Mesocosm experiments identifying hotspots of groundwater upwelling in a water column by fibre optic distributed temperature sensing

Lacustrine groundwater discharge (LGD) can substantially impact ecosystem characteristics and functions. Fibre optic distributed temperature sensing (FO‐DTS) has been successfully used to locate groundwater discharge into lakes and rivers at the sediment–water interface, but locating groundwater discharge would be easier if it could be detected from the more accessible water surface. So far, it is not clear if how and under which conditions the LGD signal propagates through the water column to the water surface–atmosphere interface, and what perturbations and signal losses occur along this pathway. In the present study, LGD was simulated in a mesocosm experiment. Under winter conditions, water with temperatures of 14 to 16 °C was discharged at the bottom of a 10 × 2.8‐m mesocosm. Water within this mesocosm ranged from 4.0 to 7.4 °C. Four layers (20, 40, 60, and 80 cm above the sediment) of the 82 cm deep mesocosm were equipped with FO‐DTS for tracing thermal patterns in the mesocosm. Aims are (a) to test whether the positive buoyancy of relatively warm groundwater imported by LGD into shallow water bodies allows detection of LGD at the lake's water surface–atmosphere interface by FO‐DTS, (b) to analyse the propagation of the temperature signal from the sediment‐water interface through the water column, and (c) to learn more about detectability of the signal under different discharge rates and weather conditions. The experiments supported the benchmarking of scale dependencies and robustness of FO‐DTS applications for measuring upwelling into aquatic environments and revealed that weather conditions can have important impacts on the detection of upwelling at water surface–atmosphere interfaces at larger scales.     

Selective destruction and differentiation of clay minerals from natural diaspore admixture by mortar grinding

A dry grinding process at several periods has been used successfully in order to differentiate among the different minerals forming a natural diaspore clay. This is achieved by selective and incongruent destruction of the clay minerals of this admixture, on the basis of their disparate structural stability, hardness and relative amount present. Kaolin clays (represented mainly by kaolinite + halloysite) are destroyed after >3 hr grinding, anatase after ～40 hr, whereas the structure of α-AlOOH is still preserved after >250 hr, as ascertained from XRD. From IR spectroscopy analysis it is inferred that as a consequence of grinding prototropy takes place in some of the clay hydroxyls. This is supported by water losses results at 600°C.     

On the individual calibration of hailpads

This paper is a comparative study between the two most common hailpad calibration systems: one annual calibration of a whole consignment of material, and the individual calibration of each plate after a hailfall. Individual calibration attempts to minimize errors due to differences in sensitivity to the impact of hailstones between plates from the same consignment, or due to differences in the inking process before the actual measurement.The comparison was carried out using calibration data from the past few years in the hailpad network in south-western France, and data from an individual calibration process on material provided by the hailpad network in Lleida (Spain). The same type of material was used in the two cases.The results confirm that the error in measuring hailstone sizes is smaller in the case of an individual calibration of hailpads than when one single calibration process was carried out for a whole consignment. The former is approximately 80% of the latter. However, this error could have been higher if it had not been the same person carrying out the single calibration process and the measuring of the dents: it has been found that differences in the inking process may account for up to 20% of the error in the case of small hailstones. Calibration errors affecting other variables, e.g. energy or parameter λ of the exponential size distribution are generally higher (5% and 18%, respectively) than errors due to the spatial variability of the hailstones. However, the calibration method does not influence the maximum size, since the relative error attributed to the spatial variability is about 8 times the calibration error.In conclusion, if errors in determining energy or parameter λ are to be reduced to a minimum, it is highly advisable to be consistent in applying the measuring procedure (if possible with the same person carrying out the measurements all the time), and even to use individual calibration on each plate, always bearing in mind that technicians have to be trained appropriately in order to achieve the highest possible degree of uniformity.     

Fish discards management: pollution levels and best available removal techniques

Fish discards and by-catch issues are highly topical subjects that are permanently under a social focus. Two main approaches are being considered to address this discard problem: reducing the by-catch and increasing by-catch utilization. Interest in increased by-catch valorization may arise from a greater demand for fish products, such as the development of new markets for previously discarded species, the use of low-value specimens for aquaculture or the creation of value-added fish products for the food, pharmaceutical or cosmetic industries. However, contaminants present in fish discards may be transferred to their valorized products, leading to possible long-term bioaccumulation and subsequent adverse health effects. In this valorization framework, the aim is to promote responsible and sustainable management of marine resources. The pollutant levels in catches from European fisheries and the best available decontamination techniques for marine valorized discards/by-products are compiled and analyzed in this work.     

The history of the Solar system's debris disc: observable properties of the Kuiper belt

The Nice model of Gomes et al. suggests that the migration of the giant planets caused a planetesimal clearing event, which led to the late heavy bombardment (LHB) at 880 Myr. Here, we investigate the infrared emission from the Kuiper belt during the history of the Solar system as described by the Nice model. We describe a method for easily converting the results of N -body planetesimal simulations into observational properties (assuming blackbody grains and a single size distribution) and further modify this method to improve its realism (using realistic grain properties and a three-phase size distribution). We compare our results with observed debris discs and evaluate the plausibility of detecting an LHB-like process in extrasolar systems. Recent surveys have shown that 4 per cent of stars exhibit 24 μm excess and 16 per cent exhibit 70 μm excess. We show that the Solar system would have been amongst the brightest of these systems before the LHB at both 24 and 70 μm. We find a significant increase in 24 μm emission during the LHB, which rapidly drops off and becomes undetectable within 30 Myr, whereas the 70 μm emission remains detectable until 360 Myr after the LHB. Comparison with the statistics of debris disc evolution shows that such depletion events must be rare occurring around less than 12 per cent of Sun-like stars and with this level of incidence we would expect approximately one of the 413 Sun-like field stars so far detected to have a 24 μm excess to be currently going through an LHB. We also find that collisional processes are important in the Solar system before the LHB and that parameters for weak Kuiper belt objects are inconsistent with the Nice model interpretation of the LHB.     

CAPE values and hailstorms on northwestern Spain

A study has been carried out in León (in the northwest of the Iberian Peninsula) on atmospheric convection during summer periods, by analyzing the values of the Convective Available Potential Energy (CAPE) around 07:00 UTC. The project analyzed the data provided by a network of voluntary observers, a hailpad network, and a meteorological station on a sample of 224 days. The CAPE values found were not high: they never reached 2000 J/kg, not even on hail days, i.e. on days with high convective activity. These values are much lower than the ones measured in convective situations in tropical regions, but they are within the usual values found in Europe. The same happens with the wet bulb potential temperature measured in León. The frequency distribution of the CAPE values shows a clear prevalence of very low or zero values. The group of days with the lowest CAPE value is that which included days with no storm. The mean value increases on storm days, and it is even higher for the days with recorded hailfalls. All these differences are significantly marked. Nevertheless, the differences across the years are not significant enough to be able to speak of an influence of the climatic change on the CAPE. The correlation of the CAPE with some of the variables previously used for hail forecasts was analyzed, and the correlation found was higher for the lifted index. The possible use of the CAPE as a thunderstorm and hailstorm forecasting method was considered. The results were encouraging, especially for hail forecasting, although the CAPE should not be used as the only variable, but combined with other parameters. Moreover, the relationships between the CAPE and the wet bulb potential temperature and between the CAPE and the physical parameters of the hailstones were also analyzed. A relationship was observed with the parameters of the hailstone size distribution. Nonetheless, these results are provisional, and they should be confirmed by analyzing a more representative sample. With a more detailed analysis of these and other relationships, the present forecast model used by the Laboratory for Atmospheric Physics at the University of León is expected to be greatly improved by including the CAPE in this model.     

Delimiting a saline water zone in Quaternary fluvial–alluvial deposits using transient electromagnetic: a case study in Punata,Bolivia

The semiarid Punata alluvial fan is located in the central part of Bolivia. The main activity of this region is the extensive agriculture, and groundwater is the main water supply. Local villagers who use groundwater reported that in some places groundwater has a salty taste. In order to investigate the origin of this problem, several TEM soundings were performed in the study area, and they were complemented with ERT surveys. The results show top layers with resistivity values ranging from 30 to 200 Ωm and a bottom layer with resistivity values ranging from 1 to 20 Ωm, which might be interpreted as the main aquifer and a layer with high clay content, respectively. Between the top and bottom layer, a transition zone with saline water has been identified, with resistivity values ranging from 0.1 to 1 Ωm. The origin of this closed-basin brine might be a product of the evaporation of paleolakes during the lower Pliocene, where saline clays were deposited. This study demonstrated the effectiveness of TEM sounding for mapping very low resistivity zones such as saline water.     

Diversity of the 2014 Iquique’s foreshocks and aftershocks: clues about the complex rupture process of a Mw 8.1 earthquake

We study the foreshocks and aftershocks of the 1 April 2014 Iquique earthquake of Mw 8.1. Most of these events were recorded by a large digital seismic network that included the Northern Chile permanent network and up to 26 temporary broadband digital stations. We relocated and computed moment tensors for 151 events of magnitude Mw?≥?4.5. Most of the foreshocks and aftershocks of the Iquique earthquake are distributed to the southwest of the rupture zone. These events are located in a band of about 50 km from the trench, an area where few earthquakes occur elsewhere in Chile. Another important group of aftershocks is located above the plate interface, similar to those observed during the foreshock sequence. The depths of these events were constrained by regional moment tensor (RMT) solutions obtained using the records of the dense broad band network. The majority of the foreshocks and aftershocks were associated to the interplate contact, with dip and strike angles in good agreement with the characteristics of horst and graben structures (>2000 m offset) typical of the oceanic Nazca Plate at the trench and in the outer rise region. We propose that the spatial distribution of foreshocks and aftershocks, and its seismological characteristics were strongly controlled by the rheological and tectonics conditions of the extreme erosive margin of Northern Chile.