Characterizing hyporheic transport processes — Interpretation of electrical geophysical data in coupled stream–hyporheic zone systems during solute tracer studies

Quantifying hyporheic solute dynamics has been limited by our ability to assess the magnitude and extent of stream interactions with multiple domains: mobile subsurface storage (MSS, e.g., freely flowing pore water) and immobile subsurface storage (ISS, e.g., poorly connected pore water). Stream-tracer experiments coupled with solute transport modeling are frequently used to characterize lumped MSS and ISS dynamics, but are limited by the ability to sample only “mobile” water and by window of detection issues. Here, we couple simulations of near-surface electrical resistivity (ER) methods with conservative solute transport to directly compare solute transport with ER interpretations, and to determine the ability of ER to predict spatial and temporal trends of solute distribution and transport in stream–hyporheic systems. Results show that temporal moments from both ER and solute transport data are well correlated for locations where advection is not the dominant solute transport process. Mean arrival time and variance are especially well-predicted by ER interpretation, providing the potential to estimate rate-limited mass transport (i.e. diffusive) parameters from these data in a distributed domain, substantially increasing our knowledge of the fate and transport of subsurface solutes.     

Imaging Hydrological Processes in Headwater Riparian Seeps with Time‐Lapse Electrical Resistivity

Delineating hydrologic and pedogenic factors influencing groundwater flow in riparian zones is central in understanding pathways of water and nutrient transport. In this study, we combined two‐dimensional time‐lapse electrical resistivity imaging (ERI) (depth of investigation approximately 2 m) with hydrometric monitoring to examine hydrological processes in the riparian area of FD‐36, a small (0.4 km²) agricultural headwater basin in the Valley and Ridge region of east‐central Pennsylvania. We selected two contrasting study sites, including a seep with groundwater discharge and an adjacent area lacking such seepage. Both sites were underlain by a fragipan at 0.6 m. We then monitored changes in electrical resistivity, shallow groundwater, and nitrate‐N concentrations as a series of storms transitioned the landscape from dry to wet conditions. Time‐lapse ERI revealed different resistivity patterns between seep and non‐seep areas during the study period. Notably, the seep displayed strong resistivity reductions (～60%) along a vertically aligned region of the soil profile, which coincided with strong upward hydraulic gradients recorded in a grid of nested piezometers (0.2‐ and 0.6‐m depth). These patterns suggested a hydraulic connection between the seep and the nitrate‐rich shallow groundwater system below the fragipan, which enabled groundwater and associated nitrate‐N to discharge through the fragipan to the surface. In contrast, time‐lapse ERI indicated no such connections in the non‐seep area, with infiltrated rainwater presumably perched above the fragipan. Results highlight the value of pairing time‐lapse ERI with hydrometric and water quality monitoring to illuminate possible groundwater and nutrient flow pathways to seeps in headwater riparian areas.     

Correction: Geostatistical Rock Physics Inversion for Predicting the Spatial Distribution of Porosity and Saturation in the Critical Zone

Mathematical Geosciences -     

Automatic Synthetic Aperture Radar based oil spill detection and performance estimation via a semi-automatic operational service benchmark

Today the health of ocean is in danger as it was never before mainly due to man-made pollutions. Operational activities show regular occurrence of accidental and deliberate oil spill in European waters. Since the areas covered by oil spills are usually large, satellite remote sensing particularly Synthetic Aperture Radar represents an effective option for operational oil spill detection. This paper describes the development of a fully automated approach for oil spill detection from SAR. Total of 41 feature parameters extracted from each segmented dark spot for oil spill and ‘look-alike’ classification and ranked according to their importance. The classification algorithm is based on a two-stage processing that combines classification tree analysis and fuzzy logic. An initial evaluation of this methodology on a large dataset has been carried out and degree of agreement between results from proposed algorithm and human analyst was estimated between 85% and 93% respectively for ENVISAT and RADARSAT.     

Arbitrary Amplitude Ion Acoustic Solitary Waves in An Unmagnetized Two Electron Population Ultra-Relativistic Dense Plasmas

The nonlinear wave structure of arbitrary amplitude ion acoustic solitary waves (IASWs) are studied in the Sagdeev’s pseudopotential framework for an ultra-relativistic degenerate dense plasma comprising cold and hot electrons and inertial ultra-cold ions. By employing standard normal-mode analysis the dispersion relation for linear waves is studied. The numerical results are presented to understand the features of ion acoustic solitary wave structures. It is shown that the present plasma model supports IASWs having positive potential well. Also, it is found that the small amplitude rarefactive double layer solution can exist in such a plasma system in some parametric region. It is shown that solitary structures and double layers are affected by relevant plasma parameters.     

Logjams as a driver of transient storage in a mountain stream

We use four stream segments along a wood-rich, pool–riffle mountain stream in the Southern Rockies of Colorado, USA to examine how spatial variations in wood load and variations in discharge during and after the snowmelt peak flow influence the magnitude of surface and subsurface transient storage. Segments range in complexity from a single channel with no large wood to an anabranching channel with closely spaced, channel-spanning logjams. Discharges at which transient storage was assessed range from base flow to snowmelt peak flow. To explore these relations, we used 10 geomorphic variables representing channel morphology and bed substrate, four wood-related variables representing wood load and associated backwater storage, and two measures of skewness from instream and bulk electrical conductivity breakthrough curves during tracer tests. Instream curves reflect surface and subsurface transient storage, whereas bulk curves primarily represent subsurface transient storage. Higher values of skewness indicate greater retention, and we used the values here as a metric of increased transient storage. Although limited sample size restricts the power of our results, our findings suggest that stream segments with greater instream large wood loads have more and larger pools, greater storage of fine sediment and particulate organic matter, and higher values of skew from instream conductivity. The results also suggest that the presence of instream wood, rather than changes in channel morphology associated with wood, is the most important driver of transient storage. This implies that river management designed to foster transient storage should focus on retaining instream large wood. We did not find significant correlations between geomorphic or wood-related variables and the skew estimated from bulk conductivity, which may reflect the relatively thin alluvium present in the field area and the prevalence of surface transient storage in this system.     

Spatiotemporal pattern of the dynamics in area,production, and yield of Aus rice in Bangladesh and its response to droughts from 1980 to 2018

Bangladesh is one of the most vulnerable countries to natural disasters such as droughts in the world. The pre-monsoon Aus rice in Bangladesh depends on rainfall and is threatened by increasing droughts. However, limited information on the changes in Aus rice as well as droughts hamper our understanding of the country’s agricultural resilience and adaption to droughts. Here, we collected all the official statistical data of Aus rice at the district level from 1980 to 2018, and examined the inter...