Coupled abiotic-biotic cycling of nitrous oxide in tropical peatlands.

Atmospheric nitrous oxide (N2O) is a potent greenhouse gas thought to be mainly derived from microbial metabolism as part of the denitrification pathway. Here we report that in unexplored peat soils of Central and South America, N2O production can be driven by abiotic reactions (≤98%) highly competitive to their enzymatic counterparts. Extracted soil iron positively correlated with in situ abiotic N2O production determined by isotopic tracers. Moreover, we found that microbial N2O reduction accompanied abiotic production, essentially closing a coupled abiotic-biotic N2O cycle. Anaerobic N2O consumption occurred ubiquitously (pH 6.4-3.7), with proportions of diverse clade II N2O reducers increasing with consumption rates. Our findings show that denitrification in tropical peat soils is not a purely biological process but rather a 'mosaic' of abiotic and biotic reduction reactions. We predict that hydrological and temperature fluctuations differentially affect abiotic and biotic drivers and further contribute to the high N2O flux variation in the region.

Dissemination of COVID-19 in cities and riverine communities in Central Amazonia / Disseminação da COVID-19 em cidades e comunidades ribeirinhas da Amazônia Central

The population of small towns and riverine communities in Amazonia are extremely vulnerable to COVID-19 due to the absence of basic health care infrastructure in the region. The objective of this study was to (1) evaluate the effect of social distancing measures in the dissemination of COVID-19 in small towns, and (2) to estimate the impact of reducing contact between rural and urban populations on the contamination of riverine communities of Central Amazon. Our results indicate that social distancing can significantly reduce the speed of dissemination of COVID-19 in the population of small towns. However, we also observed that even in towns with intense actions to combat COVID-19, social distancing is below the ideal 70% isolation mark. Regarding the contamination of riverine communities, we observed that the reduction in the number of visits and duration of stay, as well as the interruption of visits during the five weeks with larger probability of contamination has major impact on delaying the arrival of COVID-19 in these vulnerable populations. We recommend that, given the low effectiveness of social distancing measures and the rapid contamination of urban populations, each municipality should evaluate implementing more restrictive measures such as a full or partial lockdown. Our results also suggest that three measures can be effective in delaying the arrival of COVID-19 in riverine communities of Amazonia: (1) the reduction in the number of visits that each community makes to a town, (2) the reduction in duration of each visit, and (3) avoiding visits during the five weeks with the largest number of infected people in towns. It is imperative that implementation of any of the restrictive measures suggested in this publication be accompanied by a vast communication campaign as well as social assistance actions for the rural population and poor families of small towns to guarantee their basic needs for survival.

As populações da Amazônia são extremamente vulneráveis à COVID-19 devido ao intenso fluxo entre as localidades rurais e as sedes municipais e à falta de infraestrutura de saúde básica adequada na região. O objetivo deste estudo foi (1) avaliar o efeito da medida de distanciamento social sobre a disseminação da COVID-19 em sedes municipais e (2) estimar o impacto da redução do contato entre a população rural e urbana sobre a contaminação de localidades rurais da Amazônia Central, região do Médio Solimões. Nossos resultados indicam que o distanciamento social pode reduzir significativamente a velocidade de contaminação da população em sedes municipais. No entanto, mesmo em sedes municipais com atividade intensa no combate à COVID-19, o distanciamento social está muito abaixo do ideal de 70%. Observamos também que a redução do número de visitas e do tempo de permanência durante cada visita, além da interrupção do fluxo durante as cinco semanas com maior probabilidade infecção têm impacto marcante sobre a velocidade de chegada da COVID-19 nas localidades rurais. Recomendamos que, dada a baixa efetividade de medidas de distanciamento social e o rápido contágio nas sedes municipais, cada município avalie a implementação de lockdown. Nossos resultados sugerem também que três medidas podem ser eficientes em atrasar a chegada da COVID-19 às localidades rurais: (1) a redução no número de visitas que cada uma faz a um centro urbano, (2) a redução do tempo de permanência durante cada visita e (3) evitar qualquer ida às sedes municipais durante as cinco semanas com maior número de pessoas infectadas. Destacamos que todas as medidas restritivas sugeridas precisam ser acompanhadas por uma ampla campanha de conscientização e ações de assistência à população rural e às famílias mais carentes das sedes municipais para garantir acesso a itens básicos para sua sobrevivência.

Massive tree mortality from flood pulse disturbances in Amazonian floodplain forests: The collateral effects of hydropower production.

Large dams built for hydroelectric power generation alter the hydrology of rivers, attenuating the flood pulse downstream of the dam and impacting riparian and floodplain ecosystems. The present work mapped black-water floodplain forests (igapó) downstream of the Balbina Reservoir, which was created between 1983 and 1987 by damming the Uatumã River in the Central Amazon basin. We apply remote sensing methods to detect tree mortality resulting from hydrological changes, based on analysis of 56 ALOS/PALSAR synthetic aperture radar images acquired at different flood levels between 2006 and 2011. Our application of object-based image analysis (OBIA) methods and the random forests supervised classification algorithm yielded an overall accuracy of 87.2%. A total of 9800 km2 of igapó forests were mapped along the entire river downstream of the dam, but forest mortality was only observed below the first 49 km downstream, after the Morena rapids, along an 80-km river stretch. In total, 12% of the floodplain forest died within this stretch. We also detected that 29% of the remaining living igapó forest may be presently undergoing mortality. Furthermore, this large loss does not include the entirety of lost igapó forests downstream of the dam; areas which are now above current maximum flooding heights are no longer floodable and do not show on our mapping but will likely transition over time to upland forest species composition and dynamics, also characteristic of igapó loss. Our results show that floodplain forests are extremely sensitive to long-term downstream hydrological changes and disturbances resulting from the disruption of the natural flood pulse. Brazilian hydropower regulations should require that Amazon dam operations ensure the simulation of the natural flood-pulse, despite losses in energy production, to preserve the integrity of floodplain forest ecosystems and to mitigate impacts for the riverine populations.

Spatial patterns of medium and large size mammal assemblages in várzea and terra firme forests, Central Amazonia, Brazil.

Várzea forests account for 17% of the Amazon basin and endure an annual inundation that can reach 14 m deep during 6-8 months. This flood pulse in combination with topography directly influences the várzea vegetation cover. Assemblages of several taxa differ significantly between unflooded terra firme and flooded várzea forests, but little is known about the distribution of medium and large sized terrestrial mammals in várzea habitats. Therefore, our goal was to understand how those habitats influence mammalian species distribution during the dry season. Specifically, we: (1) compared the species composition between a terra firme (Amanã Sustainable Development Reserve) and a várzea forest (Mamirauá Sustainable Development Reserve); and (2) tested the influence of the várzea habitat classes on the number of records, occurrence and species composition of mammalian assemblages. The sampling design in each reserve consisted of 50 baited camera trap stations, with an overall sampling effort of 5015 camera trap days. We used Non-Metric Multidimension Scaling (NMDS) to compare species composition between terra firme and várzea forests, and used Generalized Linear Models (GLM) to assess how habitat types and a habitat diversity index affect mammal distributions. We recorded 21 medium and large sized mammalian species, including 20 species in terra firme and only six in várzea (3443 records). Flood pulse and isolation in várzea forest drove the dissimilarity between these two forest types. In várzea forest, medium size mammals, in general, avoided habitats associated with long flooding periods, while jaguars (Panthera onca) appeared to prefer aquatic/terrestrial transition zones. Habitats that remain dry for longer periods showed more mammalian occurrence, suggesting that dispersion via soil is important even for semi-arboreal species. This is the first study to evaluate differential use of várzea habitats by terrestrial mammalian assemblages.

Extension of the geographic range of Ateles chamek (Primates, Atelidae): evidence of river-barrier crossing by an amazonian primate.

The black-faced black spider monkey (Ateles chamek) is endangered because of hunting and habitat loss. There are many gaps in our understanding of its geographic distribution. The Ucayali-Solimões-Amazon fluvial complex is currently recognized as the northern boundary of the species' range, although published reports have indicated that it occurs north of the Rio Solimões. In this study we investigate published records, generate new field records, and assess the current information concerning the northern boundary of this species' range. We conducted the study at the Mamirauá Sustainable Development Reserve in the central Brazilian Amazon, an area of 1,124,000 ha that consists entirely of Amazonian flooded forest (várzea). We collected data on the occurrence of the species from museum specimens and through field surveys, including interviews with local residents, direct observations, and the collection of new museum specimens. We confirmed the presence of A. chamek at 17 locations in the reserve, one of which was an island formed by a river bend cut-off that would have effectively taken any resident spider to the (new) north bank of the Solimões. We therefore conclude that fluvial dynamics were involved in creating the conditions for the dispersal and colonization of the species on the northern bank of the Rio Solimões. The data we present extends the known distribution of the species and increases its representation in protected areas.