Testing models of step formation against observations of channel steps in a steep mountain stream

Steep streams often feature a step-pool morphology where the steps determine channel stability and dissipate the stream's energy, and thus are important for local flow hydraulics and bedload transport. Steps also play a key-role for the coupling of channels and adjacent hillslopes by controlling hillslope stability. Although step-pool systems have been investigated in various modelling and experimental efforts, the processes of step formation and destruction remain under debate. Theories of step formation consider a wide range of dominant drivers and fall into three groups favouring hydraulic controls ( HC ), granular interactions during flow ( GI ) or random drivers ( RD ) as relevant factors for step location. A direct evaluation of these models with field observations is challenging, as step formation cannot be directly observed. Based on the physical mechanisms of the various formation models we derive diagnostic morphometric parameters and test them with a field data set from a steep stream in Switzerland. Our results suggest that one class of alluvial steps form due to jamming in narrow and narrowing sections of the channel, while steps in wide and widening sections form around rarely mobile keystones. These two models of step formation apply in our study reach at the same time in different locations of the channel. A third class of steps is forced by logs. Such steps are typically located close to the original growth position of the tree and therefore reflect strong channel-hillslope coupling. Wood-forced steps make up a minor fraction of the step population, but contribute significantly to the cumulative step height and are therefore relevant to reach-scale flow resistance of the channel. © 2019 John Wiley & Sons, Ltd.     

Pilot-Scale Electrochemical Treatment of a 1,4-Dioxane Source Zone

Electrochemical treatment is a promising emerging technology in which direct current is applied to drive the degradation of aqueous contaminants. Several bench-scale studies have demonstrated the capability of electrochemical oxidation to fully mineralize refractory organics such as pesticides and perfluorinated compounds. However, insights into large-scale design and field performance are critically lacking. Here, we designed six pilot-scale reactors and tested their performance and efficiency for the treatment of groundwater contaminated with 1,4-dioxane (1,4-DX) at concentrations exceeding 1000 mg/L. Anode surface area-normalized degradation rates increased with increasing potential applied, while the process was more energy-efficient per mass unit removed at low potentials. While not all 1,4-DX was completely mineralized, the detected ring-opening intermediates are known to be readily biodegradable. Analyses of potential by-products from chloride oxidation revealed the generation of chloromethanes and perchlorate at low mg/L concentrations. Towards the end of the 8.5-month pilot test, decreasing currents and degradation rates indicated progressing passivation of the electrodes, likely due to cathodic carbonate precipitation and/or poisoning by the uniquely high organic carbon load of this source zone groundwater. The findings of our study demonstrate that electrochemical groundwater remediation is a capable approach for the treatment of persistent organic pollutants. Our pilot-scale test provides practitioners with a basis for evaluating its efficiency under site-specific conditions and collecting critical performance metrics for technology scale-up.     

Field techniques for measuring bedrock erosion and denudation

Bedrock erosion rates in natural landscapes are usually slow, of the order of millimeters per year or less, and sophisticated techniques have been developed to measure them. Different techniques have proved to be valuable depending on the spatial and temporal scale on which information is needed, on the environment and on the scientific question that is asked. Here, we give an overview of the various methods that have been developed. We introduce their working principles and outline their advantages and disadvantages. Further, we provide comprehensive references to relevant literature, both on the methods and on scientific examples of their application. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Modeling ground water flow in alluvial mountainous catchments on a watershed scale

In large mountainous catchments, shallow unconfined alluvial aquifers play an important role in conveying subsurface runoff to the foreland. Their relatively small extent poses a serious problem for ground water flow models on the river basin scale. River basin scale models describing the entire water cycle are necessary in integrated water resources management and to study the impact of global climate change on ground water resources. Integrated regional-scale models must use a coarse, fixed discretization to keep computational demands low and to facilitate model coupling. This can lead to discrepancies between model discretization and the geometrical properties of natural systems. Here, an approach to overcome this discrepancy is discussed using the example of the German-Austrian Upper Danube catchment, where a coarse ground water flow model was developed using MODFLOW. The method developed uses a modified concept from a hydrological catchment drainage analysis in order to adapt the aquifer geometry such that it respects the numerical requirements of the chosen discretization, that is, the width and the thickness of cells as well as gradients and connectivity of the catchment. In order to show the efficiency of the developed method, it was tested and compared to a finely discretized ground water model of the Ammer subcatchment. The results of the analysis prove the applicability of the new approach and contribute to the idea of using physically based ground water models in large catchments.     

Complex resistivity and radar investigation of building material: First results of field scale measurements

Moisture ingress is one of major damaging factors for masonry buildings. As the complex resistivity (CR) is sensitive to textural properties as well as to the pore fluid chemistry of wet porous media, its non-destructive application can provide helpful information for conservators. In a comprehensive laboratory study it has been shown that CR might even be able to distinguish between salt content and saturation degree in only one measurement. The combined use of electrical and electromagnetic measurement techniques in two field-scale flooding experiments has shown some unexpected differences. Possible reasons are discussed and it is shown that bringing together the information of both methods leads to a clearer picture.     

Post World War II orcharding creates present day DDT-problems in The Sørfjord (Western Norway) - A case study

The Sørfjord has a long history of agriculture and industry, and environmental monitoring has been conducted for decades, comprising analyses of contaminants in mussel, fish and sediments. DDT was used as an insecticide in orchards surrounding the fjord between World War II and 1970. Since the early 1990s, elevated concentrations of DDT were found in mussels and fish. Unexpectedly, DDT-concentrations increased towards present day, despite the discontinuation of use. The highest concentrations in mussels (in 2006) corresponded to about two orders of magnitude higher than background. Analyses of sediment core sections also indicated increased input towards present day. Shifts in climatic parameters, as well as increased amounts of soil dissolved organic carbon following a decline in atmospheric sulphate deposition may have contributed to this phenomenon. We warrant the need for increased knowledge of the effects of alterations in variables acting regionally and globally on the disposition of contaminants in ecosystems.     

FAIR Geoscientific Samples and Data Need International Collaboration

正1 Introduction The primary goal of the Deep-time Digital Earth project is to develop an open collaboration and data sharing platform that enables the transition of deep-time geoscientific research to a Big Data driven paradigm.Such an open platform will require the ability to effectively and efficiently access and integrate a wide variety of digital Earth data,from remotely sensed Earth observations and geophysical data to data generated in