Alan Cavalcanti da Cunha

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.

Precipitação sazonal sobre a Amazônia oriental no período chuvoso: observações e simulações regionais com o RegCM3

This paper presents a contribution on the climate modelling studies with emphasis on seasonal rainfall variability in eastern Amazonia, during the austral summer and autumn seasons (DJF and MAM). Based on RegCM3 regional climate simulations for a 26 years period (1982/83 to 2007/08) using high resolution domain scale (30 km) and two different convection schemes (Grell and MIT), it was investigated the model performance to simulate the regional pluviometric distribution in eastern Amazon, with reference to a new observational data base containing regional aspects extracted from a dense rain gauge station network. The quantitative analysis showed that RegCM3 presents systematic errors, especially those related to the dry bias in the Amapa and north/northeast of Para using both schemes Grell and MIT, which indicate that the model does not reproduce ITCZ characteristics over equatorial Atlantic. The simulations using MIT also indicated wet bias in the southwest/south/southeast of Para and north of Tocantins. Moreover, through composites technique, it was also investigated RegCM3 response to reproduce the anomalous spatial rainfall patterns in association with ENSO episodes and interhemispheric SSTa gradient phases across the intertropical Atlantic. The results showed that the model represented realistically well the spatial pattern related to the rainfall anomalies above (below) than normal in most of eastern Amazonia, during the known favourable scenarios, i.e., La Nina and south Atlantic SSTa gradient (unfavourable, i.e., El Nino and north Atlantic SSTa gradient).

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.

Distribution pattern of crustacean ectoparasites of freshwater fish from Brazil

The purpose of this study was to use the informations relating to parasite crustaceans species that was published over the course of one century (1913 to 2013), in order to search for infestation and distribution patterns among these ectoparasites in Brazilian freshwater fish species. This search was carried out on 445 samples of 119 host fish of 27 families within the orders Characiformes, Perciformes, Clupeiformes, Mugiliformes, Osteoglossiformes, Symbranchiformes, Tetraodontiformes and Siluriformes from various regions of Brazil. We organized different host-parasite systems into matrices grouping species at different taxonomic and infestation levels and according to host parameters. Five families of parasites (Ergasilidae, Argulidae, Lernaeidae, Lernaeopodidae and Cymothoidae) distributed into 76 species of 27 genera were analyzed in the host samples, which presented dominance of Ergasilidae species, mainly from the genus Ergasilus. Some crustaceans are host and site-specific, especially in relation to fish in particular habitats and lifestyles (e.g. Perulernaea gamitanae, Anphira branchialis and Riggia paranensis), while other parasites frequently have no preference (e.g. Lernaea cyprinacea and Braga patagonica). We found broadly similar distribution patterns for some crustacean species among the different localities, whereas other species showed well-defined geographical patterns, and these findings were discussed.

Phytoplankton of two rivers in the eastern Amazon: characterization of biodiversity and new occurrences

During the various hydrological periods in 2011, we studied the phytoplankton along an 87-km stretch of the Araguari and Falsino rivers, which are located in the eastern Brazilian Amazon, in the state of Amapa, Brazil, the most ecologically preserved state in the country. In the study area, the aquatic ecosystem is under pressure from human activities such as, mining, hydroelectric power generation and urbanization, which contrast with the surrounding areas that are designated for biodiversity conservation. The aim of this study was to characterize the composition, frequency and richness of algae species and also to identify spatial-temporal patterns of taxa distribution. During the study period, we identified 185 taxa (136 species in 49 genera). The division Chlorophyta (class: Zygnematophyceae) presented the greatest number of taxa, whereas the division Rhodophyta accounted for only 1% of the taxa recorded. Most of the species identified (69%) were classified as sporadic in occurrence. The few taxa that were classified as common belonged mainly to the group Bacillariophyta. Species richness was greatest richness in the lentic stretches (in a reservoir) and in November (during the dry season). Of the 185 taxa identified, 174 are new records for the state of Amapa.

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.

Ballast water: A threat to the Amazon Basin

Ballast water exchange (BWE) is the most efficient measure to control the invasion of exotic species from ships. This procedure is being used for merchant ships in national and international voyages. The ballast water (BW) salinity is the main parameter to evaluate the efficacy of the mid-ocean ballast water exchange. The vessels must report to the Port State Control (PSC), via ballast water report (BWR), where and how the mid-ocean BWE was performed. This measure allows the PSC to analyze this information before the ship arrives at the port, and to decide whether or not it should berth. Ship BW reporting forms were collected from the Captaincy of Santana and some ships were visited near the Port of Santana, located in Macapá (Amazon River), to evaluate the BW quality onboard. We evaluated data submitted in these BWR forms and concluded that the BWE efficacy might be compromised, because data contained in these BWR indicate that some ships did not change their BW. We found mistakes in filling the BWR forms and lack of information. Moreover, these ships had discharged BW with high level of salinity, Escherichia coli and total coliforms into the Amazon River. We concluded that the authorities of the Amazon Region need to develop more efficient proceedings to evaluate the ballast water reporting forms and BW quality, as there is potential risk of future invasion of exotic species in Brazilian ports.

MODELAGEM CLIMÁTICA REGIONAL DURANTE DOIS ANOS DE EXTREMOS DE PRECIPITAÇÃO SOBRE O ESTADO DO AMAPÁ: TESTE DE SENSIBILIDADE AOS ESQUEMAS CONVECTIVOS

O presente estudo mostra uma avaliacao da previsao sazonal do Modelo RegCM3 em dois eventos extremos de precipitacao, nos anos 2006 e 2007. Na analise foi utilizada a resolucao horizontal de 1° x 1° km e validado com 30 x 15 pontos de latitude x longitude para a regiao do Estado do Amapa. Os resultados apresentados sao referentes a comparacao entre precipitacao sazonal simulada e observada para o trimestre (MAM). De maneira geral, os resultados mostraram que a utilizacao da tecnica de reducao de escala de previsao da precipitacao sazonal, apresentou um bom desempenho em simular a variabilidade da chuva em escala regional. Porem, erros na quantidade e na posicao de alguns maximos foram observados, quando comparado com os dados observados. O vies umido foi predominante na regiao litorânea e o vies seco nas areas sul-sudeste, oeste e centro com forte persistencia na regiao sudeste. Nao se observou regioes com valores estimados de precipitacao proximos aos valores observados.

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.

Variação da radiação solar no estado do Amapá: estudo de caso em Macapá, Pacuí, Serra do Navio e Oiapoque no período de 2006 a 2008

The objective of this study was to estimate the potential of solar energy through the variation of the global solar radiation (GSR) in the State of Amapa during two seasons cycle (2006 to 2008). GSR historical time series were used from four collection data platforms (PCDs) distributed in a central area of the state. The results indicated that the distribution of RSG showed annual peak of about 4900Wh.m-2.day-1 on the Macapa station, due to its proximity to the equator line. At Serra do Navio, Pacui and Oiapoque cities the values observed were 4000, 4400 and 3800Wh.m-2.day-1, respectively. We conclude that the studied sites in Amapa State have significant potential for photovoltaic use during a complete annual cycle. The potential for generating electricity proved to be attractive, both for use in traditional urban systems and in isolated systems in remote communities.