Distribution of nutrients in the Periyar river estuary

Abstract

Levels of phosphate, nitrate, nitrite and ammonia from 9 stations in the Cochin backwaters in an area extending from barmouth to 21 km upstream, up to an industrial belt at Eloor (Alwaye) were estimated. Inorganic phosphate showed an increasing trend towards upstream from sts 1-8 and decreased at st 9 in all months. Nitrate indicated irregular pattern of spatial and temporal variations. Interface water exhibited maximum fluctuations. Partial distribution of nitrite in the surface and bottom waters revealed a gradual reduction in the nitrite content from st 5 to st 9. High values were recorded only for interface water in most of the months at sts 5 and 6. Nitrite content at the effluent discharge point (st 8) varied from 0.8-2.67 mu mo1.1 super(-1). Levels of ammonia increased towards upstream with low values at sts 1-4 and 9 and high values for surface water (844 mu mo1.1 super(-1)) at the effluent discharge point (st 8). Temporal variations were highly irregular. Interface water showed higher values compared to the surface and bottom water. Irregular pattern of distribution of ammonia was recorded at all stations. Early monsoon season showed uniform conditions in this section. Subsequently a build up of nutrients in the mid-reaches was suggested. The fluctuations noticed in the nutrient levels may be the after effect of intermittent discharges of effluents and variations in river flow.