ABSTRACT
The physical and chemical properties of water are of great importance for the survival of aquatic organisms. Aquatic insect abundance depends on these physicochemical parameters of water. A faunistic survey of the aquatic insects from three ponds of Chittagong University Campus was made for a period of twelve months whereby a total at 2490 aquatic insects belonging to six insect orders were collected. Physicochemical parameters of water of the three experimental ponds were measured in terms of water depth, Secchi depth, air temperature, water temperature, conductivity, Dissolved Oxygen (DO), Biological Oxygen Demand (BOD), free Carbondioxide (fCO2) and Calcium (Ca++) for the same period. The abundance of the aquatic insects was influenced by the physical condition of the ponds as well as the physicochemical parameters of the water. In most cases the relationship between the total abundance of aquatic insect orders and the physicochemical properties of water of the three experimental ponds were positively correlated with Secchi depth, air and water temperature, pH, DO and Calcium but negatively correlated with water depth, conductivity, BOD and fCO2.

Key words: Aquatic insect, abundance, physicochemical parameters, pond, correlation

Introduction

The presence of aquatic insects in the environment is correlated with diverse factors (Wetzel 1982). Temperature is a factor which is essential for growth of organisms. Depth of water body has also some influence in the community structure of wetland ecosystem. Turbidity is directly related with light and insects can live in optimum limit of turbidity. Conductivity is the presence of molecular electrolytes (acids, bases, and salts in solution) in water. DO indicate the concentration of oxygen content of natural waters. The pH is a measurement of the level of acid or alkali in a solution. Biochemical Oxygen Demand (BOD) refers to the amount of oxygen that would be consumed if all the organics in one liter of water were oxidized by bacteria and protozoa. Calcium is also an important limiting factor for abundance and growth of aquatic animals depending on the source and treatment of the water. Signs of water quality deterioration are evident in the result of the physicochemical analyses. In low conductivity water aquatic organisms dominate, as most organisms in low conductivity water bodies maintain high internal ion concentration relative to its surrounding medium. And also certain physiological effects on animals are affected by the number of available ions indicated by amount of TDS. DO concentration is also important, as beside the respiratory process of the organisms, the solubility and availability of nutrients also depend on DO concentration of an aquatic body, hence having direct effect on aquatic lives. Decrease of DO level of a water body below 5mg/l put aquatic life under stress. As BOD is an indication of pollution index, hence the higher the BOD values the greater will be its unsuitability for aquatic lives. Similarly, the lesser the free CO2 value of water the better will be the water quality for sustaining aquatic lives. pH influences many biological and chemical processes in organisms, hence lower pH puts aquatic lives under stress. A good number of scientific works are available on aquatic insects in different parts of the world. Hsu and Yang (1997, 2005), Wolf et al. (1999) and Traichaiyaporn (2000) studied on the relationship of macro- invertebrates especially aquatic insects with water quality. Chiangthong (2005) studied on water quality analysis in Chiang Rai province of Thailand and determined the insects as bioindicator of the water qualities. Thani and Phalaraksh (2008) studied on aquatic insect’s diversity and water quality of Mekong river of Thailand. Purkayastha and Gupta (2012) studied on insect diversity and water quality parameters of