Rainwater and throughfall chemistry in a “terra firme” rain forest: Central Amazonia

During the Global Tropospheric Experiment (GTE)‐Amazon Boundary Layer Experiment (ABLE) 2B campaign in the Amazon basin, samples of rainwater and throughfall were obtained in a “terra firme” (nonflooded forest) rain forest at the Ducke Reserve (2°57'S, 59°58'W). The samples were collected during one wet period (April 1 to May 13, 1987) and one dry period (August 1 to October 1, 1987). All samples were analyzed for Na + , K + , Mg 2+ , Ca 2+ , NH 4 + , Cl − and SO 4 2− , and p H. The rainwater was acidic, with a volume‐weighted mean p H of 4.6 for the two periods. Rainwater input from the dry period was 2 times greater for Na + , Mg 2+ , NH 4 + and SO 4 2− and about 4 times greater for K − than from the wet period. The ionic concentrations in throughfall were higher than those in rainwater, except for NH 4 + during the dry period. This enrichment of throughfall is attributed to the interaction of precipitation with the forest canopy.