Identification and Explanation of a Change in the Groundwater Regime using Time Series Analysis

Time series analysis is applied to identify and analyze a transition in the groundwater regime in the aquifer below the sand ridge of Salland in the Netherlands, where groundwater regime refers to the range of head variations throughout the seasons. Standard time series analysis revealed a discrepancy between modeled and observed heads in several piezometers indicating a possible change in the groundwater regime. A new time series modeling approach is developed to simulate the transition from the initial regime to the altered regime. The transition is modeled as a weighted sum of two responses, one representing the initial state of the system, the other representing the altered state. The inferred timing and magnitude of the change provided strong evidence that the transition was the result of significant dredging works that increased the river bed conductance of the main river draining the aquifer. The plausibility of this explanation is corroborated by an analytical model. This case study and the developed approach to identify a change in the groundwater regime are meant to stimulate a more systematic application of time series analysis to detect and understand changes in groundwater systems which may easily go unnoticed in groundwater flow modeling.     

Heli-borne gravity gradiometry in rugged terrain

For airborne gravity gradiometry in rugged terrain, helicopters offer a significant advantage over fixed-wing aircraft: their ability to maintain much lower ground clearances. Crucially, this provides both better signal-to-noise and better spatial resolution than is possible with a fixed-wing survey in the same terrain. Comparing surveys over gentle terrain at Margaret Lake, Canada, and over rugged terrain at Mount Aso, Japan, demonstrates that there is some loss of spatial resolution in the more rugged terrain. The slightly higher altitudes forced by rugged terrain make the requirements for terrain correction easier than for gentle terrain. Transforming the curvature gradients measured by the Falcon gravity gradiometer into gravity and the complete set of tensor components is done by a Fourier method over gentle terrain and an equivalent source method for rugged terrain. The Fourier method is perfectly stable and uses iterative padding to improve the accuracy of the longer wavelengths. The equivalent source method relies on a smooth model inversion, and the source distribution must be designed to suit the survey design.     

Geomorphic process signatures reshaping sub-humid Mediterranean badlands: 2. Application to 5-year dataset

Badland landscapes exhibit high erosion rates and represent the main source of fine sediments in some catchments. Advances in high-resolution topographic methods allow analysis of topographic changes at high temporal and spatial scales. We apply the Mapping Geomorphic Processes in the Environment (MaGPiE) algorithm to infer the main geomorphic process signatures operating in two sub-humid badlands with contrasting morphometric attributes located in the Southern Pyrenees. By interrogating a 5-year dataset of seasonal and annual topographic changes, we examine the variability of geomorphic processes at multiple temporal scales. The magnitude of geomorphic processes is linked to landform attributes and meteorological variables. Morphometric differences between both adjacent badlands allow us to analyse the role of landform attributes in the main geomorphic process reshaping landscapes subjected to the same external forcing (i.e. rainfall and temperature). The dominant geomorphic process signatures observed in both badlands are different, despite their close proximity and the same rainfall and temperature regimes. Process signatures determining surface lowering in the gently sloping south-facing badland, characterized by lower connectivity and more vegetation cover, are driven by surface runoff-based processes, both diffuse (causing sheet washing) and concentrated (determining cutting and filling, rilling and gullying). The steeper, more connected north-facing slopes of the other badland are reshaped by means of gravitational processes, with mass wasting dominating topographic changes. In terms of processes determining surface raising, both mass wasting and cutting and filling are most frequently observed in both badlands. There is a clear near-balanced feedback between both surface-raising and -lowering processes that becomes unbalanced at larger temporal scales due to the thresholds overcome, as the volume associated with surface lowering becomes higher than that associated with raising-based processes. Rainfall variables control surface flow processes, while those variables associated with low temperature have a significant relation with mass movement-based processes and other localized processes such as regolith cohesion loss. Finally, our results point out that morphometry (slope and connectivity) together with vegetation cover are key factors determining geomorphic processes and associated topographic changes. © 2020 John Wiley & Sons, Ltd.     

The effect of salinity on growth and weight loss of juvenile plaice (Pleuronectes platessa, L): An experimental test

Previous population estimates of the 0+ plaice (Pleuronectes platessa L.) in the Firth of Forth, east central Scotland, did not take account of the Forth estuary west of the Forth bridges. Previous work found plaice in the estuary grew as fast as, or faster than, the outer firth plaice. It was hypothesised that salinity may affect growth rates of early 0+ plaice. This hypothesis was tested in a laboratory experiment, by exposing juvenile plaice to three different, but naturally — experienced by the juveniles, salinities; 25, 30 and 35. Plaice fed a minimum ration did not grow in length. Mean weight decreased at all three salinities, however, the lowest weight loss was found at the lowest salinity (25) and the highest weight loss was found at the highest salinity (35). The minimum feeding ration was halted and plaice were then fed ad libitum. Consumption rates were not significantly different during the ad libitum feeding, while significant differences in mean weight change were found between the highest and lowest salinities.     

Higher-order neighbor analysis of the Tartarus Colles cone groups, Mars: The application of geographical indices to the understanding of cone pattern evolution

Cone fields of ambivalent origin exist in the Elysium, Amazonis, Cerberus, Isidis, Acidalia and Cydonia regions of Mars. Considerable interest exists in regard to their location and origin as their occurrence in many instances, is most likely associated with near surface ground ice; the presence of which has consequences for past and present climate, astrobiological activity, and future exploration. This research has outlined an understanding of both spatial and geomorphic processes of cone development for a region within the Tartarus Colles, Mars, as well as the manner in which spatial statistical indices can be affected by modification to the areal unit of study. This study found that cone groups for the region of the Tartarus Colles, are completely spatially random (CSR) across all distances extending to their sixth-order neighbor. However, significant statistical indices of aggregation were found for groups where post-emplacement erosional modification may have occurred by solifluction-like mechanisms or magmatic incursion into or over frozen ground. Such circumstances imply that R-indices reflect both the underlying spatial and geologic processes of cone formation, and also, an overprint of erosional modification of the cone-field within a glacial or periglacial setting, in this instance. The comparison of spatial indices can therefore offer a viewpoint from which geomorphic change can be recognized and quantitatively evaluated for cone fields.     

Pacific Pleistocene paleoclimatic stratigraphies: A comparative analysis of results

Global atmospheric and oceanic circulation effects of expansion of continental ice sheets initiated upwelling in the western equatorial Pacific and simultaneously intensified upwelling in the eastern equatorial Pacific; contraction of the ice sheets reversed the process. Published Pleistocene paleoclimatic stratigraphies correlated across the entire equatorial Pacific exhibit eight such cycles in the Brünhes epoch. The extrapolated chronostratigraphies for the equatorial Pacific compare favorably with published paleoclimatic schemes for the southeastern, eastern, and northern Pacific Ocean. The Southern Ocean record exhibits fewer, and possibly also consistently older, climatic variations. A time progression or lack of synchrony of marine Pleistocene climatic events is not inconsistent with modified “Milankovitch” hypotheses, such as that involving Antarctic ice-sheet instability.     

The response of soil erosion and sediment export to land-use change in four areas of Europe: The importance of landscape pattern

The response of erosion and sediment export to past land-use change has been studied in four agricultural areas of Europe. Three of these areas were subject to land abandonment or de-intensification and one to intensification of land-use practices. Erosion and sediment yield were modeled using the WaTEM/SEDEM model, which combines the RUSLE equation with a sediment routing algorithm. Spatial relationships between the RUSLE C-factor (i.e. land-use) and other erosion and sediment export-determining factors (slope, soil erodibility and distance to rivers) were investigated, as these account for non-linearity in the response of erosion and sediment export to land-use change.Erosion and sediment export have decreased enormously in the de-intensified areas, but slightly increased in the intensively cultivated area. The spatial pattern of land-use change in relation to other erosion and sediment export-determining factors appears to have a large impact on the response of soil erosion and sediment export to land-use change. That the drivers of abandonment of arable land and erosion coincide indicates that de-intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export. This mechanism applies not only within the study areas, but also among the European study areas where the process of intensification of some areas and de-intensification of others might result in an overall decrease of erosion and sediment yield through time.     

Detecting inter-aquifer leakage in areas with limited data using hydraulics and multiple environmental tracers,including <Superscript>4</Superscript>He, <Superscript>36</Superscript>Cl/Cl, <Superscript>14</Superscript>C and <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr

The investigation of regionally extensive groundwater systems in remote areas is hindered by a shortage of data due to a sparse observation network, which limits our understanding of the hydrogeological processes in arid regions. The study used a multidisciplinary approach to determine hydraulic connectivity between the Great Artesian Basin (GAB) and the underlying Arckaringa Basin in the desert region of Central Australia. In order to manage the impacts of groundwater abstraction from the Arckaringa Basin, it is vital to understand its connectivity with the GAB (upper aquifer), as the latter supports local pastoral stations and groundwater-dependent springs with unique endemic flora and fauna. The study is based on the collation of available geological information, a detailed analysis of hydraulic data, and data on environmental tracers. Enhanced inter-aquifer leakage in the centre of the study area was identified, as well as recharge to the GAB from ephemeral rivers and waterholes. Throughout the rest of the study area, inter-aquifer leakage is likely controlled by diffuse inter-aquifer leakage, but the coarse spatial resolution means that the presence of additional enhanced inter-aquifer leakage sites cannot be excluded. This study makes the case that a multi-tracer approach along with groundwater hydraulics and geology provides a tool-set to investigate enhanced inter-aquifer leakage even in a groundwater basin with a paucity of data. A particular problem encountered in this study was the ambiguous interpretation of different age tracers, which is attributed to diffusive transport across flow paths caused by low recharge rates.