Water Quality for Agriculture and Aquaculture in Malwathuoya Cascade-1 in Sri Lanka

Abstract

Abstract Malwathu Oya cascade-I is a prominent cascade system in Malwathu Oya river basin which is not evaluated yet, in terms of water quality and quantity. This study was conducted to find the spatial and temporal variation of salinity and some selected nutrients, related to irrigation water quality, and also to ascertain similar variations of some selected physical and chemical water parameters, related to the inland fish production, within the cascade system. Compared to the wet period, significantly higher dissolved oxygen, water temperature, turbidity, EC and alkalinity levels were recorded in dry period. During the study period lower order tanks showed slight to moderate restriction level throughout the year. Middle order tanks also recorded slight to moderate restriction level during the dry period. The water temperature levels during the dry period recorded quite higher than the optimum range and although no deaths of fishes were observed the temperature stress could affect the growth and development of fishes. Turbidity, pH and alkalinity level of the tanks in the cascade did not exceed the critical levels for irrigation or inland fisheries during the period. Total nitrate nitrogen and ammoniacal nitrogen level of the tanks in the cascade were within the ususal range. Both spatial and temporal variation of water quality parameters can be seen in the cascade during the study period. However water quality is still good for irrigation even in dry period in upper and middle parts of the cascade