Evaluation of Methane Sources in Groundwater in Northeastern Pennsylvania

Testing of 1701 water wells in northeastern Pennsylvania shows that methane is ubiquitous in groundwater, with higher concentrations observed in valleys vs. upland areas and in association with calcium‐sodium‐bicarbonate, sodium‐bicarbonate, and sodium‐chloride rich waters—indicating that, on a regional scale, methane concentrations are best correlated to topographic and hydrogeologic features, rather than shale‐gas extraction. In addition, our assessment of isotopic and molecular analyses of hydrocarbon gases in the Dimock Township suggest that gases present in local water wells are most consistent with Middle and Upper Devonian gases sampled in the annular spaces of local gas wells, as opposed to Marcellus Production gas. Combined, these findings suggest that the methane concentrations in Susquehanna County water wells can be explained without the migration of Marcellus shale gas through fractures, an observation that has important implications for understanding the nature of risks associated with shale‐gas extraction.     

Cartographie du potentiel en eau souterraine du bassin versant de la Lobo (Centre-Ouest,Côte d’Ivoire) : approche par analyse multicritère

RÉSUMÉ

Ce travail aborde le problème d’accessibilité en eau potable dans les zones fissurées de la Côte d’Ivoire notamment en saison sèche. Sur le bassin versant de la Lobo, le problème se pose avec plus d’acuité puisque les retenues aménagées pour l’alimentation en eau des populations ne sont pas correctement alimentées ces dernières années et sujettes à une très forte eutrophisation. L’approche pluridisciplinaire (télédétection, analyse multicritère et système d’information hydrogéologique à référence spatiale) a été adoptée. La cartographie des sites potentiels en eau montre que la quasi-totalité du bassin de la Lobo possède une bonne et excellente disponibilité en eau souterraine (93% de la superficie totale). Cette bonne disponibilité en eau souterraine est due à une faible pente et à une bonne densité de fracturation qui entrainent une bonne infiltration des eaux dans l’aquifère. L’identification des sites potentiels montre que près de 72% de la superficie du bassin est favorable à l’implantation d’ouvrages à gros débits. Dans l’ensemble, ces aquifères présentent une bonne accessibilité avec cependant, une exploitabilité médiocre.

Editeur Z. W. Kundzewicz; Edithur Associé M.D. Fidelibus     

Diurnal and tidal patterns of carbon uptake and calcification in geniculate inter‐tidal coralline algae

Research on coralline algal responses to ocean acidification and other environmental stressors has increased in recent years as coralline algae is thought to stand a higher chance of being affected by acidification stress than other macroalgae. To provide context and enhance the existing eco‐physiological framework for climate change studies, it is important to understand the effects of non‐extreme stressors experienced regularly by inter‐tidal coralline algae. In this study, we tested the potentially interacting effects of diurnal and tidal treatments on calcification in the geniculate coralline algae Corallina frondescens and Corallina vancouveriensis using ¹³C‐labeled bicarbonate. Both species deposited more calcium carbonate during the day than at night, and also when submerged (high tide) compared with when emerged (low tide) in their apical and mature segments (intergenicula). These results indicate that inter‐tidal coralline algae do in fact pay a cost for living inter‐tidally at the edge of an adaptive zone.     

Electrical-hydraulic conductivity model for a weathered-fractured aquifer system of Olbanita,Lower Baringo Basin,Kenya Rift

Groundwater yield in the Kenya Rift is highly unsustainable owing to geological variability. In this study, field hydraulic characterization was performed by using geo-electric approaches. The relations between electrical-hydraulic (eh) conductivities were modeled hypothetically and calibrated empirically. Correlations were based on the stoch-astic models and field-scale hydraulic parameters were contingent on pore-level parameters. By considering variation in pore-size distributions over eh conduction interval, the relations were scaled-up for use at aquifer-level. Material-level electrical conductivities were determined by using Vertical Electrical Survey and hydraulic conductivities by analyzing aquifer tests of eight boreholes in the Olbanita aquifer located in Kenya rift. VES datasets were inverted by using the computer code IP2Win. The main result is that ln T=0.537 (ln Fa)+3.695; the positive gradient indicating eh conduction through poresurface networks and a proxy of weathered and clayey materials. An inverse (1/F-K) correlation is observed. Hydraulic parameters determined using such approaches may possibly contri-bute significantly towards sustainable yield management and planning of groundwater resources.     

The isotopic composition of particulate organic carbon in mountain rivers of Taiwan

Small rivers draining mountain islands are important in the transfer of terrestrial particulate organic carbon (POC) to the oceans. This input has implications for the geochemical stratigraphic record. We have investigated the stable isotopic composition of POC (δ¹³C_org) in rivers draining the mountains of Taiwan. In 15 rivers, the suspended load has a mean δ¹³C_org that ranges from −28.1±0.8‰ to −22.0±0.2‰ (on average 37 samples per river) over the interval of our study. To investigate this variability we have supplemented suspended load data with measurements of POC in bedrock and river bed materials, and constraints on the composition of the terrestrial biomass. Fossil POC in bedrock has a range in δ¹³C_org from −25.4±1.5‰ to −19.7±2.3‰ between the major geological formations. Using coupled δ¹³C_org and N/C we have found evidence in the suspended load for mixing of fossil POC with non-fossil POC from the biosphere. In two rivers outside the Taiwan Central Range anthropogenic land use appears to influence δ¹³C_org, resulting in more variable and lower values than elsewhere. In all other catchments, we have found that 5‰ variability in δ¹³C_org is not controlled by the variable composition of the biomass, but instead by heterogeneous fossil POC.In order to quantify the fraction of suspended load POC derived from non-fossil sources (F_nf) as well as the isotopic composition of fossil POC (δ¹³C_fossil) carried by rivers, we adapt an end-member mixing model. River suspended sediments and bed sediments indicate that mixing of fossil POC results in a negative trend between N/C and δ¹³C_org that is distinct from the addition of non-fossil POC, collapsing multiple fossil POC end-members onto a single mixing trend. As an independent test of the model, F_nf reproduces the fraction modern (F_mod) in our samples, determined from ¹⁴C measurements, to within 0.09 at the 95% confidence level. Over the sampling period, the mean F_nf of suspended load POC was low (0.29 ± 0.02, n = 459), in agreement with observations from other mountain rivers where physical erosion rates are high and fossil POC enters river channels. The mean δ¹³C_fossil in suspended POC varied between −25.2±0.5‰ and −20.2±0.6‰ from catchment to catchment. This variability is primarily controlled by the distribution of the major geological formations. It also covers entirely the range of δ¹³C_org found in marine sediments which is commonly thought to derive from mixing between marine and terrigenous POC. If land-sourced POC is preserved in marine sediments, then changes in the bulk δ¹³C_org observed offshore Taiwan could instead be explained by changes in the onshore provenance of sediment. The range in δ¹³C_org of fossil organic matter in sedimentary rocks exposed at the surface is large and given the importance of these rocks as a source of clastic sediment to the oceans, care should be taken in accounting for fossil POC in marine deposits supplied by active mountain belts.     

The Role of Zooplankton Grazing and Nutrient Loading in the Occurrence of Harmful Cyanobacterial Blooms in Florida Bay,USA

Florida Bay is Florida’s (USA) largest estuary and has experienced harmful picocyanobacteria blooms for nearly two decades. While nutrient loading is the most commonly cited cause of algal blooms in Florida Bay, the role of zooplankton grazing pressure in bloom occurrence has not been considered. For this study, the spatial and temporal dynamics of cyanobacteria blooms, the microbial food web, microzooplankton and mesozooplankton grazing rates of picoplankton, and the effects of nutrients on plankton groups in Florida Bay were quantified. During the study, cyanobacteria blooms (>3 × 10⁵ cells mL⁻¹) persisted in the eastern and central regions of Florida Bay for more than a year. Locations with elevated abundance of cyanobacteria hosted microzooplankton grazing rates on cyanobacteria that were significantly lower (p < 0.001) and less frequently detectable compared to sites without blooms. Consistent with this observation, cyanobacteria abundances were significantly correlated with ciliates and heterotrophic nanoflagellates at low cyanobacteria densities (p < 0.001) but were not correlated during bloom events. The experimental enrichment of mesozooplankton abundance during blooms yielded a significant decrease in the net growth rate of picoplankton but had the opposite effect when blooms were absent, suggesting that the cascading effect of mesozooplankton grazing on the microbial food web was also altered during blooms. While inorganic nutrient enrichment significantly increased the net growth rates of eukaryotic phytoplankton and heterotrophic bacteria, such nutrient loading had no effect on the net growth rates of cyanobacteria. Hence, this study demonstrates that low rates of zooplankton grazing and low rates of inorganic nutrient loading contribute to the persistence of cyanobacteria blooms in Florida Bay.     

Sedimentary record of Triassic intraplate extension in North China: evidence from the nonmarine NW Ordos Basin, Helan Shan and Zhuozi Shan

The Helan Shan and Zhuozi Shan of the NW Ordos basin, China, contain thick (up to 4 km) sequences of nonmarine Triassic strata. These rocks represent a major intraplate sedimentary basin, the paleogeography, tectonic setting and provenance of which are poorly understood and controversial. Studies of the sedimentary geology of the basin, supported by new palinspastic reconstruction of younger deformation, demonstrate that the basin filled from three sides by fluvial, lacustrine-deltaic and alluvial fan depositional systems. The basin forms a westward-thickening wedge that reaches its maximum thickness along the western margin of the Helan Shan and thins to a relatively constant 600–800 m east of the Zhuozi Shan. The stratigraphy of the basin is strongly asymmetric; alluvial fan strata are restricted to the extreme western margin of the basin and interfinger with axial fluvial deposits low in the section and deep lacustrine facies high in the section. Much of the eastern part of the basin is dominated by west-flowing meandering river and deltaic systems. Large structures of Triassic age have not been identified in the Helan Shan or Zhuozi Shan, but small Triassic normal faults have been documented in the western and central Helan Shan. These characteristics most strongly support an extensional origin for the Triassic basin in NW Ordos. The basin is interpreted to have been a north-trending half graben, bound along its western margin by an east-dipping normal fault, presently concealed beneath Quaternary cover west of the Helan Shan. The eastern margin, now found in the Zhuozi Shan, has simple ramp-margin geometry. Driving mechanisms for this extension are not obvious due to limited documentation of Triassic structure throughout the region, but probably relate to far-field stresses from the Qinling or Jinsha active margins interacting with the stable Ordos block.     

Extracting olivine (Fo–Fa) compositions from Raman spectral peak positions

The dominant feature of the olivine Raman spectrum is a doublet that occurs in the spectral region of 815–825 cm⁻¹ (DB1) and 838–857 cm⁻¹ (DB2). These features arise from coupled symmetric and asymmetric stretching vibrational modes of the constituent SiO₄ tetrahedra. The frequencies of both peaks show monotonic shifts following cation substitution between forsterite and fayalite. We present a calibration for extracting olivine Fo contents (Fo = Mg/(Mg + Fe) molar ratio; Fo_0–100) from the peak positions of this doublet, permitting estimates of chemical composition from Raman spectra (acquired in the laboratory or field) as well as providing information on crystal structure (distinction of polymorphs). Eight samples spanning the compositional range from forsterite to fayalite were used to develop the calibration equations for the DB1 and DB2 peaks individually and together. The data indicate that the DB1 peak is more reliable for calculating the compositions of Fe-rich olivine but that the DB2 peak is better for magnesian compositions. The two-peak calibration overcomes the limitations of the single-peak calibrations and is capable of calculating olivine compositions to within ±10 Fo units.