PERTANIKA JOURNAL OF TROPICAL AGRICULTURAL SCIENCE

Photosynthetic rates and nutrient content measurements of subsurface water samples at four predetermined stations of Sungai Ibai in Trengganu indicated that the wet monsoon period lowers the values of the former while increasing the ammonium nitrogen, nitrate nitrogen and dissolved oxygen contents. A seasonal variation in net photosynthetic values is observed, being high during the dry season and low during the wet monsoon season. However the ammonium nitrogen content exceeds that o f either nitrate nitrogen or reactive phosphorus the whole year through. In relation, the nitrite nitrogen content is insignificant. The occurrence o f high nitrate nitrogen contents could be attributed to increased nitrification processes while that o f ammonium nitrogen to bacterial mineralization or decomposition.