Population dynamics of macroinvertebrates in a Shivalik stream, Banganga, Katra (J & K)

Prudent management of lotic systems requires information on their ecological status that can be estimated by monitoring water quality and biodiversity attributes. To understand the environmental conditions in Ban Ganga stream (Katra), a study was carried out to establish the relationship between water quality and macroinvertebrate assemblages between the months of Jan. and Dec., 2003. Water physico-chemical characteristics (temperature, depth, speed, pH, DO, FCO2, CO3 " , HCO3 " , Ca ++ , Mg ++ and Cl-) and biodiversity index changed markedly along the longitudinal profile of stream. In total, 13 species of phylum Annelida, Arthropoda and Mollusca were recorded. The highest number of species (12) were observed at S-I and lowest number (10) at S-III. The order of dominance of various groups was as : Arthropoda > Annelida > Mollusca. Moreover, the highest species diversity index of 5.157 was recorded at S-II and the lowest 4.151 at S-III. Thus, the present study indicated that significant changes in aquatic macroinvertebrate assemblages were primarily due to water quality rather than prevailing climatic conditions.


INTRODUCTION
Studies have shown that water quality in aquatic systems has strong impact on biological components (Harding et al., 1999;Ometo et al., 2000).According to river continuum concept, community structure and function conform with certain geomorphic, physical and biotic characteristics such as stream flow, channel morphology, detritus loading, size of particulate organic matter, autotrophic production and thermal loading (Vannote et al., 1980).However, this concept seldom holds in many lotic systems due to longitudinal changes in environmental conditions caused by agricultural, human settlements or industrial activities (Roy et al., 2003).
Macroinvertebrates constitute an important component of biodiversity in lotic systems (Merritt and Cummins, 1996).They are diverse, have short generation times and are easily dispersed.As a group, macro-invertebrates are sensitive and respond to both natural and anthropogenic changes in their environment (De Pauw and Hawkes, 1993).Several techniques, protocols and indices have been developed to monitor stream quality using changes in species composition, diversity and functional organization of its inhabitants (Lenat, 1993).(Pielou, 1975) observed that the concept of biodiversity (species richness and evenness) is a central theme ecosystem ecology and can be used to explain properties such as biological productivity, habitat heterogeneity, habitat complexity and disturbance.Species diversities are moderate in stable ecosystems, highest in intermediate and low in severely degraded ecosystems (Connell, 1978).High species diversity in moderately disturbed ecosystem is attributed to stress tolerant and pioneer species.
In India and particularly in Jammu and Kashmir, only few studies have been attempted to describe the structure and composition of macroinvertebrates in lotic systems (Dutta and Malhotra, 1986;Sunder and Subla, 1986;Zutshi, 1992;Thakial, 1997;Sharma, 1999 andSawhney, 2004).
Therefore, the study was sought to investigate water quality and macroinvertebrate community in Ban Ganga stream (Katra).The main objectives of the study were;

Study Area
The study was carried on Ban Ganga stream (Katra) in Jammu (India) for a period of 12 months (Jan.-Dec., 2003).Ban Ganga; a shallow stream originating from the snow bound hills of Shri Mata Vaishno Devi meets mighty river Chenab after traversing through Katra town.The stream is the main source of water supply to the inhabitants of Katra town and its suburbs.As soon as the stream passes through Charan paduka, it receives various effluents in the form of runoff from dhabas, excreta from ponies, wastes from kitchen (Gulshan langar), municipal sewage, flour balls and waste from crematorium.All these influence both water quality as well as aquatic ecology.For the present study, three sites were established along the longitudinal profile of stream.Site I was under least anthropogenic influence whereas, site II at a distance of 1 Km from S-I was the site under maximum urban influence and S-III, 3 Km downstream from S-I receive pollutants in the form of sewage, pony dung; etc.
Water samples and macroinvertebrates were collected monthly for a period of 12 months.All the physico-chemical parameters were analysed using APHA (1985).Macroinvertebrates were sampled using Ekman's dredge and were then sieved through sieve (No. 40 mesh size 0.02 mm -0.05mm).Organisms collected were preserved in 4% formalin for identification.These were identified using Ward and Whipple (1959), Tonapi (1980) and Pennak (1989).The number of organisms per square meter was counted using formula.0 N = × 10,000 (Welch, 1948) a.s Species divesity index (Shannon-Weiner index) was calculated using formula.

Types and quantities of benthic fauna
A total of 13 species of 3 phyla namely Annelida, Mollusca and Arthropoda were found during investigative studies on Banganga Stream (Katra).The average density from all the sites was 75.75n/m 2 .The average density of S-I was 28.37n/ m 2 , S-II was 32.37n/m 2 and S-III was 15.00n/m 2 .The lowest density of benthos at S-III (15.00n/m 2 ) may be due to the decreasing DO concentration and increasing pH (Rosillon, 1989) whereas, the highest macrobenthic invertebrate density encountered at S-II may be due to lentic-like conditions created due to embankment which has resulted in the accumulation of allochthonous material thereby, enriching the site and resulting in higher species diversity (Dutta and Malhotra, 1986;Thakial, 1997;Sharma, 1999;Sharma, 2002 andSingh, 2004).
The highest number of macrobenthic invertebrates at S-I may be due to the availability of optimal conditions (Dissolved Oxygen, temperature, water velocity and clean water) Table 1.

Dynamic structure and influence of seasonal variation of benthic fauna.
Phylum Arthropoda seems to have the highest influence to the alteration of total benthic fauna since it was the dominant phylum found all year as shown in the Table 2 and 3 Oligochaetes among Annelida constituted another group dominating the total macrobenthic fauna of Ban Ganga stream.Abundance of oligochaetes may be attributed to temperature, organic matter and flow of water (Learner et al., 1971;Hawkes, 1979;Gopal andSah, 1993 andPennak, 1989).
Phylum Arthropoda contributed maximally with an average of 67.1% to the total macrobenthic fauna of Ban Ganga stream followed by Annelida (26.2%) and Mollusca and (6.6%) respectively (Table 3, Fig. 1).The rapidly increasing pop of Chironomidae might have led to ar thropod dominance.Habitat stability and biotic interactions could be a dominant force in structuring benthic community in streams (Ometo et al., 2000).
A look at the Table 4 reveals that quantitatively, total macrobenthic fauna recorded its minima in the month of July (monsoon season) due to heavy influx of water inform of floods and maxima recorded during summer months may be due to increased DO and temperature which may have favoured the production of organic matter thereby, leading to the growth of benthic fauna (Bhatt et al., 1984;Strommer and Smock, 1989;Thakial, 1997 andSharma, 1999).

Diversity Index of benthic fauna
Along the longitudinal profile of stream, diversity index value was highest in the middle quality to macroinvertebrate densities and biodiversity indices along the stream.