Assessment of Water Pollution and its Impact on Fisheries Resources of Posna Beel, Kalihati, Tangail

Abstract

Posna Beel is an important perennial waterbody in Kalihati Upazila of Tangail District. The heel area is 121.5 ha in monsoon and 9 .0 ha in dry period. The heel is the main source of fish for Pouzan, Balla, Rampur and Elenga Bazars. A research work for two years was carried out on the water quality, Agro-chemical use, and pesticide residue and beel sediment of Posna heel. From water quality monitoring, it was found that the heel water was very suitable for open water fisheries. The levels of concentration of some water pollutants such as ammonia (0.012-0.076 mg/I) and nitrate (0.15-0.48 mg/1) were very low while the bio­chemical parameters such as BOD5 (2.70-5.43 mg/I) and COD (5.20-8.15 mg/l) were slightly high. Nitrite was found zero round the year. The values of DO vary from 6.66 mg/I to 9.66 mg/1, which was suitable for fishes and other biota. According to the field survey, the farmers in the beet area was found to using 113.14 kg urea per acre against the government recommendation level of 87.0 kg per acre. On the other hand, application of TSP, MP and Gypsum were lower than the government recommendation level. Both the bee! water and sediment were free from Organophosphorus and Carbamate pesticides. However, a very trace amount of Organochlorine (DDT, heptachlor and dieldrin) pesticide was found in the beel sediment and water sample, which was negligible in the context of pollution. From the survey on agro­chemical use, it was found that farmers around the Posna beet were not using organochlorine pesticides in HYV Boro field. The presence of a trace amount of Organochlorine pesticides in water and sediment samples may be for the past use of these pesticides for mosquito eradication in this area.