key: cord-0041704-rzjotr5n
authors: Nazneen, Saiyida
title: Influence of Hydrological Factors on the Seasonal Abundance of Phytoplankton in Kinjhar Lake, Pakistan
date: 2007-01-09
journal: nan
DOI: 10.1002/iroh.19800650213
sha: 5e0feb0f1a7fe8fa7ad0a213a7fc3222c9b0a620
doc_id: 41704
cord_uid: rzjotr5n

The correlation of various hydrological factors with the distribution of phytoplankton and bacteria has been studied in Kinjhar Lake, situated 120 km north of Karachi. This lake is highly eutrophic, containing rich concentrations of nutrients, but the temporal distribution of phytoplankton was generally related to the variations of light and temperature. The effects of light and temperature are perhaps modified by nutrients, particularly when nitrogen and phosphorus are present in surprisingly low concentrations. The effect of mechanical disturbances in the artificial lake also has a significant effect on the growth of phytoplankton and indirectly on consumers, especially fishes.

Kinjhar Lake is situated 120 kni north of Karachi in Pakistan, at 24' 47% and 68'2'E (BLATTER et al. 1929 ). Its area is 80 km2. This artificial lake is supplied by a canal, "Kalri Baghar Feeder," from the River Indus, arid the water from the lake is pumped to Karachi, a city of four million people, for daily use. It is thus important as the only soiirce of water created artificially to supply this large city. This study was undertaken not only to determine the quality of the water, but also to develop this lake for fishing.

The phytoplanktonic species in the lake, which serve as food for fishes, were studied to correlate their abundance with various physical and chemical factors. Snsh work has not been done earlier in Pakistan, and this is perhaps the first such study in this region.

Species coniposition and distribution of phytoplankton in any environment depend generally upon intensity of light, duration of illuniination, temperature, concentration of nutrients and pH. In tropical regions, the water temperature remains high and uniform throughout most of the year, and day lerigth is also uniform. Vertical sunlight provides maximum penetration cf light into the water. High tcnipr:ttures and strong radiations are thus the principal factors in the tropical areas which are rasponsible for the abundance of phytoplankton (FISH 1956) . It is also obvious that the phytoplankton of tropical lakes tolerates high temperatures (RICKER 1937 , LUND 1949 , SPENCER 1950 , MCCOMBIE 1953 , GEORGE 1962 . Climatic conditions in tropical lakes are therefore unlikely to inipost? limits on production (FISH 1956) , in contrast to temperate lakes where law temperature and light in winter are frequently liniiting factors (RUTTNER 1963) .

In addition to temperature and light, chemical factors also play an important role in determining the pattern of distribution and abundance of phytoplankton ( SINGH 1960 , RODHE 1964 , FOGG 1965 , JAVORNICKY 1966 , MEGARD 1972 , GORHAM et al. 1974 ).

The importance of various physical and chemical factors for phytcplankton growth has been thoroughly investigated in the temperate regions, but comparatively little information is available on this aspect in tropical waters. This paper drscribes physical and chemical factors and their correlation with the distribution pattern of various phytoplankton species, the survey of which appeared in an earlier publication (NAZNEEN 1974) .

The weather data were obtained from the Pakistan Meteorological Department a t Karachi.

The temperat'ure of t,he water at various depths was measured directly in the field, and data for surface temperature wcre obtained from BAQAI et al. (1974) .

Chemical factors were measured from April 1970 to March 19iI. The water samples were collerted from a rowboat, mostly fortnightly, using Nansen sampling bot,tles a t 0.3 ni intervals throiigli the water column from the surface to a depth of 3 in. Sampling was usually carried out between noon and 3 P. & I .

a t the Boat Club, the deepest area of Kinjhar Lake. The 11-ater was then stored in a deep freeze in plastic bottles of a half liter capacity, and the chcmical analyses were iiiade within 24 hoars. The pH, hoivever, was measured by the lake side using p H paper. All samples were filtered before analysis, and their optical densities were recorded in a spectrophotonieter.

Dissolved oxygen was measured by the Winkler procedure (KELCH 1952) . Free carbon dioxide was titrated against 1/44 N sodium hydroxide solution with phenolphthalein as the indic.ator (ELLIS ct ul. 1948) . The inorganic phosphate Tvas estimated with ammonium niolybdate arid ascorbic acid (FOGG 8: WILKINSON 1958) . The amount of ammonia was determined by the niodification of ELLIS et crl. (1948) of the Xessler method. Nitrite-nitrogen was estimated using C: Illosway reagent, mliile nitrate-nitrogen was determined using phenoldisulphonic acid ( SVELL & &TELL 1949) . The amount of silica mas nicasured by the nicthod recorrin~ended by the Institute of TVater Engineers, London (1953) . Total iron was determined with a potassium thiocyariate solntion, while manganese content was measured with sodium periodate, following the methods of ELLIS et ul. (1948) .

~ u 5 -, 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 , 1 1 , 1 1 1 , , 1 1 A gradual rise in the average atmospheric temperature was observed froin February to June, followed by a decrease in July, while the lowest teniperature occurred in January ' Fig. 1 ).

The tliinate of Sind, the area in which the lake is situated, is very dry. The lowest annual rainfall was observed in 1968, while the heaviest annual rainfall was recorded 7966 7969 797L7 Figure 1 . Distribution of climatic factors (monthly average of atmospheric temperature, total monthly "bright sunshine" hours and rainfall) from March 1968 to February 1971.

during 1970. The greatest proportion of the rainfall occurred during the summer months (Fig. 1) .

The time of exposure to bright sunshine increased from March to May. Sunshine hours decreased from June to August (Fig. 1 ) due to the presence of clouds (cloud cover from June to August varies between 3.6 and 6.0 oktas), as shown in Table 1 .

The annual low temperature range was recorded in January, and the highest in May and July, 1969. The water teniperature (Fig. 2) followed the same trend as that observed for atmospheric temperature (Fig. 1) water and atmospheric temperature has also been noted by GANAPATI (1940) and JAYANGOUDAR (1964) . The temperature a t various depths (0.3-3 in) was measured from March 1970 t o February 1971. Only during the period of December and January was there a difference of about 2 "C between the surface water temperature and that a t 3 m (18.6-20.6 "C), the surface water being colder than the deep water. N o reniarkable difference in the temperature of the surface and a t various depths was noticed after January. The variations of temperature a t different depths were irregular, with only minor fluctuations. They did not follow any pattern.

Observations regarding the cheniical coniposition of the different water masses show that nutrient level plays an important role regulating the growth and distribution of phytoplankton species.

The pH value generally varied from 6.9 to 7.5, but the niaxiinuni of 8.0 was noted each year in June and July (Fig. 3 ). No marked difference was observed between the surface and various depths.

There is a considerable difference of opinion regarding the effect of pH on phytoplankton abundance. Some researchers (GERLOFF et al. 1952 , GEORGE 1962 have suggested that high pH values promote the growth of phytoplankton and resnlt in "blooms." On the other hand, MCCOMBIE (1953) and PRESCOTT & VINYARD (1965) argued that high values during blooming periods are the result and not the cause of phytoplankton blooms. The latter explanation seems to be more convincing in Kinjhar Lake.

Irregular fluctuations in thc dissolved oxygen of the water occurred, and the iiionthly mean oxygen concentration varied from 2.25 to 7.31 mg/l a t the surface (Fig. 3) , and from 1.8 to 6.26 mg/l below. Relatively high values of oxygen in the surface water occurred each year in January and July. The general increase in oxygen content during July occurred because of a phytoplankton blooni (GANAPATI 1940) , while the increase during winter has been attributed by MINDER (HUTCHINSON 1967) to physical aeration rather than biological events, a hypothesis that seems to be more convincing. The differences in oxygen value could be due to one or more factors, such as tenxperature, light intensity, photosynthetic processes and respiration.

The carbon dioxide concentration fluctuated between 2.0 and 7.5 iiig/l. It usually remained nearly constant a t different depths, but irregular fluctuations were noticed below the surface during June and December. SREENIVASAN (1965) also found similar irregularities in carbon dioxide content between surface and deep water in EL Madras reservoir.

The concentration of inorganic phosphate fluctuated between 5 and 1300 pg/1 (mean monthly value in the whole water column, 700 pgll). The miniinurn concentration was recorded in November and the maxiinum in October (Fig. 4) . A significant ainount of inorganic phosphate was found throughout the year, except during November 1970 (Fig. 4) . The level varies from time to time, and it is interesting to note that these fluctuations, to significant degrees, do not seem to affect the distribution of phytoplankton species, particularly Microcystis aeruginosa. However, when the phosphate content falls below thz minimum required for phytoplankton production, growth is seriously limited. The maximum abundance of M . aeruginosa is associated with a surprisingly low concentration of phosphate (GERLOFF et al. 1952) , so a considerable amount of inorganic phosphate is left after hixurient growth of this species (GEORGE 1962) .

The excess ainount of inorganic phosphate in October a t various depths seems to be due to the deconiposition of zooplankttm (HARVEY 1960), the niaximuni rainfall (DUTHIE 1968 ) which occurred in August and September 1970 (Fig. I) , or a coinbination of both of these factors. The sudden fall in inorganic phosphate in November is also quite interesting and may be due to the iapid initial liberation of phosphate from organic detritus in October, which slowed suddenly in November, when a marked decrease in the detritus particle size occurred (SEIWELL & SEIWELL 1938) ; to the activity of phosphate utilizing bacteria, such as Achromobacter guttatus, which were present as a high percentags of total bacterla (NAZNEEN & SIDDIQUI 1976) during t h i s period; to high mixing of low phosphate water from the inlet, which diluted the phosphate concentration of the water a t the sampling spot; or tr, a combination of all these factors.

The concentration of ammonia varied very irregularly at different depths, and no definite pattern could be detected (Fig. 4) . It may be assumed that these irregularities both at the surface and at various depths could arise froiii the uneven distribution of aninial wastes or the decomposition of phytoplankton, submerged weeds and zooplankton through bacterial activity wlthout the formation of intermediate products (HUTCHIKSON 1957) .

Kitrite was present in very small amounts, usually between I and 8 pg/l (Fig. 4) .

The general pattern of nitrite distribution is siniilar to those of ammonia and nitrate, except in winter. No effect of variations in the nitrite level on phytoplankton abundance was observed.

As in the case of ammonia, the nitrate concentration was also variable, 70-200 pg/l, and no obvious pattern could be observed (Fig. 4) & SIDDIQUI 1976 ). Thus, it seems safe to suggest that the nitrate level is controlled by the bacterial activities and by nitrogen-fixing Cyanophyta, and the irregularities recorded throughout the year may also be attributed to variations induced by these factors. The iiiaxiinuni concentration of nitrate was found in June, which was also the blooniing period of phytoplankton species, especially Microcystis aeruginosa (NAZNEEN 1974) . This shows that, in spite of the nitrate being continuously used up by the algae, there was still an excess aniount left in the water. This niay be due to the regeneration of nitrate in water by bacterial species, such as Achromobacter spp. and Azobacter sp., considerable concentrations of which were observed during this period (NAZNEBN & SIDDIQUI 1976 ) and by nitrogen-fixing Cyanophyta. It has been found that Kinjhar Lake is siiiiilar in some respects to Roshanara Tank, where GEORGE (1962) observed the continuous presence of nitrate in considerable aniounts. GANAPATI (1940) , during his investigations on a fish tank a t Delhi, which contained a permanent bloom of Microcystis aeruginosa, noticed that amnionical nitrogen is a limiting factor for the species in the absence of nitrate. This does not seem to be the case in Kinjhar Lake, as both nitrate and aninionia-nitrogen concentrations were low at the surface in December. The overall abundance of the phytoplankton was, however, lower in May than in Deceiiiber, although the level of aniiiionical nitrogen was high in May conipared to December.

The concentration of silica usually remained relatively high throughout the whole water column (Fig. 4) . Insoluble silicates are the chief coinponents of the soil of the Indus Delta (BLATTER et al. 1929) . The soluble form of the silica circulates freely in the soil water, resulting in an increase of the silica level jn the river water. River waters are relatively rich in silica and often markedly affect the silica concentration of those lakes which originate from them (WELCH 1952) , thus the high concentration of silica in Kinjhar Lake seems to be due to its origin. However, quantities may vary with the season, nature and periodicity of inflowing water, depth and 0th-r factors.

The curve representing diatom abundance in Kinjhar Lake followed the curve of silica concentration (Fig. 4) , the first peak occurring in June and the second in October (NAZNEEN 1974). The maximum concentrations of silica were also observed in these two months. SINGH (1964) also recorded two peaks of silica concentration, occurring in June and August. A large diatom population was found throughout the year due to the presence of substantial amounts of silica. It has also been noted by HUT- CHINSON (1957) that waters in the tropics have more silica than those in temperate regions.

Total iron and manganese concentrations were recorded from March 1970 to January 1971, usually trimonthly. In Kinjhar Lake, the level of total iron usually did not rise above I nigll. I t has been reported that the iron concentration in water is controlled by p H values, and that it never rises above 1 ppm in alkaline waters, pH 7.2-8.6 (VANKATESWARLU 1969). The results of this study also suggest that the iron concentration is very sensitive to pH, which usually remained within the alkaline range. Besides pH, bacterial activities may also affect the iron concentration (SMITH et al. 1957 , LAMANNA et al. 1973 ) and niay account for some irregulariti-s obssrved during the period of study. A significant amount of manganese was found in Kinjhar Lake. This lake consists chiefly of river water, and it is known that such waters contain relatively large quantities of manganese (TWENHOFEL 1938) . HARVEY (1949) has suggested that nianganese content doer not affcct thz productivity. Moreover, no direct effect of inanganesa on growth of phytoplankton was observed in Kinjhar Lake.

In addition to teni.perature, the duration of sunshine periods (RICE 1938 , SINGH 1964 , STEPANEK 1959 and the intensity of t'he light (MCCOMHE 1953) have also been reported to be among the most irriportant' factors controlling th2 occurrence and abundance of phytoplankt~on spzciss. RUTTNER (1930) disoussed t'he interaction of light and ternpaature rclatiw to individual spccies, but t'he relat'jonship of the annual phytoplankton cycle t o tlia interaction of t'hcse factors has been clarified primarily by FINDEEEGG (1943). HE pointed out that if the light and teri1,peratrire requiran>.ents vary indcpoudrntly, then it is possible t>o ohtain thz following four groups of organisiiis :

(1) Low temperature and low light species of winter, ( 2 ) Low temperatare and high light species of spring, (3) High temperature and high light species of summer, (4) High temperature and low light species of autumn. These four groups arz inadequate for the description of seasonal distribution of individual species in the tropical environment due t o gradual changzs in the interaction of light and temperature. Based on our obscrvations made at Kinjhar Lake, it seems more convenient and inforiimtive to describe the distribution of tropical phytoplankton specks in terms of the ten groups described below.

Maxima of population densit'ies are generally observed at the same tinre of year. The following are the average m.aximum counts of various species observed from March 1968 t,o February 1971 Very few phytoplankton species were observed during winter. Two species (Group VIII) occurred only during winter and were eliminated with the increase in teinperature. Even during the winter season, they were not abundant (KAZNEEN 19'74) .

Theie are certain species which appeared during mid-winter (Group IX), but their niaxiIituiii concatrations were observed in spring. This means that thcse species require relatively high temperatures for their optimum growth. It is interesting to note that the species bdonging t o the above mentioned groups were all diatoius, except Aphanizomenon flos-aquae.

The number of species increased significantly during spring, both a t the surface and below (NAZNEEK 1974) . Species which appeared in spring are of two types. The first occurred during the spring and disappeared by the end of this season (Group I). These organisins seem t o require relatively high temperaturzs with longer periods of bright sunshine for their propagation. They may be terirind high teniperature and high ljght intensity species. It is interesting to note that during this period, certain species of this group were observed only below the surface. It s3enis that they are well adapted to conditions of relatively low illumination. Whm thc days have longer periods of bright sunshine (Fig. 1) , tho direct effect of iadiations might cause their absence a t the surface. The coinplete absenca of these species in suiiiiiier seems to be due to extreniely poor light penetration, resulting front cloudy skies (Table 1 ) and a thick sciini of Mfcrocystis aeruginosa at the lakz surface. Another factor requiring consideration is the rzpairing of the lake during latc spring. It may bthat inechanical disturbances are at least partly responsible f o r thc floristic differmces between sl'ring and suninier. Species of the second type appeared in spring and developed their largest populations either in spring or summer (Group 11). Slightly low tcniperatims in spring appear to be coinpensated for by longer periods of bright sunshine. That is the reason that some species appearing in spring developed their highest population densities eithzr in spring or in slmxter. These species may be termed hlgh teinperature species.

The presence of a larger number of species during spring and the sudden disappearance of many of them by the end of the season appcars to be of interest. DUTHIE (1968) has suggested that a considerable number of epiphytic and epilithic diatom species can enter a lake with the spring runoff, but they never multiply and therefore rapidly disappear. A number of epiphytic diatoms have also hezn recorded in Kjnjhar Lake. A few species appeared suddenly a t one time in considerable numbers and then all a t once disappeared. These sudden appearances and disappearances of the species seem to be due to water inflow, as suggested by DUTIIIE (1968) , in this case, spring runoff. AnotheI factor which requires serious consideration is coinpetition.

It may be that with the onset of favourable temperature in spring, a large minlber of species resunie growth, and, in due course, certain species overgrow aDd finally displace others. It seems that in the present situation either or both of these factors, depending on the species, could be responsible for the sudden disappearances.

About SO"/,, of the species which occurred only during summer (Group 111) were inyxophycean speoias. GEORGE (1962) has also noted that high temperature is the principal factor in the growth of Myxophyceae. Some rare species of the other two algal groups (Bacillariophyceae and Chlorophyceae) were also found during this period. Based on the range of teinpcrature in which they oan grow, all these species would b? expected to occur in autumn, but it was found that they appeared suddenly for a short time and then disappeared (NAZNEEN i974). It seenis that they developed due to conditions of favourable temperature, but were unable to grow due to severe coinpetition with the dominant and faster growing species, particularly Microcystis aeruginosa and Melosirn grcmulata. Only a few species (Group V) were able to survive in spite of this severe coinpetition and have been observed until autumn, but their occurrence was sporadic (NAZNEEN 1974) . Some species (Group IV) grew throughout the year intermittently, showing that they could tolerate a wide range of temperature and light conditions, but their maximuni growth took place during siinimer when the trnipcrature was high.

The species which occurred only during autumn (Group VI) were also rare. They seem to require 1ongi.r continuous periods of high temperatures for their reproduction, which may account for their absence in spring. It is interesting to note that diiring this period certain myxophycean species were absent a t the surface and appeared only some distance below, perhaps due to a need to avoid excess light.

Theri are a few species (Group X) which appeared only during autumn and spring.

This iiieans that they require relatively high temperature and longzr periods of bright sunshine for their propagation. While reduced light due to cloud cover may account for the total elimination of these species in sunxrner, the role of incrcased intersprcific coinpetition during this season should not be ignored altogather. There ari certain species which were observed intermittently throughout the year, but their inaximutn concentretioris occurred in autumn or winter (Group VII) . These speceis seem to require low temperature for their optirnum growth, but they hax-e a wide rangz of temperature tolerance, just like the species which occurred throughoiit the year, but the niaxiniuni growth of which occurred in suninier.

A significant concentration of phytoplankton was present throughout most of the year, due to the continuous growth of ceitain diatom species, including Melosira gramdata, and of Microcystis aeruginosa, which exhibit "blooms" ' in su tnnier.

Under noriiial conditions in enclosed water bodies of tropical irnpoundnients, a continuous heavy population of phytoplankton, especially Microcystis aeruginosa, occiirs throughout the year, with a bloom in summer (GANAPATI 1940) . GEORGE (1962) has suggested that high temperature acts as a principal factor causing blooms of h3yxophyceae. The pattern of phytoplankton distribution reported by GANAPATI (1910), however, is distrupted (Fig. 5 ) in Kinjhar Lake by certain mechanical disturbances during the annual repairing and cleaning periods (generally April or May) ; by the presence of an inlet and an outlet, which iiiainly affect the chemical conditions of the water; and finally by the growth of produoers. The decrease in the phytoplankton population in Kinjhar Lake, caused by certain mechanical disturbances during April or May, was followed by a stidden rise in later months, due to favourable temperatures. The decrease in growth during November was not followed by a sudden inc.reasa because of urifavourable temperatures in the following winter months. It thus appeared that the growth of phytoplankton was more rapid during the high te~l~perature period in the summer months. MCCOMRIE (1953) argued that the water temperature may be a controlling factor for the growth of phytoplankton. These species possess certain temperature tolerance ranges. Between their upper and lower tolerance limits, the species are able to develop sudden pulses of reproductive activity when other factors, such as nutrient availability, are also favourable.

The author is very grateful to Dr. PHOOL ZAHID for her help and encouragement, and to Dr. 31. YAEESH SIDDIQUI for the great help and valuable suggestions given during the preparation of this manuscript. Special thanks are due to Dr. S. K. HASAN and Dr. prl. SHAMEEL for their interest in this work. The author is also grateful to Dr. I. U. BAQAI and other colleagues involved in thc Limnological Research Scheme for Kinjhar Lake for providing collection facilities and the data for oxygen, p H and temperature a t tho surface. I should also like to thank the Department of Botany, University of Karachi, for providing the experimental facilities for the chemical analysis of water samples. The author also thanks the Pakistan Meteorological Department of Karachi for providing the meteorological data.

The influence of various hydrological factors on the seasonal distribution of phytaplankton in Kinjhar Lake was studied. This water body is an artificial lake situat'd 120 km north of Karachi. The investigations were conducted from March 1968 to February 1971. The inaxinrum atmospheric and water tempcratures werc observzd in May and June; the minimum occurred in January. The abundance of phytoplankton, especially Microcystis aeruginosa, generally followed the seasonal changes in light and temperature. During this study, it was noted that in this tropical environitlent, the seasonal distribution of individual species cannot be described in terms of the four seasons. This i s due to gradual changa in the interaction of light and tenrperature. Kinjhar Lake is highly eutrophic. In spite of their continuous utilization by phytoplankton and other plants, the nutrients were generally found to 702 present in excessive anroiints throughout mast of the year. Phosphorus and nitrogen, however, become limiting factors for phytoplankton during very short periods, when they are present in abnormally low concentrations. The supply of oxygen and varbon dioxide in the lake water was uninterrupted and adequate due to continuous niovermnt of water by the wind action throughout most of the year. &sides t h e hydrological factors, iriechanical disturbances also have an effect on the distribution pattern of the phytoplankton.

Nitzschiu signroidea (11 X lo2 cellsil.), Pinnularia rnajor ( 1 4 4~ 10' cellsil.), Surirella splendida (10 x 10' cellsil.), Chlorhorrnidium flaccidurn (171 x 103 cellsil.), Cosmarium fontigenum (64 x 106 cellsil.), Pediasfruna sp. (64 X lo6 cellsil.), P. simplex (20 X lo3 cells

Nostoc sp. (5 x 10' cellsil.), Phormidiurn boryanum (96 x 10

Epitkemiu argus (32 X lo5 cellsil.), Fragilaria virescens (162 x 104 cellsil.), Gon7,phoneis sp: (8 X lo2 cellsil.), Melosira granulata (139 x 10' cellsil.), Navicula radioso (11 x 10.1 ccllsil.), Pin?iulrrricc uiridis (1 x 10'. cellsil.), Bhopalodia gibba (313 x 104 cellsil

Species observed only during summer and autumn: Pirinulariu qibba

Naoicula rhyncocrphala ( 3 3 x 10" cells/l.), 6. eiridula (22 x loJ cells/l.), Spcccies ocxurring only below the surface Anabaena circinalis (113 ~1 0 : ' cellsil

Lywqbya polysiphonae (6 x

Microcystis ramosa (6 x 10

Group VII: Species observed intermittently throughout the year with maxima in autumn or winter

Cytnbella lacustris (26 x 102 cells/l.), C. parva (22 x 10:J cellsil

Species observed only during autumn: 9. References

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