THE NUTRIENT BUDGETS OF A WATERSHED AND ITS FOREST ECOSYSTEM IN THE TAI NATIONAL-PARK IN COTE-DIVOIRE

Atmospheric inputs and stream water outputs of P, K, Ca and Mg were es timated for an undisturbed forested watershed and the forest ecosystem within it in Tdi National Park, Cote d'Ivoire in 1990/91. The study i ncluded measurements of wet and dry deposition, and suspended sediment s, organic debris and solutes in the water flows. Base flow as well as quick flow were sampled. The nutrient budgets of the entire watershed and the forest ecosystem (comprising vegetation and rooted soil layer s) were distinguished on the basis of two assumptions (i) solutes in t he base flow are derived from the soil layers below the rooted zone on ly, and hence not from the forest ecosystem; (ii) the total soil mass in the rooted zone remains constant, i.e. the export of topsoil materi al by erosion is compensated for by deepening the root zone. The first assumption was supported by the resemblance of the molar ratios of so lutes in the base flow and those calculated for the weathering of the migmatite found in the soil layers below the rooted zone. It is conclu ded that the stocks of P, K, Ca and Mg in the watershed are decreasing with 1.4, 12.7, 15.3, and 8.1 kg ha(-1) yr(-1) respectively. Losses a re mainly a result of nutrient exports by erosion and solutes in the b ase flow. Nutrient stocks for the forest ecosystem are also apparently decreasing, but to a much lesser extent, indicating the importance of distinguishing between the watershed and the forest ecosystem within.