Characterization of organic matter in rainfall, throughfall, stemflow, and streamwater from three subtropical forest ecosystems

Little is known about the characteristics of dissolved organic matter derived from precipitation, throughfall, stemflow, and streamwater in subtropical forest ecosystems. Water samples were, thus, collected from rainfall, throughfall and stemflow of a China-fir plantation, a secondary hardwood and a natural hardwood, and streams in forest ecosystems in the central part of subtropical Taiwan on March 31 and May 8, 1999. We examined pH, electrical conductivity, dissolved organic carbon, and acid-neutralizing capacity (ANC) in the samples. Furthermore, the humic polymers (MW>1000) and fulvic acids (FAs; MW>1000) were isolated from the water samples and characterized by elemental analyses and Fourier transform infrared (FTIR) spectroscopy. Results showed that the contents of carboxylic acid of both humic polymers (MW>1000) and FAs (MW>1000) contributed to the water sample ANC, ranging from 8.7 to 61.2% and 0.2 to 38.1%, respectively. FTIR and elemental analyses of isolated humic polymers (MW>1000) and FAs (MW>1000) from throughfall and stemflow had characteristics previously reported for humic substances. The study showed that throughfall and stemflow, not affected by soils, may be additional sources of humic substances.