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
