Nighttime convection in the interior of a dense Douglas fir forest

Infrared radiative surface temperatures as observed over a dense Douglas fir forest during stable atmospheric conditions are analyzed. It is shown that the concept of a single surface temperature to describe both the thermal coupling and the radiative coupling between atmosphere and forest fails when longwave cooling is large and wind speeds are low. In such cases a decoupling of the radiative surface temperature from the air temperature aloft is observed. Conditions for decoupling are formulated in terms of an appropriate Richardson number. It is shown that a convective surface temperature comes into play that is coupled to the forest interior air temperature. Observed radiative surface temperature is then composed of this convective surface temperature and the aerodynamic surface temperature. Forest interior air temperature during nighttime is, in general, lower than air temperature above the canopy. A simple two-layer canopy model is used to explain this phenomenon in terms of the distribution of atmospheric sensible heat flux and storage heat flux over the two canopy layers.     

Authigenic albite in carbonate rocks – a tracer for deep-burial brine migration?

Euhedral, post-depositional albite from the Eastern and Western Alps, the western Carpathians and some Greek islands was examined petrographically and geochemically to gain insights into the nature of feldspar reactions in carbonate rocks. This study focuses on coarsely crystalline, homogeneously nucleated albite in order to avoid problems related to the presence of inseparable detrital material in fine-grained albite varieties. All albite samples show a very restricted compositional variability and are typically ≥ 99 mol% Ab component. Unit-cell parameters determined by Rietveld analysis are slightly more variable than previously accepted, but confirm high Al–Si ordering characteristic of low albite. The oxygen isotopic composition of albite ranges from + 19·4‰ to + 28·3‰ VSMOW. There is no direct relationship between the δ¹⁸O value and the inferred temperature of albite formation, nor is there one with stoichiometry. The coarse crystal size (up to several millimetres in diameter), petrographic evidence showing albite cross-cutting stylolites, greater abundance of albite in carbonate rocks subject to high-grade diagenetic or weak metamorphic overprinting and available fluid inclusion data suggest that albite precipitation is favoured at higher temperatures in carbonates than in sandstones. Pore fluids were invariably brines, as suggested by the inferred high positive δ¹⁸O_fluid values, the common association of albite-bearing carbonates and evaporites and reports of saline fluid inclusions in albite. The presence of authigenic albite may thus be a useful tracer of palaeobrine–carbonate reactions, particularly in deep-burial and incipient metamorphic settings.     

Tectonic and eustatic control on deposition and preservation of Upper Cretaceous ooidal ironstone and associated facies: Peace River Arch area, NW Alberta, Canada

The Late Coniacian, shallow-marine Bad Heart Formation of the Western Canada foreland basin is very unusual in that it contains economically significant ooidal ironstone. Deposition of shallow-water and iron-rich facies appears to have been localized over the crest and flanks of a subtle intrabasinal arch, in part interpreted as a forebulge and partly attributed to reactivation of the long-lived Peace River Arch. The formation comprises two upward-shoaling allomembers, typically 5–10 m thick, that are bounded by regionally mappable ravinement surfaces. The lower unit, allomember 1, grades up from laminated mudstone to bioturbated silty sandstone, which is abruptly overlain by bioturbated ooidal silty sandstone grading into an almost clastic-free ooidal ironstone up to 7 m thick. Ooidal ironstone was concentrated into NW- to SE-trending ridges, kilometres wide and tens of kilometres long. Ironstone formation appears to have been promoted by: (a) drowning of the arch, which progressively curtailed sediment supply; and (b) enhanced reworking over the shallowly submerged arch and over a fault-bounded block that underwent episodic vertical movement of 10–20 m during Bad Heart deposition. Allomember 2 also shoals upwards from mudstone to bioturbated and laminated silty sandstone but lacks ooids, apparently reflecting a rejuvenated supply of detrital sediment from the arch. The marine ravinement surface above allomember 2 is a Skolithos firmground, above which is developed a regional blanket of ooidal sediment. In the east, ooids are dispersed in a bioturbated silty sandstone with abundant evidence of repeated reworking and early siderite and phosphate cements. Westwards, this facies grades, over about 40 km, into almost clastic-free ooidal ironstone about 5 m thick; the lateral facies change may reflect progressive clastic starvation distal to a low-relief source area. The two allomembers are interpreted to reflect eustatic oscillations of about 10 m, superimposed on episodic tectonic warping and block-faulting events. The development of ooidal ironstone immediately above initial marine flooding surfaces indicates a close relationship to marine transgression, reflecting sediment-starved conditions. Ironstone does not appear to be related to either sequence boundaries or maximum flooding surfaces. The Bad Heart Formation is blanketed by marine mudstone deposited in response to major flexural subsidence and rejuvenation of clastic sources in the Cordillera to the SW.     

Was the M<Subscript>w</Subscript> 7.5 1952 Kern County,California, earthquake induced (or triggered)?

Several recent studies have presented evidence that significant induced earthquakes occurred in a number of oil-producing regions during the early and mid-twentieth century related to either production or wastewater injection. We consider whether the 21 July 1952 M_w 7.5 Kern County earthquake might have been induced by production in the Wheeler Ridge oil field. The mainshock, which was not preceded by any significant foreshocks, occurred 98 days after the initial production of oil in Eocene strata at depths reaching 3 km, within ~1 km of the White Wolf fault (WWF). Based on this spatial and temporal proximity, we explore a potential causal relationship between the earthquake and oil production. While production would have normally be expected to have reduced pore pressure, inhibiting failure on the WWF, we present an analytical model based on industry stratigraphic data and best estimates of parameters whereby an impermeable splay fault adjacent to the main WWF could plausibly have blocked direct pore pressure effects, allowing the poroelastic stress change associated with production to destabilize the WWF, promoting initial failure. This proof-of-concept model can also account for the 98-day delay between the onset of production and the earthquake. While the earthquake clearly released stored tectonic stress, any initial perturbation on or near a major fault system can trigger a larger rupture. Our proposed mechanism provides an explanation for why significant earthquakes are not commonly induced by production in proximity to major faults.     

Compartmentalisation and groundwater–surface water interactions in a prospective shale gas basin: Assessment using variance analysis and multivariate statistics on water quality data

An environmental concern with hydraulic fracturing for shale gas is the risk of groundwater and surface water contamination. Assessing this risk partly involves the identification and understanding of groundwater–surface water interactions because potentially contaminating fluids could move from one water body to the other along hydraulic pathways. In this study, we use water quality data from a prospective shale gas basin to determine: if surface water sampling could identify groundwater compartmentalisation by low-permeability faults; and if surface waters interact with groundwater in underlying bedrock formations, thereby indicating hydraulic pathways. Variance analysis showed that bedrock geology was a significant factor influencing surface water quality, indicating regional-scale groundwater–surface water interactions despite the presence of an overlying region-wide layer of superficial deposits averaging 30–40 m thickness. We propose that surface waters interact with a weathered bedrock layer through the complex distribution of glaciofluvial sands and gravels. Principal component analysis showed that surface water compositions were constrained within groundwater end-member compositions. Surface water quality data showed no relationship with groundwater compartmentalisation known to be caused by a major basin fault. Therefore, there was no chemical evidence to suggest that deeper groundwater in this particular area of the prospective basin was reaching the surface in response to compartmentalisation. Consequently, in this case compartmentalisation does not appear to increase the risk of fracking-related contaminants reaching surface waters, although this may differ under different hydrogeological scenarios.     

Sediment yield of the lower Tana River,Kenya, is insensitive to dam construction: sediment mobilization processes in a semi‐arid tropical river system

Dam construction in the 1960s to 1980s significantly modified sediment supply from the Kenyan uplands to the lower Tana River. To assess the effect on suspended sediment fluxes of the Tana River, we monitored the sediment load at high temporal resolution for 1 year and complemented our data with historical information. The relationship between sediment concentration and water discharge was complex: at the onset of the wet season, discharge peaks resulted in high sediment concentrations and counterclockwise hysteresis, while towards the end of the wet season, a sediment exhaustion effect led to low concentrations despite the high discharge. The total sediment flux at Garissa (c. 250 km downstream of the lowermost dam) between June 2012 and June 2013 was 8.8 Mt yr^‐1. Comparison of current with historical fluxes indicated that dam construction had not greatly affected the annual sediment flux. We suggest that autogenic processes, namely river bed dynamics and bank erosion, mobilized large quantities of sediments stored in the alluvial plain downstream of the dams. Observations supporting the importance of autogenic processes included the absence of measurable activities of the fall‐out radionuclides ⁷Be and ¹³⁷Cs in the suspended sediment, the rapid lateral migration of the river course, and the seasonal changes in river cross‐section. Given the large stock of sediment in the alluvial valley of the Tana River, it may take centuries before the effect of damming shows up as a quantitative reduction in the sediment flux at Garissa. Many models relate the sediment load of rivers to catchment characteristics, thereby implicitly assuming that alterations in the catchment induce changes in the sediment load. Our research confirms that the response of an alluvial river to external disturbances such as land use or climate change is often indirect or non‐existent as autogenic processes overwhelm the changes in the input signal. Copyright © 2015 John Wiley & Sons, Ltd.     

Time series analysis of the world's longest fluvial nitrate record: evidence for changing states of catchment saturation

Processes that drive the occurrence of nitrate concentrations in surface waters are known to operate over many decades longer than the available observations. This study considers the world's longest water quality record of nitrate concentrations in the River Thames (1868–2009) in order to understand whether the nature of the time series has changed with time and such external drivers as climate change and land use of hydrology. The study considers the linear trend, the seasonality, the memory and the impulsivity relative to river flow of the time series for moving windows of 6 years in length. The study can show that:

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