Tracing anthropogenically driven groundwater discharge into a coastal lagoon from southern Brazil

We investigated the distribution of naturally occurring geochemical tracers (²²²Rn, ²²³Ra, ²²⁴Ra, ²²⁶Ra, CH₄, δ¹⁸O, and δ²H) in the water column and adjacent groundwater of Mangueira Lagoon as proxies of groundwater discharge. Mangueira Lagoon is a large (90 km long), shallow (4–5 m deep), fresh, and non-tidal coastal lagoon in southern Brazil surrounded by extensively irrigated rice plantations and numerous irrigation canals. We hypothesized that the annual, intense irrigation for rice agriculture creates extreme conditions that seasonally change groundwater discharge patterns in the adjacent lagoon. We further supposed that dredging of irrigation canals alters groundwater fluxes.

While the activities of ²²²Rn in shallow groundwater were 2–3 orders of magnitude higher than in surface water, CH₄ and radium isotopes were only 1 order of magnitude higher. Therefore, ²²²Rn appears to be the preferred groundwater tracer in this system. Radon concentrations and conductivities were dramatically higher near the pump house of rice irrigation canals, consistent with a groundwater source. Modeling of radon inventories accounting for total inputs (groundwater advection, diffusion from sediments, and decay of ²²⁶Ra) and losses (atmospheric evasion, horizontal mixing and decay) indicated that groundwater advection rates in the irrigation canals (25 cm/d) are over 2 orders of magnitude higher than along the shoreline (0.1 cm/d). Nearly 75% of the total area of the canals is found in the southern half of the lagoon, where groundwater inputs seem to be higher as also indicated by methane and stable isotope trends. In spite of the relatively small area of the canals, we estimate that they contribute nearly 70% of the total (57,000 m³/d) groundwater input into the entire Mangueira Lagoon. We suggest that the dredging of these canals cut through aquitards which previously restricted upward advection from the underlying permeable strata. The irrigation channels may therefore represent an important but previously overlooked source of nutrients and other dissolved chemicals derived from agricultural practices into the lagoon.     

Variability of carbon dioxide flux from tropical (Cerrado) hydroelectric reservoirs

Hydroelectric reservoirs generate energy without significant combustion of fossil fuels. However, these systems can, potentially, emit greenhouse gases (GHG’s) at a rate which may be significant at the global scale, and, possible, co-equal, per kilowatt-hour, to that from conventional coal or oil-fired systems. Although much of the new construction of hydroelectric reservoirs is in the tropics, most of the data on GHG emissions comes from temperate regions. Further, much of the existing data on reservoir gas emissions comes from single sites, usually near the terminal dams. Large tropical reservoirs often involve the impoundments of river systems with complex morphology which in turn can cause spatial heterogeneity in gas flux. We evaluated spatial and seasonal variability in CO₂ concentrations and gas flux for five large (50–1,400 km²) reservoirs in the Cerrado region of Brazil. Most of data set (87% of all measurements) showed CO₂ supersaturation and net efflux to the atmosphere. There was as much or more variation in pCO₂ over space and among seasons. The large studied reservoirs showed different zones in terms of CO₂ emission because those fluxes are dependent on flooded biomass, watershed input of organic matter and dam operation regime. Here we demonstrate that the reservoirs in the Brazilian Cerrado have low rates of CO₂ emissions compared to existing global comparisons. Our results suggest that ignoring the spatial variability can lead to more than 25% error in total system gas flux.     

Improving GSMaP V06 precipitation products over the Upper Tocantins River basin in the Brazilian Cerrado,based on local rain-gauge network

Theoretical and Applied Climatology - Gridded precipitation products from remote sensing are currently available and could potentially enhance the use of precipitation data in regions with sparse...     

The effectiveness of “clay” liners as basal isolation of landfills: a case study

A sodium bentonite is being used in the basal-isolation of landfills installed on strongly fractured granitic rocks of N Portugal (NW Iberia). To evaluate the performance of this clay as the ultimate impermeable basal barrier, a detailed study was carried out of the granite fracture network; the Na-bentonite was tested to characterize its mechanical and geotechnical behavior; geophysical surveys were made to search for landfill leakage and the waters found around the landfill were geochemically characterized. Fractures in the granite are usually open and devoid of mineral infillings or clay materials and, thus, permeability of the granite is very high. Dispersal of contaminants can be further enhanced by the position of the landfill on a high steep-sided ridge. Geophysical and geochemical data show evidence for seepage and dispersion of pollutants, which means that the clay failed as an ultimate isolation barrier against seepage. This investigation shows that this can be due to fracturing of the clay under load and/or to its non-homogeneous saturation and extreme shrinking character upon drying, which are accompanied by the formation of extensive cracking. Observations and experimental results suggest that the use of synthetic clays in the safe building of landfill bottom liners needs further research, and extreme care should be taken in preventing that clay water content suffers large variations after saturation, as this process considerably degrades the mechanical behavior and sealing properties of the studied Na-bentonite.     

Submarine groundwater discharge of nutrients to the ocean along a coastal lagoon barrier, Southern Brazil

The Patos–Mirim Lagoon system along the southern coast of Brazil is linked to the coastal ocean by a narrow mouth and by groundwater transport through a Holocene barrier. Although other groundwater systems are apparently active in this region, the hydraulic head of the lagoon, the largest in South America, drives groundwater transport to the coast. Water levels in wells placed in the barrier respond to changing water level in the lagoon. The wells also provide a measure of the nutrient concentrations of groundwater flowing toward the ocean. Additionally, temporary well points were used to obtain nutrient samples in groundwater on the beach face of the barrier. These samples revealed a subterranean freshwater–seawater mixing zone over a ca. 240 km shoreline. Previously published results of radium isotopic analyses of groundwater and of surface water from cross-shelf transects were used to estimate a water flux of submarine groundwater discharge (SGD) to nearshore surface waters of 8.5 × 10⁷ m³/day. Using this SGD and the nutrient concentrations in different compartments, nutrient fluxes between groundwater and surface water were estimated. Fluxes were computed using both average and median reservoir (i.e. groundwater and surface water) nutrient concentrations. The SGD total dissolved inorganic nitrogen, phosphate and silicate fluxes (2.42, 0.52, 5.92 × 10⁶ mol day^− 1, respectively) may represent as much as 55% (total N) to 10% (Si) of the nutrient fluxes to the adjacent shelf environment. Assuming nitrogen limitation, SGD may be capable of supporting a production rate of ca. 3000 g C m² year^− 1in the nearshore surf zone in this region.     

Nonlinear Evolution of Thermal Structures. Numerical Approach

A numerical algorithm using a two stage, two level difference scheme has been developed to solve the heat transfer equation with nonlinear heat diffusion and bulk energy losses. The algorithm is an extension of the scheme developed by Meek and Norbury (1982). The first stage calculates an intermediate value which is used in a second stage to estimate a new value. The scheme is consistent, second-order convergent in space and almost second order in time. It has been applied to the nonlinear stability and time evolution of thermal structures constituted by optically thin plasmas with solar abundances. The configuration has been assumed to be heated at a rate T^m, cooled at a rate Tⁿ and a thermal conduction coefficient T^k. In particular, the second order analytical approximation considered in previous papers (Ibáñez and Rosenzweig, 1995; Steele and Ibáñez, 1997) has been worked out for arbitrary amplitude of the initial temperature disturbance. Particular cases of interest in Astrophysics are considered.     

Effects of Explicit Urban-Canopy Representation on Local Circulations Above a Tropical Mega-City

The Advanced Regional Prediction System (ARPS) is coupled with the tropical town energy budget (tTEB) scheme to analyze the effects of the urban canopy circulation over the metropolitan area of São Paulo and its interactions with the sea breeze and mountain-valley circulation in the eastern state of São Paulo, Brazil. Two experiments are carried out for the typical sea-breeze event occurring on 22 August 2014 under weak synoptic forcing and clear-sky conditions: (a) a control run with the default semi-desert surface parametrization and; (b) a tTEB run for the urban canopy of São Paulo. A realistic land-use database over the south-eastern domain of Brazil is used in the downscaling simulation to a horizontal grid resolution of 3 km. Our results indicate that ARPS effectively simulates features of the nighttime and early morning land-breeze circulation, which is affected by the surrounding hills and the nocturnal heat island of São Paulo. By early afternoon, the south-eastern sea-breeze circulation moves inland perpendicular to the upslope of the Serra do Mar scarp, which generates a line of moisture convergence and updrafts further inland. Later, the convergence line reaches São Paulo and interacts with the circulation arising from the urban heat island (UHI), which increases the moisture convergence and strength of updrafts. The surface energy balance indicates that the UHI is caused by large sensible heat storage within the urban canopy during the day, which is later released in the afternoon and at night. The simulations are verified with available radiosonde and surface weather station data, land-surface-temperature estimates from the moderate resolution imaging spectroradiometer, as well as the National Center for Atmospheric Research reanalysis databases. The three-dimensional geometry of the urban canyons within the tTEB scheme consistently improves the thermodynamically-induced circulation over São Paulo.     

Salmon aquaculture and coastal ecosystem health in Chile: Analysis of regulations,environmental impacts and bioremediation systems

In 2007 salmon, mollusk and seaweed aquaculture production in Chile totaled 904 thousand tonnes, making the nation the leading marine aquaculture producer in the western world. Salmonids grown in open cage net pens account for over 73% of the production. This review summarizes the current status of Chilean aquaculture and proposes the establishment of new regulations and monitoring programmes that encourage and accommodate emerging bioremediation technologies. In contrast to a rapidly expanding, well-financed and technologically advanced industry, the regulatory structure in Chile is outdated and based on insufficient science. The number of publications on the environmental impacts of salmon aquaculture in Chile is low relative to its production level. Nevertheless, the impacts of organic and inorganic waste on benthic communities, pelagic organisms and bird populations are documented. The technology to reduce these impacts using integrated multi-trophic aquaculture (IMTA) strategies exists, but has not been implemented at commercial scales. We call on the government and industry to support the creation of a well-financed and politically independent agency responsible for developing and enforcing science-based environmental regulations in Chile. The agency's immediate goal should be to fund research required to develop a transparent, ecosystem-based regulatory framework that promotes IMTA. Monitoring programs and licensing procedures must consider the impacts of individual sites and the cumulative impacts from multiple sites across a wide range of spatial scales. Before such changes are realized, environmental threats and human health risks will remain unacceptably high and salmon farming in Chile will not meet any reasonable definition of sustainability.     

Simulation of Geological Contacts from Interpreted Geological Model Using Multiple-Point Statistics

Applications of multiple-point statistics (mps) algorithms to large non-repetitive geological objects such as those found in mining deposits are difficult because most mps algorithms rely on pattern repetition for simulation. In many cases, an interpreted geological model built from a computer-aided design system is readily available but suffers as a training image due to the lack of patterns repetitiveness. Porphyry copper deposits and iron ore formations are good examples of such mining deposits with non-repetitive patterns. This paper presents an algorithm called contactsim that focuses on reproducing the patterns of the contacts between geological types. The algorithm learns the shapes of the lithotype contacts as interpreted by the geologist, and simulates their patterns at a later stage. Defining a zone of uncertainty around the lithological contact is a critical step in contactsim, because it defines both the zones where the simulation is performed and where the algorithm should focus to learn the transitional patterns between lithotypes. A larger zone of uncertainty results in greater variation between realizations. The definition of the uncertainty zone must take into consideration the geological understanding of the deposit, and the reliability of the contact zones. The contactsim algorithm is demonstrated on an iron ore formation.     

Stellar Motions in Galactic Satellites

The study of the motions of the stars that belong to a galactic satellite (i.e. a globular cluster or a dwarf galaxy orbiting a larger one) has some similarities, as well as significant differences, with that of the restricted three-body problem of celestial mechanics. The high percentage of chaotic orbits present in some models is of particular interest because it rises, on the one hand, the question of the origin of those chaotic motions and, on the other hand, the question of whether an equilibrium stellar system can be built when the bulk of the stars that make it up behave chaotically.