Improving the Understanding of N Transport in a Rural Catchment Under Atlantic Climate Conditions From the Analysis of the Concentration–Discharge Relationship Derived From a High-Frequency Data Set

[Abstract] Understanding processes controlling stream nutrient dynamics over time is crucial for implementing effective management strategies to prevent water quality degradation. In this respect, the study of the nutrient concentration–discharge (C–Q) relationship during individual runoff events can be a valuable tool for extrapolating the hydrochemical processes controlling nutrient fluxes in streams. This study investigated nitrogen concentration dynamics during events by analyzing and interpreting the nitrogen C–Q relationship in a small Atlantic (NW Iberian Peninsula) rural catchment. To this end, nitrate (NO3-N) and total Kjeldahl nitrogen (TKN) concentrations were monitored at a high temporal resolution during 102 runoff events over a 6-year period. For each of the selected runoff events, C–Q response was examined visually for the presence and direction of hysteresis loops and classified into three types of responses, namely clockwise, counterclockwise, and no hysteresis. Changes in concentration (ΔC) and the hysteresis direction (ΔR) were used to quantify nitrogen ( and TKN) patterns during the runoff events. The transport mechanisms varied between compounds. The most frequent hysteretic response for was counterclockwise with enrichment. On the contrary, the main TKN dynamic was enrichment with clockwise hysteresis. Event characteristics, such as rainfall amount, peak discharge (i.e., maximum discharge of the runoff event), and event magnitude relative to the initial baseflow (i.e., the difference between the maximum discharge of the runoff event and the initial baseflow divided by initial baseflow) provided a better explanation for hysteresis direction and magnitude for TKN than antecedent conditions (antecedent precipitation and baseflow at the beginning of the event). For hysteresis, the role of hydrometeorological conditions was more complex. The hysteresis magnitude was related to the magnitude of the event relative to the initial baseflow and the time elapsed since a preceding runoff event. These findings could be used as a reference for the development of N mitigation strategy in the region.This research has been supported by the Spanish Ministry of Education and Science (grant no. REN2003-08143) and Xunta of Galicia (grant nos. PGIDIT05RAG10303PR and 10MDS103031PR)Xunta of Galicia; PGIDIT05RAG10303PRXunta of Galicia; 10MDS103031P

Characteristics principals of soils of Holguín province (Cuba). Use and soils management

[Abstract] In this paper was performed an compilation of the main characteristic and degradation processes of soils Holguín province (Cuba) in order to stablish a proposal management leading to soil preservation. The main soils in the zone are of four types. According to the cuban classification system the major soils are Fersialitics, Vertisoils, Bruns and Ferritic, which are respectively equivalent to the Luvisols, Vertisols, Cambisols and Ferralsols of the FAO system (1998). About 70% of the agricultural soils of the Holguín province are affected by different erosion degree. About 17% of soils are affected by salinity and are associated mainly to the group of Vertisoils, that in the greater part are dedicated to the sugarcane cultivated and at grassland. Together with the erosion and salinity procceses others limiting factors of the soils are the sodicity, contents of gravels and stones, efective deepth, carbonates content and relief

Improving the understanding of N transport in a rural catchment under Atlantic climate conditions from the analysis of the concentration–discharge relationship derived from a high-frequency data set

Understanding processes controlling stream nutrient dynamics over time is crucial for implementing effective management strategies to prevent water quality degradation. In this respect, the study of the nutrient concentration–discharge (C–Q) relationship during individual runoff events can be a valuable tool for extrapolating the hydrochemical processes controlling nutrient fluxes in streams. This study investigated nitrogen concentration dynamics during events by analyzing and interpreting the nitrogen C–Q relationship in a small Atlantic (NW Iberian Peninsula) rural catchment. To this end, nitrate (NO3-N) and total Kjeldahl nitrogen (TKN) concentrations were monitored at a high temporal resolution during 102 runoff events over a 6-year period. For each of the selected runoff events, C–Q response was examined visually for the presence and direction of hysteresis loops and classified into three types of responses, namely clockwise, counterclockwise, and no hysteresis. Changes in concentration (ΔC) and the hysteresis direction (ΔR) were used to quantify nitrogen (NO3- and TKN) patterns during the runoff events. The transport mechanisms varied between compounds. The most frequent hysteretic response for NO3- was counterclockwise with enrichment. On the contrary, the main TKN dynamic was enrichment with clockwise hysteresis. Event characteristics, such as rainfall amount, peak discharge (i.e., maximum discharge of the runoff event), and event magnitude relative to the initial baseflow (i.e., the difference between the maximum discharge of the runoff event and the initial baseflow divided by initial baseflow) provided a better explanation for hysteresis direction and magnitude for TKN than antecedent conditions (antecedent precipitation and baseflow at the beginning of the event). For NO3- hysteresis, the role of hydrometeorological conditions was more complex. The NO3- hysteresis magnitude was related to the magnitude of the event relative to the initial baseflow and the time elapsed since a preceding runoff event. These findings could be used as a reference for the development of N mitigation strategy in the region.</p

Distribution and Origin of Iron Oxides in Soils over Limestone

[Resumen] Se pretende conocer la distribuci6n y el origen de los compuestos de hierro en suelos formados sobre calizas en Galicia. Predominan las formas minerales de hierro, encontrando en la fracción arena magnetita, goethita y/o hematites y excepcionalmente ilmenita, que se consideran heredadas del material de partida. En lámina delgada se observaron goethita y hematites como granos aislados, constituyendo nódulos e integrados en fragmentos de caliza. En la arcilla, trazas de goethita están presentes en casi todos los perfiles; s610 en uno de ellos la hematites es el único 6xido de hierro. La goethita puede haberse formado tanto por neoformaci6n como por microdivisi6n a partir de las fracciones gruesas, siendo este último fen6meno el que ha originado la hematites de la fracci6n arcilla. En dos perfiles la goethita va acompañada de magnetita y se discute la posible existencía y formaci6n de maghemita.[Abstract] Iron distribution in soils formed over limestone of Galicia is studied an the origin of the different iron forms is established. Organic iron is very scarce and mineral iron components dominate. Magnetite, goethite and / or hematite, less cornmonly ilmenite, are found in the sand fraction; they are considered as interited from the parent material. In polished sections goethite an hematite appear as single grains, nodules and il1corporated into limestone fragments. In the clay fraction, traces of goethite are present in aH except one of the profiles where only traces of hematite are indentified. Neoformation and microdivision from coarse fractions can act in the genesis of goethite; only microdivision is considered as the origin of hematite. Magnetite accompanies goethite in two profiles; the possible presence of maghemite and its origin is also discusse

Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory

The Crab Nebula is the brightest TeV gamma-ray source in the sky and has been used for the past 25 years as a reference source in TeV astronomy, for calibration and verification of new TeV instruments. The High Altitude Water Cherenkov Observatory (HAWC), completed in early 2015, has been used to observe the Crab Nebula at high significance across nearly the full spectrum of energies to which HAWC is sensitive. HAWC is unique for its wide field-of-view, nearly 2 sr at any instant, and its high-energy reach, up to 100 TeV. HAWC's sensitivity improves with the gamma-ray energy. Above $\sim$1 TeV the sensitivity is driven by the best background rejection and angular resolution ever achieved for a wide-field ground array. We present a time-integrated analysis of the Crab using 507 live days of HAWC data from 2014 November to 2016 June. The spectrum of the Crab is fit to a function of the form $\phi(E) = \phi_0 (E/E_{0})^{-\alpha -\beta\cdot{\rm{ln}}(E/E_{0})}$. The data is well-fit with values of $\alpha=2.63\pm0.03$, $\beta=0.15\pm0.03$, and log$_{10}(\phi_0~{\rm{cm}^2}~{\rm{s}}~{\rm{TeV}})=-12.60\pm0.02$ when $E_{0}$ is fixed at 7 TeV and the fit applies between 1 and 37 TeV. Study of the systematic errors in this HAWC measurement is discussed and estimated to be $\pm$50\% in the photon flux between 1 and 37 TeV. Confirmation of the Crab flux serves to establish the HAWC instrument's sensitivity for surveys of the sky. The HAWC survey will exceed sensitivity of current-generation observatories and open a new view of 2/3 of the sky above 10 TeV.Comment: Submitted 2017/01/06 to the Astrophysical Journa

All-particle cosmic ray energy spectrum measured by the HAWC experiment from 10 to 500 TeV

We report on the measurement of the all-particle cosmic ray energy spectrum with the High Altitude Water Cherenkov (HAWC) Observatory in the energy range 10 to 500 TeV. HAWC is a ground based air-shower array deployed on the slopes of Volcan Sierra Negra in the state of Puebla, Mexico, and is sensitive to gamma rays and cosmic rays at TeV energies. The data used in this work were taken from 234 days between June 2016 to February 2017. The primary cosmic-ray energy is determined with a maximum likelihood approach using the particle density as a function of distance to the shower core. Introducing quality cuts to isolate events with shower cores landing on the array, the reconstructed energy distribution is unfolded iteratively. The measured all-particle spectrum is consistent with a broken power law with an index of $-2.49\pm0.01$ prior to a break at $(45.7\pm0.1$) TeV, followed by an index of $-2.71\pm0.01$. The spectrum also respresents a single measurement that spans the energy range between direct detection and ground based experiments. As a verification of the detector response, the energy scale and angular resolution are validated by observation of the cosmic ray Moon shadow's dependence on energy.Comment: 16 pages, 11 figures, 4 tables, submission to Physical Review

Search for very-high-energy emission from Gamma-ray Bursts using the first 18 months of data from the HAWC Gamma-ray Observatory

The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory is an extensive air shower detector operating in central Mexico, which has recently completed its first two years of full operations. If for a burst like GRB 130427A at a redshift of 0.34 and a high-energy component following a power law with index -1.66, the high-energy component is extended to higher energies with no cut-off other than from extragalactic background light attenuation, HAWC would observe gamma rays with a peak energy of $\sim$300 GeV. This paper reports the results of HAWC observations of 64 gamma-ray bursts (GRBs) detected by $\mathit{Swift}$ and $\mathit{Fermi}$, including three GRBs that were also detected by the Large Area Telescope ($\mathit{Fermi}$-LAT). An ON/OFF analysis method is employed, searching on the time scale given by the observed light curve at keV-MeV energies and also on extended time scales. For all GRBs and time scales, no statistically significant excess of counts is found and upper limits on the number of gamma rays and the gamma-ray flux are calculated. GRB 170206A, the third brightest short GRB detected by the Gamma-ray Burst Monitor on board the $\mathit{Fermi}$ satellite ($\mathit{Fermi}$-GBM) and also detected by the LAT, occurred very close to zenith. The LAT measurements can neither exclude the presence of a synchrotron self-Compton (SSC) component nor constrain its spectrum. Instead, the HAWC upper limits constrain the expected cut-off in an additional high-energy component to be less than $100~\rm{GeV}$ for reasonable assumptions about the energetics and redshift of the burst.Comment: 19 pages, 6 figures, published in Ap