Benthos Composition and Abundance in Lentic Ecosystems

Freshwater ecosystems are considered as one of the most essential natural resources for the survivability and success of all the living organisms including man. The habitat is generally divided into Lentic and Lotic ecosystems. The term lentic refers to standing bodies of water such as lakes, reservoirs, and ponds. These ecosystems generally have three zones – Littoral, Limnetic and Benthic zone. The term Benthos is derived from two Greek words “Ben” meaning ‘the collection of organisms living in or on the sea or lakes’ and “Thos” ‘the bottom of sea or lakes’. Benthos can be classified on a number of basis i.e., on the basis of size; Macrobenthos, Meiobenthos and Micro benthos; On the Basis of Location; Endobenthos, Epibenthos and Hyperbenthos; On the basis of Type; Zoobenthos includes animals and Phytobenthos which comprises of plants. The Benthic invertebrates such as nymphs of stonefly, mayfly, caddisfly larvae, snails, mussels, crustaceans, rattailed maggot, etc., convert and transport nutrients from one part of the water body to another, influencing nutrient cycling. They ingest organic matter such as leaf litter and detritus and in turn serve food for higher aquatic organisms such as fish, forming a basic link between organic matter and higher aquatic animals in food web. They are sensitive to changes in habitat and pollution, especially to organic pollution [1].


Introduction
Freshwater ecosystems are considered as one of the most essential natural resources for the survivability and success of all the living organisms including man. The habitat is generally divided into Lentic and Lotic ecosystems. The term lentic refers to standing bodies of water such as lakes, reservoirs, and ponds. These ecosystems generally have three zones -Littoral, Limnetic and Benthic zone. The term Benthos is derived from two Greek words "Ben" meaning 'the collection of organisms living in or on the sea or lakes' and "Thos" 'the bottom of sea or lakes'. Benthos can be classified on a number of basis i.e., on the basis of size; Macrobenthos, Meiobenthos and Micro benthos; On the Basis of Location; Endobenthos, Epibenthos and Hyperbenthos; On the basis of Type; Zoobenthos includes animals and Phytobenthos which comprises of plants. The Benthic invertebrates such as nymphs of stonefly, mayfly, caddisfly larvae, snails, mussels, crustaceans, rattailed maggot, etc., convert and transport nutrients from one part of the water body to another, influencing nutrient cycling. They ingest organic matter such as leaf litter and detritus and in turn serve food for higher aquatic organisms such as fish, forming a basic link between organic matter and higher aquatic animals in food web. They are sensitive to changes in habitat and pollution, especially to organic pollution [1].

Sites (Plate 1-4)
The present study was carried out on four fresh water bodies of Aligarh (latitude 27° 30' N and longitude 79° 40' E), namely Shekha Jheel, Nai Basti pond, Laldiggi pond and Chautal pond. Laldiggi, Chautal and Nai Basti ponds having 1 ha area, located in the vicinity of the Aligarh Muslim University campus receive water from domestic discharge and rain water which accumulates during rainy season. These are used by washer men extensively for washing clothes, thus adding detergents and certain chemicals that bring changes in its chemical composition. The Shekha Jheel is a 25 ha lake near the village of Shekha, 17 km east of Aligarh. It is a fresh water perennial water body that came into existence after the formation of the Upper Ganges Canal which flows adjacent to the lake. It is maintained by the Forest Department. Sampling was done fortnightly from 9th March, 2016 to 23 rd April, 2016. Samples were collected from selected water bodies between 8 am and 9 am and were analysed for following physicochemical parameters were analysed: Air and water temperatures, dissolved oxygen (DO) and free carbon dioxide (CO 2 ).

Benthos collection, separation and identification
The bottom mud scrapper with low towline designed and described by Miclhae [2] was used to collect the samples from the waterbodies. For benthos analysis, samples were diluted with tap water to prepare slurry in a bucket and sticks, leaves, debris were removed. Then slurry was divided into ten subsamples. Each subsample was first sieved by B.S. no. 30 (0.5 mm) mesh sieve kept above the sieve B.S. no. 72 (0.2 mm) in order to retain smaller organisms (meio) on the latter. Organisms were kept in separate vials and fixed in 10% formalin solution (4% formaldehyde) and labelled. For qualitative and quantitative analysis 1 mL of fixed sample was taken on glass slide and studied under dissecting microscope. Individuals were identified up to genus level with the help of keys given by Edmondson et al. [3] and Needham and Needham [4] and frequency of each taxon was noted and expressed as individual/m² [2][3][4].
during the month of March. Increase in both air and water temperature during the month of April is attributed to the increase in solar radiation comparatively due to longer day length. pH values of all selected water bodies ranged from a minimum of 7.0 to a maximum of 8.0 during month of March, 2016 whereas during the month of April, it ranged from a minimum of 7.5 to a maximum of 8.5. Increased values of pH in all selected waterbodies during the study period could be related to increased level of photosynthesis carried out by phytoplankton and macrophytes, wherein CO 2 is consumed, and hence pH is raised. The decrease in dissolved oxygen and the increase in Carbon dioxide in all the selected water bodies from 8th March to 23rd April, 2016 clearly justify the fact that as temperature increases oxygen holding capacity of water decreases while carbon dioxide increases due to high rate of decomposition. Lower values of carbon dioxide were observed in Nai Basti The decrease in dissolved oxygen and the increase in Carbon dioxide in all the selected water bodies from 8th March to 23rd April,2016 clearly justify the fact that as temperature increases oxygen holding capacity of water decreases while carbon dioxide increases due to high rate of decomposition. Lower values of carbon dioxide were observed in Nai Basti The decrease in dissolved oxygen and the increase in Carbon dioxide in all the selected water bodies from 8th March to 23rd April, 2016 clearly justify the fact that as temperature increases oxygen holding capacity of water decreases while carbon dioxide increases due to high rate of decomposition. Lower values of carbon dioxide were observed in Nai Basti The decrease in dissolved oxygen and the increase in Carbon dioxide in all the selected water bodies from 8th March to 23rd April, 2016 clearly justify the fact that as temperature increases oxygen holding capacity of water decreases while carbon dioxide increases due to high rate of decomposition (Tables 1-4).
Lower values of carbon dioxide were observed in Nai Basti pond during study period (Table 2), might be due to high photosynthesis of phytobenthos and macrophytes.

Benthos
In distribution of benthic flora, light plays a very important role when the water is sufficiently shallow. The studied waterbodies, being shallow light reaches the bottom sediments in plenty and as a result of it, phytobenthos grow in greater abundance. The phytobenthos comprised of three major groups namely Bacillariophyceae, Chlorophyceae and Myxophyceae. The variations in Phytobenthos density in the selected water bodies were recorded from a minimum of 38 No/m² to a maximum of 151 No/m² (Tables 5-7 (Figure 5a-5d). Chlorophyceae showed a direct relation with the temperature. Kumar et al. [5] reported that higher water temperature and low dissolved oxygen support the growth of Chlorophyceae. Statistically, phytobenthos showed positive significant correlation with Water temperature, Carbon dioxide and pH whereas as negative but significant correlation with zoobenthos, in all the four studied waterbodies. With dissolved oxygen significant positive correlation in shekha jheel only whereas significant negative in rest of the waterbodies (Tables 8-11). Benthic fauna are widespread in their      present investigation Cladocerans were found to be abundant in Nai Basti pond while Dipterans in Chautal pond and Gastropods in Shekha jheel. The abundance of dipterans was represented by Chironomus and Culex. Chironomus can survive in low oxygen condition as well as polluted water body. Therefore, its high number in Chautal pond indicated polluted nature [6]. The availability of maximum number of Gastropods could be correlated to the cumulative effect of alkaline nature of water, high calcium contents and macrophytic vegetation [7]. Trichopterans were found to be the least abundant in all ponds. Kabir et al. [6] reported that these insects are sensitive to pollution. The zoobenthos showed negative but significant correlation with Water temperature and pH in Chautal pond, Shekha jheel and in Lal Trichoptera -

Odonata
Libellula sp.  distribution and can live on all bottom types and thus found even in the soil beneath puddles. The zoobenthos comprised of eleven major groups namely Protozoa, Rotifera, Cladocera, Ostracoda, Coleoptera, Diptera, Ephemeroptera, Hemiptera, Trichoptera, Gastropoda and Odonata (Tables 12-15). Among zoobenthos, Dipterans were found to be abundant followed by Cladocerans and least were Trichopterans. In the present investigation, zoobenthos of Nai Basti pond ranged from a minimum of 59 No/m² to a maximum of 117 No/m²: in Lal Diggi pond, it was ranged from a minimum of 121 No/m² to a maximum of 179 No/m²; in Chautal pond, it was ranged from a minimum of 75 No/m² to a maximum of 128 No/ m²: in Shekha jheel, it ranged from a minimum of 92 No/m² to a maximum of 120 No/m² (Tables 8-11) (Figure 6a-6d). During study period it was observed that Nai Basti pond is the most productive in terms of phyto benthos whereas Lal Diggi pond in terms of zoobenthos. During the Diggi; with CO 2 in Chautal pond and Shekha jheel, whereas in Nai Basti pond zoobenthos showed positive significant correlation with water temperature, pH and CO 2 . However, with dissolved oxygen these animals showed positive significant correlation in all water bodies (Tables 10-13). The result of present investigation revealed that zoobenthos were more dominant than phytobenthos (Table  16). The negative but significant correlation between zoobenthos and phytobenthos in all selected water bodies during study indicated grazing of former on latter proving top down control in these lentic ecosystems [8][9][10].

Conclusion
Present investigation revealed that zoobenthos were more