Comparison of dissolved inorganic and organic carbon yields and fluxes in the watersheds of tropical volcanic islands,examples from Guadeloupe (French West Indies)

Organic matter is an important factor that cannot be neglected when considering global carbon cycle. New data including organic matter geochemistry at the small watershed scale are needed to elaborate more constrained carbon cycle and climatic models. The objectives are to estimate the DOC and DIC yields exported from small tropical watersheds and to give strong constraints on the carbon hydrodynamic of these systems. To answer these questions, we have studied the geochemistry of eleven small watersheds around Basse-Terre volcanic Island in the French West Indies during different hydrological regimes from 2006 to 2008 (i.e. low water level versus floods). We propose a complete set of carbon measurements, including DOC and DIC concentrations, δ¹³C data, and less commonly, some spectroscopic indicators of the nature of organic matter. The DOC/DIC ratio varies between 0.07 and 0.30 in low water level and between 0.25 and 1.97 during floods, indicating that organic matter is mainly exported during flood events. On the light of the isotopic composition of DOC, ranging from ? 32.8 to ? 26.2‰ during low water level and from ? 30.1 to ? 27.2‰ during floods, we demonstrate that export of organic carbon is mainly controlled by perennial saprolite groundwaters, except for flood events during which rivers are also strongly influenced by soil erosion. The mean annual yields ranged from 2.5 to 5.7 t km^? 2 year^? 1 for the DOC and from 4.8 to 19.6 t km^? 2 year^? 1 for the DIC and exhibit a non-linear relationship with slopes of watersheds. The flash floods explain around 60% of the annual DOC flux and between 25 and 45% of the DIC flux, highlighting the important role of these extreme meteorological events on global carbon export in small tropical volcanic islands. From a carbon mass balance point of view the exports of dissolved carbon from small volcanic islands are important and should be included in global organic carbon budgets.     

Über das Verhältnis von Westalpen und Ostalpen

Ohne Zusammenfassung     

Combined amino acid speciation in lake sediment and porewater (Aydat Lake, France)

Dissolved and particulate fractions extracted from a lake diatom ooze were examined for individual amino acids. The study focused on combined amino acids, the predominant form in the interstitial dissolved pool (> 90%). An abundance of glycine and -alanine was observed in porewater samples of sediments both squeezed manually and gathered with in-situ dialysis (peeper). Sedimentpress squeezing and leaching of the sediment by water gave higher total quantities and different compositions (with more aliphatic and aromatic protein amino acids, -alanine being predominant). These two methods modify the original composition, presumably due to the formation of Fe-oxides and dissolution of sediment organic fractions, the alteration being aggravated if squeezing is delayed.Filtration after acidification of porewaters enabled us to distinguish two compartments: a protein-like agglutinated fraction, and a filtrate with a high glycine and -alanine content. Further division of the filtrate by adsorption on XAD or cation-exchange resins did not reveal additional fractions with different individual amino acid compositions. A link is suggested between the agglutinated fraction and the special composition of the porewaters extracted with sediment-press.Dissolved organic carbon (DOC) and total dissolved hydrolysable amino acids (TDHAA) ( 10 mg/l and 13 M, respectively) did not increase with depth, as opposed to dissolved inorganic carbon and volatile carbon. Amino acid-C accounted for less than 4% of DOC in porewaters.Individual amino acid compositions in the sediments were similar in all grain size fractions. Chemically extracted fractions had specific compositions: (l) organic fractions (alkali extracts and HF-insoluble residues) have a similar protein amino acid composition; (2) acid extracts have more acidic amino acids (HCI) or more glycine and non protein amino acids (BF). The similarity of amino acid compositions in the sediment HF-soluble fraction and the dissolved pool is discussed with respect to interactions between iron-silicate authigenic phases and porewaters.     

Self-organization maps (SOM) in the definition of a “transfer function” for a diatoms-based climate proxy

Climate Dynamics - This study utilizes self-organizing maps (SOM) —a particular type of artificial neural network (ANN) — as a nonlinear analysis tool for identifying species that can...     

Improvement of Ground Penetrating Radar (GPR) Data Interpretability by an Enhanced Inverse Scattering Strategy

This paper is inserted into the framework of inverse scattering with application to Ground Penetrating Radar (GPR) data and is meant to provide a method helping to apply inverse scattering algorithms to electrically large investigation domains. In particular, we focus on the depth slices that are particularly important in application on cultural heritage and propose in relationship with the depth slices a strategy that we will call “shifting zoom” that is specifically a method to mitigate the effects of the limited view angle in the linear tomographic inversion applied to GPR data. In particular, this paper is an extended version of the contribution (Persico et al. in: Proceedings of Imeko international conference on metrology for archaeology and cultural heritage, Lecce, Italy, 2017a), published in the Proceedings of the conference metrology for archaeology 2017. We propose here a validation of the shifting zoom versus experimental data gathered in a controlled test site, and we will show the effect of the shifting zoom on depth slices achieved from these data after a linear inverse scattering processing has been applied for their focusing.     

Laghi di Monticchio (Southern Italy,Region Basilicata): genesis of sediments—a geochemical study

The sedimentation record of Lago Grande di Monticchio (LGM) is one of the most prominent paleoclimatic archives in the non-glaciated areas of Europe. However, the modern lake system has never been the subject of intense limnological studies. On the basis of hydrochemical water profiles, detailed investigations of sediment short cores and in situ pore water profiles from the littoral to the profundal zone, we elucidate spatial variations of sediment genesis within the lake basin and the importance of various depth sections for the lake’s internal nutrient cycling. Sediments from the smaller meromictic Lago Piccolo di Montichio are discussed as a reference. Our study demonstrates: (i) distinctly higher sediment accumulation for the centre of the lake basin by focussing of the settling particle flux; (ii) decline of carbonate from the littoral to the profundal zones; (iii) non-synchronous change of calcite net-accumulation for various water depths; (iv) exceptionally high cation release from sediments covering the steeply inclining sector of the lake basin; (v) relatively constant dissolved silica concentrations in the pore waters (SiO₂ ∼42 mg/l) independent of water depth and sediment composition; (vi) influx of oxygen-bearing groundwater into the anoxic hypolimnion after heavy rainfall and the associated precipitation of Fe-oxihydroxides; (vii) higher release of NH₄ by anaerobic degradation of organic matter at a water depth of 23 m than for sediments at a maximum water depth of 32 m, whereby the latter reflects the importance of seasonal sediment re-oxidation for anaerobic degradation of organic debris; (viii) although seasonal re-oxidation of sediments from various water depths is quite different, Oxygen Index values of LGM sediments fall in a small range, which reflects rapid microbial consumption of seasonally re-generated easily bio-degradable organic molecules.