Hydrogen isotopic composition of NBS and IAEA stable isotope water reference samples

The hydrogen isotopic compositions of several isotope water reference samples have been determined on a cycloidal double-collecting isotope ratio mass spectrometer that can resolve HD⁺ from the ‘contaminant’ H₃⁺ ion beam.     

Normal modes and resonance in Ontario Lacus: a hydrocarbon lake of Titan

Ocean Dynamics - The natural modes of Ontario Lacus surface oscillations, the largest lake in Titan’s southern hemisphere, are simulated and analyzed as they are potentially of broad interest...     

Secondary Hydrogeologic Regions of the Conterminous United States

The U.S. Geological Survey (USGS) previously identified and mapped 62 Principal Aquifers (PAs) in the U.S., with 57 located in the conterminous states. Areas outside of PAs, which account for about 40% of the conterminous U.S., were collectively identified as “other rocks.” This paper, for the first time, subdivides this large area into internally-consistent features, defined here as Secondary Hydrogeologic Regions (SHRs). SHRs are areas of other rock within which the rocks or deposits are of comparable age, lithology, geologic or physiographic setting, and relationship to the presence or absence of underling PAs or overlying glacial deposits. A total of 69 SHRs were identified. The number and size of SHRs identified in this paper are comparable to the number and size of PAs previously identified by the USGS. From a two-dimensional perspective, SHRs are complementary to PAs, mapped only where the PAs were not identified on the USGS PA map and not mapped where the PAs were identified. SHRs generally consist of low permeability rocks or deposits, but can include locally productive aquifers. The two maps, taken together, provide a comprehensive, national-scale hydrogeologic framework for assessing and understanding groundwater systems.     

A distributed analysis of lateral inflows in an Alaskan Arctic watershed underlain by continuous permafrost

Lateral inflows control the spatial distribution of river discharge, and understanding their patterns is fundamental for accurately modelling instream flows and travel time distributions necessary for evaluating impacts of climate change on aquatic habitat suitability, river energy budgets, and fate of dissolved organic carbon. Yet, little is known about the spatial distribution of lateral inflows in Arctic rivers given the lack of gauging stations. With a network of stream gauging and meteorological stations within the Kuparuk River watershed in northern Alaska, we estimated precipitation and lateral inflows for nine subcatchments from 1 July to 4 August,2013, 2014, and 2015. Total precipitation, lateral inflows, runoff ratios (area-normalized lateral inflow divided by precipitation), percent contribution to total basin discharge, and lateral inflow per river kilometre were estimated for each watershed for relatively dry, moderate, or wet summers. The results show substantial variability between years and subcatchments. Total basin lateral inflow depths ranged 24-fold in response to a threefold change in rainfall between dry and wet years, whereas within-basin lateral inflows varied fivefold from the coastal plain to the foothills. General spatial trends in lateral inflows were consistent with previous studies and mean summer precipitation patterns. However, the spatially distributed nature of these estimates revealed that reaches in the vicinity of a spring-fed surficial ice feature do not follow general spatial trends and that the coastal plain, which is typically considered to produce minimal runoff, showed potential to contribute to total river discharge. These findings are used to provide a spatially distributed understanding of lateral inflows and identify watershed characteristics that influence hydrologic responses.     

Modeling Situation Factors Used in MCE Procedures for Raster GIS

Multi‐criteria evaluation (MCE) procedures are widely used in raster‐based geographic information systems (GIS) to perform a variety of land use siting applications. Many of the criteria used in an MCE analysis are based on spatial relationships or situation characteristics. Situation factors measure the accessibility that each raster cell is to resources or land uses that generate spatial externalities for the activity being sited. This accessibility can be measured either in terms of distance to the nearest target cell containing resources or the overall level of resource availability as measured by a spatial interaction model. This paper examines the spatial structure of these situation factors to identify the set of critical target cells for which distance estimates are most sensitive. Critical target cells are especially important in the case of positive externalities in which an activity would be inclined to locate near these cells to use or consume the resources there. Critical target cells are useful for evaluating the utility of the final site selection with respect to resource/activity ratios.     

Geochemical Indication of Sinian Bedded Siliceous Rocks in the Hunan-Guizhou-Guangxi Area and Their Environmental Significance

In the Hunan-Guizhou-Guangxi area there have developed very thick bedded siliceous rocks of the late Sinian. The rocks have a fairly pure composition, with an average content of siliceous minerals exceeding 95%. They are relatively rich in Fe and Mn, and poor in Al, Ti and Mg. The Fe/Ti, (Fe+Mn)/Ti, Al/(Al+Fe+Mn) and U/Th ratios and the Al-Fe-Mn and Fe-Mn-(Ni+Co+Cu)×10 triangle diagrams all show that they are hydrothermal sedimentary siliceous rocks. In the rocks the total amount of REEs is low, the δCe shows an obvious negative anomaly and the 8Eu a weak anomaly, and LREE>HREE, all indicating that they are products of hydrothermal processes. The δ30Si and δ18O values, as well as the formation temperature of the rocks all clearly show that the silica forming the rocks comes from hot water. Besides, analyses of the depositional environment of the rocks using the MnO/TiO2 ratio and the δCe and δ30Si values yield the same conclusion that they are formed in environments from continental marginal slope     

Spatial,seasonal, and source variability in the stable oxygen and hydrogen isotopic composition of tap waters throughout the USA

To assess spatial, seasonal, and source variability in stable isotopic composition of human drinking waters throughout the entire USA, we have constructed a database of δ¹⁸O and δ²H of US tap waters. An additional purpose was to create a publicly available dataset useful for evaluating the forensic applicability of these isotopes for human tissue source geolocation. Samples were obtained at 349 sites, from diverse population centres, grouped by surface hydrologic units for regional comparisons. Samples were taken concurrently during two contrasting seasons, summer and winter. Source supply (surface, groundwater, mixed, and cistern) and system (public and private) types were noted. The isotopic composition of tap waters exhibits large spatial and regional variation within each season as well as significant at‐site differences between seasons at many locations, consistent with patterns found in environmental (river and precipitation) waters deriving from hydrologic processes influenced by geographic factors. However, anthropogenic factors, such as the population of a tap's surrounding community and local availability from diverse sources, also influence the isotopic composition of tap waters. Even within a locale as small as a single metropolitan area, tap waters with greatly differing isotopic compositions can be found, so that tap water within a region may not exhibit the spatial or temporal coherence predicted for environmental water. Such heterogeneities can be confounding factors when attempting forensic inference of source water location, and they underscore the necessity of measurements, not just predictions, with which to characterize the isotopic composition of regional tap waters. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Precipitation climatology over India: validation with observations and reanalysis datasets and spatial trends

Changing rainfall patterns have significant effect on water resources, agriculture output in many countries, especially the country like India where the economy depends on rain-fed agriculture. Rainfall over India has large spatial as well as temporal variability. To understand the variability in rainfall, spatial–temporal analyses of rainfall have been studied by using 107 (1901–2007) years of daily gridded India Meteorological Department (IMD) rainfall datasets. Further, the validation of IMD precipitation data is carried out with different observational and different reanalysis datasets during the period from 1989 to 2007. The Global Precipitation Climatology Project data shows similar features as that of IMD with high degree of comparison, whereas Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation data show similar features but with large differences, especially over northwest, west coast and western Himalayas. Spatially, large deviation is observed in the interior peninsula during the monsoon season with National Aeronautics Space Administration-Modern Era Retrospective-analysis for Research and Applications (NASA-MERRA), pre-monsoon with Japanese 25 years Re Analysis (JRA-25), and post-monsoon with climate forecast system reanalysis (CFSR) reanalysis datasets. Among the reanalysis datasets, European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim) shows good comparison followed by CFSR, NASA-MERRA, and JRA-25. Further, for the first time, with high resolution and long-term IMD data, the spatial distribution of trends is estimated using robust regression analysis technique on the annual and seasonal rainfall data with respect to different regions of India. Significant positive and negative trends are noticed in the whole time series of data during the monsoon season. The northeast and west coast of the Indian region shows significant positive trends and negative trends over western Himalayas and north central Indian region.     

Combining price and quantity instruments: insights from South Africa

A carbon tax will form the central carbon pricing instrument in South Africa. The country, however, is also in the process of setting specific short-term emissions limits at a subnational level. Additional mitigation policy instruments will thus be required to meet these targets. Although it is possible to combine sector-level quantity targets with a broad-based carbon tax, this article finds that this greatly complicates mitigation policy design, increasing both the information requirements and the likelihood of unintended consequences. The trade-offs between economic efficiency (optimized by the use of a broad-based price set by a carbon tax) and environmental effectiveness (optimized by using instruments that ensure emissions reduction targets are met) are ever present. A clear understanding of subnational quantity targets and an appreciation of the characteristics of the instruments to achieve such targets (quantity-based instruments, QBIs), the framework through which the instruments are combined, and their possible interactions, are required for effective policy making. Three possible frameworks for combining instruments are identified in the article, and some specific implications of interaction between particular QBIs and a carbon tax are suggested.

Policy relevance

This article explores the interaction of a carbon tax with mitigation policy instruments to meet subnational emissions targets in the South African context (where both a carbon tax and subnational emissions targets are currently being developed). As international negotiations progress towards countries accepting binding GHG emissions restrictions, quantity-based mitigation policy approaches become more important. In countries where a broad-based emissions trading scheme (ETS) is not feasible in the short to medium term, combining a broad-based carbon tax with subnational emission targets provides an alternative mechanism for achieving the economic efficiency and emissions certainty benefits derived from an ETS. This paper considers the mechanisms through which such a combination of instruments can be achieved. Three possible frameworks for combining instruments are identified, some specific implications of interaction between particular QBIs and a carbon tax are suggested, and guidelines and concept tools are presented to assist policy-makers in designing efficient and coherent mitigation policy.