End member and Bayesian mixing models consistently indicate near-surface flowpath dominance in a pristine humid tropical rainforest

The impacts of forest conversion on runoff generation in the tropics have received much interest, but scientific progress is still hampered by challenging fieldwork conditions and limited knowledge about runoff mechanisms. Here, we assessed the runoff generation, flow paths and water source dynamics of a pristine rainforest catchment in Costa Rica using end member mixing analysis (EMMA) and a Bayesian mixing model (MixSIAR). Geochemical tracer data collected over a 4-week field campaign were combined with tritium data used to assess potential deeper groundwater flow pathways to the perennial stream. The streamflow composition was best captured using three end-members, namely throughfall, shallow (5–15 cm) and deeper (15–50 cm) soil water. We estimated the end-member contributions to the main stream and two tributaries using the two mixing approaches and found good agreement between results obtained from EMMA and MixSIAR. The system was overwhelmingly dominated by near-surface sources, with little evidence for deeper and older groundwater as tritium-derived baseflow mean transit time was between 2.0 and 4.4 years. The shallow soil flow pathway dominated streamflow contributions in the main stream (median 39% and 49% based on EMMA and MixSIAR, respectively), followed by the deeper soil (32% and 31%) and throughfall (25% and 19%). The two tributaries had even greater shallow soil water contributions relative to the main stream (83% and 74% for tributary A and 42% and 63% for tributary B). Tributary B had no detectable deep soil water contribution, reflecting the morphology of the hillslope (steeper slopes, shallower soils and lower vegetation density compared to hillslope A). Despite the short sampling campaign and associated uncertainties, this study allowed to thoroughly assess runoff generation mechanisms in a humid tropical catchment. Our results also provide a first comparison of two increasingly used mixing models and suggest that EMMA and MixSIAR yield comparable estimates of water source partitioning in this tropical, volcanic rainforest environment.     

Regional provenance from southwestern Colombia fore‐arc and intra‐arc basins: implications for Middle to Late Miocene orogeny in the Northern Andes

Andean orogenic processes controlled the spatial and temporal distribution of the magmatic and sedimentary record. This contribution integrates new U/Pb zircon ages, heavy mineral analyses and biostratigraphic constraints from the Neogene sedimentary record of the fore‐arc and intra‐arc basins and volcano‐plutonic rocks of southwestern Colombia, to reconstruct these orogenic processes. The results reveal continuous arc magmatism since the Late Oligocene, with a major post‐Middle Miocene magmatic peak and exhumation. When integrated with other geological constraints, the tectonic evolution of the margin includes Eocene‐Oligocene oblique convergence with limited magmatic activity, followed by the initiation of a Late Oligocene‐Early Miocene arc that migrated to the east in the Middle Miocene, when it experienced a major increase in magmatic activity, crustal deformation, exhumation and thickening. This orogenic evolution is related to the shallowing of the slab dip due to the subduction of the Neogene Nazca Plate.     

Hydrochemical and isotopic characterization of the hydrological budget of a MAB Reserve: Mar Chiquita lagoon,province of Buenos Aires,Argentina

Mar Chiquita is a coastal lagoon located in the Argentine Buenos Aires province in South America. The aim of this study was to perform a hydrochemical and stable isotopes characterization in order to better the understanding of the hydrology of the Mar Chiquita lagoon’s catchment and its water budget. Groundwater samples were taken from 144 wells and 21 samples from main streams, and seven lagoon water samples were also collected. Chemical analyses were carried out using standard laboratory methods, and isotopic determinations were made through laser spectroscopy using a DLT-100 liquid–water isotope analyzer. Hydrochemical analysis permits a general classification of groundwater and streamwater as sodium bicarbonate waters, while the lagoon chemical composition shows an evolution toward seawater composition, from the north to its mouth, which is located southerly. Isotopic data show a source of aquifer recharge from rainfall and a groundwater domain into the streams’ flow. Three main components can be recognized as end members in a plot of electrical conductivity (EC) versus δ¹⁸O: seawater, streamwater and groundwater. Obtained EC values for groundwater in the discharge zone (EC average value = 3,516 μS/cm) allow minimizing its direct contribution and to take into consideration two dominating end members: streamwater and seawater. Mar Chiquita lagoon’s water falls close to the line between streamwater and seawater end members according to its EC and δ¹⁸O. The obtained seawater proportion for these samples ranges from 84 % in the lagoon’s mouth to around 0 % in the more distal area.     

A note on lower bounds for relative equilibria in the main problem of artificial satellite theory

In the analytical approach to the main problem in satellite theory, the consideration of the physical parameters imposes a lower bound for normalized Hamiltonian. We show that there is no elliptic frozen orbits, at critical inclination, when we consider small values of H, the third component of the angular momentum. The argument used suggests that it might be applied also to more realistic zonal and tesseral models. Moreover, for almost polar orbits, when H may be taken as another small parameter, a different approach that will simplify the ephemerides generators is proposed.     

Some ring-shaped potentials as a generalized 4-D isotropic oscillator. Periodic orbits

A generalized integrable biparametric family of 4-D isotropic oscillators is proposed. It allows to treat in a unified way, Pöschl-Teller, Hartmann and other ring-shaped systems. This approach, based in the use of two canonical extensions, helps to simplify the studies of classical aspects of those systems. As an illustration, an analysis of the periodic solutions of those system is presented.     

10,000 years of climate control over carbon accumulation in an Iberian bog(southwestern Europe)

The northwest region of the Iberian Peninsula is home to a unique ecosystem of bogs,which are particularly sensitive to projected climate cha nge.In this context,the rate of carbon(C)accumulation in Chao de Veiga Mol.an intact raised bog,was analysed.Changes in the accumulation rate over the past10 millennia were determined in a peat core of 847 cm in depth,with a high mean rate of peat growth(11 yr cm^-1,0.09 cm yr^-1).An age-depth model was generated from 22 14C dates and fallout radionuclides.Chronological,stratigraphical and physico-chemical data confirmed the existence of a single cycle of peat formation throughout the Holocene and the formation of ombrotrophic peat 9500 years ago.The total mean C content was 50.2%,and over 10 millennia 583 kg C m^-2 accumulated at a mean rate of 35.3 g C m^-2 yr^-1,with a long-term(apparent)rate of carbon accumulation in the catotelm of59.9 g C m^-2 yr^-1.These values are much higher than reported for other Iberian peatlands and are amongst the highest documented for peatlands in the northern hemisphere.The dynamics of C accumulation and other measured parameters reveals important variations throughout the Holocene.They could be associated with the main climatic events described in the northern hemisphere and are highly consistent with models established for northern latitudes.The Chao de Veiga Mol raised bog is unique and of great potential value for carrying out high resolution palaeoenvironmental studies,especially in relation to regional and Iocal modulations in southern Europe.     

Linking earthquake-triggered paleolandslides to their seismic source and to the possible seismic event that originated them in a portion of the Argentine Precordillera (31°–33°S)

Natural Hazards - A total of 36 rock slides were selected for analysing a probable seismic source in the active Andean Precordillera (31°–33°S), the most seismic region of...     

Numerical Modelling of the Destructive Meteotsunami of 15 June, 2006 on the Coast of the Balearic Islands

A destructive tsunami-like event (locally known as “rissaga” waves) occurring on 15 June, 2006 in Ciutadella Harbour (Menorca, Balearic Islands) is reproduced by a numerical model forced by a travelling atmospheric disturbance. The disturbance is reconstructed from microbarograph measurements, being the only available instrumental data at the time of the event. The model is verified based on two weaker 1997 events, which were recorded by a number of bottom pressure recorders operating at that time on the Menorca shelf, in Ciutadella Inlet and adjacent Platja Gran Inlet. Both 1997 events are numerically simulated and good agreement is achieved with observations in time, frequency (including eigenfrequencies of the affected inlets) and wave heights. Subsequently the same model is applied to simulate the 2006 event. The vigorous currents with speeds up to 400 cm/s are found to occur specifically at those areas of the harbour where the most severe damage and sinking of boats had been reported. Maximum simulated sea-level heights of 2.5 m were about one half of those reported by eyewitnesses. This difference is apparently caused by quality and spatial resolution of bathymetry data. However, in general, the model is capable of reproducing the event fairly well and can probably be used for future assessment and mitigation activities on the coasts of the Balearic Islands.     

Fluvial transport of coarse particulate organic matter in a coastal mountain stream of a rainy-temperate evergreen broadleaf forest in southern Chile

Coarse particulate organic matter (CPOM, i.e. particles such as leaves, wood fragments, twigs, branches, flowers, seeds and fruits) in aquatic systems influences the flow, provides an important food source, and at the catchment scale, may significantly contribute to total carbon export. CPOM exports have rarely been quantified in subtropical, broadleaf forest streams. We captured CPOM in Bunte traps in the rainfall-dominated Vuelta de Zorra stream in southern Chile to (a) propose a novel classification to characterize the different CPOM components, (b) analyze the frequency of each matter class (i.e. leaves, wood fragments, and ‘others’) and its seasonal variability, (c) quantify the CPOM transported, (d) derive a model to quantify CPOM transport rates, and (e) compare the transported CPOM data with those from a unique long-term (> seven years) large wood monitoring dataset. Results showed that leaves were significantly more abundant than other types of CPOM in all seasons. The dry CPOM transport rate ranged over three orders of magnitude, and there was a significant relationship with mean discharge. Mean dry CPOM yield for the study period 2015–2017 was 4.6 kg/ha/yr when normalizing to the total forested catchment area. The 2009–2018 decadal average yield was 6.8 kg/ha/yr when normalizing to the total forested catchment area. These values are similar to measurements from deciduous and coniferous forests in streams in the United States and the Brazilian Mato Grosso and ~1/10 of the yields obtained in a Swiss torrent. Over a three-year period, the CPOM exports in Vuelta de Zorra ranged between 13 and 36% of the exported large wood (particles with diameters ≥ 100 mm and length ≥ 1 m) exports. Our data collected from an underrepresented area improve the understanding of global carbon budgets and cycling. © 2020 John Wiley & Sons, Ltd.     

Comprehensive wave climate analysis of the Uruguayan coast

Ocean Dynamics - A detailed analysis of how the wave climate gradually varies from the Atlantic coast to the Rio de la Plata (RDP) estuary coast of Uruguay is undertaken, exploiting a recently...