Evaluation of Spatio-temporal Changes in Surface Water Quality and Their Suitability for Designated Uses,Mettur Reservoir,India

Natural Resources Research - Freshwater has a significant role in determining the ecological environment, public health and socio-economic development. This study analyzed the spatio-temporal...     

The role of rock surface hardness and internal moisture in tafoni development in sandstone

The development of cavernous weathering features such as tafoni remains poorly understood. In particular, the roles played by internal moisture and case hardening remain unclear. In this study, Electric Resistivity Tomography (ERT) has been used to map moisture distribution within inner walls of tafoni developed in sandstone, and an Equotip device used to measure rock surface hardness as a proxy measure of the degree of weathering and case hardening. Seven large tafoni in the Golden Gate Highlands National Park (South Africa), varying in size and degree of development have been monitored. A dynamic relationship between surface hardness, degree of weathering and internal moisture regimes has been found. We propose a new conceptual model which illustrates the complex interaction between case hardening and internal moisture and suggests a new direction for cavernous weathering research. Copyright © 2011 John Wiley & Sons, Ltd.     

Integrating structure-from-motion photogrammetry into rock weathering field methodologies

Despite recent rapid advances in the field of structure-from-motion (SfM) photogrammetry, the use of high-resolution data to investigate small-scale processes is a relatively underdeveloped field. In particular, rock weathering is rarely investigated using this suite of techniques. This research uses a combination of traditional non-destructive rock weathering measurement techniques (rock surface hardness) and SfM to map deterioration and loss of cohesion of the surface using three-dimensional data. The results are used to interpret weathering behaviour across two different lithologies present on the site, namely shale and limestone. This new approach is tested on seven sites in Longyearbyen, Svalbard, where active weathering of a rock surface was measured after 13 years of exposure to extreme temperature regimes and snow cover. The surface loss was quantified with SfM and combined with rock surface hardness measurement distributions extrapolated in geographic information system (GIS). The combined results are used here to quantify the difference in response of both lithologies to these extreme temperatures. This research demonstrates the potential for further integration of SfM in rock weathering research and other small-scale geomorphological investigations, in particular in difficult field conditions where portability of field equipment is paramount. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

Investigation of parameterization effect on the methane flux estimation from the regional climate model of the main geophysical observatory for the territory of Russia

An effect is studied of parameterization method of the methane flux from the wetlands of Siberia on the results of model estimates carried out using the one-dimensional model of heat transfer in the soils. The results of computations of the regional climate model of the Main Geophysical Laboratory are used as the input data of this model. The computation estimates of seasonal methane flux variations at certain observation points are compared with the measured values of the methane flux. It is shown that the optimal choice of methane flux parameterization at the use of the grid climate model data as the forcing should correspond to the conditions of prevailing subgrid natural complex of one or another type of wetlands. A spatial distribution of methane emission intensity under conditions of the present-day climate and at the end of the 21st century is obtained. The analysis revealed that the methane fluxes in Western Siberia will increase by 1.5–2.5 times by the end of the 21st century.     

Exposing drying patterns: using electrical resistivity tomography to monitor capillary rise in sandstone under varying drying conditions

Rising damp and other moisture movements through porous stone and rock are known to cause weathering and deterioration, as noted in a range of recent field and laboratory studies. However, relatively little is known about the behaviour of moisture within a porous stone under realistic conditions because of lack of suitable monitoring methods. This paper has two main aims: firstly, to evaluate different electrical (resistivity and capacitance) methods to monitor subsurface and surface moisture regimes and, secondly, to use these methods to monitor the movement of water by capillary rise in a sandstone block under (a) conditions of constant moisture ingress at the base and (b) an enhanced drying regime with and without constant moisture ingress at the base. Our results indicate that, for electrical resistance tomography (ERT) measurements on a sandstone block, medical electrodes provide more reliable contact with the stone than spring-loaded pointed metal electrodes, and that the combination of ERT and handheld moisture meters gives a realistic picture of moisture movements within the block. The capillary rise and drying experiments reveal complex moisture movement over time and space. Under conditions of constant moisture supply, accelerated drying results in maintained or enhanced capillary rise. These findings are presented to further our understanding of the behaviour of moisture within porous sandstone.     

Investigations into the relationship between changes in internal moisture regimes and rock surface deterioration in cavernous sandstone features

Cavernous features commonly develop in sandstone, but their development over time remains enigmatic. It has been suggested that moisture movements within the rock mass play a key role in the location, development and dynamics of cavernous features. In this research the role of internal moisture movement is tested through monitoring moisture and surface deterioration dynamics in April 2008 and April 2009 within two large cavernous features (mega‐tafoni) in the Golden Gate Highlands National Park, South Africa (GGHNP). Data are presented from surveys of internal moisture (using electrical resistivity tomography, ERT), surface moisture (using a Protimeter) and deterioration (using surface hardness as recorded with an Equotip as a proxy for surface deterioration) across five 2.45 m long transects. In addition a high resolution temperature record is presented to assess the influence of micro‐climates within the caverns. The results indicate consistency in the gross spatial pattern of moisture flow within the rock mass over a one year period, but significant changes in mean moisture contents and in the fine detail of moisture patterning. Some noticeably weakened areas had developed within the central parts of the cavernous features, often linked to wetter subsurface conditions, supporting the theory that ‘core softening’ is a main driver of cavernous feature formation. However, in some areas surface hardening is also found to be associated with wetter subsurface conditions, supporting the theory that ‘case hardening’ is a main driver of cavernous feature formation. In addition, the presence of well‐established biofilms suggests an even more complex interaction between moisture, surface development and biological activity. A model is presented therefore which integrates this paradox by proposing a non‐linear relationship between moisture dynamics, facilitation of biofilm formation, and deterioration within cavernous features. Copyright © 2013 John Wiley & Sons, Ltd.     

A simple method to classify diamicts by scanning electron microscope from surface microtextures

Interpretation of quartz sand grain surface microtextures with scanning electron microscopy has been riddled with inconsistencies, invalid assumptions and much subjectivity. Therefore, a novel classification for analysing grain surface microtextures is presented based on the origin of complete grain surfaces. This novel method has solved most of the earlier problems of interpretation of surface microtextures, and it is easy to use and to quickly find evident genetic interpretations of diamicts. The data are plotted graphically in ‘2‐History Diagrams’ or ‘3‐History Diagrams’ for quick visual inspection and statistical evaluation. Source rocks and Quaternary glacial deposits from Scandinavia and Southern Ontario, representing different ice‐substrate dynamics, are analysed to define surface microtextures from typical glacigenic grains, bedrock and fluvially transported grains. Typical glacially crushed grains display large‐scale fractures and abrasion. Shield bedrock grains display large or small‐scale fractures and solution/precipitation microtextures. Fluvially transported grains exhibit abrasion and solution/precipitation microtextures.     

Thérèse Mound: a case study of coral bank development in the Belgica Mound Province,Porcupine Seabight

High-resolution seismic profiles, swath bathymetry, side-scan sonar data and video imageries are analysed in this detailed study of five carbonate mounds from the Belgica mound province with special emphasis on the well-surveyed Thérèse Mound. The selected mounds are located in the deepest part of the Belgica mound province at water depths of 950 m. Seismic data illustrate that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime. Sigmoidal sediment bodies create local slope breaks on the most recent local erosional surface, which act as the mound base. No preferential mound substratum is observed, neither is there any indication for deep geological controls on coral bank development. Seismic evidence suggests that the start-up of the coral bank development was shortly after a major erosional event of Late Pliocene–Quaternary age. The coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current regime. The summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes. Deposition of the encased drift sequence has been influenced by the coral bank topography. Sediment waves are formed besides the coral banks and are the most pronounced bedforms. These seabed structures are probably induced by bottom current up to 1 m/s. Large sediment waves are colonised by living corals and might represent the initial phase of coral bank development. The biological facies distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral populations toward the lower flanks. The data suggest that the development of the coral banks in this area is clearly an interaction between biological growth processes and drift deposition both influenced by the local topography and current regime.