A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Throughfall exclusion in a moist tropical forest: Impacts on solution nutrient fluxes.Ricardo de O. Figueiredo and Wanderley Rocha da SilvaInstituto de Pesquisa Ambiental da AmazôniaDaniel Markewitz and Elizabeth L. BelkThe University of GeorgiaEric A. Davidson and Daniel NepstadThe Woods Hole Research CenterAlex V. KruscheCentro de Energia Nuclear na Agricultura – USPLuciana Pimentel da SilvaUniversidade Federal do Pará – Bolsista ITI, CNPq/LBAAddress of corresponding author:Instituto de Pesquisa Ambiental da AmazôniaAv. Nazaré, 669 - Belém - PA - 66035-170 - BrazilEmail: rofig@amazon.com.brIn recent years, the world’s major moist tropical forest have experienced increasinglysevere and prolonged droughts associated with the El Nino Southern Oscillation (ENSO).If this current trend is sustained due to changing climatic conditions the effects ontropical forest could be dramatic. To investigate the effect of prolonged drought ontropical forest nutrient fluxes in solution we established a throughfall exclusionexperiment in the Tapajos National Forest. The experiment consists of paired onehectareplots that are trenched to >1.5m depth and a network of plastic panels excluding~50% of throughfall in the treatment plot. After nine months of pre-treatmentmeasurements the throughfall exclusion panels were installed in February 2000. Panelsare removed in the dry season (June-Nov.) and re-installed in the rainy season (Dec.-May) every year. Here we report solution chemical results from bulk precipitation,throughfall, litter leachate, and 25 and 200 cm soil solutions for the period May 1999 toJuly 2001. During the pretreatment period few significant differences were apparent insolution chemical concentrations. During the following two wet seasons of throughfallexclusion no changes in throughfall chemistry were observed, but increases in litterleachate and soil solution concentrations in the exclusion plot were apparent, particularlyfor NO 3 , K, and Ca. Because this effect was not observed for all elements, we do notthink it is due only to the concentration of nutrients in a smaller volume of soil water, butrather is also due to effects of drought on nutrient cycling processes. We are currentlydeveloping a soil hydrologic model to calculate the rate of movement of these nutrientsthrough the soil profile.