Daimio C. Brito

The reactivity of plant‐derived organic matter and the potential importance of priming effects along the lower Amazon River

Here we present direct measurements of the biological breakdown of 13C-labeled substrates to CO2 at seven locations along the lower Amazon River, from Obidos to the mouth. Dark incubation experiments were performed at high and low water periods using vanillin, a lignin phenol derived from vascular plants, and at the high water period using four different 13C-labeled plant litter leachates. Leachates derived from oak wood were degraded most slowly with vanillin monomers, macrophyte leaves, macrophyte stems, and whole grass leachates being converted to CO2 1.2, 1.3, 1.7, and 2.3 times faster, respectively, at the upstream boundary, Obidos. Relative to Obidos, the sum degradation rate of all four leachates was 3.3 and 2.6 times faster in the algae-rich Tapajos and Xingu Rivers, respectively. Likewise, the leachates were broken down 3.2 times more quickly at Obidos when algal biomass from the Tapajos River was simultaneously added. Leachate reactivity similarly increased from Obidos to the mouth with leachates breaking down 1.7 times more quickly at Almeirim (midway to the mouth) and 2.8 times more quickly across the river mouth. There was no discernible correlation between in situ nutrient levels and remineralization rates, suggesting that priming effects were an important factor controlling reactivity along the continuum. Further, continuous measurements of CO2, O2, and conductivity along the confluence of the Tapajos and Amazon Rivers and the Xingu and Jaraucu Rivers revealed in situ evidence for enhanced O2 drawdown and CO2 production along the mixing zone of these confluences.

Carbon Dioxide Emissions along the Lower Amazon River

A large fraction of the organic carbon derived from land that is transported through inland waters is decomposed along river systems and emitted to the atmosphere as carbon dioxide (CO2). The Amazon River outgasses nearly as much CO2 as the rainforest sequesters on an annual basis, representing ~25% of global CO2 emissions from inland waters. However, current estimates of CO2 outgassing from the Amazon basin are based on a conservative upscaling of measurements made in the central Amazon, meaning both basin and global scale budgets are likely underestimated. The lower Amazon River, from Obidos to the river mouth, represents ~13% of the total drainage basin area, and is not included in current basin-scale estimates. Here, we assessed the concentration and evasion rate of CO2 along the lower Amazon River corridor and its major tributaries, the Tapajos and Xingu Rivers. Evasive CO2 fluxes were directly measured using floating chambers and gas transfer coefficients (k600) were calculated for different hydrological seasons. Temporal variations in pCO2 and CO2 emissions were similar to previous observations throughout the Amazon (e.g. peak concentrations at high water) and CO2 outgassing was lower in the clearwater tributaries compared to the mainstem. However, k600 values were higher than previously reported upstream likely due to the generally windier conditions, turbulence caused by tidal forces, and an amplification of these factors in the wider channels with a longer fetch. We estimate that the lower Amazon River mainstem emits 0.2 Pg C yr-1 within our study boundaries, or as much as 0.48 Pg C yr-1 if the entire spatial extent to the geographical mouth is considered. Including these values with updated basin scale estimates and estimates of CO2 outgassing from small streams we estimate that the Amazon running waters outgasses as much as 1.39 Pg C yr-1, increasing the global emissions from inland waters by 43% for a total of 2.9 Pg C yr-1. These results highlight a large missing gap in basin-scale carbon budgets along the complete continuum of the Amazon River, and likely most other large river systems, that could drastically alter global scale carbon budgets.

Evento extremo de chuva-vazão na bacia hidrográfica do rio Araguari, Amapá, Brasil

O objetivo da investigacao foi analisar vazoes extremas ocorridas entre 9 e 14 de abril de 2011 na bacia do Rio Araguari-AP. A metodologia consistiu de tres etapas principais: 1) re-analise da precipitacao estimada pelo Modelo BRAMS (Brazilian in Development Regional Atmospheric Model System),utilizando como suporte a sinotica do mesmo periodo; 2) analise de vazao nas secoes de monitoramento hidrologico em Porto Platon, Capivara e Serra do Navio (ADCP-Accustic Doppler Profiller Current); 3) analise estatistica da serie historica de vazoes maximas em Porto Platon utilizando distribuicao de Gumbel. Observou-se que o modelo BRAMS capturou parcialmente o padrao do sistema de precipitacao quando comparado com a analise sinotica e com os dados da literatura, mas demandando ainda otimizacao na representacao de respostas hidrologicas extremas. Em Porto Platon foi registrada uma vazao recorde de 4036 m3/s, cujo comportamento foi analisado sob a otica dos mecanismos disponiveis de monitoramento no Estado. Concluiu-se que tais eventos extremos sao pouco detectaveis e oferecem riscos consideraveis aos usuarios da bacia. A previsao de vazao, baseada na serie hidrologica disponivel, era de 100 anos de retorno, mas as analises revelaram que este periodo seria de 360 anos, indicando significativa fragilidade do sistema de previsao de eventos extremos no Estado.

Evaluation of Primary Production in the Lower Amazon River Based on a Dissolved Oxygen Stable Isotopic Mass Balance

The Amazon River outgasses nearly an equivalent amount of CO2 as the rainforest sequesters on an annual basis due to microbial decomposition of terrigenous and aquatic organic matter. Most research performed in the Amazon has been focused on unraveling the mechanisms driving CO2 production since the recognition of a persistent state of CO2 supersaturation. However, although the river system is clearly net heterotrophic, the interplay between primary production and respiration is an essential aspect to understanding the overall metabolism of the ecosystem and potential transfer of energy up trophic levels. For example, an efficient ecosystem is capable of both decomposing high amounts of organic matter at lower trophic levels, driving CO2 emissions, and accumulating energy/biomass in higher trophic levels, stimulating fisheries production. Early studies found minimal evidence for primary production in the Amazon River mainstem and it has since been assumed that photosynthesis is strongly limited by low light penetration attributed to the high sediment load. Here, we test this assumption by measuring the stable isotopic composition of O2 (δ18O-O2) and O2 saturation levels in the lower Amazon River from Obidos to the river mouth and its major tributaries, the Xingu and Tapajos rivers, during high and low water periods. An oxygen mass balance model was developed to estimate the input of photosynthetic oxygen in the discrete reach from Obidos to Almeirim, midway to the river mouth. Based on the oxygen mass balance we estimate that primary production occurred at a rate of 0.39 ± 0.24 g O m3 d-1 at high water and 1.02 ± 0.55 g O m3 d-1 at low water. This translates to 41 ± 24% of the rate of O2 drawdown via respiration during high water and 67 ± 33% during low water. These primary production rates are 2-7 times higher than past estimates for the Amazon River mainstem. It is possible that at high water much of this productivity signal is the result of legacy advection from floodplains, whereas limited floodplain connectivity during low water implies that most of this signal is the result of in situ primary production in the Amazon River mainstem.

Challenges and Solutions for Hydrodynamic and Water Quality in Rivers in the Amazon Basin

Alan Cavalcanti da Cunha1, Daimio Chaves Brito1, Antonio C. Brasil Junior2, Luis Aramis dos Reis Pinheiro2, Helenilza Ferreira Albuquerque Cunha1, Eldo Santos1 and Alex V. Krusche3 1Federal University of Amapa Environmental Science Department and Graduated Program in Ecological Sciences of Tropical Biodiversity 2Universidade de Brasilia. Laboratory of Energy and Environment 3Environmental Analysis and Geoprocessing Laboratory CENA Brazil

Physicochemical Characterization of Water Quality - Lagoa dos Índios in Macapá, Brazil

Aims: To characterize relevant physicochemical parameters of water quality in an Amazonian tropical lake and compare them with the reference values of the Brazilian Resolution CONAMA 357/2005 and those recommended by the similar US-EPA law. In addition, to correlate statistically the parameters in two different climatic periods. Study Design: The sampling procedures occurred in five sites of a tropical lagoon (Lagoa dos