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824 Ergebnisse:

Nitrate vulnerability projections from Bayesian inference of multiple groundwater age tracers
Journal of Hydrology (2016)
Jamal Alikhani, Amanda Deinhart, Ate Visser, Richard Bibby, Roland Purtschert, Jean Moran, Arash Massoudieh, Brad Esser

Nitrate is a major source of contamination of groundwater in the United States and around the world. We tested the applicability of multiple groundwater age tracers (3H, 3He, 4He, 14C, 13C, and 85Kr) in projecting future trends of nitrate concentration in 9 long-screened, public drinking water wells in Turlock, California, where nitrate concentrations are increasing toward the regulatory limit. Very low 85Kr concentrations and apparent 3H/3He ages point to a relatively old modern fraction (40-50 years), diluted with pre-modern groundwater, corroborated by the onset and slope of increasing nitrate concentrations. An inverse Gaussian-Dirac model was chosen to represent the age distribution of the sampled groundwater at each well. Model parameters were estimated using a Bayesian inference, resulting in the posterior probability distribution – including the associated uncertainty – of the parameters and projected nitrate concentrations. Three scenarios were considered, including combined historic nitrate and age tracer data, the sole use of nitrate and the sole use of age tracer data. Each scenario was evaluated based on the ability of the model to reproduce the data and the level of reliability of the nitrate projections. The tracer-only scenario closely reproduced tracer concentrations, but not observed trends in the nitrate concentration. Both cases that included nitrate data resulted in good agreement with historical nitrate trends. Use of combined tracers and nitrate data resulted in a narrower range of projections of future nitrate levels. However, use of combined tracer and nitrate resulted in a larger discrepancy between modeled and measured tracers for some of the tracers. Despite nitrate trend slopes between 0.56 and 1.73 mg/L/year in 7 of the 9 wells, the probability that concentrations will increase to levels above the MCL by 2040 are over 95% for only two of the wells, and below 15% in the other wells, due to a leveling off of reconstructed historical nitrate loadings to groundwater since about 1990.

Compositional variation and palaeoenvironment of the volcanolithic Fort Cooper Coal Measures, Bowen Basin, Australia
International Journal of Coal Geology (2016)
S.A. Ayaz, S. Rodrigues, S.D. Golding, J.S. Esterle

Megascopic lithotype and microscopic maceral and mineral composition were supplemented by sedimentary logging of the interburden and stable carbon isotope data from a single well to interpret the response of the Late Permian Fort Cooper Coal Measures (FCCM) to regional and global environmental influences. The FCCM are differentiated from underlying, relatively high vitrinite Moranbah Coal Measures, and overlying higher inertinite Rangal Coal Measures in the Bowen Basin by their intercalation with abundant tuff and siliciclastic partings and interbeds. Besides this, there is little described about the variation in the organic composition of the FCCM and its causes. The FCCM can be subdivided into a lower aggradational Fair Hill Formation, transgressed by the shallow marine-derived Black Alley Shale that interfinger with/is overlain by the progradational Middle Main Seams and Burngrove Formation. The coals are dominantly dull with minor bright bands that are more abundant in the Burngrove Formation representing a change in plant composition. The maceral analysis shows that the coals in the Fair Hill Formation and Middle Main Seams are vitrinite-rich (80–90% mmf) albeit with high mineral matter suggesting the formation of precursory peat under rising water levels and with high sediment (tuff) influx and preservation. The coals in the Burngrove Formation have an increased inertinite content (30% mmf) but are also high in mineral matter suggesting a shift to increased decomposition arising from a fluctuating water table, possibly increased aridity and/or microbial activity. Tuffs occur throughout, and although the frequency is higher in the lower Fair Hill Formation, the preservation of thicker tuffs in the Burngrove Formation indicates increased intensity of volcanism that could have modified the environment. Variation in carbon isotope compositions show a parabolic trend, from around −24.1‰ in the Fair Hill Formation to more variable values in the Middle Main Seams with an overall 13C-enrichment upwards in the Burngrove Formation, prior to the δ13C values becoming negative (depleted between −1 to −4% from the average −24.1‰) in the top seams and into the overlying Rangal Coal Measures. The 13C-depletion trend in the upper part of the section is unexpected in view of the high inertinite content of the coals and does not show a positive correlation indicating that the δ13C values/plant composition and inertinite content are decoupled. Similar stable carbon isotope depletion trends have been observed in an equivalent stratigraphic section of the Bowen Basin that suggests the carbon isotope values are responding to local basin tectonics and the climatic transition near end-Permian time, which is represented globally by negative excursions in carbon isotopes before the P-T boundary. Increasing inertinite can also be a function of increasing aridity before the P-T boundary or the result of increased microbial activity as a function of volcanic ash deposition. Overall, the basin was continuously subsiding with excessive sedimentation and volcanic eruptions. The low proportion of bright bands coupled with high vitrinite content suggest a marsh environment, possibly open and wet capable of preserving incoming volcanic ash and clastics resulting in vitrinite-rich and high ash coals.

Identifying recharge and salinization sources of groundwater in the Oussja Ghar el Melah plain (northeast Tunisia) using geochemical tools and environmental isotopes
Environmental Earth Sciences (2016)
Safouan Ben Ammar, Jean-Denis Taupin, Kamel Zouari, Mohamed Khouatmia

The recharge sources and groundwater degradation in the coastal plain of Oussja Ghar el Melah were investigated using geochemical and isotopes tools. We demonstrate that the water quality of shallow groundwater in the phreatic aquifer is impacted by long-term intensive irrigation. We show that the factors controlling the salinity and composition of groundwater are the return flow of the irrigation water, the water–rock interaction in the aquifer and salts formed on the surface by marine sprays. In the low plain where NO3 − content is of up to about 140 mg/L, groundwater is affected by diffuse pollution caused by intensive agricultural activities. In the upstream part of the plain and in the area situated in the SW, stable isotopes and tritium values indicate recent recharge by local precipitation

Investigation of the geographical provenance of the beer available in South Korea using multielements and isotopes
Food Control (2016)
Yeon-Sik Bong, Jong-Sik Ryu, Seung-Hyun Choi, Mi-Ran La, Kwang-Sik Lee

Although beer has the largest share of the global alcoholic beverage market, only limited studies of beer have been performed in terms of elemental and isotopic compositions. Here, we measured elemental and isotopic compositionsdincluding carbon and oxygen isotopes as well as 87Sr/86Sr ratiosdof beers available in South Korea to examine geographical differences. Although most of the elements analyzed in this study were not markedly different between the beer samples, there was a clear distinction in the isotopic compositions of the samples. d13CDIC values indicated that most of the beer samples were produced from C3 plants, such as barley or wheat. d18O values allowed the samples to be discriminated by latitude, reflecting a negative correlation between latitude and isotopic composition. Similarly, 87Sr/86Sr ratios were different between the samples due to the bedrock. Statistical analysis of the combination of elemental and isotopic compositions showed a clear difference between the beer samples according to the geographical provenance on a continental scale. This study demonstrated a powerful method for distinguishing diverse beers according to their geographical provenance, and will make an important contribution to research into discrimination of the geographical origin of diverse processed foods available commercially

Hydrogeological and isotope mapping of the karstic River Savica in NW Slovenia
Environmental Earth Sciences (2016)
Mihael Brenčič, Polona Vreča

Hydrogeological mapping comprises a group of methods with which the area of interest is carefully inspected for the appearance of groundwater related phenomena. During the mapping of groundwater and surface water, samples can be collected for further analysis. On the karstic River Savica (NW Slovenia) the methodology of detailed hydrogeological mapping was tested by which, every 100 m along the river course, samples of water were collected for stable isotopic composition of oxygen (δ 18O). River Savica results from two main tributaries (Velika Savica and Mala Savica) recharging on a high mountain karstified plateau with an average discharge of 5.08 m3/s. Application of hydrogeological mapping methodology to the riverbed resulted in a conceptual model of the groundwater components entering the river. Based on the end member mixing models and with the application of isotope and electrical conductivity data as conservative tracers, it was possible to estimate the contribution of different karstic groundwater components to the river outflow. For the first time it was estimated that, under low and average water conditions, Mala Savica contributes from 12 to 17 % and Velika Savica from 78 to 82 % of the total River Savica discharge, there being only minor inflow from the other sources.

Moon jellyfish, Aurelia aurita, in the Gulf of Gdansk: threatening predator or not?
Dominika Bruli, Marcelina Zi, Stella Mudrak-cegio, Maciej Wo

The seasonal population dynamics and feeding preferences of the moon jellyfish, Aurelia aurita, in the Gulf of Gdansk (southern Baltic Sea) were investigated. Medusae were present in the water column from June to November, with maximum occurrence in August and September. The medusa bell diameter and weight increased during the study period reached maximum values in October. The relationship between bell diameter and wet weight was strong. No ephyrae were observed during the study period. Gastric content analysis revealed that the medusae fed mainly on copepods and cladocerans. Rotifers that dominated the water column throughout the study period were not found in the jellyfish guts, but the stable isotope signature indicated that they could have been a significant source of derived carbon. Low numbers of plankton prey and the lack of fish larvae in A. aurita guts suggest that the jellyfish is of minor relevance as a predator and competitor in the Gulf of Gdansk

Stable isotopes and digital elevation models to study nutrient inputs in high-arctic lakes
Rendiconti Lincei (2016)
Edoardo Calizza, Maria Letizia Costantini, David Rossi, Vittorio Pasquali, Giulio Careddu, Loreto Rossi

Five major factors control nutrient and organic matter inputs in high-Arctic lakes, all potentially affected by climate change: ice cover; run-off from the watershed; aquatic and terrestrial primary productivity; guano deposition from birds. Quantifying these controls is a key first step to understand what combination of factors underlies the biological productivity in Arctic lakes and drives their ecological response to climate change. Based on C and N elemental content and stable isotope analysis in sediments belonging to three lakes in North Spitsbergen (Svalbard), Digital Elevation Models and drainage maps, we propose an integrated approach for the analysis of nutrient and organic matter inputs in lakes and the role of catchment hydro-geomorphology in determining inter-lake differences in the isotopic composition of sediments. Given its high run-off and large catchment, organic deposits in Tvillingvatnet were dominated by terrestrial inputs, whereas inputs were mainly of aquatic origin in Storvatnet, a lowland lake characterised by low potential run-off. In Kolhamna, organic deposits seemed to be dominated by inputs from birds. Isotopic signatures were similar between samples within each lake, representing precise tracers for studies on the effect of climate change on biogeochemical cycles in lakes. The presented approach proved to be an effective research pathway for the identification of factors underlying nutrient and organic matter inputs within each water body, as well as for the modelling of expected changes in nutrient content associated with changes in isotopic composition of sediments.
Schlagworte: C , N , ge , ec , EA

Environmental context for the terminal Ediacaran biomineralization of animals.
Geobiology (2016)
H Cui, A J Kaufman, S Xiao, S Peek, H Cao, X Min, Y Cai, Z Siegel, X-M Liu, Y Peng, J D Schiffbauer, A J Martin

In terminal Ediacaran strata of South China, the onset of calcareous biomineralization is preserved in the paleontological transition from Conotubus to Cloudina in repetitious limestone facies of the Dengying Formation. Both fossils have similar size, funnel-in-funnel construction, and epibenthic lifestyle, but Cloudina is biomineralized, whereas Conotubus is not. To provide environmental context for this evolutionary milestone, we conducted a high-resolution elemental and stable isotope study of the richly fossiliferous Gaojiashan Member. Coincident with the first appearance of Cloudina is a significant positive carbonate carbon isotope excursion (up to +6‰) and an increase in the abundance and (34) S composition of pyrite. In contrast, δ(34) S values of carbonate-associated sulfate remain steady throughout the succession, resulting in anomalously large (>70‰) sulfur isotope fractionations in the lower half of the member. The fractionation trend likely relates to changes in microbial communities, with sulfur disproportionation involved in the lower interval, whereas microbial sulfate reduction was the principal metabolic pathway in the upper. We speculate that the coupled paleontological and biogeochemical anomalies may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin, which stimulated primary productivity, the spread of an oxygen minimum zone, and the development of euxinic conditions in subtidal and basinal environments. Enhanced production and burial of organic matter is thus directly connected to the carbon isotope anomaly, and likely promoted pyritization as the main taphonomic pathway for Conotubus and other soft-bodied Ediacara biotas. Our studies suggest that the Ediacaran confluence of ecological pressures from predation and environmental pressures from an increase in seawater alkalinity set the stage for an unprecedented geobiological response: the evolutionary novelty of animal biomineralization.
Schlagworte: S , ge , ar , EA

The main nitrate transporter of the dinoflagellate Lingulodinium polyedrum is constitutively expressed and not responsible for daily variations in nitrate uptake rates
Harmful Algae (2016)
Steve Dagenais Bellefeuille, David Morse

Dinoflagellates are unicellular eukaryotes capable of forming spectacular harmful algal blooms (HABs). Eutrophication of coastal waters by fertilizer runoff, nitrate in particular, has contributed to recent increases in the frequency, magnitude and geographic extent of HABs. Although physiological nitrate uptake and assimilation in dinoflagellates have often been measured in the field and in the laboratory, no molecular components involved in nitrate transport have yet been reported. This study reports the first identification and characterization of dinoflagellate nitrate transporters, found in the transcriptome of the bloom-forming Lingulodinium polyedrum. Of the 23 putative transporters found by BLAST searches, only members of the nitrate transporter 2 (NRT2) family contained all key amino acids known to be essential for nitrate transport. The dinoflagellate NRT2 sequences have 12 predicted transmembrane domains, as do the NRT2 sequences of bacteria, plants and fungi. The NRT2 sequences in Lingulodinium appear to have two different evolutionary origins, as determined by phylogenetic analyses. The most expressed transcript of all putative nitrate transporters was determined by RNA-Seq to be LpNRT2.1. An antibody raised against this transporter showed that the same amount of protein was found at different times over the light dark cycle and with different sources of N. Finally, global nitrate uptake was assessed using a 15N tracer, which showed that the process was not under circadian-control as previously suggested, but simply light-regulated.

A small number of anadromous females drive reproduction in a brown trout ( Salmo trutta ) population in an English chalk stream
Freshwater Biology (2016)
Jill C. A. Goodwin, R. Andrew King, J. Iwan Jones, Anton Ibbotson, Jamie R. Stevens

Brown trout, Salmo trutta, exhibit one of the most highly variable and polytypic life-history strategies of all salmonids. Populations may be wholly freshwater-resident or almost exclusively migratory (anadromous), or fish of a single population may exhibit varying proportions of the two life-history strategies. Both anadromous and freshwater-resident trout freely interbreed to produce fertile offspring. We quantify maternal reproductive provisioning by anadromous and freshwater-resident brown trout to their offspring and assess relative parental fitness (in terms of number, size and time of emergence of offspring). Newly emerged juvenile trout (fry) were sampled (n = 119) over the emergence period in March–April 2007 in a lowland English chalk stream; samples of adult trout [anadromous (6F : 12M) and freshwater-resident (22F : 56M)], river-resident trout parr and macroinvertebrate prey were also collected. Using a novel combination of stable isotope analysis and microsatellite genotyping we demonstrate the overwhelming contribution of anadromous parents (both female and male) to fry production, despite the obvious presence and numerical dominance of resident adults. We unambiguously identify the maternal origins of 78% of juveniles sampled and show that maternal reproductive contribution to juvenile production in the river was higher for anadromous females (76%) than freshwater-resident fish (2.5%). Offspring of anadromous females emerged earlier and at a larger body size than offspring of resident females. Similarly, while the relative contribution of resident males (37%) was higher than that of resident females, anadromous males sired considerably more offspring (63%) than resident males. This is the first study of its kind to accurately assess the reproductive contribution of anadromous male trout. Overall, this study suggests that anadromous maternal traits provide offspring with an adaptive advantage and greater fitness in early ontogeny, and that a small number of anadromous females (six of 96 adults sampled) are the main drivers of reproduction in this system.
Schlagworte: C , N , ec , EA