Similar potential ATP-P production and enzymatic activities in the microplankton community off Concepción (Chile) under oxic and suboxic conditions

The effects of the oxygen minimum zone on the metabolism of the heterotrophic microplankton community (0.22-100 μm) in the Humboldt Current System, as well as the factors controlling its biomass production, remain unknown. Here we compare the effect of four sources of dissolved organic carbon (glucose, oxaloacetate, glycine, leucine) on microbial biomass production (such as ATP-P) and the potential enzymatic activities involved in catabolic pathways under oxic and suboxic conditions. Our results show significant differences (p < 0.05) in the ATP-P production when induced by the different substrates that are used as dissolved organic carbon herein. The induction of ATP-P production is enhanced from glucose < oxaloacetate < glycine < leucine. Nevertheless, for individual substrates, no significant differences were found between incubation under oxic and suboxic conditions except in the case of leucine. For this amino acid, the induction of ATP-P synthesis was higher under suboxic than oxic conditions. The data sets of all the substrates used showed greater potential ATP-P production under suboxic than oxic conditions. The results of the potential enzymatic activities suggest that malate dehydrogenase has the highest signal of NADH oxidization activity in the microbial assemblage. Furthermore, for all experiments, the malate dehydrogenase activity data set had a significant relationship with ATP-P production. These findings suggest that the microbial community inhabiting the oxygen minimum zone has the same or greater potential growth than the community inhabiting more oxygenated strata of the water column and that malate dehydrogenase is the activity that best represents the metabolic potential of the community.     

Nb–Ta–(Ti–Sn) oxide mineral chemistry as tracer of rare-element granitic pegmatite fractionation in the Borborema Province,Northeastern Brazil

The Borborema Pegmatitic Province (BPP), northeastern Brazil, is historically important for tantalum mining and also famous for top-quality specimens of exotic Nb–Ta oxides and, more recently, for the production of gem quality, turquoise blue, ‘Paraíba Elbaite.’ With more than 750 registered mineralized rare-element granitic pegmatites, the BPP extends over an area of about 75 by 150 km in the eastern part of the Neoproterozoic Seridó Belt. The Late Cambrian pegmatites are mostly hosted by a sequence of Neoproterozoic cordierite–sillimanite biotite schists of the Seridó Formation and quartzites and metaconglomerates of the Equador Formation. The trace-element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl–columbite phosphate subtype. Electron microprobe analyses (EMPA) of columbite, tapiolite, niobian–tantalian rutile, ixiolite and wodginite group minerals from 28 pegmatites in the BPP are used to evaluate the effectiveness of Nb–Ta oxide chemistry as a possible exploration tool, to trace the degree of pegmatite fractionation and to classify the pegmatites. The columbite group mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite. This trend is typical of complex spodumene- and/or lepidolite-subtype pegmatites. It clearly contrasts with another trend, from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions, typical of pegmatites of the beryl–columbite phosphate subtype. Large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns. This indicates that a large representative data set of heavy mineral concentrate samples, collected systematically along cross-sections, would be necessary to predict the metallogenetic potential of individual pegmatites. Other mineral species, e.g. garnets and/or tourmaline, with a more regular distribution than Nb–Ta oxides, would be more appropriate and less expensive for routine exploration purposes. The currently available Nb–Ta oxide chemistry data suggest the potential for highly fractionated Ta–Li–Cs pegmatites in the BPP, so far undiscovered, and encourages further, more detailed research.     

Late-Pleistocene and mid-Holocene environmental changes in highland valley head areas of Santa Catarina state, Southern Brazil

Low resolution of the continental sedimentary record is a common source of skepticism about the application of geomorphology and sedimentology to Quaternary studies. In spite of this, when supported by independent proxy data, geomorphology and sedimentology may favor palaeo-hydrologic interpretation. This paper associates geomorphologic, stratigraphic, sedimentologic, isotopic, palynologic and geochronologic data. The research was conducted in valley head sites in southern Brazilian highlands, under mild subtropical climate. The results point to environmental changes, the ages of which coincide to Marine Isotopic Stages (MIS) 5b, 3, 2 and 1. Although late-Pleistocene temperatures and precipitation were lower than those of today, the study valley heads seem to have sustained locally wetter environments, which fed shallow soil–water saturated zones. These saturated zones are believed to have expanded during transitions between stadial and interstadial states, contributing to hillslope erosion and sedimentation regardless of the sign of the climatic change. The interior organization of holocenic slope-wash deposits suggests that the mid-Holocene climate was drier than today’s and was under the influence of seasonally contrasting precipitation regimes. The predominance of overland flow-related sedimentary records suggests that an excess of precipitation over evaporation influenced local palaeo-hydrology. This palaeo-hydrologic condition seems to have been recurrent and also explains the alternating periods of pedogenesis and sedimentation.     

Taphonomy and zooarchaeology in the Neotropics: A view from northwestern Patagonian forest and steppe

Modes of faunal exploitation in NW Chubut Province (Patagonia, Argentina) during the last 3500 calibrated years BP are discussed, based on taphonomic and zooarchaeological analyses. Bone assemblages were recovered from archaeological sites of the Sub-Antarctic forests and the extra-Andean Patagonian steppe, where huemul (Hippocamelus bisulcus) and guanaco (Lama guanicoe) were, respectively, the main staple. In the steppe, lesser rhea (Pterocnemia pennata), a medium-sized flightless bird, also was integrated into the hunter-gatherer diet. Rodents, carnivores, flying birds, and fishes also were recovered. Different processes and agents were involved in the accumulation of small vertebrates bone assemblages (e.g. birds of prey, foxes, and small carnivores). In the steppe, only two taxa of small vertebrates—birds and mountain viscacha (Lagidium viscacia)—can be related with human subsistence activities. These two taxa and all large vertebrates reveal fat-oriented carcass processing.Guanaco bone assemblages associated both with ceramic and non-ceramic technologies do not show changes in carcass processing. Moreover, the similarities in bone grease exploitation suggest boiling prior to the appearance of pottery.     

Impact of intensive fish farming on methane emission in a tropical hydropower reservoir

Fisheries and aquaculture are important sources of food for hundreds of millions of people around the world. World fish production is projected to increase by 15% in the next 10 years, reaching around 200 million tonnes per year. The main driver of this increase will be based on fish farming management in developing countries. In Brazil, fish farming is increasing due to the climate conditions and large supply of water resources, with the production system based on Nile tilapia (Oreochromis niloticus) farming in reservoirs. Inland waters like reservoirs are a natural source of methane (CH₄) to the atmosphere. However, knowledge of the impact from intensive fish production in net cages on CH₄ fluxes is not well known. This paper presents in situ measurements of CH₄ fluxes and dissolved CH₄ (DM) in the Furnas Hydroelectric Reservoir in order to evaluate the impact of fish farming on methane emissions. Measurements were taken in a control area without fish production and three areas with fish farming. The overall mean of diffusive methane flux (DMF) (5.9?±?4.5 mg CH₄ m^?2 day^?1) was significantly lower when compared to the overall mean of bubble methane flux (BMF) (552.9?±?1003.9 mg CH₄ m^?2 day^?1). The DMF and DM were significantly higher in the two areas with fish farming, whereas the BMF was not significantly different. The DMF and DM were correlated to depth and chlorophyll-a. However, the low production of BMF did not allow the comparison with the limnological parameters measured. This case study shows that CH₄ emissions are influenced more by reservoir characteristics than fish production. Further investigation is necessary to assess the impact of fish farming on the greenhouse gas emissions.     

Investigation of terrain illumination effects on vegetation indices and VI-derived phenological metrics in subtropical deciduous forests

We used RapidEye and Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra data to study terrain illumination effects on 3 vegetation indices (VIs) and 11 phenological metrics over seasonal deciduous forests in southern Brazil. We applied TIMESAT for the analysis of the Enhanced Vegetation Index (EVI) and the Normalized Difference Vegetation Index (NDVI) derived from the MOD13Q1 product to calculate phenological metrics. We related the VIs with the cosine of the incidence angle i (Cos i) and inspected percentage changes in VIs before and after topographic C-correction. The results showed that the EVI was more sensitive to seasonal changes in canopy biophysical attributes than the NDVI and Red-Edge NDVI, as indicated by analysis of non-topographically corrected RapidEye images from the summer and winter. On the other hand, the EVI was more sensitive to terrain illumination, presenting higher correlation coefficients with Cos i that decreased with reduction in the canopy background L factor. After C-correction, the RapidEye Red-Edge NDVI, NDVI, and EVI decreased 2%, 1%, and 13% over sunlit surfaces and increased up to 5%, 14%, and 89% over shaded surfaces, respectively. The EVI-related phenological metrics were also much more affected by topographic effects than the NDVI-derived metrics. From the set of 11 metrics, the 2 that described the period of lower photosynthetic activity and seasonal VI amplitude presented the largest correlation coefficients with Cos i. The results showed that terrain illumination is a factor of spectral variability in the seasonal analysis of phenological metrics, especially for VIs that are not spectrally normalized.     

The ecohydrological imprint of deforestation in the semiarid Chaco: insights from the last forest remnants of a highly cultivated landscape

The semiarid Chaco plains present one of the highest rates of forest clearing and agricultural expansion of the world. In other semiarid plains, such massive vegetation replacements initiated a groundwater recharge and salt mobilization process that, after decades, raised regional water tables and salts to the surface, degrading agricultural and natural ecosystems. Indirect evidence suggests that this process (known as dryland salinity) began in the Chaco plains. Multiple approaches (deep soil profiles, geoelectric surveys and monitoring of groundwater salinity, level and isotopic composition) were combined to assess the dryland salinity status in one of the oldest and most active agricultural hotspots of the region, where isolated forest remnants occupy an extremely flat cultivated matrix. Full vadose moisture and chloride profiles from paired agriculture‐forest stands (17 profiles, six sites) revealed the following: a generalized onset of deep drainage with cultivation (32 to >87 mm year^?1), full leaching of native chloride pools (13.7 ± 2.5 kg m^?2) down to the water table after >40 years following clearing and differential groundwater table rises (0.7 to 2 m shallower water tables under agriculture than under neighbouring forests). Continuous level monitoring showed abrupt water table rises under annual crops (up to 2.6 m in 15 days) not seen under forests or pastures. Varying deep drainage rates and groundwater isotopic composition under agricultural plots suggest that these pulses are strongly modulated by crop choices and sequences. In contrast to other dryland salinity‐affected areas of the world, forest remnants in the study area (10–20% of the area) are not only surviving the observed hydrological shifts but also sustaining active salty groundwater transpirative discharge, as evidenced by continuous water table records. The overall impact of these forest remnants on lowering neighbouring water tables would be limited by the low hydraulic conductivity of the sediments. As highly cultivated areas of the Chaco evolve to new hydrological conditions of shallower saline water tables, innovative crop rotations that minimize recharge, enhance transpirative discharge and tolerate salinity will be needed. Copyright © 2016 John Wiley & Sons, Ltd.