Limnology and Rotifer Fauna of Khushalsar Lake, Kashmir

Kashmir traditionally known as heaven on earth for its beauty is gifted with water resources comprising rivers, lakes, streams and springs. Lakes provide a multitude of uses and are prime regions of human settlement and habitat. One such water body is Khushalsar Lake located in the downtown area of Srinagar city. It is noticed that Khushalsar at present has fallen victim to extensive encroachment, garbage dumping and the release of untreated sewage. Taking the pathetic condition of this lake and dynamic nature of water bodies in general into consideration this study was taken up to analyse the different physicochemical parameters and the rotifer abundance of this water body since rotifers are considered to be important indicators of trophic conditions of any aquatic habitat. The data collected was analysed using standard tools, statistical software’s SPSS (version 20) and PAST3. Nutrient content of this water body was found to be high and only sixteen species of Rotifera were observed. Statistically different physico-chemical parameters were compared at inlet, middle and outlet of the study lake. Only few parameters showed significant differences. Shannon-Wiener index of rotifer signifies the water body to be moderately diverse as the values lies below 5.00 while as values of Simpson diversity index indicate accelerated eutrophication.


Introduction
Water resource of any region has a particular importance. Among all the water bodies' lakes provide a multitude of uses and are prime regions of human settlement and habitat. Uses include drinking water supply, industrial cooling water supply, generation of power, navigation, commercial and recreational fisheries, boating and other aesthetic uses. In addition to this, lake water is also used for agricultural irrigation, canalization and for waste disposal. In Kashmir, lakes too occupy special importance because they serve as a prime attraction that draws tourists to this place. Not only are this they also of great cultural, ecological and socioeconomic importance to the people of this valley.
One such water body is Khushalsar lake located in the downtown area of Srinagar city. This water body is located towards the north west of the city at a distance of about 8.5 km from city centre, at an elevation of 1589 m.a.s.l having an average depth of 3.5 meters. It is a single basined water body. Once known for its crystal clear waters the lake at present is in a highly deteriorated state. It is under immense anthropogenic pressure with surroundings having dense human habitation and vegetable gardens for commercial marketing. At present the lake occupies approximately 647 kanals (main water body), 949 kanals being under marshy area (Recent updates of Lakes and Waterways development authority, 2018). The inlet of lake receives water from Nigeen basin of Dal lake by a channel or nallah dug under the rule of an Afghan governor (Amir Khan) and known by his name even today (Nallah Amir Khan).
There is no known source of underground springs feeding this lake till date. The main outlet is again a channel which drains its water in Anchar Lake. Earlier a small channel (Mar khol) used to connect this lake to Brarinambal lagoon but it was filled later on and converted to road which is known today by the name of Nallah Mar road,thus further deteriorating its ecological conditions. Though relatively small it still has got its own importance by providing livelihood, acting as source of groundwater recharge, feeding, nesting and breeding site for many bird species. Taking into account the pathetic condition of this lake and the changing nature of water bodies in general into consideration, this study was taken up to analyse the different physicochemical parameters and the rotifer composition and abundance of this water body.

Site 1 st (K1):
This is the site where water from Nigeen (one of the basins of Dal Lake) enters Khushalsar via Gilsar (a small lake where water from Dal Lake accumulates before it enters in Khushalsar). Only few macrophytic associations were found here. On both sides of this site emergent species of macrophytes like Polygonum, Phragmitesand Typha spcould be seen.

Site 2 nd (K2):
This is the open water area of the lake which is mainly used for nadroo (Lotus stems) cultivation by the locals. Floating leaf type macrophytes like Nelumbo nucifera, Nymphoides peltatum and submergents like Potamogeton species could be observed.

Site 3 rd (K3):
Through this site water leaves the lake and the depth of this site is least of all the sites with few plants of Lemna sp. floating on the surface. On one side proper bunding of the lake is not done and on the other side some area is occupied by salix trees and human habitation is also found (Figure 1-4).

Methodology
For the collection of data for present investigation, the water samples were collected from the sampling sites by dipping one litre polyethylene bottle just below the surface of water. Specially recommended glass bottles (Winklers bottles) were used for the estimation of dissolved oxygen. For estimation of dissolved oxygen, samples were fixed at the sampling site in accordance with modified Winkler method. The analysis of water samples was done by adopting standard and internationally accepted methods [1][2][3][4][5] . The methods employed for the determination of different physico-chemical parameters of water are enumerated as follows.

Collection and Preservation of Zooplankton Samples
Zooplankton samples were collected from all sites of the lakes under study, which differ in water depth, vegetation and other characteristics. The samples were collected by sieving 10 litres of the subsurface lake water through nylon cloth conical zooplankton net having 75 meshes/linear cm.

Diversity Indices
In the literature, we come across various diversity indices like Simpson, Shannon-Wiener Index etc. Shannon-Wiener Index is most commonly used index and is given by the following function: The contents collected in the plankton tube attached to lower end of net were transferred to separate polyethylene tubes and after sedimentation a subsample was taken for study. The organisms were preserved in 4% formalin.

Qualitative Analysis
Preserved Zooplankton samples were identified upto specific level by observing them under a Research Microscope (model-Magnus MLX -Bi). Systematic identification was done by taking the help of Edmondson 6 , Penak (1978).

Quantitative Estimation of Zooplankton
For quantitative zooplankton study, a sedge-wick rafter cell of 1ml capacity was used which is 50mm long, 20mm wide and 1mm deep. The samples were transferred to the cell with a large graduated bore pipette or a dropper. The air bubbles were avoided while transferring the sample to the cell. Before counting the zooplankton, it was ensured that all the organisms have settled down. Every sample was counted for the zooplankton at least three times and an average was taken for the samples of each month. The number of each species or genus was calculated by the following formula 9 and then total zooplanktons were accounted on monthly basis:

Results
The data for various physic-chemical parameters and rotifer abundance was collected from December 2012 to September 2014. The readings could not be procured in October and November (2014) due to floods. The data presented in (Table 1)

Rotifer Composition and Abundance
Rotifer composition and population abundance as depicted in Table 6 and 7 shows only sixteen species in 2013 as well as in 2014. Seasonal distribution of different species is also given in the said tables. Genus Brachionus was represented by four speciesit thrived well in this water body. Three species i.e., B. calyciflorus, B. quadridentata and B. bidentata were well represented in all the seasons except winter when the population density dropped. Brachionus angularis had lower population density in all the seasons in both the study periods. Asplanchna priodonta showed highest population density in summer and lowest in spring. It followed almost same trend in the following time period. Genus Keratella was represented by two species Keratella cochlearis and Keratella quadrata. Keratella cochlearis showed low abundance in winter and spring in 2013 and 2014 respectively. It gradually increased its population and reached highest in summer in both the study periods. Lecane luna appeared in both the study periods. It disappeared in winter season of both the years and gradually increased its population density and attained its peak in summer season. Same trend was observed for this species in the following year. Polyarthra vulgaris attained highest population density in summer in both the years. Winter population was however also well represented in the lake. Synchaeta sp. was well represented in cooler period and it disappeared in summer of both the years. Lepadella sp. was well represented in summer and was seen in lower population density in other seasons. It showed similar behavior in the next year. Genus Filinia was represented by two species Filinia longiseta and Filinia terminalis. Filinia longiseta attained highest population density in summer months in both the years but filinia terminalis had very low population density in both years and acquired higher population density in cooler months. Pompholyx sulcata,Cephalodella gibba and Trichocerca longiseta showed low population density in winter period but gradually increased in number and attained peak population density in warmer period i.e.,summer and autumn.
On analyzing the data of year 2013 statistically it was revealed that dominance index showed lowest value in spring (0.0819) as depicted in (Table 8) and uppermost dominance value was observed during winter (0.1551). The Simpson index varied from 0.8449 (winter) to 0.9208 (summer), indicating heavy pollution. The Evenness ranged from 0.7586 (winter) to 0.8774 (summer) indicating summer is slightly diverse than other seasons. The Shannon Wiener (H') diversity index was noticed highest during spring (2.619) and least during winter (2.122). This means the water body was moderately diverse as the value of H' was less than 5.00. In the year 2014 diversity values are presented in (Table 9). It revealed that dominance index showed least value during spring (0.09637) and uppermost dominance index during winter (0.1217). The Simpson index varied from 0.8783 (winter) to 0.9036 (spring), indicates water being highly polluted. The Evennes ranges from 0.7958 (winter) to 0.9175 (summer). The Shannon Wiener (H) diversity index was noticed highest during spring (2.456) and least during winter (2.336). It again depicted moderate diversity of the water body and a variety of species appear during spring season.

Discussion
Aquatic ecosystems are often dynamic. Their quick response to surrounding environment biotically as well as abiotically makes them a subject of interest besides being naturally important in regulating the microclimate of any area. The faunal communities they hold inturn respond to changing conditions speedily.Morphological and behavioral changes are induced in aquatic communities by alterations in temperature. Not only metabolism but swimming, feeding as well reproductive rate gets changed in a significant way. It affects the biotic components of a water body besides
Since the water body is shallow in nature water temperature quickly responded to the change in air temperature. Similar findings were reported by some workers in case of shallow water bodies 7 . Seasonal changes were momentous but the difference among different sites was insignificant. Few workers 8 considered siltation, microscopic organisms and suspended organic matter to affect transparency of water. The water body under study is shallow. It has an average depth of about 3m. Therefore bottom sediments get easily mixed with water column even with the slightest disturbance. Hence overall transparency was low. Statistically differences were significant in 2014 as continuous rains brought much mud and silt from surrounding areas at inlet and outlet of the lake.
High pH value in summer season which may be due to high photosynthetic activity of micro and macro vegetation making the water alkaline, was also marked by a number of workers 9 . The water body under study showed the low annual pH value which may be due to the shallow nature and high organic matter present which is continuously decomposing resulting in high production of Free CO 2 . The middle of the lake is well infested with macrophytes and hence free carbon dioxide (Free CO 2 ) is utilized due to prolonged photoperiod during summer by growing plants and phytoplankton. Therefore the differences between three sites were well marked in both the years. On analyzing the specific conductivity of the water body it was found to be high in 2013 as well as in 2014. Some of the workers 10 attributed the high value of water conductivity mainly with decomposed organic matter.
In spring and winter Dissolved oxygen content goes up in most lakes. Here the values showed slight changes but overall concentration remained low. Low values of dissolved oxygen may be attributed to high organic matter present as in such cases BOD of the water body increases which depletes oxygen content. Low oxygen content due to high organic matter was also observed by few worker 11 . In 2013 statistically significant variations were observed among three sites which may be attributed to flushing of lake from Dal Lake in spring as the dilution with freshwater increases the DO levels. Dissolved oxygen levels go up at inlet and outlet but remain unchanged in the middle site. Inlet and outlet of the lake lie opposite to each other.Whileas in the second year (2014) profound rainfall increased the water level in Dal Lake which subsequently paved the way for entry of excess water into the lake under study (since the two are connected via Gilsar Lake). Dilution with excess water kept the Dissolved oxygen content at all sites almost similar. Since the lake is very shallow and receives higher loads of sewage from the surrounding residential area therefore decomposition of organic matter leads to increase in CO 2 levels too. Shallow lakes often tend to accumulate more materials than deeper lakes therefore concentration of chloride ion was also reported to be high. A number of workers 12 reported similar findings while working on some Kashmir lakes. Moreover in the surroundings there is a dense human habitation.
All the domestic sewage enters into the lake. Pesticides, manures and other fertilizers are often used to increase the yield of the crops which could be another reason for high chloride concentration in this lake. It had highly alkaline water during the whole study period as the alkalinity values were recorded above 200 mg/l in every month therefore it is considered to be strongly alkaline. The ammonical nitrogen recorded was also towards higher scale which may be attributable to the fact that it receives high load of organic matter which decomposes in summer and autumn season. However here as already mentioned, a greater part of this water body is used for growing vegetables on commercial scale which may be the reason for high concentration of this nutrient in this lake where fertilizers are used. Moreover the weed infestation which acts as sink of nutrients is less leading to high concentration of nutrients important for plant growth. Nitrates and total phosphorus were also on higher level and their concentration increased more in winter. This happens when the winters are usually dry.
In this lake a number of drains carrying sewage water from surrounding residential area open directly and release detergent rich waters. Moreover use of fertilizers within and in the water shed of this water bodies can be the main reason for nutrient rich waters.
During a two year study total 16 rotifer taxa were identified. Rotifers are considered as important components of freshwater zooplankton communities. They act as herbivores, predators, or omnivores 13 . They also serve as a major food source for many invertebrates 14  Some of the workers 16 are of the opinion that most species of this genus thrive well in warm waters as was found in the present study. Their population density increased mostly in summer. In genus Keratella, Keratella cochlearis showed peak population in summer but Keratella quadrata was abundantly found in winter season. Many workers 17 also observed its (Keratella quadrata) restricted population growth during the period of food availability in central Himalayan lakes. Family lecanidae was represented by species Lecane luna. The members of this group usually thrive in fresh and saline waters and are found in littoral habitats 18 . Seasonal distribution of Lecane luna showed it to be present during warmer period in all the three water bodies. It was absent in colder months. Moreover this genus is a tropic centered genus. Asplanchna priodonta is known to effectively control populations of algae and rotifers since it is a predatory rotifer species 19 . It was present throughout the study period making it perennial. A number of investigators from Kashmir 19 however also reported it to be perennial rotifer.
Polyarthra vulgaris and Synchaeta sp. were the members that appeared from family Synchaetidae. Synchaeta sp. has been reported to be cold water genus by number of workers.It was also reported it to be present in oligotrophic and mesotrophic waters 20 . In the present study it showed its abundance in colder months and was present only at site K2 in Khushalsar lake. Polyarthra vulgaris attained high population in warmer period and winter population remained low. It was observed to tolerate temperature range from less than 1⁰C to more than 20⁰C 21 . It shows similarity with the present findings. Lepadella ovalis is a cosmopolitan rotifer. It was reported to be abundant in macrophytes 26 which are in line with the present finding where it was present in low numbers in inlet and outlet of Khushalsar. Genus Filinia was represented by two species Filinia longiseta and Filinia terminalis. In the present study Filinia longiseta was present abundantly at littoral sites and avoided open water zone. It was reported to be omnivorous feeding on any kind of food 27 .
Trichocerca is a warm water preffering genus as reported by few workers 28 which is similar to the findings of the present study where it showed peak populations in summer and autumn. This species was reported to be a pelagic form 29 . In the present study Trichocerca longiseta was almost uniformly present at all the sites indicating that it can survive equally in littoral and limnetic areas. Family Notommatidae was represented by only one species i.e., Cephalodella gibba. Some workers reported this genus to have restricted distribution, Jammu and Kashmir being one of the states 15 .

Conclusion
After observing different physico-chemical characteristics and rotifer species composition and abundance it was observed that nutrient content of this lake is high and very few rotifer species are observed. The rotifer diversity being low also suggests contamination of water body which does not allow the different species to flourish. The water body needs to be monitored continuously for its abiotic and biotic features. Moreover people living in surrounding areas need to be sensitized and various awareness programmes should be organised to make them understand the importance of water bodies. Illegal encroachment needs to be checked by concerned authorities and opening of inlet and outlet channels that used to exist in past should be made functional again. Agricultural practices carried in and around the lake should not exceed threshold levels that could lead to further damage of the water body. Construction should be limited in catchment area. Moreover Government and local people should work in collaboration to protect this asset.