Trap. Eeal. 27 157-165, 1986 ISSN 0564-3295

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STUDIES ON THE RIVERINE ECOLOGY OF TORRENTIAL WATERS IN THEINDIAN UPLANDS OF THE GARHWAL REGION. III. FLORISTIC AND

FAUNISTIC SURVEY

PRAKASH NAUTIYAL

Department of Zoology, University of Garitwal, Srinagar 246 174, India

Abstrdct: The present study revealed that the rivers Alaknanda and Nayar differed eco­logically. A vivid picture of the physico-chemical and biotic environment prevailing in thesewater bodies, has been drawn in the text. The current velocity, turbidity and the thermalreg'imes prevailing in them were considered to exert significant influence on' the aquatic life.Enhanced turbidity and water current during monsoon, individually act as lethal and detrimin­tal factors respectively for they retard plankton development. The composition and abundanceof neustonic, nektonic, planktonic and benthic life in these torrential waters are primarily govern­ned by water current a~d temperature. Based on these observations a classification applicable toall the streams and the rivers of the Indian uplands of Garhwal region has been propounded,turbulent-stenothermal of which the Alaknanda is an appropriate representative and placid-eurythermal well represented by the Nayar. /

Resume: La pr~sente [tude montre que les deux rivieres suivantes: AI..\knanda et Nayardifferent du poi de vue ecologique. Vne image tres nette de l'environnment physico-chmiqueet biotique dominant dans ces eaux a ~l~ etablie dans ce texte. La vitesse du courant, la turbidit~et les regimes thrmiques dominants sont considires comme exer,ant une influence significativesur la vie aquatique. L'augmentation de la turbidit~ et du courant de l'eau durant la mousson,agissent individuellement et respcctivement en tant que facteurs mortels et nuisibles car ils retar­

dent Iedeveloppment du plancton. La composition et l'abondance de vei neustonique, nectoniqueplanctonique et benthonique dans ces eaux torrentielles sont principalement gouvern[es par lavitesse de l'eau et la temperature. Basee sur ces observations une classification applicable a tousles fiueves et toutes les rivieres des hautes terres indiennes de la r· gion Lie Garhwal a et~ etablie:Ie terme tumultueux stenothermique bien represente par l'Alaknando, Ie therme placide-eury­thermal bien repr~sent('e par la Na)'ar.

Resumen: El presente estudio revel a las diferencias ecologicas entre Ius rios Alaknanda yNayar. En el texto se logra una imagen vivida del ambiente fisicoquimico y biotico prev..\lecienteen estos cuerop5 de agua. Se considero que la velocidad de la corriente, la turbidez y eI r' gimentermico son los factores determinantes para la vida acuatica. El aumento en tu~bidez ycorriente del agua durante los monsones, actuan individualmente como factores letales, ydeletereos respettivamente para el desarrollo de plancon. La composicion y abundancia de

los componentes neustonicos, nectonicos, planctonicos y bencticos, en estos torrentes, estancontrolados principalmente por la corriente y temperatura del agua. Con base en estasobserv~cones ba sido propuesta una clasificacion que incluye : turbulento-stenotermico ytranquilo: Z-euritermico, aplicable a todo los rios y corrietes de las tierras altas de India en

h region de Garhwal. er,tre los cuales el rio Alaknanda es un buen representaute del primertipo y el rio Nayar del segundo.

Key Word,r: Indian uplands, Riverine ecology, Diversity, Classification.

INTRODUCTIO~

Rare are the studies that have been conducted on the riverine ecology in the torren­tial reaches of the Indian uplands, to which the major rivers, the Ganga and Brahamputra

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158 RIVERINE ECOLOGY OF TORRENTIAL WATERS

owe their existence. Gaumukh, the headwaters of the Ganga is situated high in the snowpeaks of Central Himalaya in Garhwal region. The Ganga at its origin is known as theBhagirathi till it merges with its counterpart, the Alakanda flowing down the deep gorgesfrom the Alkapuri glacier. \'\Thile a number of significant tributaries such as lvlandakini,Pindar, Nandakini, Dhauli Ganga etc. form prayagas (confluences) with the Alakananda,only a few join the mainstream of the Bhagirathi, Bhilangna being one of them. Preli­minary investigations on various ecological parameters of these tributaries of the Gangahave been conducted in past few years by Sharma and Singh (1980), Badola and Singh(1981), Singh anfl Dobriyal (1981), Nautiyal et at. (1982) and Nautiyal (1984, 1985).

The present study was conduted in order to obtain an over~ ~ic;t~ of the pre­vailing ecological conditions and thus the water quality, iri'ili~"'spnn~1'ea, Alakananda.However, special emphasis was laid on the factors which profoundly influence theaquatic life, based on which a scheme was propouncled for classifying the Ganga riversystem in the Garhwal Himalaya .

. ,MATERIALS AND METHODS

The physical parameters-water temperature, turbidity and current were recordedduring 1981 and 1932. Simultaneous qualitative-cum-quantitative studies were conductedon plankton and only qualitative in the neustonic, nektonic and benthic communities.

RESULTS AND DISCUSSION

\Vith ever increa~ing load on aquatic eco<;ystems,studies on riverine ecology havebecome necessary ta the quali ty of life for mankind. Central Himalaya is enriched bywater resources in the form of the Ganga river system. The holy river well known for itscuring capabilities origin ates in the Ind.ian uplands where numerous brooks, streamletsand rivulets join the mainstream, Bhagirathi (Fig. 1). Investigations pertaining toriverine ecology have been conducted on the Ganga river system in the alluvial plains atvarious centres by Roy (1955), Chakrabarty et ai. (1959). Lakshminai'ayana (1965),Ray et at. (1966), Pahwa and Mehrotra (1966), to name a few. In almost all of themthe plankton has been considered in great detail.

The present study was designed to describe ecological differences, if any, anddetermine the status of some torrential streams in the Indian uplands. The physico­chemical parameters of both the rivers exhibited similar patterns of fluctuations (Fig. 2, 3).The water temperature, current and turbidity in both, the AJaknanda and the Nayar wererecorded to be low during winter. Thereafter these parameters record a gradual increasewith current and turbidity attainir.g peak during monsoon and water temperature duringsummer.

Four major aquatic communities were observed in the Alaknanda and the Nayarwhich were defined by different vertical zones inhabited by them.

NEUSTON

Individuals associated with air-water interface are categorised as neuston. Theywere represented t<:>a certain extent in the Alaknanda as well as tl~e Nayar by variousspecies of Cerrids (water striders) and the Gyrinids (Whirligig beetles) ,of which the formerwere abundant in the Nayar. The rock pools along the course of the Alaknanda at lower

NAUTIYAL 159

(F ig 1)

THE GANGA RIVER SYSTEM : CARHWAI.. HIMAI..AYA

Fig. 1. The Ganga river system in Garhwal Himalaya

altitudes, however, harbour both the bugs and the beetles as compared to themainstream.

PLANKTON

Plankton are free floating organisms with little or no locomotry power and are atthe mercy of water turbulence and as~ociated with liquid-liquid interface. In the Alak­nanda as well as the Nayar various members of diatoms, desmids, green and bluegreenalgae contributed to the existance of different planktonic populations. It is noteworthythat the diatoms constitute the majority of the algae.

The golden brown diatoms, a colour which they owe to the abundance of carote­noid pigments, are of various shape and .size. All the diatoms. encountered belong to thePennaJes group, the common ones being Fragilaria, Cymbella, Navicula, Nitzschia in the

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160 RIVERINE ECOLOGY OF TORRENTIAL WATERS

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Fig. 2. & 3. Monthly variations in certain physico-chemical factors at study sites.

Nayar and Alaknanda. Surirella was common in the Nayar only. Nitzschia and Naviculabeing prominent forms were observed throughout the year in both the water bodies.Overall the diatoms constituted an average of 49% and 69% of all organisms recordedfrom the Alaknanda and the Nayar rivers respectively (Nautiyal1984, 1985). It has beenreported by Pearsall (1921, 1923) that waters having large amount of silica and nitrateexhibit high diatom density, and that floods enhance their growth. Lakshminarayana(1965) has reported that diatoms account for the major .bulk of phytoplankton in theGanga at Varanasi.

The abundance of diatoms was attributed to low temperature, lesser current velo­cities and little turbidity. High velocity and turbidity were responsible for fall in the

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NAUTIYAL 161

diatom population. They were thus considered as detrimental and lethal factors respec­tively. This is based on the observation that only 30-36% of diatoms were recorded in theAlaknanda when the turbidity was observed to range from 15-68% and the current from1.09-1.94 m/sec. Similarly, in the Nayar the diatom density declined during high tur­bidity (45-70%) and when current velocities were 0.9-1.4 m/sec. As far as these two waterbo:lies are concerned higher values of turbidity and current were recorded only duringmonsoon and were attributed to sudden influx of monsoon run-off. In the Alaknanda,howe\'er, when snow begins to melt during March-April the flow and velocity of the riverincreases and carries with it silt which enhances the turbidity. The Nayar being fedby springs, become flood-like only when the catchment areas receive heavy showers.Phytoplankton autotrophic activity is adversely affected by turbidity due to the blanke­ting effecr which blocks the passage of light. According to Gran (1902) and Patrick(1948) the duration of light penetration is of immense significance from the viewpoint ofdense growth of diatoms. Similarly, current velocities according to Kofoid (1908),Chandler and Weeks (1945), Berner (1951) and Nautiyal (1984), is yet anotherparameter of importance in determining the density of diatoms. Currents higher thanmoderate velocity have been observed during low density of diatoms and has beentermed a detrimental factor to diatom growth (Chakrabarty et al. 19.59).

Green algae are the second most abundant phytoplankton and account for 32%of Chlorophyceae members in the Alaknanda and 19% in the Nayar. However, Lakshmi­narayana (1965) has reported that green algae constitute a low percentage of the orga­nisms downstream in the Ganga, at Varanasi, blue-green algae being the second mostimportant group, preceeded by diatoms. In the torrential reaches of Garhwal hill­streams, a m<>.ximaof green algae in the Alaknanda as well as in the Nayar wasrecorded during January and December respectively. The onset of spring was markedby a decreasing trend and a minima was recorded during June in the cold waters ofAlaknanda and in the Nayar during July and August. \

The green algae-Spirogyra, Cladophora and Ulothrix we,e observed to dominate thesetorrential waters. While Cladophora flourishes during low temperatures (autumn andwinter) it is absent during monsoon. There are occasional groups such as Spirogyra,

Ulothrix, Scengdesmus and Sligeoclonium, however. The development of these colonial orsolitary forms in the torrential reaches is influenced by water current and turbidity as thenumber of plankters per ml. tend to decrease with increasing turbidity and current.However, a high percentage was maintained during such conditions, 48% in the Alak­nand a and 40% in the Nayar, attributed to increased turbulence which consequentlyleads to detachment of algal filaments from the substratum and accounts for theirincreased appearance in the plankton.

The blue-green algae constitutes 20% and 13% of the phytoplankton populationin the Alaknanda and the Nayar. Very few species are prevalent in these waters. A lowconcentration was recorded throughout the year except monsoon. Tte blanketing effectof silt does not influence their density and they were observed commonly during moderatetemperatures.

The behaviour of the phytopJankton follows the trend exhibited by the diatomswhich constitute the bulk of its members. Low temperature and reduced turbidity andcurrent velocity was observed during the winter maxima which suggested an inverse rela­tionship between these physical factors and the phytoplanktonic populations in both

162 RIVERINE ECOLOGY OF TORRENTIAL WATERS

rIvers. A unimodal periodicity was exhibited by these p'-ytoplanktonic communitiescompared to the bimodal distribution reported by Lakshminarayana (1965). and Pahwaand Mehrotra (1966) in the Ganga. It was concluded that turbidity is a lethal factor whilecurrent a detrimental factor which together inhibit plankton development. Blanketing andtheir adverse effects of turbidity on plankton density have been reported earlier by Welch(1952), Roy (1955) and Chakrabarty et al. (1959). Favourable current, intermittent tur­

bidity and warm waters prevail in the Nayar and result in a diverse crop of phytoplank­ton. The scarcity in the Alakananda may be attributed to high turbulence and conti­nuous turbidity for 6 months (April to September).

Zooplankton is a minor community and accounts for only 2.71% in the Alaknandaand 3.79% in the Nayar. The planktonic genera belong to Daphnia, Cyclops and Bosmina,

and a few protozoans in the Nayar compared IO chironimid larva.;:, protozoans and a fewrotifers in th~ Alaknanda. High current v~locities and turbidity adversely effect theseanimal communities and monsoon season is characterised by lack of Zooplankton in thesamples. The water temperature also io>a significant factor in their abundance and distri­bution; The fact that the Alaknanda lacks the popu1ation of Daphnia etc. can be attri­buted to turbulent-cold waters as compared to placid-warm waters of the Nayar.

NEKTON

The major communities existing in the riverine ecosystem as nekton were fishes,amphibians (anura), reptilians (water snake) and mammals (otter). These are organismspossessing powerful means of locomotion.

Both rivers possessed characteristic nektonic fauna. Though fish were commonto both the rivers, the major species in the Alaknanda belonged to the genera Schizo thorax,

·Carra, Crosso,cheiluf and Pseudechenies. The Nayar, howe\er, harbours Tor, B~rilius, Puntius

and iVIastacembelus. Migratory forms of Tor putitara, were however, observed to frequentthe Alaknanda also, from March-April to June-July (Nautiyal and Lal 1984). In thesame period Labeo was also observed in the Alaknanda.

The amphibian population was found to inhabit the sidewaters while the reptilianfauna, the mainstream in case of the Nayar. The Nayar, however; lacks the semi-aquaticmammalian otters, which are also a rare feature of the Alaknanda. There is no reptilian

or amphibian po'pulation in the Alakananda ..A passing reference must be given to the avian population as they are very much

a part of food chain in aquatic ecosystems. Although migratory as well as residential·p~pulati 'ns were common to these rivers, birds like white breasted King:fihsher andwagtails were very frequently observed along the river banks.

BENTHOS

The nature of biota Aourishing in a particular stretch is governed mainly by thevelocitYVVithwhich the water flows and substrate. Alternating rapids and placid poolsare common in the hilly tracts, implying fast flowing water along shallow, stony bottomswith high gradient and slowly flowing water in the stretches with deep sandy, stony

· bottom with little or no gradient. In hi!lstreams sandy bottoms are a. rare feature: For a· major stretch the river bed is covered by substratum in the form of cobbles, .boulders and.rocks. In.such situations the submerged substratum forms the,river bed and hence the

I- NAUTIYAL 163

organisms inhabiting it are termed 'as benthos (organisms associated with solid-liquidinterface) .

Autotrophic populations occurring as algal scum or filamentous colonies are charac­teristic features of rapids and mayor may not exist along placid pools. These stretchesharbour heterotrophic populations in haptobenthic form (Hutchinson 1967). They wereorganisms which creep (water penny larvae); crawl (may-fly ·nymphs-Family Baetidae,stone-fly nymphs-Family Nemouridae; caddis-fly larvae with portable cases and a fewdipteran larvae-Family Chironomidae) or remain attached (caddis-fly with glued cases).Ephemeropteran nymphs and dipteran larvae also flourish on the rhizobenthic colonies ofCladJphora, Spirogyra, and Ulothrix.

In the Alaknanda other haptobenthic forms observed were beetles, (Dysticids­Hydaticus vittatus, Eretes sticticus) and dragon-fly naids. They were found to inhabit theriver banks, the beetles ~t a depth of·I-2' and the naidsjust at the moist edges of thebanks. Besides beetles and odonats the Nayar harbours water scorpion, Belostomatids(Diplonychus rusticum), crustaceans (crabs), mites and molluscans (snails). 'Besides' Hapto­benthos' there are 'Psammon' which include bugs (corixids) which move on the sandy 01

muddy patches on the river bed of the Nayar and the annelids (leeches) which burrowinto it. Corixids are quite common in the Nayar but rare in the Alaknanda. Leecheswere never observed in the Alaknanda.

CONCLUSION

An overall assessment of various interrelationships and the ecological conditionsprevailing in the torrential reaches can· thus be made from the.above observations. Thebiota flourishing in the riverine ecosystems of the Indian uplands was observed to be im­mensely influenced by water temperature, current and turbidity.

Low \vater temperature (8-12'C) was considered to be essential for diatom maximaand slightly greater values for flourishing growth of the heterotrophic populations. Watercurrent velocities exercises significant influence ·on the biota as a whole. Velocities abovemoderate limits (O.8-1.9m sec) were observed to be detrimental to development of aquaticlife and was thus termed as a detrimental factor. Turbidity which was caused mainly by siltresulting from surface run-off during monsoon and also by melting of snow during summer(as in the Alakhanda), blocks the passage of light, and inhibits primary productivitydirectly and secondary productivity indirectly. It was hence assessed to be a lethal factor.

It is obvious from the above discussion that water current, temperature and tur­bidity are parameters of prime importance in fluvial systems. Based on their interrela­tionships and signiEcant influence exerted on·the biota the classification, Placid-Eurythermaland Turbulent-Stenothermal, has been coined to accommodate various rivers draining theIndi<Jn uplands of Garhwal Himalaya. In this classification the term placid implies thatthe river has gentle flow as compared to others where mixing is vigourous due to highcurrent velocities and increased turbu lence, which can be appropria tely signified by theterm turbulent. It should be born~ in mind that since streams with higher velocities remainturbid for a greater period (as settling rate of silt is greatly reduced), these terms shall alsoexpress the extent and the period for which they remain turbid. It was observed thatsnow-fed streams have large discharge and are turbulent thus limiting the thermal regime ..which accounts for the usage of the term~ stenothermal and eurythermal, in the present classi­fication.

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164 RIVERINE ECOLOGY OF TORRENTIAL WATERS

Riverine system has been cla,sified earlier also and it was a common practice todesignate them as snow-fed or spring-fed or as trout, snow-trout and mahseer streams(Jhingran and Sehgal 1978). In Jammu Province streams have been classified into twocategories only, as compared to three mentioned above, by Joshi et al. (!978) viz. mahseerand snow-trout streams. These classifications, have thus been based on the fish faunafrom which the idea of physico-chemical charcteristics may be framed. The present classi­fication is based on the physical characteristics, which can give an idea of the nature ofbiota flourishing in it. In Garhwal Himalaya although turbulent-stenothermal streams sup­port snow-trout p:Jpulations, not a11placid-eurythermal streams support m2hseer popula­tions and hence can not be classified on that basis. A classification based on the dis­

solved oxygen content only has also been coined for European waters by Illis (1962).According to him there are two types of streams, Rithron and PotJmon, the former havingDO contents more than 10 ppm and less in the latter.

Regarding the status of these hillstreams, it can be safely concluded that placideurythmnal streams can support high primary as well as secondary rroductivity and tur­bulent-stenothmnal reduced productivity. Also that the major source of pollution is siltwhich hampers productivity to a great extent. The rivers of the Garhwal Himalayaif compared to the lakes on the basis of appearance <';1dprvductivity can be consideredsimilar to oligotrophic lakes.

ACKNOWLEDGEMENTS

Acknowledgements are due to Dr. H. R.Singh, Prof. & Head Department ofZoology, University of Garhwal, Srinagar for laboratory facilities. Thanks are alsodue toDr. M. S. Lal, Reader, Department of Zoology, University of Garhwal, Srinagar, for hisinvaluable suggestions and going through the MS critically.

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GRAN, H. H. 1902. Das plankton der Norweigischen nordmenes von biologischen behandle. Rep. Norweign.Fish & Marine Inv. 2: 1-222.

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(Accepted for publication on 25 March 1986)