Input and output of nutrients in a diked flooded savanna.
There is a lack of information concerning input and output of nutrients in savanna ecosystems (llanos). The south-western Venezuelan llanos are seasonally flooded; therefore an extensive network of dykes has been built to alleviate flooding and retain water throughout the dry period. Net losses of calcium and magnesium in Mantecal's dyked savanna were in general lower than the values found in other ecosystems. Net losses of potassium in dyked flooded savannas were greater than those of forested ecosystems indicating that, although the dyking did not induce a marked change in nutrient budgets, it nevertheless affected the magnitude of output for this element. Inputs in precipitation water should play an important role in the calcium and potassium economy of those environments, although the fluxes of these were below the internal recycling rate for above-ground vegetation. Phosphorus and trace element (Zn and Cu) outputs were low; consequently positive budgets were reported for those elements. Major losses of P, Zn and Cu occurred as particulate materials. After the construction of the dykes, the biomass of vegetation doubled and its species composition changed. This biomass accretion might be responsible for an increase in nutrient uptake and immobilization. The losses in potassium can thus be regulated through appropriate management of the floodgate to synchronize nutrient release with plant incorporation.