The Holocene-Pleistocene boundary zone in the Lagoon of Venice (Italy)

The results of a detailed study on the sediments representative of the boundary area from the Late-Pleistocene and the Lower-Holocene sedimentations are reported. Mineralogical, granulometric and geochemical investigations have been carried out to characterize the clay-rich samples taken along the littoral bar and representative of the continental and marine sedimentations. Particular attention was devoted to the study of the overconsolidated clay layer considered to be the last continental deposit before the Holocene (Flandrian) transgression and interpreted as a paleosol

I sedimenti tardo-quaternari dell'area litorale veneziana: analisi delle caratteristiche fisico-meccaniche

Abstract: This paper describes the geotechnical properties of the Venetian littoral. Analyses of 110 cohesive soil samples and 338 granular, taken from 30 cores, 25-30 meters in depth, were considered. The classical geotechnical classification supported by statistical analysis has pointed out that the compression index presents the best correlations with void ratio index and natural water content. Moreover, this paper shows the importance of the Atterberg limits to distinguish the cohesive soils of the late Pleistocene from those of the Holocene. Granular sediments have shown a zonation of both the grain size distribution and permeability coefficient. Resumé: Pour l'analyse des caractéristiques géotecniques du littoral venitien, qui est le sujet de ce travail, on a étudié 110 échantillons de terrains cohérents et 338 de terrains granulaires. Ces échantillons ont été prélevés de 30 carottages efféctués à la profondité moyenne de 25-30 m., et ils représentent les dernières 25.000-30.000 années de sèdiments quaternaires. En considérant la masse des donneés disponibles pour l'elaboration traditionnelle des propriétés géotechniques, une élaboration statistique a été utilisée pour obtenir des meilleures rélations de synthèse. En particulier, on a vu l'importance des limites de Attemberg pour effectuer la distinction entre les terrains cohérents du Pleistocene tardif et ceux de l'Olocene. En plus, la correlation du plus haut niveau de l'indice de compression est celle avec le pourcentage naturel d'eau et l'indice des vides. En ce qui concerne les terrains granulaires, on a verifié qu'il existe des zonations de la distribution granulometrique et du coeficient de perméabilité. Riassunto: Per l'analisi delle caratteristiche geotecniche del litorale veneziano, argomento di questo lavoro, sono stati studiati 110 campioni di terreni coesivi e 338 di terreni granulari prelevati da 30 sondaggi terebrati lungo il cordone litoraneo a profondità medie di 25-30 metri che rappresentano gli ultimi 25.000-30.000 anni di sedimentazione quaternaria. In considerazione della massa di dati disponibili all'elaborazione tradizionale delle proprietà geotecniche si è affiancata un'elaborazione statistica (analisi discriminante) che ha permesso di fornire relazioni di sintesi maggiormente interpretative. In particolare è emerso il potere selettivo dei limiti di Atterberg per distinguere i terreni coesivi tardo-pleistocenici da quelli olocenici. Inoltre si è visto che l'indice di compressione presenta le correlazioni più elevate con il contenuto naturale d'acqua e l'indice dei vuoti. Per quanto concerne i terreni granulari si sono riscontrate zonazioni della distribuzione granulometrica e del coefficiente di permeabilità

Studio sedimentologico di un livello di argilla sovraconsolidata sottostante il litorale veneziano

ABSTRACT The effect of global climatic changes that occurred since the last Würmian glaciation is recognizable in the stratigraphic sequences of the Pleistocene-Holocene boundary zone from several coastal areas in different locations around the world. This study gives the results of mineralogical, chemical, and textural investigations of about fifty samples of the hard clay layers and the clay layers above and below underlying the Venice littoral. This hard clay layer, locally known as caranto, from few centimeters to few meters thick, represents the Holocene/Pleistocene boundary and it carries the marks of climate changes that characterized the last phase of the Pleistocene and the early part of the Holocene. The very dry climate during a period of very limited sedimentation and a long subaerial exposition, desiccated, compacted and oxidized the clay previously deposited, to form the overconsolidated clay level (caranto). RIASSUNTO Gli effetti delle variazioni climatiche succedutesi, su scala globale, a partire dall'ultima glaciazione würmiana sono riconoscibili nelle sequenze stratigrafiche in varie località costiere sparse in tutto il mondo. In questo studio vengono riportati i risultati preliminari di una indagine sulle caratteristiche mineralogiche, geochimiche e tessiturali di circa cinquanta campioni di un livello di argilla sovraconsolidata e degli strati argillosi sopra e sottostanti, lungo il litorale veneziano. Questo strato di argilla sovraconsolidata, noto come "caranto", con spessore variante da pochi centimetri ad alcuni metri, rappresenta il limite Olocene/Pleistocene e conserva gli effetti dei cambiamenti climatici che hanno caratterizzato l'ultima fase del Pleistocene e quella iniziale dell'Olocene. Il clima freddo e molto arido, durante un periodo di sedimentazione molto limitata e la prolungata esposizione subaerea hanno determinato l'essiccamento, la compattazione e l'ossidazione dell'ultima sedimentazione continentale argillosa, sino a formare quel livello sovraconsolidato che e' noto col nome locale di caranto

Studio dei sedimenti tardo-quaternari del litorale veneziano: contributo alle indagini paleoclimatiche ed ambientali

ABSTRACT The imprints of paleoevolutionary processes that affected the Venice lagoon and its littoral during the Late-Quaternary can be found in the sand and c/ay layers underlying the Venetian basin. Sedimentological characteristics of the Late-Pleistocene and Holocene sand and clay sedimentation during the past 25-30.000 years, before the human impact, in the lagoon of Venice, are reported. The multidisciplinary investigation of clay and sand sediments and the development and application of new analytical techniques and methodologies, allowed the detailed mineralogical, geochemical and textural characterization of the recent sediments. The new data obtained not only may contribute to better understand the paleoevolutionary events that took place in the Venetian basin and the impact of the paleoclimatic variations on the depositional environments, but also they may be used as a sediment natural reference base for a more accurate quantification of the pollution level in the bottom sediments of the lagoon of Venice. RIASSUNTO Gli strati di sabbia e di argilla sottostanti il bacino veneziano conservano le tracce dei processi paleoevolutivi che hanno influenzato la laguna di Venezia ed il suo litorale. Lo studio multidisciplinare dei sedimenti sabbiosi ed argillosi depositatisi durante gli ultimi 25-30.000 anni, prima dell'impatto antropico, e lo sviluppo ed utilizzo di nuove metodologie analitiche, hanno permesso una caratterizzazione mineralogica, geochimica e tessiturale dettagliata dei sedimenti recenti. I nuovi dati ottenuti possono non solo contribuire a meglio comprendere gli eventi paleoevolutivi succedutisi nel bacino veneziano e l'impatto delle variazioni paleoclimatiche sugli ambienti deposizionali, ma possono anche servire come base naturale di riferimento per una più accurata quantificazione dei livelli di inquinamento dei sedimenti di fondo soggetti ad antropizzazione della laguna di Venezia

The impact of drought length and intensity on N cycling gene abundance, transcription and the size of an N2O hot moment from a temperate grassland soil

This study aimed to investigate the relationship between drought length, drought intensity and the size of the N2O hot moment. It selected two treatments to deduce the main nitrogen cycling process producing N2O (increasing WFPS from 40% to 90%, and from 70% to 90%), by destructively sampling soil cores to analyse gene abundance, transcription, and changes in soil chemistry (TON, NH4+, DOC). Five other drought and rewetting treatments on packed soil cores were selected to create the drought curves described in Barrat et al. (2020): these included increases of WFPS from 40% to 90%, 50%–90%, 60%–90%, 70%–90%, and 30%–60%. For each treatment, drought lengths were imposed from 0 to 30 days. A quadratic linear regression was fitted to the cumulative emissions data. This model explained a significant proportion of the total variation in the data (R2 =0.72, p ≤ 0.001). All treatments had an increase in daily N2O emissions post wetting typical of a hot moment apart from the 30%–60% WFPS treatment. In terms of drought intensity, the 40%–90% WFPS was significantly larger than rest, probably due to a relatively larger change in water potential compared to the other treatments. The response to drought length followed a quadratic curve with a downward linear trend, with the largest emissions observed between 10 and 15 days of drought, and the smallest at 0 and 30 days. We suggest a 2-stage dormancy strategy to explain this, where microbes under dry conditions store osmolytes which are catabolised upon rewetting, however at prolonged negative water potentials this strategy is no longer effective, and so they enter a deeper state of dormancy where they can no longer rapidly respond to the changing water potential. Given the delayed response after rewetting, and the inverted U shaped curve in terms of drought length, it seems likely that the majority of emissions are of biological origin. The soil’s chemistry data suggested that NH4+ was a key factor controlling the emission flux, but the transcriptional and genomic data were inconclusive. This study therefore suggests that future experiments should focus changes in osmolyte accumulation and catabolism as the key explanation for N2O hot moments, rather than changes in genomic and transcriptomic data or soil substrates, which do not always correlate with emissions

Ammonia oxidation: Ecology, physiology, biochemistry and why they must all come together

Ammonia oxidation is a fundamental core process in the global biogeochemical nitrogen cycle. Oxidation of ammonia (NH3) to nitrite (NO2 −) is the first and rate-limiting step in nitrification and is carried out by distinct groups of microorganisms. Ammonia oxidation is essential for nutrient turnover in most terrestrial, aquatic and engineered ecosystems and plays a major role, both directly and indirectly, in greenhouse gas production and environmental damage. Although ammonia oxidation has been studied for over a century, this research field has been galvanised in the past decade by the surprising discoveries of novel ammonia oxidising microorganisms. This review reflects on the ammonia oxidation research to date and discusses the major gaps remaining in our knowledge of the biology of ammonia oxidation

Advances in Surface-Groundwater Modelling in Lagoon Environment with Airborne Electromagnetics and High Resolution Seismic: Example from the Venice Lagoon

Lagoon environments are very important for groundwater modeling in costal areas, they are delicate and in rapid evolution due to global climatic changes. Airborne electromagnetics (AEM)is a very valuable methodology that can provide high density, high quality data to produce 3D hydrogeological models to depths in excess of hundred meters below surface water column. We present the results from the SkyTEM Venice lagoon survey of 2009, integrated with data from very high resolution seismic survey. The AEM data results enhance greatly the understanding of the hydrogeology and surface-groundwater interactions in the lagoon area, where indirect measurements abound but wells are missing. For example, there is clear evidence of fresh water aquifers underneath the central part of the lagoon, at depth of about 40 m. The near surface part of the AEM data compare well with seismic data, showing that main reflectors come from the interface between the superficial Late Pleistocene looser, saline water saturated sediments and the deeper, more compact and fresher Holocene sediments. There is also clear evidence of submarine groundwater discharge in the lagoon, of paleorivers, and a possible indication of gas seepage trough shallow sediments. Seismic and AEM provide complimentary datasets to discriminate between pore water salinity, lithology and gas. Seismic horizons can actually be included during inversion of AEM data, producing more robust output. AEM data from the southern part of the survey that crosses the shore line and continued also onshore allow a clear mapping of the saline water intrusion inland, and highlight the relationship between pore water salinity of the lagoon sediments and spatial distribution of salt marshes. The latter seem to act like salt sinks, increasing sediments electrical conductivity

Light-Induced N₂O Production from a Non-Heme Iron–Nitrosyl Dimer

Two non-heme iron–nitrosyl species, [Fe₂(N-Et-HPTB)(O₂CPh)(NO)₂](BF4)₂(1a) and [Fe₂(N-Et-HPTB)(DMF)₂(NO)(OH)](BF₄)₃ (2a), are characterized by FTIR and resonance Raman spectroscopy. Binding of NO is reversible in both complexes, which are prone to NO photolysis under visible light illumination. Photoproduction of N₂O occurs in high yield for 1a but not 2a. Low-temperature FTIR photolysis experiments with 1a in acetonitrile do not reveal any intermediate species, but in THF at room temperature, a new {FeNO}⁷ species quickly forms under illumination and exhibits a ν(NO) vibration indicative of nitroxyl-like character. This metastable species reacts further under illumination to produce N₂O. A reaction mechanism is proposed, and implications for NO reduction in flavodiiron proteins are discussed.National Institutes of Health (U.S.) (GM074785)National Institutes of Health (U.S.) (GM032134