Central configurations of the planar 1+N body problem

In this paper, we give a new derivation of the equations for the central configurations of the 1+n body problem. In the case of equal masses, we show that forn large enough there exists only one solution. Our lower bound forn improves by several orders of magnitude the one previously found by Hall.     

Scientists' warning on extreme wildfire risks to water supply

2020 is the year of wildfire records. California experienced its three largest fires early in its fire season. The Pantanal, the largest wetland on the planet, burned over 20% of its surface. More than 18 million hectares of forest and bushland burned during the 2019–2020 fire season in Australia, killing 33 people, destroying nearly 2500 homes, and endangering many endemic species. The direct cost of damages is being counted in dozens of billion dollars, but the indirect costs on water-related ecosystem services and benefits could be equally expensive, with impacts lasting for decades. In Australia, the extreme precipitation (“200 mm day −1 in several location”) that interrupted the catastrophic wildfire season triggered a series of watershed effects from headwaters to areas downstream. The increased runoff and erosion from burned areas disrupted water supplies in several locations. These post-fire watershed hazards via source water contamination, flash floods, and mudslides can represent substantial, systemic long-term risks to drinking water production, aquatic life, and socio-economic activity. Scenarios similar to the recent event in Australia are now predicted to unfold in the Western USA. This is a new reality that societies will have to live with as uncharted fire activity, water crises, and widespread human footprint collide all-around of the world. Therefore, we advocate for a more proactive approach to wildfire-watershed risk governance in an effort to advance and protect water security. We also argue that there is no easy solution to reducing this risk and that investments in both green (i.e., natural) and grey (i.e., built) infrastructure will be necessary. Further, we propose strategies to combine modern data analytics with existing tools for use by water and land managers worldwide to leverage several decades worth of data and knowledge on post-fire hydrology.     

Microbiological composition of native and exotic clams from Tagus estuary: Effect of season and environmental parameters

The influence of seasonal and environmental parameters on the occurrence of bacteria was investigated in two clam species (Venerupis pullastra and Ruditapes philippinarum), water and sediment from the Tagus estuary. Total viable counts (TVC), Escherichia coli, Salmonella spp. and Vibrio spp. were evaluated during one-year. Overall, significant seasonal variations were found in both sampling sites, especially for E. coli and Vibrio spp. levels. In summer, significantly higher Vibrio spp. levels were found in R. philippinarum and sediment samples, but not in V. pullastra clams and water samples. In contrast, significantly higher TVC and E. coli levels were observed in winter months in water and sediment samples. Salmonella spp. was generally isolated when higher levels of E. coli were detected, particularly in R. philippinarum. This study is useful for authorities to develop monitoring strategies for coastal contamination and to estimate human health risks associated with the consumption of bivalves.     

Tidal and Groundwater Fluxes to a Shallow, Microtidal Estuary: Constraining Inputs Through Field Observations and Hydrodynamic Modeling

Increased nutrient loading to estuaries has led to eutrophication, degraded water quality, and ecological transformations. Quantifying nutrient loads in systems with significant groundwater input can be difficult due to the challenge of measuring groundwater fluxes. We quantified tidal and freshwater fluxes over an 8-week period at the entrance of West Falmouth Harbor, Massachusetts, a eutrophic, groundwater-fed estuary. Fluxes were estimated from velocity and salinity measurements and a total exchange flow (TEF) methodology. Intermittent cross-sectional measurements of velocity and salinity were used to convert point measurements to cross-sectionally averaged values over the entire deployment (index relationships). The estimated mean freshwater flux (0.19?m³/s) for the 8-week period was mainly due to groundwater input (0.21?m³/s) with contributions from precipitation to the estuary surface (0.026?m³/s) and removal by evaporation (0.048?m³/s). Spring?Cneap variations in freshwater export that appeared in shorter-term averages were mostly artifacts of the index relationships. Hydrodynamic modeling with steady groundwater input demonstrated that while the TEF methodology resolves the freshwater flux signal, calibration of the index?Csalinity relationships during spring tide conditions only was responsible for most of the spring?Cneap signal. The mean freshwater flux over the entire period estimated from the combination of the index-velocity, index?Csalinity, and TEF calculations were consistent with the model, suggesting that this methodology is a reliable way of estimating freshwater fluxes in the estuary over timescales greater than the spring?Cneap cycle. Combining this type of field campaign with hydrodynamic modeling provides guidance for estimating both magnitude of groundwater input and estuarine storage of freshwater and sets the stage for robust estimation of the nutrient load in groundwater.     

Fingerprint of tropical climate variability and sea level in sediments of the Cariaco Basin during the last glacial period

High‐resolution palaeorecords of climate are critical to improving current understanding of climate variability, its sensitivity and impact on the environment in the past and in the future. Sediments from the Cariaco Basin off the coast of Venezuela have proven to be sensitive recorders of tropical palaeoclimate variability down to an annual scale. However, the fingerprint of climate and sea level in the sediments of the last glacial period is still not completely understood. In this study, lamination analysis of sediments from the Cariaco Basin is extended to the last glacial period. Detailed sedimentological and geochemical analysis (laser ablation–inductively coupled plasma–mass spectrometry) reveals couplets of light‐coloured, terrigenous‐rich and dark‐coloured, biogenic opal‐rich laminae, which are interpreted to reflect the seasonal migration of the Intertropical Convergence Zone. In addition, a previously undescribed, nearly pure terrigenous lamina type is observed, which is referred to hereafter as a ‘C‐layer’. The C‐layers in the sedimentary sequence are interpreted as flood layers that originate from local rivers. The occurrence of these C‐layers is investigated for two core locations in the Cariaco Basin over the last 110 kyr by continuous X‐ray fluorescence scanning. Dansgaard–Oeschger oscillations are most clearly traced by proxies reflecting productivity and marine organic matter content of the sediment. In contrast, the abundance of terrigenous material differs at times between the two sites. On an interglacial to glacial timescale, the ability to record events causing C‐layers is likely to be influenced by changes in sea level and source proximity. On a millennial scale, both sediment cores contain more C‐layers during warmer interstadials compared with colder stadials during Marine Isotope Stage 3. This finding implies that interstadials were not only wetter than stadials, but probably also characterized by increased rainfall variability, leading to an enhanced frequency of flooding events in the hinterland of the Cariaco Basin.     

Geostatistical Seismic Inversion with Direct Sequential Simulation and Co-simulation with Multi-local Distribution Functions

Stochastic sequential simulation is a common modelling technique used in Earth sciences and an integral part of iterative geostatistical seismic inversion methodologies. Traditional stochastic sequential simulation techniques based on bi-point statistics assume, for the entire study area, stationarity of the spatial continuity pattern and a single probability distribution function, as revealed by a single variogram model and inferred from the available experimental data, respectively. In this paper, the traditional direct sequential simulation algorithm is extended to handle non-stationary natural phenomena. The proposed stochastic sequential simulation algorithm can take into consideration multiple regionalized spatial continuity patterns and probability distribution functions, depending on the spatial location of the grid node to be simulated. This work shows the application and discusses the benefits of the proposed stochastic sequential simulation as part of an iterative geostatistical seismic inversion methodology in two distinct geological environments in which non-stationarity behaviour can be assessed by the simultaneous interpretation of the available well-log and seismic reflection data. The results show that the elastic models generated by the proposed stochastic sequential simulation are able to reproduce simultaneously the regional and global variogram models and target distribution functions relative to the average volume of each sub-region. When used as part of a geostatistical seismic inversion procedure, the retrieved inverse models are more geologically realistic, since they incorporate the knowledge of the subsurface geology as provided, for example, by seismic and well-log data interpretation.     

Is filter packing important in a small-scale vermifiltration process of urban wastewater?

Nowadays, natural resources are under increasing stress which fosters wastewater reuse planning and emphasizes on the decentralized wastewater treatment. Vermifiltration has been described as a viable alternative to treat domestic and urban wastewater, but few studies have focused on the impact of different filter packings on vermifiltration performance. This study evaluates the effect of vermicompost and sawdust in a single-stage vermifilter (VF) for urban wastewater treatment. After an acclimation period of 45 days, urban wastewater from a combined sewage collection system was applied continuously for 24 h. Earthworm stock density was of 20 g L^?1, HRT of 6 h, HLR of 0.89 m³ m^?2 day^?1 and OLR of 7.38 g BOD₅ day^?1. System performance was assessed by the removal efficiencies of BOD₅, COD, TSS, NH₄ ⁺, TN and TP, and fecal coliforms and helminth eggs elimination. Vermicompost (VE) and sawdust (SE) were tested, using an earthworm abundance of 20 g L^?1. Treatment efficiencies were 91.3% for BOD₅, 87.6% for COD, 98.4% for TSS and 76.5% for NH₄ ⁺ in VE, and 90.5% for BOD₅, 79.7% for COD, 98.4% for TSS and 63.4% for NH₄ ⁺ in SE. Earthworms contributed to reduce NH₄ ⁺ and TN removal and to increase NO₃ ^? concentration. No treatment was able to eliminate fecal coliforms down to guidelines values for wastewater irrigation as helminth eggs were completely eliminated. Single-stage vermifiltration system using both filter packings is inconsistent and cannot meet EU guideline values for discharge in sensitive water bodies and WHO guidelines for irrigation with treated wastewater.     

Subantarctic macrotidal flats, cheniers and beaches in San Sebastian Bay, Tierra Del Fuego, Argentina

San Sebastian Bay is a large, semicircular coastal embayment situated on the Atlantic coast of Tierra del Fuego, Argentina. It is a high-energy, subantarctic environment with a tidal range of 10.4 m, influenced by large waves of Atlantic and local origin and swept by constant, strong westerly winds. A 17 km long gravel spit protects the Northern part of the Bay giving rise to a gradient in sedimentary processes. From south to north, are seven distinct sedimentary environments. Coastal sedimentation started at least 5200 years before present (BP) and a rapid progradation related to a relative sea-level drop has infilled about 6 kilometres of the Bay with a sedimentary sequence 10–11 m thick. 14-C dating of unabraded shells in the Chenier ridges of the relict part of the complex allows for a precise reconstruction of the stages of the progradation, that has slowed from 2.35 m/year at 5000 years BP to 0.6 m/year at present. The possible causes of the sea-level drop are discussed.