Insect Diversity and Water Quality Parameters of Two Ponds of Chatla Wetland , Barak Valley ,

An investigation was carried out on two ponds of Chatla floodplain, Barak valley, Assam with special reference to aquatic insects. Pond 1 is purely a fish pond where as pond 2 is a community pond too. Present study revealed the status of water quality and in turn diversity, density, dominance and abundance of aquatic insects in both the ponds. Almost all the physico chemical parameters of both the ponds were found within permissible range for aquatic life .However in pond 2 level of phosphate was found little higher than pond 1 due to release of soaps and detergents by human influence. In both the ponds order Hemiptera showed maximum relative abundance ( 98% in pond 1 and 94% in pond 2). The study revealed lower diversity of aquatic insects in pond 2 than that in pond 1.


INTRODUCTION
Among different ecosystems, wetlands constitute one of the most important ecosystems for man offering numerous regulating services.Water quality assessment of small water bodies of the wetlands are of immense importance in the management of fisheries, water supply, and irrigation.Pollution status of water bodies are usually expressed as biological and physico-chemical parameters 1 .Several authors have extensively documented the responses of macro-invertebrates to organic and inorganic pollution 2,3 .Chatla floodplain (24 0 42 / 697 // N and 92 0 46 / 264 // E) situated in the south of Silchar town, Barak Valley, Assam has 1500 fishery ponds and 12 seasonal lakes.(Fig. 1).Although the wetland is resourceful with variety of macrophytes, trees and fishes it is in a derelict or near derelict state due to high rates of siltation, infestation of weeds, unscientific fishing activities, and use of pesticides in the surrounding tea gardens and agricultural fields 4 which led to a loss of 73% wetland area of Chatla floodplain 5 .All these factors can affect the communities of aquatic organisms leading to loss of diversity and species extinction 6 .Since, fluctuations in aquatic insect community can give quick information of their surrounding water quality and are commonly used as tools for marking an integrated assessment of water quality, investigation on water quality of two fishery ponds of Chatla wetland with special reference to aquatic insects was carried out.

MATERIALS AND METHODS
The topography of the Chatla floodplain is fenland type with small hillocks strewn among large stretches of lowland.Pond 1 is a fish pond and is relatively undisturbed.Pond 2 is a fishery cum community pond.Water and insect samples were collected in replicates from both the sites during 2009-2010.Physico-chemical parameters such as Air temperature (AT), Water temperature (WT), Transparency, pH, Electrical Conductivity (EC), Dissolved oxygen (DO), Free CO ) content of water were analyzed by standard methods 7,10 .The aquatic insects were collected by kick method whereby the vegetation was disturbed and the circular net (mesh size 60µm) was dragged around the vegetation for one minute [11][12] .They were immediately sorted, preserved in 70% ethyl alcohol and were later identified using Dewinter advanced stereo zoom microscope with the help of standard keys [13][14][15][16][17][18][19] 1. Table 2 showed the distribution of aquatic insects in pond 1 and 2. The significant correlations that exist among environmental variables, diversity and density of insect are shown in Table 3. Fig. 2 showed the relative abundance of aquatic insect orders recorded from pond 1 and pond 2 during the study period.Relative abundance of aquatic insect families and aquatic insect species in pond 1 and 2 are shown in the Fig. 3 and Fig. 4 respectively.Pattern of variation in the levels of Shannon -Weiner Diversity index (H') and Evenness index (J') and Berger-Parker index of Dominance (d) are shown in the Fig. 5.The study revealed that in pond 1 and 2 both air and water temperature did not show much variation.In pond 1 DO, EC, NH 4 and NO 3 -concentration were slightly higher than that of pond 2 while other parameters such as Transparency, Free CO 2 , TA, pH, and PO 4 3concentration were recorded to be higher in pond 2. The solubility and availability of nutrients is affected by oxygen content of water and therefore the productivity of aquatic ecosystems 18 .The range of DO recorded in the present study is similar to the DO concentration reported in a previous study in the same area 21 .In pond 1 correlation coefficient analyses revealed a significant negative relationship of WT with pH and DO.Classical negative relationship of WT with DO was also recorded in a previous study on Chatla floodplain 22 which is attributed to the fact that in lower temperature oxygen carrying capacity of water increases 23 .Negative relationship of DO with Rainfall might be an indication that surface runoff transported sewage, fertilizer etc. into the pond which have lowered DO value by bacterial respiration 22 .EC was found to be higher in pond 1 (4.59ms/ppt ± 2.93) compared to pond 2 ( 3.24ms/ ppt ± 0.20) where it showed significant positive correlation with TA and NO 3 -.The range of NO 3 -.
concentration was found within the said range indicating their suitability for fish production.In pond 2 EC showed significant positive correlation with TA, Free CO 2, and DO.Higher free CO 2 accompanied by higher TA and higher pH in pond 2 could be due to external application of lime.It is known that addition of lime increases fish production in soft (low total hardness) waters by stabilizing the pH of bottom mud and increasing the availability of Phosphorus and Carbon dioxide for photosynthesis.The overall effect of liming is to increase phytoplankton production which results in increased fish production 26 .Another reason might be that in heavily stocked fish ponds, Carbon dioxide (CO 2 ) concentration can become high as a result of respiration.High CO 2 concentrations are almost always accompanied by low DO concentrations (high respiration).Acidity of rain water has impact on the pH of natural water bodies.
As rain falls to the earth, each droplet becomes saturated with CO 2 and pH is lowered 27 .This explained the negative relationship of Rainfall with pH in pond 1. However in pond 2 no such relationship could be found due to application of lime.In pond 1 DO has shown significant positive correlation with pH , such type of positive correlation in between DO and pH have been recorded from the study of Asa lake llorin , Nigeria 28 where DO distribution followed a similar annual cycle with the pH.In pond 2 DO has shown a positive significant correlation with TA.These alkalinity relationships are extremely important in water chemistry, since the most prominent water problems are deposits and corrosion, and these are closely related to the instability of each specific water caused by the tendency of CaCO 3 to dissolve in or precipitate from it 29 .Range of PO 4 3-( 0.86 ± 0.27 in pond 1 and 1.25 ± 0.72 in pond 2) recorded in the present study is supported by the previous study in a marsh of the same floodplain 30 .Relatively high concentration of PO 4 3-in pond 2 might be due to its use as community pond where PO 4 3-is contributed by household activities such as washing, bathing etc.In pond 1 PO 4 3-has shown significant positive correlation with NO 3 -.Actually large concentration of PO 4 3-and NO 3 -reported together from a water body indicate that water is eutrophic in nature 31 but as the water of this pond showed low concentration o f b o t h , i t i n d i c a t e s t h e w a t e r i s n o t eutrophicated.Rainfall showed significant negative relationship with NO 3 -and positive correlation with NO 2 -in pond 2. A previous study conducted in the same study area also reported relatively high concentration of NO 3 during dry months 32 .A positive correlation between NO 2 -and NH 4 + is supported by the fact that the most possible way of Nitrate entry in an aquatic system is through oxidation of Ammonia form of Nitrogen to NO 2 -and to NO 3 -consequently 31 .
Aquatic insect community of pond 1 was represented by two orders-Hemiptera, Odonata; four families-Gerridae, Notonectidae, Mesoveliidae (Hemiptera), Coenagrionidae (Odonata) and seven species.Pond 2 was represented by three orders Hemiptera, Odonata, Diptera; five families-Notonectidae, Gerridae, Mesoveliidae (Hemiptera), Coenagrionidae (Odonata); Culicidae (Diptera) and seven species (Table 2).In both the ponds order Hemiptera was the most prominent order, having 98% relative abundance in pond 1 and 94% in pond 2. The most abundant family in Pond 1 is Notonectidae (64%), followed by Gerridae (32%), Mesoveliidae (2%), and Coenagrionidae (2%).In Pond 2 the relative abundance of Gerridae was highest (76%) followed by Notonectidae (16%), Coenagrionidae (5%), Mesoveliidae (2%) and Culicidae (1%) (Fig. 2 and 3).The aquatic insect species found common in both the ponds were Gerris lepcha Distant, Limnogonus nitidus Mayr, Enithares fusca Brooks, Mesovelia vittigera Horvath, Enallagma sp. and Anisops barbata Brooks.In addition to these species Neogerris parvula Stål was recorded in pond 1 and Culex sp. in pond 2 (Fig. 4).Values of Shannon -Weiner Diversity index (H') and Evenness index (J') were found higher in pond 1 than that of Pond 2 while Berger-Parker index of Dominance (d) value was found higher in pond 2 (Fig. 5).However the H' values were found to be less than 1 in both the ponds indicating polluted nature of water 35 .In pond 1 insect density has shown negative correlations with PO 4 3-and NO 2 -.This might be due to the reason that increased pollution level with high concentration of PO 4 3and NO 2 -.might have disturbed the colonization as many species of aquatic insects are very susceptible to pollution or alteration of their habitat 33 .In pond 2 density of aquatic insects showed positive correlation with Free CO 2 which might be due to increased respiration by more number of insects.Rainfall 34 has shown no significant relationship with diversity or density of aquatic insects in both the ponds.The diversity of aquatic insects showed positive correlation with Transparency.Such kind of positive correlation was reported from lake Victoria 37 .From the study, it can be said that different physico chemical parameters of water quality are inter related and these factors influence diversity, density and distribution of aquatic insects in a particular water body.

Fig. 5 :Fig. 4 :
Fig. 5: Pattern of variation in the levels of Shannon diversity index, Evenness index and Berger-Parker dominance of different insect species in both the Ponds

Table 3 : Significant Correlations among environmental variables, diversity and density of aquatic insects for pond 1 and pond 2
* Correlation is significant at the 0.05 level(2-tailed).** Correlation is significant at the 0.01 level (2-tailed).