Are fiddler crabs potentially useful ecosystem engineers in mangrove wastewater wetlands?

The effect of different organic-rich sewage concentration (0%, 20% and 60% diluted in seawater) and absence or presence of mangrove trees on the survival, bioturbation activities and burrow morphology of fiddler crabs species was assessed. After 6 months, males of both species always showed higher survival (80%) when compared to females (20%). Crabs inhabiting pristine conditions achieved higher survival (67–87%) than those living in sewage-exposed mesocosms (40–71%). At 60% sewage loading, fiddler crabs processed less sediment (34–46%) during feeding and excavated slightly more sediment (45–80%) than at pristine conditions. While percent volume of the burrow chambers increased (13–66%) at contaminated mesocosms for both vegetation conditions, burrows were shallower (33%) in bare cells loaded with sewage. The results show that fiddler crabs presented moderate mortality levels in these artificial mangrove wetlands, but mainly in sewage impacted cells. However, they still function as ecosystem engineers through bioturbation activities and burrow construction.     

A Comparison of Unstructured and Structured Principal Component Analyses and their Interpretation

Multivariate analysis is employed to investigate the structure of variations within highly heterogeneous data. Traditionally, principal component analysis (PCA) is run by analyzing the entire wireline log and using PCA scores to characterize variability within and between lithologies. In this paper, we propose a technique using only specific subsets of all well records to quantify reservoir heterogeneity due to second order lithological variability. These subsets are chosen from uniform lithofacies parts of the wireline log in order to reduce the variability in the correlation matrix that otherwise would cause lithological changes. The purpose is to assess the efficiency of structured PCA in analyzing small-scale heterogeneity that is captured by wireline logs but often masked by traditional PCA approaches. This paper shows that a structured PCA procedure based upon special lithological units is superior to an unstructured PCA, when the focus is within lithology variations. This structured procedure is applied to data from the Heidrun field, offshore mid-Norway. The results demonstrate clear benefits from added insight into the variability of a complex fluviodeltaic heterolithic sequence that poses great challenges to hydrocarbon development.     

Open-system degassing of sulfur from Krakatau 1883 magma

We present the first sulfur and oxygen isotopic data for tephra from the catastrophic 1883 eruption of Krakatau. Sulfur isotopic ratios in unaltered Krakatau tephra erupted August 26–27, 1883 are markedly enriched in ³⁴S relative to mantle sulfur. High δ³⁴S values of +6.3 to +16.4‰ can best be explained by open-system or multi-stage degassing of SO₂ from the oxidized rhyodacitic and gray dacitic magmas with ³⁴S enrichment of SO²⁻₄ remaining in the melt. Lower whole-rock δ³⁴S values of +2.6‰ and +4.0‰ in two oxidized gray dacitic samples indicate more primitive subarc mantle sulfur in the 1883 magma chamber. Initial δ³⁴S of the rhyodacitic magma was probably in the +1.5‰ to +4.0‰ range and similar to δ³⁴S values measured in arc volcanic rocks from the Mariana Arc.     

Numerical support of laboratory experiments: Attenuation and velocity estimations

We show that numerical support of laboratory experiments can significantly increase the understanding and simplify the interpretation of the obtained laboratory results. First we perform simulations of the Seismic Wave Attenuation Module to measure seismic attenuation of reservoir rocks. Our findings confirm the accuracy of this system. However, precision can be further improved by optimizing the sensor positions. Second, we model wave propagation for an ultrasonic pulse transmission experiment used to determine pressure- and temperature-dependent seismic velocities in the rock. Multiple waves are identified in our computer experiment, including bar waves. The metal jacket that houses the sample assembly needs to be taken into account for a proper estimation of the ultrasonic velocities. This influence is frequency-dependent.     

Spatiotemporal analysis of NORA10 data of significant wave height

This paper presents a spatiotemporal analysis performed by applying a Bayesian hierarchical model on NORA10 data of significant wave height. The model has previously been applied to corrected ERA-40 data of significant wave height and was generally found to perform well. However, a new set of high-resolution significant wave height data has recently become available, which is believed to be an improvement compared to the C-ERA-40 data, and a similar spatiotemporal analysis is performed on this new data set. NORA10 differs from C-ERA-40 in various ways and in particular the spatial resolution is significantly increased. Hence, one main motivation for the study presented in this paper is to investigate how the model performs on data with very high spatial resolution. In particular, the model contains a separate component for identifying long-term trends in the wave climate, possibly due to climate change. For the C-ERA-40 data, significant increasing trends were detected in the selected area in the North Atlantic Ocean. These trends are not reproduced in the NORA10 data, but there are differences in geographical and temporal coverage that may, at least partly, explain such differences. The new analysis and the results pertaining to the NORA10 data are presented in this paper.     

A Bayesian hierarchical spatio-temporal model for significant wave height in the North Atlantic

Bad weather and rough seas continue to be a major cause for ship losses and is thus a significant contributor to the risk to maritime transportation. This stresses the importance of taking severe sea state conditions adequately into account in ship design and operation. Hence, there is a need for appropriate stochastic models describing the variability of sea states, taking into account long-term trends related to climate change. Various stochastic models of significant wave height are reported in the literature, but most are based on point measurements without considering spatial variations. As far as the authors are aware, no model of significant wave height to date exploits the flexible framework of Bayesian hierarchical space-time models. This framework allows modelling of complex dependence structures in space and time and incorporation of physical features and prior knowledge, yet at the same time remains intuitive and easily interpreted. This paper presents a Bayesian hierarchical space-time model for significant wave height. The model has been fitted by significant wave height data for an area in the North Atlantic ocean. The different components of the model will be outlined, and the results from applying the model to monthly and daily data will be discussed. Different model alternatives have been tried and long-term trends in the data have been identified for all model alternatives. Overall, these trends are in reasonable agreement and also agree fairly well with previous studies. Furthermore, a discussion of possible extensions to the model, e.g. incorporating regression terms with relevant meteorological data will be presented.     

Alternate bars in a sandy gravel bed river: generation,migration and interactions with superimposed dunes

A field study was carried out to investigate the development of alternate bars in a secondary channel of the Loire River (France) as a function of discharge variations. We combined frequent bathymetric surveys, scour chains and stratigraphical analysis of deposits with measurements and modelling of flow dynamics. The channel exhibited migrating bars, non‐migrating bars and superimposed dunes. Possible mechanisms of bar initiation were found to be chutes associated with changes of bank direction and instability resulting from interactions between existing bars during the fall in water level after floods. We propose that the reworking of bar sediments during low flows (high width‐to‐depth ratio β), reinforced by high values of the Shields mobility parameter, can explain the formation or re‐generation of new alternate migrating bars during a subsequent flood. The migration pattern of the bars was found to be cyclic and to depend mainly on (i) channel layout and (ii) the dynamics of superimposed dunes with heights and lengths depending on location and discharge value. For instance, the hysteresis affecting the steepness of dunes influences the flow resistance of the dunes as well as the celerity of migrating bars during flood events. We compare the findings from the field with results from theoretical studies on alternate bars. This gives insight in the phenomena occurring in the complex setting of real rivers, but it also sheds light on the extent to which bar theories based on idealized cases can predict those phenomena. Copyright © 2014 John Wiley & Sons, Ltd.