Central Amazon Floodplain Research Articles

Hydrological and climate intensification induces conservative behavior in the Hydrochorea corymbosa xylem production in a Central Amazon floodplain forest

IntroductionTrees from flooded forests have to adjust their xylem hydraulic structure to face the annual flooding and the climatic conditions of the atmosphere. Usually, this adjustment of anatomical tissues in the tropics is driven by drought events inducing conservative behavior and can be recorded annually in tree rings. However, how the flood pulse and the climatic conditions influence the xylem hydraulic structure in floodplain trees is unknown.MethodsTo fill this gap, we explore if flooded periods and monthly climate variation affect the annual tree growth and xylem anatomy structure for the tree species Hydrochorea corymbosa (Fabaceae) from the várzea flooded forest in the Central Amazon. We developed a 41-year ring width chronology (1971–2018) and a 30-year time series of xylem anatomy parameters (1988–2018) as mean hydraulic vessel diameter (Dh), vessel frequency (VF), and parenchyma quantity (PQ). We correlated the series with monthly hydrological and climatic data.ResultsThe hydrological regime did not correlate with annual tree growth in that species as we previously expected but showed correlations with the xylem anatomical structure. High flood levels during the end of the flooding period induced conservative patterns of the anatomical structure, with a negative correlation with Dh (rho June = −0.40, p < 0.05) and a positive correlation with the PQ (rho September/October = 0.42, p < 0.05). These responses show that these trees are responding to flooding similar to the tree responses to drought. Regarding the climatic variation, the annual tree growth showed a negative correlation with the vapor pressure deficit (VPD), after the second half of the flooded period with the strongest correlation happening during the non-flooded period (rho December = −0.66, p < 0. 01). These conservative patterns in tree behavior also happened when the maximum temperature negatively affected the vessel diameter (rho September = −0.42, p < 0.05).DiscussionIn that case, we recognized two different moments that the environment is inducing conservative patterns in the xylem structure of those trees: 1) increasing the flood levels and 2) the high evaporative demand during the non-flooded period. In this way, the intensification of the hydrological regime, as well as the strong drought conditions during the non-flooded periods, can be a risk for H. corymbosa in the Central Amazonian floodplains.

A dynamic model for assessing soil denitrification in large-scale natural wetlands driven by Earth Observations.

The Wetland Soils Denitrification Model (WSDM) developed here for natural wetlands, is a physical based model that proposes: (i) the inclusion of soil moisture and temperature from satellite-based Earth Observations at diurnal temporal resolution and (ii) the distinction of soils under different wetland typologies (i.e., flooded forests, freshwater marshes, brackish wetlands, peatlands, and complex wetlands). Despite uncertainties involved, these two features are key to upscale nitrification/denitrification dynamics in natural wetlands at landscape, regional and global scales. In this study, the performance of WSDM was validated with soils in flooded forests and freshwater marshes in the central Amazonian floodplain. WSDM multiannual time series (2012–2019) show that climate anomalies intensify denitrification events. Flooded forests were identified with the highest annual denitrification rates. Annual denitrification and N2O emissions estimated in this study are in line with previous studies.

Length‐weight relationship of fish species from Central Amazon floodplain

Length-weight relationship (LWR) for 39 freshwater fish species captured in the Catalão Lake, a floodplain area at the confluence of the Amazonas and Negro rivers is presented. LWRs were calculated based on fish sampled over 18 years (1999–2017) using a set of ten gill nets with different mesh sizes, monthly immersed in water for 24-hr with 6-hr interval catches. Measurements were done for standard length (SL – 0.1 cm precision) and total weight (TW – 0.01 g precision). The LWRs were calculated by the linear regression of natural log-transformed SL and TW data: TW = a × SLb. All statistical analyses were performed with R software. From all species considered, 32 are new LWR records for the international literature as well as for the Amazonian ichythyofauna; additional records expand the known size range for seven species.

Carbon Dioxide Fluxes to the Atmosphere From Waters Within Flooded Forests in the Amazon Basin

AbstractInundated tropical forests are underrepresented in analyses of the global carbon cycle and constitute 80% of the surface area of aquatic environments in the lowland Amazon basin. Diel variations in CO2 concentrations and exchanges with the atmosphere were investigated from August 2014 to September 2016 in two flooded forests sites with different wind exposure within the central Amazon floodplain (3°23′S, 60°18′W). CO2 profiles and estimates of air–water gas exchange were combined with ancillary environmental measurements. Surface CO2 concentrations ranged from 19 to 329 μM, CO2 fluxes ranged from −0.8 to 55 mmol m−2 hr−1 and gas transfer velocities ranged from 0.2 to 17 cm hr−1. CO2 concentrations and fluxes were highest during the high water period. CO2 fluxes were three times higher at a site with more wind exposure (WE) compared to one with less exposure (WP). Emissions were higher at the WP site during the day, whereas they were higher at night at the WE site due to vertical mixing. CO2 concentrations and fluxes were lower at the W P site following an extended period of exceptionally low water. The CO2 flux from the water in the flooded forest was about half of the net primary production of the forest estimated from the literature. Mean daily fluxes measured in our study (182 ± 247 mmol m−2d−1) are higher than or similar to the few other measurements in waters within tropical and subtropical flooded forests and highlight the importance of flooded forests in carbon budgets.

Dendroecology of Macrolobium acaciifolium (Fabaceae) in Central Amazonian floodplain forests

ABSTRACT The forest dynamics in the Amazonian floodplains is strongly triggered by the flood pulse. Trees respond to unfavorable growth conditions during the flood period by cambial dormancy, which results in the formation of annual growth rings. We determined tree age and compared the mean annual rates of increase in the diameter of Macrolobium acaciifolium with hydrological and climatic factors in three regions of central Amazonian floodplain forest. A wood sample was obtained from each tree using an increment borer. Ring growth was assessed by marginal parenchyma bands to determine tree age and the mean diameter increment. Ring widths were indexed to construct cross-dating chronologies and correlated with climatic and hydrological variables. The analyses demonstrate that the mean annual diameter increment did not differ between the three study sites. The chronologies correlated significantly with the terrestrial phase. There was no significant difference in the ring-width index between El Niño years and other years, and between La Niña and other years. These results show that the hydrological variables can be considered crucial to the rates of tree growth and diameter increment in floodplains, and El Niño signals were not detected in the tree-ring chronologies.

Influence of plankton metabolism and mixing depth on CO2 dynamics in an Amazon floodplain lake

We investigated plankton metabolism and its influence on carbon dioxide (CO2) dynamics in a central Amazon floodplain lake (Janauacá, 3°23′ S, 60°18′ W) from September 2015 to May 2016, including a period with exceptional drought. We made diel measurements of CO2 emissions to the atmosphere with floating chambers and depth profiles of temperature and CO2 partial pressure (pCO2) at two sites with differing wind exposure and proximity to vegetated habitats. Dissolved oxygen (DO) concentrations were monitored continuously during day and night in clear and dark chambers with autonomous optical sensors to evaluate plankton metabolism. Overnight community respiration (CR), and gross primary production (GPP) rates were higher in clear chambers and positively correlated with chlorophyll-a (Chl-a). CO2 air-water fluxes varied over 24-h periods with changes in thermal structure and metabolism. Most net daily CO2 fluxes during low water and mid-rising water at the wind exposed site were into the lake as a result of high rates of photosynthesis. All other measurements indicated net daily release to the atmosphere. Average GPP rates (6.8gCm−2d−1) were high compared with other studies in Amazon floodplain lakes. The growth of herbaceous plants on exposed sediment during an exceptional drought led to large carbon inputs when these areas were flooded, enhancing CR, pCO2, and CO2 fluxes. During the period when the submerged herbaceous vegetation decayed phytoplankton abundance increased and photosynthetic uptake of CO2 occurred. While planktonic metabolism was often autotrophic (GPP:CR>1), CO2 out-gassing occurred during most periods investigated indicating other inputs of carbon such as sediments or soils and wetland plants.

Composition, diversity and structure of vascular epiphytes in two contrasting Central Amazonian floodplain ecosystems

ABSTRACT Research focusing on assemblages of vascular epiphytes in the Amazon are scarce. This is especially true for Amazonian floodplain forests, for which only two previous studies have been published. We compared composition, richness and structure of epiphyte assemblages in white-water and black-water floodplains (varzea and igapo) in Central Amazonia in order to close knowledge gaps concerning the distribution and richness of epiphytes. We established sixteen 25x25 m plots in each forest type, and counted and identified all species of vascular epiphytes occurring on trees with a diameter at breast height (DBH) ≥10 cm. We observed a clear distinction in epiphytic species composition (r2=0.83, p=0.001) and diversity (t=3.24, P=0.003) between the two environments, with 61.5 % of species being restricted to varzea, 22.9 % restricted to igapo and only 15.6 % common to both ecosystems. The floodplains were also structurally different for the most abundant species and those with the highest Epiphytic Importance Value (IVe). The diversity of trees did not influence the epiphyte diversity in either ecosystem. The forests were found to differ in the composition, diversity and structure of their epiphytic assemblages, which must be taken into account when designing conservation action plans for these ecosystems and for their vascular epiphytes.

Nematode larvae with zoonotic importance found in peacock bass Cichla monoculus (Spix & Agassiz, 1831) from floodplain lakes in Central Amazon

This study exhibits data pertaining to the zoonotic potential of larvae of nematode of peacock bass (Cichla monoculus). Thirty-eight specimens were collected from Central Amazon floodplain lakes throughout the four seasons of a complete hydrological cycle: rising, high, receding and low water level. Third-stage larvae (L3) of Anisakis sp. and Contracaecum sp. Nematode larvae were found at prevalences of 13.15% and 7.89% respectively. The results indicated there being low infection hazard to humans consuming C. monoculus from floodplain lakes in Central Amazon.

Stand dynamics of the drought-affected floodplain forests of Araguaia River, Brazilian Amazon

BackgroundThe floodplain forests of Araguaia River, a clear-water river in the southeastern Amazon (Tocantins State, Brazil), are characterized by seasonal flooding up to 3.5 m height, low nutrient levels in the water, and seasonal drought periods of 4–5 months.MethodsWe studied the forest dynamics (tree diameter growth, tree mortality and recruitment) of this unique forest ecosystem over a 5-year period by repeated censuses in 12 permanent plots established along a flooding gradient.ResultsThe cumulative basal area in the plots increased by 0.84 (±0.45) m2∙ha–1∙yr–1 (mean ±SD) in the annually-flooded (AF) plots in lower terrain and by 0.69 (±1.00) m2∙ha–1∙yr–1 in the higher non-annually flooded (NAF) plots, corresponding to an aboveground biomass increase of 0.81 (±0.57) and 0.69 (±1.58) Mg∙ha–1∙yr–1 in the AF and NAF plots, indicating a recent carbon sink in the biomass. Mean diameter growth rate was 1.8 (±0.44) mm∙yr–1 in the AF and 2.0 (±0.56) mm∙yr–1 in the NAF plots (corresponding to a coarse wood production of 1.53 (±1.29) and 2.02 (±0.52) Mg∙ha–1∙yr–1), indicating no flooding effect on radial growth. Mean mortality rates in the 5-year period were 1.9 (±0.37)%∙yr–1 in the AF plots and 1.8 (±0.87)%∙yr–1 in the NAF plots with no differences along the flooding gradient. Highest mortalities were registered in the AF plots for the 10–20 cm dbh class (2.4%∙yr–1), likely as a consequence of flooding, and in the NAF plots for the 40–50 cm dbh class (3.0%∙yr–1), probably mainly caused by ENSO-related droughts.ConclusionsWe conclude that these drought-affected tropical floodplain forests have a lower standing biomass and aboveground productivity than central Amazonian floodplain forests in more humid climates, and the imprint of the flooding gradient on stand dynamics is relatively weak, which may result from the lower flooding height and the interaction of flooding with low nutrient supply and periodic drought.

Regional and seasonal variability in planktonic photosynthesis and planktonic community respiration in Amazon floodplain lakes

Results from two regional surveys and multi-lake seasonal studies were used to investigate the variability of phytoplankton photosynthesis and planktonic community respiration in central Amazon floodplain lakes. Hypothesized effects of optical and chemical variables on planktonic photosynthesis and respiration were examined statistically. Changes in dissolved oxygen in light and dark bottles distributed along light-gradients in a shipboard incubator or in situ were used to calculate volumetric community respiration (Rc), volumetric gross photosynthesis (P), daily integral gross photosynthesis (Π), and daily integral community respiration rates (Λ). Π varied significantly among all lakes with source-water river stage and source-water river type. Λ also varied significantly with source-water river stage. Variation in maximum depth linked to source-water river stage was a key factor controlling seasonal variations in Π through its influence on total suspended solids and total phosphorus concentrations which affected light extinction and light-saturated photosynthesis, respectively. The predominance of sub-saturated dissolved O2 in the pelagic surface waters of Amazon floodplain lakes was attributed to high integral Rc:P ratios, indicating the existence of large sustained inputs of non-phytoplankton organic carbon to these environments.

The fate of C4 and C3 macrophyte carbon in central Amazon floodplain waters: Insights from a batch experiment

The central Amazon floodplains are particularly productive ecosystems, where a large diversity of organic carbon sources are available for aquatic organisms. Despite the fact that C 4 macrophytes generally produce larger biomasses than C 3 macrophytes, food webs in the central Amazon floodplains appear dominantly based on a C 3 carbon source. In order to investigate the respective fate and degradation patterns of C 4 and C 3 aquatic plant-derived material in central Amazon floodplains, we developed a 23-days batch experiment. Fatty acid and carbon concentrations as well as stable isotope compositions were monitored over time in 60 L tanks. These tanks contained Amazon water, with different biomasses of C 3 and C 4 macrophyte, representative of in situ densities occurring in central Amazon floodplains. In the C 4 Paspalum repens treatments, organic (POC, DOC) and inorganic carbon (DIC) got rapidly enriched in 13 C, whereas in the C 3 Salvinia auriculata treatments, POC and DOC showed little change in concentration and isotopic composition, and DIC got depleted in 13 C. The contribution of P. repens to POC and DOC was estimated to reach up to 94.2 and 70.7%, respectively. In contrast, no differences were reported between the C 3 S. auriculata and control treatments, an observation attributed to the lower C 3 biomass encountered in the field, to a slower degradation rate of C 3 compared to C 4 compounds, and to similar isotopic compositions for river POC and DOC, and C 3 compounds. The 13 C enrichments of POC, DOC, and DIC from P. repens treatments were attributed to an enhanced bacterially-mediated hydrolysis and mineralization of C 4 material. Evolutions of bacterial abundance and branched fatty acid concentrations confirmed the role of heterotrophic microbial communities in the high P. repens decomposition rate. Our experiment highlights the predominant role of C 4 aquatic plants, as a large source of almost entirely biodegradable organic matter available for heterotrophic activity and CO 2 outgassing to the atmosphere.

Abiotic variability among different aquatic systems of the central Amazon floodplain during drought and flood events.

This paper examines water properties from lakes, (depression lakes, sensu Junk et al., 2012), channels (scroll lakes with high connectivity, sensu Junk et al., 2012) and paleo-channels (scroll lakes with low connectivity-sensu Junk et al., 2012, locally called ressacas) located in Mamirauá Sustainable Development Reserve, in Central Amazon floodplain, Amazonas, Brazil. We analysed surface temperature, conductivity, pH, dissolved oxygen, turbidity, transparency, suspended inorganic and organic matter, chlorophyll-a, pheophytin, total nitrogen, total phosphorus, organic and inorganic carbon in 2009 high water phase, 2009 and 2010 low water phases. Multivariate statistical analyses of 24 aquatic systems (6 ressacas, 12 lakes and 6 channels, 142 samples) were applied to the variables in order to: 1) quantify differences among aquatic system types; 2) assess how those differences are affected in the different phases of the hydrological year. First, we analysed the entire set of variables to test for differences among phases of the hydrological year and types of aquatic systems using a PERMANOVA two-way crossed design. The results showed that the all measured limnological variables are distinct regarding both factors: types of aquatic systems and hydrological phases. In general, the magnitude and amplitude of all variables were higher in the low water phase than in the high water phase, except for water transparency in all aquatic system's types. PERMANOVA showed that the differences between aquatic system's types and hydrological phases of all variables were highly significant for both main factors (type and phase) and for the type x phase interaction. Limnological patterns of Amazon floodplain aquatic systems are highly dynamic, dependent on the surrounding environment, flood pulse, main river input and system type. These patterns show how undisturbed systems respond to natural variability in such a diverse environment, and how distinct are those aquatic systems, especially during the low water phase. Aquatic systems in Mamirauá floodplain represent limnological patterns of almost undisturbed areas and can be used as future reference for comparison with disturbed areas, such as those of the Lower Amazon, and as a baseline for studies on the effects of anthropogenic influences and climate change and on Amazon aquatic ecosystem.

Effects of flooding on trees in the semi-deciduous transition forests of the Araguaia floodplain, Brazil

The Araguaia floodplain, one of the large floodplain areas in the Neotropics, is located in the transition zone of Amazon forests and Cerrado. The region is characterized by annual floodings and a pronounced dry season of three months. We examined the influence of flooding from low to high terrain on floristic composition, forest structure and aboveground live biomass (AGB). We recorded all trees (dbh >5 cm) in 30 permanent plots (50 × 50 m) located at different topographic positions across a flooding gradient.Sixty-nine tree species from 30 plant families were recorded; Fabaceae (15 species) was the most abundant family, followed by Myrtaceae (5), Anacardiaceae (4) and Rubiaceae (4). Family composition was similar to Central Amazonian floodplain forests and many widely distributed flood-tolerant tree species were shared. Tree species richness was relatively low with 14–31 tree species per plot and was not affected by flood level, but tree species composition and family importance values differed markedly between annually flooded and non-annually flooded forest stands.Forest top canopy height varied between 10.5 and 18.5 m and was negatively correlated with flood level (R2 = 0.25, p = 0.002). Mean wood specific gravity (WSG) of the plots increased with the flood level (R2 = 0.43, p < 0.001) and apparently was unrelated to drought intensity. Stem density (plot mean 1040 ha−1), mean dbh, tree basal area (19.4 m2 ha−1) and AGB (116.8 Mg ha−1) were not dependent on flood level. The low AGB compared to Central Amazonian floodplain forests is probably a result of the pronounced dry season and limited nutrient availability in the igapó forests of the Araguaia floodplain. In view of the predicted increase of extended drought periods with global warming, we assume that future forests in the study area may lose some or all drought-sensitive tree species and likely may face a reduction in AGB.

Trophic opportunism of central Amazon floodplain fish

SummaryThe food web of the central Amazon basin displays one of the largest discrepancies in food source utilisation versus availability for consumers. While C4macrophytes dominate the primary producing biomass in floodplains, the food web is dominated by the use of C3carbon sources. Amazon fish species have wide‐ranging diets and show feeding flexibility in response to spatial and temporal patterns in food source availability. Fish are therefore expected to use a range of available resources. Fatty acids and stable carbon and nitrogen isotopic compositions were studied to investigate their trophic behaviour and provide a better assessment of food source utilisation by nine fish species from two Amazon floodplains.Although nitrogen stable isotopes positioned detritivores at the base of the food chain, their large proportions of polyunsaturated fatty acids (FAs) suggest selection of a high‐quality food source, such as microalgae. Omnivores and insectivores displayed a wide range of food source utilisation, indicating opportunist feeding behaviour. Piscivores displayed the most15N‐enriched signature (up to 10.6‰), concomitant with their predator position in the studied food web.C3carbon was the dominant source for most species, which is a finding consistent with current classical knowledge. However, consumption of C4macrophytes was detected for the herbivoreSchizodon fasciatus, in line with the spatial availability of this food source in the floodplain system. Large amounts of polyunsaturated and essential FAs in these C4macrophytes indicate their high nutritive value. Our results suggest that this food source is rather neglected by fish due to low digestibility, with the exception of the herbivore that may possess modification of its digestive system that allows the use of C4plants.

Combining ALOS/PALSAR derived vegetation structure and inundation patterns to characterize major vegetation types in the Mamirauá Sustainable Development Reserve, Central Amazon floodplain, Brazil

Remote sensing studies of vegetation cover and hydrologic dynamics in Amazonian wetlands have been mostly limited temporally or spatially, and the distribution and spatial configuration of Amazonian varzea habitats remains poorly known. This study uses multitemporal PALSAR L-band radar imagery combined with object-based image analysis, data mining techniques and field data to derive vegetation structure and inundation patterns and characterize major vegetation types in varzea forests of the Mamiraua Sustainable Development Reserve. Our results show that the combination of vegetation cover and inundation extent information can be a good indicator of the complex gradient of habitats along the floodplain. The intersection between vegetation and flood duration classes showed a wider range of combinations than suggested from field based studies. Chavascal areas—chacaracterized as a dense and species-poor shrub/tree community developing in old depressions, abandoned channels, and shallow lakes—had shorter inundation periods than the usually recognized hydroperiod of 180–240 days of flooding, while low varzea—a diverse community that have fewest and smallest species, and highest individual density and that tolerate 120–180 days of flooding every year—was distributed between flood duration ranges that were higher than reported by the literature. Forest communities growing at sites that were never mapped as flooded could indicate areas that only flood during extreme hydrological events, for short periods of time. Our results emphasize the potential contribution of SAR remote sensing to the monitoring and management of wetland environments, providing not only accurate information on spatial landscape configuration and vegetation distribution, but also important insights on the ecohydrological processes that ultimately determine the distribution of complex floodplain habitat mosaics.

Alimentación y ontogenia trófica alimentar de juveniles de characiformes en bancos de macrófitas acuáticas en el río Solimões/Amazonas

El ambiente de macrófitas acuáticas desempeña un importante papel como sítio de alimentación de peces juveniles del Orden Characiformes en la várzea de la Amazonia Central. En el presente trabajo fueron evaluadas las variaciones ontogenéticas en la dieta, en función del aumento corporal de juveniles de Brycon amazonicus, Triportheus angulatus, Mylossoma duriventre y Semaprochilodus insignis recolectados en bancos de macrófitas en un trecho del río Solimões/Amazonas. Fueron analizados 1.181 ejemplares, los especímenes fueron divididos arbitrariamente en tres clases de desarrollo de acuerdo con la longitud estándar (CP): clase I (15-30 mm), clase II (31-45 mm) y clase III (46-60 mm). Para el análisis de la dieta fue calculado el Índice Alimentar (IAi), combinando los métodos de frecuencia de ocurrencia y volumen relativo. Fueron observadas variaciones ontogenéticas en la dieta de M. duriventre y de T. angulatus durante la fase juvenil. Todas las especies muestreadas poseen forrajeo selectivo y llegan al fin de la fase juvenil con comportamiento trófico semejante al que presentan en la fase adulta.

Chromosomal and electric signal diversity in three sympatric electric knifefish species (Gymnotus, Gymnotidae) from the Central Amazon Floodplain

We describe chromosomal and electric signal diversity in three sympatric species of Gymnotus (Gymnotidae) fish from the Central Amazon Floodplain. Gymnotus arapaima presents a karyotype of 2n = 44 (24 m-sm + 20st-a), G. mamiraua 2n = 54 (42 m-sm + 12st-a), and G. jonasi 2n = 52 (12 m-sm + 40st-a). No evidence for a chromosomal sexual system was observed in two species for which both males and females were analyzed (G. mamiraua and G. arapaima). In all three species the constitutive heterochromatin is located primarily in pericentromeric regions, but also at some other sites. G. arapaima and G. mamiraua exhibit simple nucleolar organizing regions (NORs) on short arms of chromosome pairs 19 and 24, respectively. Gymnotus jonasi exhibits a multiple interstitial NOR on the long arm of pairs 9 and 10, and on the short arm of pair 11. G. arapaima and G. mamiraua exhibit several additional similarities in their karyotypic formulas—reflecting the phylogenetic proximity of these species within a G. carapo group clade (based on molecular phylogenetic evidence). The chromosomal differences among these three sympatric species imply complete post-zygotic reproductive isolation. A prominent pattern of partitioning of the peak power frequency of the electric organ discharge of these three species indicates pre-zygotic reproductive isolation of mate attraction signals. We conclude by discussing the evolutionary events that may have promoted signal divergence and reproductive isolation in Gymnotus of the Central Amazon, and the role that chromosomal rearrangements may place in diversification.

Growth and population structure of the tree species Malouetia tamaquarina (Aubl.) (Apocynaceae) in the central Amazonian floodplain forests and their implication for management

The long-term success of forest management depends primarily on the sustainability of timber production. In this study we analyse the population structure, tree age and wood increment of Malouetia tamaquarina (Aubl.) (Apocynaceae) to define a species-specific minimum logging diameter (MLD) and felling cycle by modelling volume growth. Contrary to other timber species in the nutrient-rich white-water floodplains forests (várzea), M. tamaquarina grows in the subcanopy of old-growth várzea forests. The wood of this species is utilized by local inhabitants in the floodplains for handicraft. In 35 plots of 25 m × 50 m we measured diameter at breast height (DBH) and tree height of all trees taller than 150 cm height. From 37 individuals with DBH > 15 cm we sampled two cores by increment borers to determine the wood density, tree age and diameter increment rates. In the management area of a várzea settlement with about 150 ha recently harvested trees of M. tamaquarina have been recorded and DBH was measured. The species presents an inverse J-shaped diameter distribution indicating that the species is obviously regenerating in the old-growth forests. Tree-ring analysis indicates a mean age of 74.5 years for a DBH of 22.7 cm for a studied population comprising 37 trees with maximum ages of up to 141 years for an individual with a DBH of 45.7 cm. The tree species has low annual diameter increment rates (3.16 ± 0.6 mm) despite a low wood density (0.36 ± 0.05 g cm −3). The volume growth model indicates a MLD of 25 cm and a felling cycle of 32.4 years. In the management area 35 trees with a mean DBH of 24 cm were recorded, similar to the defined MLD. The abundance of trees above the MLD is 2.7 trees ha −1, or 405 trees, when extrapolated to the whole management area. Considering a felling cycle of 32.4 years (annual production unit of 4.63 ha) this results in total of 12.5 harvestable trees, almost three times less than actually harvested. The actual practice of harvesting M. tamaquarina risks the overexploitation of this slow-growing species.

Production and some properties of crude alkaline proteases of indigenous Central Amazonian rhizobia strains

Two rhizobia strains isolated from soils of the Central Amazonian floodplain produced appreciable quantities of crude alkaline protease extracts with inexpensive carbon and nitrogen sources. These protease crude extracts were optimally active at pH 9.0-11.0. The optimum temperatures were 35 ºC for Rhizobium sp. strain R-986 and 55 ºC for Bradyrhizobium sp. strain R-993. Protease activities in the crude extracts were enhanced in the presence of 5 mM metal ions, such as Na+, Ca2+, Mg2+ and Mn2+. Rhizobia proteases were strongly inhibited by PMSF, a serine-protease inhibitor. The enzymes were active in the presence of surfactants (SDS and Triton X-100) and stable in oxidizing (H2O2) and reducing agents (β-mercaptoethanol), and organic solvents (acetone, hexane, methanol, 1-propanol and toluene).

Seasonal catch distribution of tambaqui (Colossoma macropomum), Characidae in a central Amazon floodplain lake: implications for sustainable fisheries management

Summary Tambaqui, Colossoma macropomum (Cuvier 1818), is one of the largest and most commercially important freshwater fishes in South America, attaining a body size of up to 1 m length and a mass of ≥ 30 kg. We hypothesize that the mean length of the captured tambaqui was impacted by the fishery. The present study used GIS information to map the Manacapuru Lake system and record tambaqui caught by fishermen from February 2007 to January 2008. Fork lengths of fish were measured and compared to the legal size limit of 55 cm, corresponding to the reproductive age as set by IBAMA (Brazilian Institute of the Environment and Natural Renewable Resources). Only 1% of 1271 fish measured were at or above this limit. Spatial distribution of the catch within this floodplain lake system varied, depending on the stage of the hydrologic cycle, but the greatest number of fish was caught within the Piranha Sustainable Development Reserve where fishing is prohibited by law. The results of this study indicate an acute need for enforcement of the law to avoid collapse of the fishery.