Nitrogen concentrations in a small Mediterranean stream: 1. Nitrate 2. Ammonium

The importance of storm frequency as well as the groundwater and hyporheic inputs on nitrate (NO₃-N) and ammonium (NH₄-N) levels in stream water were studied in a small perennial Mediterranean catchment, Riera Major, in northeast Spain. NO₃-N concentrations ranged from 0.15 to 1.9 mg l^-1. Discharge explained 47% of the annual NO₃-N concentration variance, but this percentage increased to 97% when single floods were analysed. The rate of change in nitrate concentration with respect to flow, &#916;NO₃-N/&#916;Q, ranged widely from 0 to 20 &#956;g NO₃-N s l^-2. The &#916;NO₃-N/&#916;Q values fitted to a non linear model with respect to the storm flow magnitude (&#916;Q) (r²&#61;0.48, d.f.&#61;22, P<0.01). High values of &#916;NO₃-N/&#916;Q occurred at intermediate &#916;Q values, whereas low &#916;NO₃-N/&#916;Q values occurred during severe storms (&#916;Q > 400 l s^-1). N₃-N concentrations exhibit anticlockwise hysteresis patterns with changing flow and the patterns observed for autumnal and winter storms indicated that groundwater was the main N₃-N source for stream and hyporheic water. At baseflow, NO₃-N concentration in groundwater was higher (t&#61;4.75, d.f.&#61;29, P>0.001) and co-varied with concentrations in the stream (r&#61;0.91, d.f.&#61;28, P<0.001). In contrast, NO₃-N concentration in hyporheic water was identical to that in stream water. The role of the hyporheic zone as source or sink for ammonium was studied hyporheic was studied comparing its concentrations in stream and hyporheic zone before and after a major storm occurred in October 1994 that removed particulate organic matter stored in sediments. Results showed high ammonium concentrations (75&#177;28 s.d. &#956;g NH₄-N l^-1) before the storm flow in the hyporheic zone. After the storm, the ammonium concentration in the hyporheic dropped by 80% (13.6&#177;8 &#956;g N₄-N l^-1) and approached to the level found in stream water (11&#177;8 &#956;g NH₄-N l^-1) indicating that indisturbed hyporheic sediments act as a source for ammonium. After the storm, the ammonium concentrations in the stream, hyporheic and groundwater zones were very similar suggesting that stream ammonium concentrations are sustained mainly by input from groundwater. The present study provides evidence that storm flow magnitude is an important source of variability of nitrate concentration and fluxes in Mediterranean streams subjected to an irregular precipitation regime with prolonged dry periods

Finite mixture model: decompose a cytogram into "n" sub adjacent asymmetric Gaussian bells. A Mathematica 9 script.

The script works with Mathematica (version 9 or latest) however, the Laplacian filter and the finite mixture should be implement with any other mathematical software. The scripts includes different steps: 1) To import the original cytogram and convert it into a matrix f(x,y) of dimension "n x n" 2) To detect all potential pics in f(x,y) with the laplacian filter, 2, and create the list Ln that include the coordinate of each potential peak 3) To extract all i distinct proper subsets of Ln: P(Ln)={{ 1}1,{2}2,{3}3,{ 1, 2} 4……. {1, 2, 3,…, n}i} (where i=2n-1) 3) To run the finite mixture model for each subset 4) To select the bet model with the optimal number of peak according the Bayesian Information Criterion (BIC) descriptor.This script implements the Laplacian filter and the finite mixture approach to decompose a surface into an arbitrary number “n” of bi-dimensional asymmetric Gaussian probability distributions. Finite mixture are widely used in data mining or pattern recognition. Here, this tool in implemented to decompose an arbitrary surface f(x,y) with some peaks and shoulders. This approach can be useful to decompose any bidimensional data array. This document describes how to use this approach to deconvolve a cytogram

A comparison of reliability prediction methodologies to observed field failure data

Reliability predictions of electronic equipment are considered highly valuable; yet the most widely used technique, Military Handbook 217 is criticized as inaccurate. The industry response to the Handbook has been to develop a myriad of methodologies for failure rate prediction. This paper uses four (4) reliability prediction methods to forecast the failure rate of two (2) circuit boards for which a field failure history exists. The predicted failure rate for each procedure on each board is compared to the actual failure rate; and a first-order correction factor is calculated

The influence of riparian-hyporheic zone on the hydrological responses in an intermittent stream

Stream and riparian groundwater hydrology has been studied in a small intermittent stream draining a forested catchment for a system representative of a Mediterranean climate. The relationship between precipitation and stream runoff and the interactions between stream water and the surrounding riparian groundwater have been analysed under a wide spectrum of meteorological conditions. The hypothesis that the hydrological condition of the near-stream groundwater compartment can regulate the runoff generation during precipitation events was tested. Stream runoff is characterised by a summer dry period, and precipitation input explained only 25% of runoff variability over the study period (r² =0.25, d.f.=51, p<0.001). The variability of precipitation v. stream runoff is explained partly by the hydrogeological properties of the riparian near-stream zone. This zone is characterised by high hydrological conductivity values and abrupt changes in groundwater level in summer. The summer dry period begins with a rapid decrease in near-stream groundwater level, and ends just after the first autumnal rain when the original groundwater level recovers suddenly. Within this period, storms do not cause major stream runoff since water infiltrates rapidly into the riparian compartment until it is refilled during the subsequent winter and spring; then the precipitation explains the 80% of the stream runoff variability (r²=0.80, d.f.=34, p<0.001). These results suggest that the hydrological interaction between the riparian groundwater compartment and the stream channel is important in elucidating the hydrological responses during drought periods in small Mediterranean streams.</p> <p style='line-height: 20px;'><b>Keywords:</b> riparian zone, groundwater hydrology, runoff, intermittent stream, Mediterranean climate</p

Modelling the inorganic nitrogen behaviour in a small Mediterranean forested catchment, Fuirosos (Catalonia)

The aim of this work was to couple a nitrogen (N) sub-model to already existent hydrological lumped (LU4-N) and semi-distributed (LU4-R-N and SD4-R-N) conceptual models, to improve our understanding of the factors and processes controlling nitrogen cycling and losses in Mediterranean catchments. The N model adopted provides a simplified conceptualization of the soil nitrogen cycle considering mineralization, nitrification, immobilization, denitrification, plant uptake, and ammonium adsorption/desorption. It also includes nitrification and denitrification in the shallow perched aquifer. We included a soil moisture threshold for all the considered soil biological processes. The results suggested that all the nitrogen processes were highly influenced by the rain episodes and that soil microbial processes occurred in pulses stimulated by soil moisture increasing after rain. Our simulation highlighted the riparian zone as a possible source of nitrate, especially after the summer drought period, but it can also act as an important sink of nitrate due to denitrification, in particular during the wettest period of the year. The riparian zone was a key element to simulate the catchment nitrate behaviour. The lumped LU4-N model (which does not include the riparian zone) could not be validated, while both the semi-distributed LU4-R-N and SD4-R-N model (which include the riparian zone) gave satisfactory results for the calibration process and acceptable results for the temporal validation process

Use of metal oxide semiconductor sensors to measure methane in aquatic ecosystems in the presence of cross-interfering compounds

Monitoring dissolved methane in aquatic ecosystems contributes significantly to advancing our understanding of the carbon cycle in these habitats and capturing their impact on methane emissions. Low-cost metal oxide semiconductors (MOS) gas sensors are becoming an increasingly attractive tool to perform such measurements, especially at the air–water interface. However, the performance of MOS sensors in aquatic environmental sciences has come under scrutiny because of their cross-sensitivity to temperature, moisture, and sulfide interference. In this study, we evaluated the performance and limitations of a MOS methane sensor when measuring dissolved methane in waters. A MOS sensor was encapsulated in a hydrophobic extended polytetrafluoroethylene membrane to impede contact with water but allow gas perfusion. Therefore, the membrane enabled us to submerge the sensor in water and overcome cross-sensitivity to humidity. A simple portable, low-energy, flow-through cell system was assembled that included an encapsulated MOS sensor and a temperature sensor. Waters (with or without methane) were injected into the flow cell at a constant rate by a peristaltic pump. The signals from the two sensors were recorded continuously with a cost-efficient microcontroller. Tests specifically focused on the effect of water temperature and sulfide interference on sensor performance. Our experiments revealed that the lower limit of the sensor was in the range of 0.1–0.2 µmol¿L-1 and that it provided a stable response at water temperatures in the range of 18.5–28°C. Dissolved sulfide at a concentration of 0.4¿mmol¿L-1 or higher interfered with the sensor response, especially at low methane concentrations (0.5 µmol¿L-1 or lower). However, we show that if dissolved sulfide is monitored, its interference can be alleviated.Postprint (published version

Variability of DOC and nitrate responses to storms in a small Mediterranean forested catchment

International audienceSevere drought periods followed by intense rainfall often leads to major floods in Mediterranean catchments. The resulting hydrology is complex and the response of solutes in the streams is often unpredictable. This study aimed to identify the most relevant factors controlling the hydrological responses to storms of an intermittent Mediterranean stream and to link those factors with dissolved organic carbon (DOC) and nitrate during storm events. Measurements of climate, hydrology, DOC and nitrate concentrations during 26 storm events over three hydrological years were analysed. The contribution of the storm events to the total DOC and nitrate annual export was also calculated. Nitrate was mainly mobilised during high flow, while most of the DOC export occurred during baseflow. Solute concentrations peaked after drought periods and the solute export was maximal during the largest rainfalls (i.e. > 100 L m-2). One single large storm contributed some 22% of the total annual export of DOC, and about 80% of that of nitrate. Discharge was a good predictor of neither DOC nor nitrate responses, so variables other than discharge were considered. Factor Analysis was used to identify the main factors controlling the biogeochemical responses. Antecedent moisture conditions and the magnitude of the storm event were the most relevant factors and accounted for 63% of the total variance. Solute responses during high flow were highly variable. However, solute concentration changes showed a significant and moderate relationship with the factors controlling the hydrological responses (i.e. ? DOC v. the antecedent moisture conditions and ? NO3-N v. the magnitude of the storm event). Keywords: dissolved organic carbon, nitrate, Mediterranean, drought, Fuirosos catchment, storms</p

Il segreto giornalistico sulla fonte: : terreno di interpretazioni differenti tra diritto interno e Convenzione europea dei diritti dell’uomo

L’articolo approfondisce l’ambito di applicazione del diritto in capo ai giornalisti di rifiutarsi di rivelare all’autorità giudiziaria l’identità della fonte dalla quale hanno attinto le notizie di interesse pubblico. In particolare, il contributo analizza le differenze di orientamento interpretativo tra giurisprudenza della Corte europea dei diritti dell’uomo egiurisprudenza italiana in ordine alla protezione del segreto professionale sulla fonte delle informazioni, tenendo altresì conto del fatto che l’istituto del segreto professionale sulla fonte costituisce un ineludibile presidio democratico-costituzionale a tutela del libero flusso di informazioni fra media e società

Redox regulation of STAT1 and STAT3 signaling

STAT1 and STAT3 are nuclear transcription factors that regulate genes involved in cell cycle, cell survival and immune response. The cross-talk between these signaling pathways determines how cells integrate the environmental signals received ultimately translating them in transcriptional regulation of specific sets of genes. Despite being activated downstream of common cytokine and growth factors, STAT1 and STAT3 play essentially antagonistic roles and the disruption of their balance directs cells from survival to apoptotic cell death or from inflammatory to anti-inflammatory responses. Different mechanisms are proposed to explain this yin-yang relationship. Considering the redox aspect of STATs proteins, this review attempts to summarize the current knowledge of redox regulation of STAT1 and STAT3 signaling focusing the attention on the post-translational modifications that affect their activity

Effects of riparian vegetation removal on nutrient retention in a Mediterranean stream

We examined the effects of riparian vegetation removal on algal dynamics and stream nutrient retention efficiency by comparing NH4-N and PO4-P uptake lengths from a logged and an unlogged reach in Riera Major, a forested Mediterranean stream in northeastern Spain. From June to September 1995, we executed 6 short-term additions of N (as NH4Cl) and P (as Na2HPO4) in a 200-m section to measure nutrient uptake lengths. The study site included 2 clearly differentiated reaches in terms of canopy cover by riparian trees: the first 100 m were completely logged (i.e., the logged reach) and the remaining 100 m were left intact (i.e., the shaded reach). Trees were removed from the banks of the logged reach in the winter previous to our sampling. In the shaded reach, riparian vegetation was dominated by alders (Alnus glutinosa). The study was conducted during summer and fall months when differences in light availability between the 2 reaches were greatest because of forest canopy conditions. Algal biomass and % of stream surface covered by algae were higher in the logged than in the shaded reach, indicating that logging had a stimulatory effect on algae in the stream. Overall, nutrient retention efficiency was higher (i.e., shorter uptake lengths) in the logged than in the shaded reach, especially for PO4-P. Despite a greater increase in PO4-P retention efficiency relative to that of NH4-N following logging, retention efficiency for NH4-N was higher than for PO4-P in both study reaches. The PO4-P mass-transfer coefficient was correlated with primary production in both study reaches, indicating that algal activity plays an important role in controlling PO4-P dynamics in this stream. In contrast, the NH4-N mass-transfer coefficient showed a positive relation-ship only with % of algal coverage in the logged reach, and was not correlated with any algal-related parameter in the shaded reach. The lack of correlation with algal production suggests that mechanisms other than algal activity (i.e., microbial heterotrophic processes or abiotic mechanisms) may also influence NH4-N retention in this stream. Overall, this study shows that logging disturbances in small shaded streams may alter in-stream ecological features that lead to changes in stream nutrient retention efficiency. Moreover, it emphasizes that alteration of the tight linkage between the stream channel and the adjacent riparian zone may directly and indirectly impact biogeochemical processes with implications for stream ecosystem functioning