Landscape controls on long‐term runoff in subhumid heterogeneous Boreal Plains catchments

We compared median runoff (R) and precipitation (P) relationships over 25 years from 20 mesoscale (50 to 5,000 km²) catchments on the Boreal Plains, Alberta, Canada, to understand controls on water sink and source dynamics in water‐limited, low‐relief northern environments. Long‐term catchment R and runoff efficiency (RP^?1) were low and varied spatially by over an order of magnitude (3 to 119 mm/year, 1 to 27%). Intercatchment differences were not associated with small variations in climate. The partitioning of P into evapotranspiration (ET) and R instead reflected the interplay between underlying glacial deposit texture, overlying soil‐vegetation land cover, and regional slope. Correlation and principal component analyses results show that peatland‐swamp wetlands were the major source areas of water. The lowest estimates of median annual catchment ET (321 to 395 mm) and greatest R (60 to 119 mm, 13 to 27% of P) were observed in low‐relief, peatland‐swamp dominated catchments, within both fine‐textured clay‐plain and coarse‐textured glacial deposits. In contrast, open‐water wetlands and deciduous‐mixedwood forest land covers acted as water sinks, and less catchment R was observed with increases in proportional coverage of these land covers. In catchments dominated by hummocky moraines, long‐term runoff was restricted to 10 mm/year, or 2% of P. This reflects the poor surface‐drainage networks and slightly greater regional slope of the fine‐textured glacial deposit, coupled with the large soil‐water and depression storage and higher actual ET of associated shallow open‐water marsh wetland and deciduous‐forest land covers. This intercatchment study enhances current conceptual frameworks for predicting water yield in the Boreal Plains based on the sink and source functions of glacial landforms and soil‐vegetation land covers. It offers the capability within this hydro‐geoclimatic region to design reclaimed catchments with desired hydrological functionality and associated tolerances to climate or land‐use changes and inform land management decisions based on effective catchment‐scale conceptual understanding.     

Coral reef ecosystems protect shore from high-energy waves under climate change scenarios

Coral reefs and other coastal ecosystems such as seagrasses and mangroves are widely recognized to provide protection against the devastating effects of strong waves associated with tsunamis and storms. The predicted warming climate brings to fore the role of these ecosystems in providing protection against stronger typhoons that can result in more devastating waves of greater amplitude. We performed a model simulation of storm generated waves on a Philippine reef, which is located along the path of tropical storms, i.e., at least 10 typhoons on the average pass through the study site yearly. A model to simulate wave propagation was developed using Simulating Waves Nearshore (SWAN) and DELFT3D-WAVE computer simulation software. Scenarios involving local monsoonal wind forcing and storm conditions were simulated. In addition, as climate change may also result to increased relative sea level, a 0.3 m and 1 m rise in sea level scenarios were also used in the wave model simulations. Results showed that the extensive reef system in the site helped dissipate wave energy that in turn reduced wave run-up on land. A significant reduction in wave energy was observed in both climate change, i.e., stronger wind and higher sea level, and non-climate change scenarios. This present study was conducted in a reef whose coral cover is in excellent condition (i.e., 50 to 80% coral cover). Estimates of coral reef growth are in the same order of magnitude as estimates of relative sea level rise based on tide gauge and satellite altimeter data, thus it is possible that the role of reefs in attenuating wave energy may be maintained if coral reef growth can keep up with the change in sea level. Nonetheless, to maintain reef growth, it is imperative to manage coral reef ecosystems sustainably and to eliminate the stressors that are within human control. Minimizing activities such as illegal and destructive blast and poison fishing methods, pollution and siltation, is crucial to minimize the impacts of high-energy waves that may increase with climate change.     

Monitoring the status of a mechanical cable while in operation by means of the acoustic emission method

The mechanical cable is an essential element in towing operations, remote control of equipment, salvage operations, civil engineering applications, etc.Failure of these cables can result in loss of life and loss of equipment worth hundreds of thousands of dollars. Obviously then, sensors that can indicate the condition of these cables so that the risk to their continued use and their remaining safe life can be determined when in operation are very important from the point of view of commercial and military interest.This paper presents a brief review of research into failure mechanisms of various cables and the acoustic emission signatures of the various cables under simulated loading. The development of a specific operational monitor for a towed cable system is also given.     

Significance of post‐peak metamorphic reaction microstructures in the ultrahigh temperature Eastern Ghats Province,India

Ultrahigh temperature (UHT) granulites in the Eastern Ghats Province (EGP) have a complex P–T–t history. We review the P–T histories of UHT metamorphism in the EGP and use that as a framework for investigating the P–T–t history of Mg–Al‐rich granulites from Anakapalle, with the express purpose of trying to reconcile the down‐pressure‐dominated P–T path with other UHT localities in the EGP. Mafic granulite that is host to Mg–Al‐rich metasedimentary granulites at Anakapalle has a protolith age of c. 1,580 Ma. Mg–Al‐rich metasedimentary granulites within the mafic granulite at Anakapalle were metamorphosed at UHT conditions during tectonism at 960–875 Ma, meaning that the UHT metamorphism was not the result of contact metamorphism from emplacement of the host mafic rock. Reworking occurred during the Pan‐African (c. 600–500 Ma) event, and is interpreted to have produced hydrous assemblages that overprint the post‐peak high‐T retrograde assemblages. In contrast to rocks elsewhere in the EGP that developed post‐peak cordierite, the metasedimentary granulites at Anakapalle developed post‐peak, generation ‘2’ reaction products that are cordierite‐absent and nominally anhydrous. Therefore, rocks at Anakapalle offer the unique opportunity to quantify the pressure drop that occurred during so‐called M2 that affected the EGP. We argue that M2 is either a continuation of M1 and that the overall P–T path shape is a complex counter‐clockwise loop, or that M1 is an up‐temperature counter‐clockwise deviation superimposed on the M2 path. Therefore, rather than the rocks at Anakapalle having a metamorphic history that is apparently anomalous from the rest of the EGP, we interpret that other previously studied localities in the EGP record a different part of the same P–T path history as Anakapalle, but do not preserve a significant record of pressure decrease. This is due either to the inability of refractory rocks to extensively react to produce a rich mineralogical record of pressure decrease, or because the earlier high‐P part of the rocks history was erased by the M1 loop. Irrespective of the specific scenario, models for the tectonic evolution of the EGP must take the substantial pressure decrease during M2 into account, as it is probable the P–T record at Anakapalle is a reflection of tectonics affecting the entire province.     

The seagrass skeletal assemblage from modern to fossil and from tropical to temperate: Insight from Maldivian and Mediterranean examples

Seagrasses are marine angiosperms that form extensive submarine meadows in the photic zone where carbonate producing biota dwell as epiphytes on the leaves or as infaunal forms, and act as prolific carbonate sediment factories. Because seagrasses have a low preservation potential and records of exceptionally well‐preserved and plant material from marine settings are rare, these palaeoenvironments are difficult to identify in the rock record. Consequently, sedimentological and palaeontological proxies are the main indicators of the presence of seagrass‐dominated ecosystems. This work investigates the skeletal assemblage of Modern (Maldivian and western Mediterranean) and fossil (Eocene; Apula and Oman carbonate platforms and Oligocene; Malta platform) seagrass examples to characterize the skeletal assemblage of modern and fossil seagrasses. Two main types of grains, calcareous algae and foraminifera, constitute around 50% of the bioclastic sediment in both tropical Maldivian and temperate Mediterranean scenarios. However, in the tropical setting they are represented by green algae (Halimeda), while in the Mediterranean they are represented by corallinacean red algae. In contrast, in the Eocene examples, the foraminifera are the most conspicuous group and the green algae are also abundant. The opposite occurs in the Maltese Chattian, which is dominated by coralline algae (mean 42%), although the foraminifera are still abundant. It is suggested to use the term foralgal to identify the seagrass skeletal assemblage. To discriminate between red algae and green algae dominance, the introduction of the prefixes ‘GA’ (green algae) and ‘RA’ (red algae) is proposed. The investigated examples provide evidence that the green algae–foralgal assemblage is typical of tropical, not excessively dense seagrass meadows, characterized by a well‐illuminated substrate to support the development and calcification of the Halimeda thallus. Contrarily, the red algae‐foralgal assemblage is typical of high density tropical to subtropical seagrass meadows which create very dense oligophotic conditions on the sea floor or in temperate settings where Halimeda cannot calcify.     

A water retention model accounting for void ratio changes in double porosity clays

This paper presents a constitutive model that predicts the water retention behaviour of compacted clays with evolving bimodal pore size distributions. In line with previous research, the model differentiates between the water present inside the saturated pores of the clay aggregates (the microstructure) and the water present inside the pores between clay aggregates (the macrostructure). A new formulation is then introduced to account for the effect of the macrostructural porosity changes on the retention behaviour of the soil, which results in a consistent evolution of the air-entry value of suction with volumetric deformations. Data from wetting tests on three different active clays (i.e. MX-80 bentonite, FEBEX bentonite, and Boom clay), subjected to distinct mechanical restraints, were used to formulate, calibrate, and validate the proposed model. Results from free swelling tests were also modelled by using both the proposed double porosity model and a published single porosity model, which confirmed the improvement in the predictions of degree of saturation by the present approach. The proposed retention model might be applied, for example, to the simulation of the hydromechanical behaviour of engineered bentonite barriers in underground nuclear waste repositories, where compacted active clays are subjected to changes of both suction and porosity structure under restrained volume conditions.

     

Tree-Ring δD as an Indicator of Asian Monsoon Intensity

Oxygen and hydrogen isotopic compositions of meteoric water are known to correlate with surface air temperature, except in tropical areas. This relationship has been described using a number of terms corresponding to specific observations, such as latitude, altitude and seasonal effects. However, these temperature effects do not seem to apply to precipitation in monsoonal areas of Asia. Questions have been raised as to whether the isotopic composition of meteoric water can be used to reconstruct paleomonsoon intensity. Tree rings of two modern spruce trees (Picea meyeri) and a 10,000-yr-old timber (Picea jezoensis) were analyzed for hydrogen isotopic composition. On average, the older tree is depleted in deuterium by 45‰ compared to the modern trees. We attribute this isotopic depletion to the strength of summer monsoons, which were more intense in the early Holocene than at present. Although this study is not definitive, it suggests that paleomonsoon intensity can be reconstructed by direct or proxy methods that yield the oxygen or hydrogen isotopic composition of meteoric water.     

Distribution and Abundance of Arsenic in the Soils and Sediments of O‘ahu,Hawai‘i

Lack of high-spatial-resolution soil and sediment arsenic data for Hawai‘i has generated substantial disagreement between researchers and regulators regarding the magnitude of natural levels of arsenic in Hawai‘i and rendered difficult the defining of areas of anthropogenically elevated arsenic. Our earlier research into the occurrence of arsenic in terrestrial and marine environments revealed widely disparate concentrations of arsenic with no apparent spatial pattern. To better understand the distribution and abundance of arsenic in soils and sediments of O‘ahu, we collected an additional 64 samples at locations chosen to represent different environments with varying degrees of human impact. We found surface arsenic values that ranged from 0.28 to 740 ppm with a median concentration of 8.1 ppm, which is above the global median of 5 ppm and US soil median of 5.2 ppm. Higher concentrations of arsenic (up to 913 ppm) were encountered at depth in soil cores. The median arsenic in streambed sediments from one of our earlier studies of 6.1 ppm was comparable to the conterminous US median of 6.3 ppm; however, we encountered arsenic concentrations as high as 43.9 ppm (median = 8.60 ppm, n = 75) in marine sediments in recent work off the leeward coast of O‘ahu. Overall, arsenic in the soils and sediments of O‘ahu is elevated relative to world and national values, but there still is no readily discernible pattern in the distribution of arsenic to explain these elevated values.