Rock Mechanical Laboratory Testing of Thebes Limestone Formation (Member I), Valley of the Kings, Luxor, Egypt

The Thebes Limestone Formation of Lower Eocene age is one of the most extensive rock units in Egypt. It is of importance to the apogee of the ancient Egyptian civilization, particularly in Luxor (South-Central Egypt), where the rock formation hosts the Theban Necropolis, a group of funerary chambers and temples from the New Kingdom Egyptian era (3500-3000 BP). In this work, we investigated the petrophysical and rock mechanical properties (e.g., rock strength, critical crack stress thresholds) through laboratory tests on eleven rock blocks collected from one area within the Theban Necropolis known as the Valley of the Kings (KV). The blocks belong to Member I of the Thebes Limestone Formation, including six blocks of marly limestone, three blocks of micritic limestone, one block of argillaceous limestone from the Upper Esna Shale Formation, and one block of silicified limestone of unknown origin. Special attention was given to the orientation of bedding planes in the samples: tests were conducted in parallel (PA) and perpendicular (PE) configurations with respect to bedding planes. We found that the marly limestone had an average unconfined compressive strength (UCS) of 30 MPa and 39 MPa for the PA and PE tests, respectively. Similarly, the micritic limestone tests showed an average UCS of 24 MPa for the PA orientation and 58 MPa for the PE orientation. The critical crack thresholds were the first ever reported for Member I, as measured with strain gauge readings. The average crack initiation (CI) stress thresholds for the marly limestone (PA: 14 MPa) and the micritic limestone (PA: 11 MPa; PE: 24 MPa) fall within the typical ratio of CI to UCS (0.36-0.52). The micritic limestone had an average Young's modulus (E) of 19.5 GPa and 10.3 GPa for PA and PE, respectively. The Poisson's ratios were 0.2 for PA and 0.1 for PE on average. Both marly and micritic limestone can be characterised by a transverse isotropic strength behaviour with respect to bedding planes. The failure strength for intact anisotropic rocks depends on the orientation of the applied force, which must be considered when assessing the stability of tombs and cliffs in the KV and will be used to understand and improve the preservation of this UNESCO World Heritage site

Source and age of carbon in peatland surface waters: new insights from 14C analysis

Peatlands are a significant source of carbon to the aquatic environment which is increasingly being recognised as an important flux pathway (both lateral and vertical) in total landscape carbon budgets. Determining the source and age of the carbon (in its various forms) is a key step to understanding the stability of peatland systems as well as the connectivity between the soil carbon pool and the freshwater environment. Novel analytical and sampling methods using molecular sieves have been developed for (1) within-stream, in situ sampling of CO2 in the field and (2) for the removal/separation of CO2 in the laboratory prior to 14C analysis of CH4. Here we present dual isotope (δ13C and 14C) data from freshwater systems in UK and Finnish peatlands to show that significant differences exist in the source and age of CO2, DOC (dissolved organic carbon) and POC (particulate organic carbon). Individual peatlands clearly differ in terms of their isotopic freshwater signature, suggesting that carbon cycling may be “tighter” in some systems compared to others. We have also measured the isotopic signature of different C species in peatland pipes, which appear to be able to tap carbon from different peat depths. This suggests that carbon cycling and transport within “piped-peatlands” may be more complex than previously thought. Some of our most recent work has focussed on the development of a method to measure the 14C component of CH4 in freshwaters. Initial results suggest that CH4 in peatland streams is significantly older than CO2 and derived from a much deeper source. We have also shown that the age (but not the source) of dissolved CO2 changes over the hydrological year in response to seasonal changes in discharge and temperature. Radiocarbon measurements in the peat-riparian-stream system suggest that a significant degree of connectivity exists in terms of C transport and cycling, although the degree of connectivity differs for individual C species. In summary, 14C analysis of peatland surface waters reveals multiple sources and ages for CO2, CH4, DOC and POC with different ages characterising individual peatlands. This implies that carbon transport from peat to stream is more complex than previously thought. Dual isotope (δ13C and 14C) analysis of carbon in its various aquatic forms is clearly a powerful tool in developing a better understanding of the functioning and stability of carbon-rich landscapes

In situ strain detection of stress-strain relationships and their controls on progressive damage in marble and quartzite by neutron diffraction experiments

The application of data derived from rock mechanical experiments to large spatial and temporal scales required to assess rock slope stability and landscape evolution is complicated, as these processes of rocks are affected by its lithology, tectonic heritage and rheological behavior under the contemporary stress field. Interpretations of experiments and field sites are restricted to surficial, pre and post state observations of deformations, under almost always subcritical near surface stress fields. We set up an novel experiment to quantify a) the level of inherited residual elastic strains, b) the effect of subcritical low magnitude load steps, c) load magnitudes at which deformation become permanent and further strains are induced and d) differences of rheological behavior due to lithology. In order to gain greater insight into the stress-strain relationships and their control on progressive damage we employed in situ neutron diffraction techniques to observe crystal lattice strains in pure marble (Carrara marble, > 98 vol% CaCO3) and quartzite (Dalsland quartzite, > 98 vol% SiO2) samples during stepped Brazilian tests. We measure a gauge volume of ∼42mm3 in the center of cylindrical samples (Ø= 30 mm, l = 22 mm quartzite, l = 26 mm marble) using the EPSILON neutron time-of-flight (TOF) strain diffractometer in Dubna, Russia. Surface-mounted strain gauges provide macroscopic strain data, and acoustic emission sensors are used to detect microcrack initiation. Initial states are measured without load to determine the load-free lattice parameters. Load is increased in three to four stages of approximately 15%, 33%, 66%, and 75-80% of the ultimate intact rock strength (σ1 max), and maintained during diffraction measurements (up to 12 hours each). Each load step is followed by a load-free state. Deviatoric strain in both major principal compressive (σ1) and minor principal in plane (σ3) direction, as well as residual strain, with reference to a strain-free state of powdered samples are calculated for whole diffraction patterns. We obtained initial residual contractional strains of ∼-150 μstrain for Carrara marble and of ∼-50 μstrain for the Dalsland quartzite samples. Already during the first load step of ∼10-15% σ1 max superposition of the residual strain state is observed and strains partially remain during unloading step. Increased stress magnitudes of the load steps enable us to identify strains as a function of external load and subsequent unloading, indicating, in both rocks, that upon unloading from former loads to less than 75% σ1 max, the material remains partially extensionally strained

Carbon concentrations in natural and restoration pools in blanket peatlands

Open-water perennial pools are common natural features of peatlands globally, and peatland restoration often results in new pool creation, yet the concentrations of different forms of aquatic carbon (C) in natural and artificial restoration pools are not well studied. We compared carbon concentrations in both natural pools and restoration pools (4–15 years old) on three blanket peatlands in northern Scotland. At all sites, restoration pools were more acidic and had mean dissolved organic carbon (DOC) concentrations in restoration pools of 23, 22, and 31 mg L−1 compared with natural pool means of 11, 11 and 15 mg L−1 respectively across the three sites. Restoration pools had a greater fulvic acid prevalence than the natural pools and their DOC was more aromatic. Restoration pools were supersaturated with dissolved CO2 at around 10 times atmospheric levels, whereas for natural pools, CO2 concentrations were just above atmospheric levels. Dissolved CH4 concentrations were not different between pool types, but were ~200 times higher than atmospheric levels. Regular sampling at one of the peatland sites over 2.5 years showed that particulate organic carbon (POC) concentrations were generally below 7 mg L−1 except during the warm, dry summer of 2013. At this regularly-sampled site, natural pools were found to process DOC so that mean pool outflow concentrations in overland flow were significantly lower than mean inflow DOC concentrations. Such an effect was not found for the restoration pools. Soil solution and pool water chemistry, and relationships between DOC and CO2 concentrations suggest that different processes are controlling the transformation of C, and therefore the form and amount of C, in natural pools compared to restoration pools

Refining the role of phenology in regulating gross ecosystem productivity across European peatlands

Abstract The role of plant phenology as regulator for gross ecosystem productivity (GEP) in peatlands is empirically not well constrained. This is because proxies to track vegetation development with daily coverage at the ecosystem scale have only recently become available and the lack of such data has hampered the disentangling of biotic and abiotic effects. This study aimed at unraveling the mechanisms that regulate the seasonal variation in GEP across a network of eight European peatlands. Therefore, we described phenology with canopy greenness derived from digital repeat photography and disentangled the effects of radiation, temperature and phenology on GEP with commonality analysis and structural equation modeling. The resulting relational network could not only delineate direct effects but also accounted for possible effect combinations such as interdependencies (mediation) and interactions (moderation). We found that peatland GEP was controlled by the same mechanisms across all sites: phenology constituted a key predictor for the seasonal variation in GEP and further acted as distinct mediator for temperature and radiation effects on GEP. In particular, the effect of air temperature on GEP was fully mediated through phenology, implying that direct temperature effects representing the thermoregulation of photosynthesis were negligible. The tight coupling between temperature, phenology and GEP applied especially to high latitude and high altitude peatlands and during phenological transition phases. Our study highlights the importance of phenological effects when evaluating the future response of peatland GEP to climate change. Climate change will affect peatland GEP especially through changing temperature patterns during plant-phenologically sensitive phases in high latitude and high altitude regions.Peer reviewe

The role of deep-seated landsliding in the geomorphic evolution of the Esk Valley, Hawke's Bay: an innovative approach to hazard evaluation

An engineering geomorphological investigation of the Esk River catchment has been undertaken to quantify the relationships between the valley's geomorphic evolution, the many 1-10km2 deep-seated landslides present within the catchment, and a significant flood event that inundated the lower valley in April 1938. The identification of key geomorphic processes enabled the assessment of catchment's geomorphic stability, the development of generalised models for landsliding, and the delineation of a pre-disposed zone of instability. This information is then applied to assess key geomorphic controls on the flood event. The region lies within the forearc basin of the obliquely convergent Hikurangi Margin, and is underlain by soft, gently eastward dipping Pliocene marine strata. Structurally it is dominated by its close proximity to the Mohaka Fault, as well as two westward-dipping blind thrusts beneath the valley identified in this study: the Wakarara Fault – Trelinnoe Sector, and the Eastern Patoka Fault. Evidence from seismic reflection surveys indicates that these have both been active since the early Mangapanian (2.8 - 3.2 Ma), and an analysis of stream longitudinal profiles and plan form suggests limited displacement may have taken place within the last 10,000 years. A survey of rock mass defects within a representative sample area in the centre of the valley highlights four sub-vertical joint sets; conjugate sets strike 153° and 246°, and another sub-parallel to the folding strikes 033°. These defects correlate well with lineaments identified in aerial and satellite photographs and are attributed to extension of the sediments across the top of fault-propagated folds. The generally low power streams have exploited these defects and highly incised channels now run almost exclusively along them. Deep-seated landslides occur generally within the area of folding and their extents are defined by lineaments inferred to correspond to persistent joints in the rock mass. The slides are translational, and are facilitated by up to 80m of incision - ongoing since the abandonment of an extensive terrace inferred to be Ohakean (18-10ka) in age. Basal failure surfaces commonly dip at angles as low as 6°, and a combination of tectonically induced flexural shears sub-parallel to bedding and very low shear strength tuffaceous horizons are inferred to provide planes of sufficiently low shear strength to facilitate failure. While most deep-seated landslides appear active, there is no evidence to suggest they were substantially affected by recent major tectonic (e.g. 1931 Ms7.8 Hawke's Bay Earthquake) or climatic events (e.g. 1938 c.1 :1000yr Esk Valley Storm). The headwaters of the catchment are located on the Maungaharuru Range. This rises from 500m - l300m and provides baseflow to the Esk River. Extensive deep-seated landslides dominate the eastern face of the range. These are inferred to have been triggered by the removal of lateral support at the foot of the range following significant incision and denudation in the last interglacial c.125ka. A deep-seated gravitational slope deformation is proposed to extend to 1.2km below sea level, and provide a driving mechanism for the slides. While the 1938 Esk Valley flood was primarily a result of an exceptional three day storm event, suspended sediment load was also an important factor. This is inferred to have resulted primarily from channel erosion in soft colluvial sediments on the Maungaharuru Range. Combined with significant sediment load from shallow landsliding and possible tectonic subsidence preconditioning the lower reaches of the aggradational valley, this lead to c.1 m of silt being deposited in the lower reaches of the aggradational valley. Rapid stream incision in response to uplift in 1931 and aggradation in 1938 is returning the lower reach of the river to grade and decreasing the flood hazard

Reconstruction of erosional stages in the Bhutan Himalaya through a combination of hillslope extracted morphological markers and knickpoint analysis

ISSN:1029-7006ISSN:1607-796

A glacial or fluvial origin for Alpine valleys: How personality, politics, and war killed one of the great debates in geomorphology

ISSN:1029-7006ISSN:1607-796

Peatland carbon production and transport: the role of the riparian zone

Northern peatlands are an important carbon store in which the carbon cycling is intrinsically linked to hydrological state. Changes in climate and land management can alter the hydrology of peatlands, with artificial drainage (and its subsequent remediation) a significant driver of hydrochemical change across UK peatlands. With fluxes associated with the aquatic pathway (Particulate Organic Carbon (POC), Dissolved Organic Carbon (DOC)), and dissolved CO2 and CH4) representing ~30% of Net Ecosystem Exchange (NEE) (Dinsmore et al. 2010), changes in peatland hydrology have the potential to significantly alter catchment carbon balances. Riparian soils occur in a key transition zone between the peatland and the stream, and have the potential to modify carbon transport pathways (Lyon et al. 2011), while being a hotspot for CH4 emissions (Dinsmore et al. 2009). It is therefore important at the catchment scale despite its limited spatial extent. This research aims to investigate the production, retention, transformation and transport of aquatic carbon species within the riparian zone. Instrumented nested piezometers have been installed in a peatland-riparian zone-stream transect of an ombrotrophic peatland near Edinburgh, UK. The experimental setup is replicated in a shallow peat site (~0.5 m peat depth) and a deeper peat site (~2 m depth) with piezometers installed at two depths corresponding to the surface and subsurface soils. At these sites a range of hydrochemical parameters (electrical conductivity, pH, temperature, water table and stream height) are combined with continuous CO2 measurements using Vaisala© non-dispersive infra-red (NDIR) sensors, weekly headspace measurements of dissolved CO2 and CH4 and water samples analysed for POC, DOC and DIC in both the piezometers and the stream. This setup provides high temporal resolution data to investigate diurnal cycling and storm event scale processes which are often shorter than routine weekly sampling would allow. Measurements are being made for at least 12 months to allow seasonal effects to be investigated under a wide range of hydrological conditions. This study is unique in its deployment of multiple NDIR CO2 sensors across the peat-stream interface. The results of 12 months monitoring will be presented and linked with carbon concentration-discharge relationships. These measurements will also be combined with hydrological tracer experiments to investigate flow paths through the riparian zone. Overall this study aims to provide new insights into both the hydrological and biogeochemical processes occurring in peatland riparian zones and to assess their importance for peatland carbon budgets. Dinsmore, K.J., Skiba, U.M., Billett, M.F., Rees, R.M. & Drewer, J., 2009. Spatial and temporal variability in CH4 and N2O fluxes from a Scottish ombrotrophic peatland: Implications for modelling and up-scaling. Soil Biology and Biochemistry 41(6): 1315-1323. Dinsmore, K.J., Billett, M.F., Skiba, U.M., Rees, R.M., Drewer, J & Helftner, C., 2010. Role of the aquatic pathway in the carbon and greenhouse gas budgets of a peatland catchment. Global Change Biology 16(10): 2750-2762. Lyon, S.W., Grabs, T., Laudon, H., Bishop, K.H. & Seibert, J., 2011. Variability of groundwater levels and total organic carbon in the riparian zone of a boreal catchment. J. Geophys. Res 116(G1): G01020