Radiation balance at the surface in the city of S?o Paulo, Brazil: diurnal and seasonal variations

The main goal of this work is to describe the diurnal and seasonal variations of the radiation balance components at the surface in the city of S?o Paulo based on observations carried out during 2004. Monthly average hourly values indicate that the amplitudes of the diurnal cycles of net radiation (Q*), downwelling and upwelling shortwave radiation (SW_DW, SW_UP), and longwave radiations (LW_DW, LW_UP) in February were, respectively, 37%, 14%, 19%, 11%, and 5% larger than they were in August. The monthly average daily values indicate a variation of 60% for Q*, with a minimum in June and a maximum in December; 45% for SW_DW, with a minimum in May and a maximum in September; 50% for SW_UP, with a minimum in June and a maximum in September; 13% for LW_DW, with a minimum in July and a maximum in January; and 9% for LW_UP, with a minimum in July and a maximum in February. It was verified that the atmospheric broadband transmissivity varied from 0.36 to 0.57; the effective albedo of the surface varied from 0.08 to 0.10; and the atmospheric effective emissivity varied from 0.79 to 0.92. The surface effective emissivity remained approximately constant and equal to 0.96. The albedo and surface effective emissivity for S?o Paulo agreed with those reported for urban areas in Europe and North America cities. This indicates that material and geometric effects on albedo and surface emissivity in S?o Paulo are similar to ones observed in typical middle latitudes cities. On the other hand, it was found that S?o Paulo city induces an urban heat island with daytime maximum intensity varying from 2.6°C in July (16:00 LT) to 5.5°C in September (15:00 LT). The analysis of the radiometric properties carried out here indicate that this daytime maximum is a primary response to the seasonal variation of daily values of net solar radiation at the surface.     

Drivers of peatland water table dynamics in the central Andes,Bolivia and Peru

Cushion plant dominated peatlands are key ecosystems in tropical alpine regions of the Andes in South America. The cushion plants have formed peat bodies over thousands of years that fill many valley bottoms, and the forage produced by the plants is critical for native and nonnative domesticated mammals. The sources and flow paths of water supporting these peatlands remain largely unknown. Some studies have suggested that glacier meltwater streams support some peatlands, and that the ongoing loss of glaciers and their meltwaters could lead to the loss or diminishment of peatlands. We analysed the hydrologic regime of 10 peatlands in four mountain regions of Bolivia and Peru using groundwater monitoring. Groundwater levels in peatlands were relatively stable and within 20 cm of the ground surface during the rainy season, and many sites had water tables 40–90 cm below the ground surface in the dry season. Topographic and groundwater elevations in the peatlands demonstrated that the water source of all 10 peatlands was hillslope groundwater flowing from lateral moraines, talus, colluvium, or bedrock aquifers into the peatlands. There was little to no input from streams, whether derived from glacier melt or other sources, and glacier melt could not have recharged the hillslope aquifers supporting peatlands. We measured the stable water isotopes in water samples taken during different seasons, distributed throughout the catchments, and the values are consistent with this interpretation. Our findings indicate that peatlands in the study region are recharged by hillslope groundwater discharge rather than stream water and may not be as vulnerable to glacial decline as other studies have indicated. However, both glaciers and peatlands are susceptible to changing thermal and precipitation regimes that could affect the persistence of peatlands.     

Inverse modeling of coastal aquifers using tidal response and hydraulic tests

Remediation of contaminated aquifers demands a reliable characterization of hydraulic connectivity patterns. Hydraulic diffusivity is possibly the best indicator of connectivity. It can be derived using the tidal response method (TRM), which is based on fitting observations to a closed-form solution. Unfortunately, the conventional TRM assumes homogeneity. The objective of this study was to overcome this limitation and use tidal response to identify preferential flowpaths. Additionally, the procedure requires joint inversion with hydraulic test data. These provide further information on connectivity and are needed to resolve diffusivity into transmissivity and storage coefficient. Spatial variability is characterized using the regularized pilot points method. Actual application may be complicated by the need to filter tidal effects from the response to pumping and by the need to deal with different types of data, which we have addressed using maximum likelihood methods. Application to a contaminated artificial coastal fill leads to flowpaths that are consistent with the materials used during construction and to solute transport predictions that compare well with observations. We conclude that tidal response can be used to identify connectivity patterns. As such, it should be useful when designing measures to control sea water intrusion.     

Evolution of mineralizing fluids in the Zn–Pb–Cu(–Ag ± Au) skarn and epithermal deposits of the world-class San Martín district, Zacatecas, Mexico

Mineralizing fluids at the San Martín skarn show an evolution characterized by prograde and retrograde associations. The prograde mineral associations consist of (1) a massive garnet zone, (2) a tremolite ± garnet zone, and (3) a late association of quartz, sphalerite, calcite and fluorite lining the vugs in the garnet zone. The fluids of the prograde associations exhibit decreasing temperatures of homogenization (Th) and variable salinities. The fluids of the massive garnet zone have salinities of 36 wt.% NaCl equiv. and Th of 645 to 570 °C, corresponding to pressures of 1055 bar. At the tremolite ± garnet zone, Th range from 438 to 354 °C. In the late association at the endoskarn, the following evolution can be drawn: (a) salinities of 50 to 42 wt.% NaCl equiv., and Th of 455 to 346 °C in quartz, (b) salinities of 46 wt.% NaCl equiv., and Th of 415 to 410 °C in sphalerite, (c) salinities of 50 to 37 wt.% NaCl equiv., and Th of 479 to 310 °C in calcite, (d) salinities of 33 to 28 wt.% NaCl equiv. and of 24 to 22 wt.% KCl in fluorite, and (e) two types of fluids with salinities of 2 and 39 wt.% NaCl equiv. and Th 344 and 300 °C, respectively, in later saccharoidal quartz segregations. The retrograde mineral associations comprise pervasive propylitic alteration to carbonization, and mantos with sulfides. Fluids in epidote have salinities of 7.6 wt.% NaCl equiv. and Th of 287 to 252 °C, and in calcite have salinities of 9.2 to 1 wt.% NaCl equiv. and Th of 188 to 112 °C. Fluids in the sulfide assemblages in the mantos have salinities of 8 to 3 wt.% NaCl equiv. and Th 300 °C, with corresponding pressures of 94 bar. Fluids in late epithermal veins close to the intrusive body have salinities of 10 to 5 wt.% NaCl equiv. and Th of 275 to 200 °C, and distal veins show salinities of 2 to 1 wt.% NaCl equiv. and Th of 160 °C.     

The evolution of a tropical rainforest/grassland mosaic in southeastern Brazil since 28,000 C yr BP based on carbon isotopes and pollen records

The lack of paleoecological records from the montane Atlantic Rainforest of coastal Brazil, a hotspot of biological diversity, has been a major obstacle to our understanding of the vegetational changes since the last glacial cycle. We present carbon isotope and pollen records to assess the impact of the glaciation on the native vegetation of the Serra do Mar rainforest in São Paulo, Brazil. From ca. 28,000 to  22,000 ¹⁴C yr BP, a subtropical forest with conifer trees is indicative of cool and humid conditions. In agreement carbon isotopic data on soil organic matter suggest the presence of C₃ plants and perhaps C₄ plants from  28,000 to  19,000 ¹⁴C yr BP. The significant increase in the sedimentation rate and algal spores from  19,450 to  19,000 ¹⁴C yr BP indicates increasing humidity, associated to an erosion process between  19,000 and  15,600 ¹⁴C yr BP. From  15,600 ¹⁴C yr BP to present there is a substantial increase in arboreal elements and herbs, indicating more humid and warmer climate. From  19,000 to  1000 ¹⁴C yr BP, δ¹³C values indicated the predominance of C₃ plants. These results are in agreement with studies in speleothems of caves, which suggest humid conditions during the last glacial maximum.     

Photoautotrophic community changes in Lagunillo del Tejo (Spain) in response to lake level fluctuation: Two centuries of sedimentary pigment records

Lagunillo del Tejo is a small doline lake in a karstic region of the Iberian Ranges (central-eastern Spain) that undergoes significant lake level fluctuation in response to changing aquifer influxes. In order to assess changes in the primary producer community in the lake over the last two centuries and to elucidate whether these were conditioned by climatic variability, photosynthetic pigments and their derivatives were extracted from the sediments and the data analysed using multivariate statistical techniques. Quantitative variations in total pigment concentrations through the sedimentary sequence are considered a result of changes in sedimentation rate, largely due to lake level fluctuation. Rapid lowering of the level results in an increase in detritic mineral matter eroded from the sides of the lake, which accumulates in the sediment and dilutes the organic matter content in the corresponding sediment layers. On the other hand, shifts in the relative abundances of the different pigments suggest the development of two different primary producer communities: (i) planktonic, comprising cyanobacteria, chlorophytes, cryptophytes and purple sulfur bacteria and (ii) primary producers related to the littoral environment, mostly submerged macrophytes. These two communities showed alternating relative importance over the last two centuries, as a biotic response to lake level fluctuation during wet and dry periods, respectively.     

IPHAS discoveries of young stars towards Cyg OB2 and its southern periphery

We report on the discovery of over 50 strong Hα emitting objects towards the large OB association Cyg OB2 and the H  ii region DR 15 on its southern periphery. This was achieved using the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS), combined with follow-up spectroscopy using the MMT multi-object spectrometer HectoSpec. We present optical spectra, supplemented with optical r ',  i ' and H α photometry from IPHAS, and near-infrared J ,  H and K photometry from Two Micron All Sky Survey. The position of the objects in the ( J − H ) versus ( H − K ) diagram strongly suggests most of them are young. Many show Ca  ii infrared triplet emission indicating that they are in a pre-main-sequence phase of evolution of T Tauri and Herbig Ae nature. Among these, we have uncovered pronounced clustering of T Tauri stars roughly a degree south of the centre of Cyg OB2, in an arc close to the H  ii region DR 15, and the radio ring nebula G79.29+0.46, for which we discuss its candidacy as a luminous blue variable. The emission-line objects towards Cyg OB2 itself could be the brightest most prominent component of a population of lower mass pre-main-sequence stars that has yet to be uncovered. Finally, we discuss the nature of the ongoing star formation in Cyg OB2 and the possibility that the central OB stars have triggered star formation in the periphery.     

Future climate impacts on the hydrology of headwater streams in the Amazon River Basin: Implications for migratory goliath catfishes

Climate-driven alterations of hydro-meteorological conditions can change river flow regimes and potentially affect the migration behaviour of fishes and the productivity of important fisheries in the Amazon basin, such as those for the continental-scale migratory goliath catfishes (Brachyplatystoma, Pimelodidae). In this study, we investigated hydrologic responses to climate change using a hydrologic model forced with climate inputs, which integrate historical (2001–2010) observations and general circulation model (GCM) projections under the emission scenario Representative Concentration Pathway 8.5. We developed an empirical model to characterize future (2090–2099) climate-change impacts on goliath catfish spawning migrations as a function of river flow depth dynamics at the upstream elevational limit of spawning (250 m) in headwater basins of the Amazon. The model results revealed spatially variable impacts of climate change on the catfish spawning migrations. The Marañón, Ucayali, Juruá, Purus, and Madeira basins had a predicted increase in the annual mean (3–8%) and maximum (1.1–4.9%) spawning migration rate (i.e., the fraction of fish that migrate to the spawning grounds in a day), mainly due to the lengthened rising phase of flow-driven migratory events during wet seasons. The Caquetá-Japurá, Putumayo-Içá, Napo, and Blanco rivers had predicted decreases (3–7%) in the mean migration rate because of decreases in the length of the rising season of flow depth and the frequency of migratory events. The predicted timing of fish spawning migrations (quantified by the temporal centroid of migration rates) was delayed by 7–10 days in the west-central and southwest regions and was 8 days earlier in the northwest and northcentral areas, due to changes in the onset of the rising season. We established a river depth baseline that controls the onset of goliath catfish spawning migration. This depth varies between 0.9–5.6 m across study sites. We found that the estimated depth baseline was most sensitive to uncertainties in river width and cross-sectional channel shape. These results may help inform sustainable adaptation strategies for ecosystem conservation and local fisheries management in the Amazon basin.