Characterising the vertical separation of shale-gas source rocks and aquifers across England and Wales (UK)

Shale gas is considered by many to have the potential to provide the UK with greater energy security, economic growth and jobs. However, development of a shale gas industry is highly contentious due to environmental concerns including the risk of groundwater pollution. Evidence suggests that the vertical separation between exploited shale units and aquifers is an important factor in the risk to groundwater from shale gas exploitation. A methodology is presented to assess the vertical separation between different pairs of aquifers and shales that are present across England and Wales. The application of the method is then demonstrated for two of these pairs—the Cretaceous Chalk Group aquifer and the Upper Jurassic Kimmeridge Clay Formation, and the Triassic sandstone aquifer and the Carboniferous Bowland Shale Formation. Challenges in defining what might be considered criteria for ‘safe separation’ between a shale gas formation and an overlying aquifer are discussed, in particular with respect to uncertainties in geological properties, aquifer extents and determination of socially acceptable risk levels. Modelled vertical separations suggest that the risk of aquifer contamination from shale exploration will vary greatly between shale–aquifer pairs and between regions and this will need to be considered carefully as part of the risk assessment and management for any shale gas development.     

Projected changes in meteorological drought over East Africa inferred from bias-adjusted CMIP6 models

Natural Hazards - The ongoing global warming has caused unprecedented changes in the climate system, leading to an increase in the intensity and frequency of weather and climate extremes. This...     

Recovery of the seabed following marine aggregate dredging on the Hastings Shingle Bank off the southeast coast of England

The aim of this study was to investigate the effect of dredging intensity on the physical and biological recovery times of the seabed following marine aggregate dredging. Two areas of seabed, previously subject to, respectively, relatively high and lower levels of dredging intensity, were identified on the Hastings Shingle Bank. Two reference areas were also selected for comparative purposes. All four sites were monitored annually over the period 2001–2004, using a combination of acoustic, video and grab sampling techniques. Since the site was last dredged in 1996, this was intended to provide a sequence of data 5–8 years after cessation of dredging. However, an unexpected resumption of dredging within the high intensity site, during 2002 and 2003, allowed an additional assessment of the immediate effects and aftermath of renewed dredging at the seabed. The early stages of recovery could then be assessed after dredging ceased in 2003. Results from both dredged sites provide a useful insight into the early and latter stages of physical and biological recovery. A comparison of recent and historic dredge track features provided evidence of track erosion. However, tracks were still visible 8 years after the cessation of dredging. Within the high dredging intensity site, recolonisation was relatively rapid after the cessation of dredging in 2003. Rather than indicating a full recovery, we suggest that this initial ‘colonization community’ may enter a transition phase before eventually reaching equilibrium. This hypothesis is supported by results from the low intensity site, where biological recovery was judged to have taken 7 years. Further monitoring is needed in order to test this. An alternative explanation is that the rapid recovery may be explained by the settlement of large numbers of Sabellaria spinulosa. As the resumption of dredging within the high intensity site limited our assessment of longer-term recovery it is not yet possible to assume that a 7-year biological recovery period will be applicable to other, more intensively dredged areas at this or more distant locations.     

Mapping Seabed Geology by Ground-Truthed Textural Image/Neural Network Classification of Acoustic Backscatter Mosaics

We present a novel, automated method for seabed classification based on shallow water backscatter mosaics from Sydney Harbour. Our approach compares the results between two different methods of image feature extraction when combined with artificial neural networks. The association of image textures with seabed geology is used to train the artificial neural networks to recognise the variability of textural attributes for three seabed classes comprising mud, sand and gravel. After network training, we classify unknown portions of the backscatter mosaic with a success rate ranging from 77% to 92%. Our results suggest that the computationally fast grey-level co-occurrence iteration algorithm holds promise for benthic habitat mapping in space and time, leading to real-time data analysis at sea.     

Sediment-charged flash floods on Montserrat: The influence of synchronous tephra fall and varying extent of vegetation damage

On 20th May 2006 the Soufrière Hills Volcano on the Caribbean island of Montserrat experienced a large dome collapse and intense rainfall generated flash floods. The floods had very high loads of volcanic debris derived both from this and previous eruptions and can thus be classified as lahars. The floods reached unusually high water levels and caused substantial geomorphic change in the Belham Valley. Detailed rainfall and geomorphological data, coupled with the precise timing of events and yewitness accounts have facilitated an assessment of the relative importance of rainfall volume and intensity, older volcanic debris, pre- and syn-flood tephra fall and the extent of pre-flood vegetation damage for the behavior of this and subsequent sediment-laden floods in this setting. The change in runoff behavior was controlled by preexisting vegetation damage and synchronous tephra fall and this was critically important in controlling the impact of these flash floods. Although rainfall intensity and volume have some control on flood occurrence they are not the critical control on flash flood impact on the geomorphology in the Belham Valley. A significant conclusion of this study is that the extreme nature of the flash floods was not caused by extreme rainfall (as is commonly believed to be the primary cause of flash floods) but rather it was the result of changed runoff behaviour caused by the widespread syn-flood tephra deposition and importantly the widespread vegetation damage by volcanic-associated acid rain in the preceding weeks.     

峰峰煤田断裂地震识别技术及其发育规律分析

正煤矿开采过程中,断层构造是影响矿业发展的重要问题之一。如果不了解地下结构和断层的发育情况,可能会造成巨大的经济损失,甚至会导致透水等事故的发生。因此,寻找煤层中的小断层对煤矿开采具有重要意义。峰峰煤田断裂构造非常发育,本文通过地震勘探对小断层进行识别,并分析分析该地区断层发育规律,为今后该井田的煤炭勘探提供参考。     

Partial substitution of peat moss with biochar for sustainable cultivation of <Emphasis Type="Italic">Durio zibethinus L</Emphasis>. in nurseries

The extensive use of peat moss as potting medium in nurseries worldwide is not sustainable causing peatland depletion and greenhouse gas emissions. This research seeks to explore whether wood biochar produced by the environment-friendly flame curtain method can partially substitute peat moss in plant nurseries without affecting plant growth and health. Biochar was produced from durian wood logs in a top-quenched Kon-Tiki earth kiln, crushed, and mixed with peat moss at dosages of 0, 1, 2.5 and 5% (w/w). Durian seedlings were grown in 2.5 L polybags arranged in randomised complete block design with 4 replicates per treatment. Plant height, collar diameter, pH, moisture content, number of branches and leaves, and plant health were monitored weekly for 94 days. Liquid fish fertiliser was used as organic fertiliser. Our results demonstrated that biochar can substitute at least 5% (w/w) peat moss without negatively affecting plant height, collar diameter, number of leaves and branches, and plant health. In addition, organic fertiliser is not required during the first 3 months of cultivation resulting in cost savings to the nursery operator. Plant height was found to be the most accurate yet simple monitoring parameter studied. A better understanding of the effect of higher biochar application rates as well as the number of times the potting medium can be reused without loss of potting medium properties and health can help to further cut nursery cost and reduce reliance on peat moss.     

Base-salt relief controls salt-related deformation in the Outer Kwanza Basin,offshore Angola

Salt-influenced passive margins are widespread and commonly hydrocarbon-rich. However, they can be structurally complex, with their kinematic development being poorly understood. Classic models of salt tectonics divide such margins into updip extensional, mid-slope translational and downdip contractional kinematic domains. Furthermore the faults, folds, and salt walls associated with each kinematic domain are typically assumed to form perpendicular to the maximum principal stress, which in gravitationally driven systems means broadly perpendicular to base-salt dip. We use high-resolution 3D seismic reflection data from the Outer Kwanza Basin, offshore Angola to show that these models cannot explain the diversity of salt structures developing on passive margins, especially those defined by considerable relief on the base-of-salt surface. Overburden seismic-stratigraphic patterns record the basinward translation and rotation, allowing us to reconstruct the origin and evolution of the salt structures. We show structures in the transitional domain of the Outer Kwanza Basin display three dominant trends, each characterised by different structural styles: (a) salt walls perpendicular to the overall base-salt dip, (b) salt walls parallel to the base-salt dip and (c) salt walls oblique to the base-salt dip. We show that each set of walls has a unique history, with synchronous phases of extension and compression occurring in adjacent structures despite their close spatial relationship. Our analysis suggests that, in the Outer Kwanza Basin, the structural evolution of the salt and overburden is predominantly controlled by translation over relief on the base-salt surface formed above fault scarps associated with a preceding phase of rifting. Changes in the downdip volumetric flux and velocity of the salt over topographic features can cause local extension or contraction of the salt and its overburden, associated with local acceleration or deceleration of the salt, respectively. This interaction with base-salt relief creates locally variable stress fields that deform the salt and its overburden, overprinting the broader, margin-scale salt tectonics typically associated with gravity gliding and spreading.     

Marine spatial planning in the high seas

Although high seas resources are being exploited, reciprocal legal obligations to protect its environment have not been met. Marine spatial planning (MSP) is clearly a practical way forward, particularly for the high seas, where non-spatial monitoring is difficult, and where data gaps obstruct conventional management approaches. To ensure the effective application of MSP in the high seas, however, some institutional reforms are necessary. This paper outlines the main hurdles, summarizes existing high seas spatial protections, presents an example of a high seas marine protected area that resulted through MSP, identifies three institutional priorities, and suggests three immediate steps.