EFFECT OF NITROGEN AND PHOSPHOROUS ENRICHMENT ON THE NET CHANGES OF NUTRIENTS AND PHYTOPLANKTONIC PRODUCTION AT SEVILLA RIVER MOUTH, CIÉNAGA GRANDE DE SANTA MARTA

Abstract

At the Ciénaga Grande de Santa Marta (CGSM) in the Colombian Caribbean, high primary production (PP) values compared to other aquatic ecosystems worldwide have been registered. As N appears to be the limiting element for PP, owing to its relatively low concentration with respect to P, nutrient addition experiments were carried out to evaluate the response of the pelagic community in terms of its use or release and of primary production in the mouth of Sevilla river, a representative area of high biological activity observed in this tropical coastal lagoon. The net changes of concentration of various ions and the evolution of dissolved oxygen were determined after 4 hrs. In general, there was a slight net release of N and P in controls without nutrient additions and a trend for consumption in the experiments with additions. Net primary production increased significantly only when ammonium or nitrate plus phosphorous were added at low concentration. These results show that additional subsidies of N and P may be quickly used by the planktonic community, although this was not accompanied by immediate increases in primary production, the latter of which could even decrease at high concentrations of nutrients, possibly by the effect of inhibition and/or competition between physiological processes.