 0.03 mm3/1 (Figue 28A). The vetical distibution of this biovolume was appoimately unifom fom 0 to 60 m. At the end of the season the highest values wee located at the intemediate level (20 to 40 m) (Figue 28B). Stauastum tetaceum (Desmidiaceae) was the species involved duing winte (Figue 28C). At the same time the biomass of Chysophyceae was vey low and was composed of Dinobyon divegens (Figue 29A). The biovolume values wee below 0.01 mm3/1 and wee evenly

69 59 Zs 4.0 J ine E 2 w 2.0 = 0... > M A M J J Bacillaiophyceae.05;B 60 It'E E w i CD 8 Ea 1111 Figue 27. Chonological distibution of biovolume of the (A and B) Bacillaiophyceae. (C) Melosia ganulata.

70 J q 0.2 F M A M J J A S 0 N InE Chloophyceae 0g 20 Ia. PI 40 poi o ad) 008 (.1 IO W t) 002 I.00e ell 1002j1/4 `.001 X/ 02 I) LI.01,005 U.005( I fop' I /.9:./D.00/ L A B InE *.,,,,,/**' w C D Figue 28. Chonological distibution of biovolume of the (A and B) Chloophyceae. (C) Stauastum tetaceum (D) Botyococcus baunii.

71 Chysophyceae <00/ 0.03\ B Figue 29. Chonological distibution of biovolume of the (A and B) Chysophyceae: Dinobyon divegens.

72 62 distibuted in the wate column (Figue 29B). In 1981 the elative biomass of D. divegens anged fom 1.9 to 7.6% and in 1982 fom 0.02 to 0.2%. Duing the winte of 1981 the elative biomass of Dinohyceae vaied fom 3.4% to zeo by the end of the winte and in 1982 they wee absent. The othe algal classes wee pesent occasionally and the biomass anged between and 4.0% (Figue 26). In the sping, the biomass of Bacillaiophyceae deceased, this was moe evident in 1982 than in This decease fom a maimum of pg/l, 98.54% of the total biomass, in Octobe to a minimum of pg/1 (9.67%) in Decembe, was accompanied by the development of the bloom of Chloophyceae (Figue 26). The same elationship occued in 1981 when the geen algae had a bloom in ealy sping. The decline in the biovolume of the 4 main species of the Diatoms which occued thoughout the sping, was moe evident in the uppe 20 m wheeas and the geate concentations occued between 20 and 40 m (Figue 27A and B). Again a population of Melosia ganulate (Figue 27C) ehibited the same patten. The sping bloom of Chloophyceae poduced a biomass of pg/1 (79.52%) in 1981 and pg/1 (71.42%) in 1982 (Figue 26). The composite biovolume of the 5 most abundant species of geen algae is pesented in Figue 28A. The maimum biomass of this goup at this season was obseved at 32 m (Figue 28B). The species involved in this peak was Botyococcus

73 63 baunii (Figue 28D). At the end of sping, the biomass of Chysophyceae and Dinophyceae inceased fom the minimal levels in winte to and 45.23%, espectively (Figue 26). The vetical distibution of Dinobyon divegens biovolume showed the geatest concentations between 20 and 40 m (Figue 29A and B). At this time, Peidinium cinctum had the majo biomass in the uppe statum between 0 and 15 m (Figue 30A and B). Duing the summe time the dominant taa o taon wee not as easily detemined as in the othe seasons. The most numeous membe of the Chysophyceae was Dinobyon divegens with 41% abundance (Figue 19). But its aveage biomass was only ca. 20% (Figue 26). The diatom Melosia ganulata was the subdominant species in numbe of cells but had the geate biomass of ove 50% (Figue 26). Dinophyceae also wee epesented aely, but Peidinium cinctum was the species with highest volume, eaching a biomass between 15 to 25% of the total (Figue 26). The Chloophyceae wee pesent with a low biomass anging between and pg/1 (1.31 to 1.94%). The Cyanophyceae plus Cyptophyceae elative biomass anged fom 0.01 to 0.45% (Figue 26). The biovolume of the Bacillaiophyceae eached a maimum of 3.8 mm 3/1 in Januay (Figue 27A). This concentation occued at 26 m and in geneal, the biomass was concentated in the statum fom 20 to 40 m while the suface layes wee poo in diatoms (Figue 27B). The species that contibuted to

74 64 l 0.8J E LII J J Dinophyceae J A a_.00/ 40 <.00/ 60 /000 <.00/ 0.4 C Figue 30. Chonological distibution of biovolume of the (A and li) Dinophyceae. (C) Peidinium cinctum.

75 65 the peak was Melosia ganulata (Figue 27C). The biovolume of Chloophyceae showed a smooth cuve duing the summe, with vey low concentations in all the wate columns analyzed (Figue 28A and B). The species pesent was a desmid, Stauastum tetaceum (Figue 28C). The biovolume of Chysophyceae, epesented by the species Dinobyon divegens showed its maimum biomass duing the summe (Figue 29A). This highe biomass was found in the suface layes at the beginning of the season but sank to the metalimnion by the end of the season (Figue 29B). The lage biovolume of Peidinium cinctum indicated that the Dinophyceae had an impotant biomass duing the summe (Figue 30A). The highest values occued in the suface layes (Figue 30B). Duing autumn, the Bacillaiophyceae maintained a elatively high biomass with a decline in May when the geen algae eached thei maimum concentation (Figue 26). The biovolume of the diatoms inceased fom the end of summe to the end of fall in the uppe statum (0 to 20 m) (Figue 27A and B). The main species involved was Melosia ganulata (Figue 27C). The biomass of the Chloophyceae was ug/1 (35.30%) (Figue 26). Duing the fall the biovolume inceased vey notably (Figue 28A), between 20 and 40 depth (Figue 28B). The dominant species in this bloom wee Botyococcus baunii and Stauastum tetaceum (Figues 28C and D). The biovolume of the Chysophyceae

76 66 deceased fom its summe maimum to the end of the fall (Figue 29A). In the ealy fall the highest concentations of Dinobyon divegens wee close to the suface and by the end of the season, the values wee lowe and distibuted evenly in the wate column (Figue 29B). The biomass of the dinoflagellate, Peidinium cinctum deceased duing this season, eaching minimal values by the end of fall (Figue 30A). The highest concentations wee ecoded at the suface layes, 0 to 8 m (Figue 30B). The biomass of Cyanophyceae and Cyptophycae, at this time, was vey low, anging fom 0.04 to 0.52%.