THE DISTRIBUTIONS OF COLLOIDAL AND DISSOLVED ORGANIC-CARBON, MAJOR ELEMENTS, AND TRACE-ELEMENTS IN SMALL TROPICAL CATCHMENTS

In tropical surface waters, ultrafiltration, differential pulse anodic stripping voltametry, and atomic absorption spectrometry were used to determine the distribution and association of major and trace element s with different size fractions of dissolved organic carbon (DOG < 0.4 5 mu m). DOC is mainly concentrated in the low molecular size ranges ( < 20 kD). However, in podzolization areas, an important part of the DO C is found in the higher molecular weight fractions (20 kD < DOC < 100 kD). The higher molecular weight fractions have a higher site density . Complexation capacities are in the range of 1-11 mu m in bulk soluti on. In podzolization areas the higher molecular weight fractions contr ol the speciation of Ca, Mg, and Fe. In the other tropical environment s major elements are present as free ions and the low molecular weight fraction of DOC controls the speciation of trace metals (Cu).