Seasonal and within-event dynamics of rainfall and throughfall chemistry in an open tropical rainforest in Rondônia, Brazil

Abstract

Prolonged dry periods, and increasingly the generation of smoke and dust in partiallydeforested regions, can influence the chemistry of rainfall and throughfall in moist tropical forests. We investigated rainfall and throughfall chemistry in a palm-rich open tropical rainforest in the southwestern Brazilian Amazon state of Rondônia, where precipitation averages 2300 mm year -1 with a marked seasonal pattern, and where the fragmentation of remaining forest is severe. Covering the transition from dry to wet season (TDWS) and the wet season (WS) of 2004-2005, we sampled 42 rainfall events on event basis as well as 35 events on a within-event basis, and measured concentrations of DOC, Na + , K + , Ca 2+ , Mg 2+ , NH 4 + , Cl -, SO 4 2-, NO 3 -and pH in rainfall and throughfall. We found strong evidence of both seasonal and within-event solute rainfall concentration dynamics. Seasonal volume-weighted mean (VWM S ) concentrations in rainfall of DOC, K + , Ca 2+ , Mg 2+ , NH 4 + , SO 4 2-and NO 3 -were significantly higher in the TDWS than the WS, while VWM S concentrations in throughfall were significantly higher for all solutes except DOC. Patterns were generally similar within rain events, with solute concentrations declining sharply during the first few millimeters of rainfall. Rainfall and throughfall chemistry dynamics appeared to be strongly influenced by forest and pasture burning and a regional atmosphere rich in aerosols at the end of the dry season. These seasonal and within-event patterns of rainfall and throughfall chemistry were stronger than those recorded in central Amazônia, where the dry season is less pronounced and where regional deforestation is less severe. Fragmentation and fire in Rondônia now appear to be altering the patterns in which solutes are delivered to remaining moist tropical forests.

Disproportionate single-species contribution to canopy-soil nutrient flux in an Amazonian rainforest

“…While the geographic stetting influences the concentration of nutrient inputs by rainfall, tree characteristics and meteorological settings influence the potential for nutrient concentration increase of throughfall and stemflow. Both, input and output concentrations are highly influenced by seasonal effects (Germer et al, 2007).…”

“…The collectors were cleaned of organic deposits after each event. The samplers collected wet deposition plus the gravimetrically settling coarse particulate deposition, which is low in Rondônia during the mid rainy season (Germer et al, 2007). We knew from previous observations that babassu palms are effective at funneling rainfall towards their stems.…”

Groundwater quality comparison between rural farms and riparian wells in the western Amazon, Brazil

“…Climate in the region is characterized by a mean annual temperature of 25.6 ºC and a mean annual precipitation of approximately 2,000 mm, based on measurements from 2000 to 2008 at Ji-Paraná city, 18 most of which falls as rain between November and April; this value is close to reported in other studies in Rondônia. 19,20 Ballester et al provides a detailed description of the Urupá basin. According to these authors, the total area is 4,209 km 2 , with 49.9% occupied by forest and 42.6% with pasture.…”

Métodos e técnicas de pesquisa em bacias hidrográficas

“…A conversão de fl orestas em diferentes sistemas de cultivo ou áreas urbanizadas tem afetado a dinâmica desse nutriente, ocasionando, na maioria dos casos, um aumento do seu fl uxo para os rios e riachos (GERMER et al, 2007;JICKELLS et al, 2013;SALEMI et al, 2015).…”

“…No Brasil, a maioria dos estudos envolvendo a ciclagem de nutrientes em microbacias tem sido realizada na Amazônia (GERMER et al, 2007;CHAVES et al, 2009;NEILL et al, 2001NEILL et al, , 2011DEEGAN et al, 2011); Cerrado (PARRON; BUSTAMANTE; MARKEWITZ, 2011) e na Mata Atlântica no sudeste brasileiro (ANDRADE et al, 2011;SALEMI et al, 2013SALEMI et al, , 2015. Mas, sobre as microbacias na Mata Atlântica no nordeste do país, pouco se sabe a respeito da infl uência dos diferentes usos do solo na ciclagem de nutrientes.…”