Review: Hydrogeology of Northern Mendoza (Argentina), from the Andes to the eastern plains,in the context of climate change

Hydrogeology Journal - In the drylands of Northern Mendoza, Argentina, water supply depends on rivers and groundwater. Climate change makes this region vulnerable due to the snow-glacial-melt...     

A new implementation of narrowband interference detection,characterization, and mitigation technique for a software-defined multi-GNSS receiver

Due to the very low power of satellite signals when reaching the earth’s surface, global navigation satellite system receivers are vulnerable to various types of radio frequency interference, and, therefore, countermeasures are necessary. In the case of a narrowband interference (NBI), the adaptive notch filtering technique has been extensively investigated. However, the research on the topic has focused on the adaptation of the notch frequency, but not of the notch width. We present a fully adaptive solution to counter NBI. The technique is capable of detecting and characterizing any number of narrow interfered bands, and then optimizing the mitigation process based on such characterization, namely the estimates of both interference frequency and width. Its full adaptiveness makes it suitable to cope with the unpredictable and diverse nature of unintentional interfering events. In addition to a thorough performance evaluation of the proposed method, which shows its benefits in terms of signal quality improvement, an analysis of the impact of different NBI profiles on GPS L1 C/A and Galileo E1 is also conducted.     

Historical shoreline trend analysis and drivers of coastal change along the Ravenna coast,NE Adriatic

One of the most important aspects of coastal zone management is the analysis of shoreline dynamics. Over the last years, beaches of the Ravenna coast (NE Italy) experienced large modifications, in some places narrowing or even being completely lost, thus threatening tourism, coastal assets and nature. Coastal erosion has direct consequences for Ravenna tourist-based economy, which largely depends on the attraction provided by sandy beaches. In this study, long-term (>?50 years) coastal analysis was used to identify the sectors along the coast where the shoreline position has changed, either advancing or retreating. Shoreline changes were measured on GIS environment by means of Digital Shoreline Analysis System (DSAS) extension. Net Shoreline Movement (NSM) and Linear Regression Rate (LRR) strategies were employed to examine shoreline variability and reveal erosional/accretional trends. The results show that significant shoreline changes affected the entire coastal region, with most of the study area under retreat, mainly in the most valuable tourist assets of the littoral. The effects were found to be worsened by impacts of land subsidence, presence of harbor infrastructure and deficit in sediment budget. A simple shoreline classification was performed over the DSAS results and cross-checked with local knowledge of the area. The measurement of erosion or accretion rates in each studied segment is found to be useful for land use planning and coastal management plans, especially regarding the prediction of future shoreline positions. Especially important is the potential of the classification to identify areas of significant position change, with current and future implications for the design of sustainable shoreline management and mitigation measures.     

Changes in hydrology and erosion over a transition from grassland to shrubland

The degradation of grasslands is a common problem across semi‐arid areas worldwide. Over the last 150 years, much of the south‐western United States has experienced significant land degradation, with desert grasslands becoming dominated by shrubs and concurrent changes in runoff and erosion which are thought to propagate further the process of degradation. Plot‐based experiments to determine how spatio‐temporal characteristics of soil moisture, runoff and erosion change over a transition from grassland to shrubland were carried out at four sites over a transition from black grama (Bouteloua eriopoda) grassland to creosotebush (Larrea tridentata) shrubland at the Sevilleta NWR LTER site in New Mexico. Each site consisted of a 10 × 30 m bounded runoff plot and adjacent characterization plots with nested sampling points where soil moisture content was measured. Results show distinct spatio‐temporal variations in soil moisture content, which are due to the net effect of processes operating at multiple spatial and temporal scales, such as plant uptake of water at local scales versus the redistribution of water during runoff events at the hillslope scale. There is an overall increase in runoff and erosion over the transition from grassland to shrubland, which is likely to be associated with an increase in connectivity of bare, runoff‐generating areas, although these increases do not appear to follow a linear trajectory. Erosion rates increased over the transition from grassland to shrubland, likely related in part to changes in runoff characteristics and the increased capacity of the runoff to detach, entrain and transport sediment. Over all plots, fine material was preferentially eroded which has potential implications for nutrient cycling since nutrients tend to be associated with fine sediment. Copyright © 2009 John Wiley & Sons, Ltd.     

Impact of debris dams on hyporheic interaction along a semi‐arid stream

Hyporheic exchange increases the potential for solute retention in streams by slowing downstream transport and increasing solute contact with the substrate. Hyporheic exchange may be a major mechanism to remove nutrients in semi‐arid watersheds, where livestock have damaged stream riparian zones and contributed nutrients to stream channels. Debris dams, such as beaver dams and anthropogenic log dams, may increase hyporheic interactions by slowing stream water velocity, increasing flow complexity and diverting water to the subsurface. Here, we report the results of chloride tracer injection experiments done to evaluate hyporheic interaction along a 320 m reach of Red Canyon Creek, a second order stream in the semi‐arid Wind River Range of Wyoming. The study site is part of a rangeland watershed managed by The Nature Conservancy of Wyoming, and used as a hydrologic field site by the University of Missouri Branson Geologic Field Station. The creek reach we investigated has debris dams and tight meanders that hypothetically should enhance hyporheic interaction. Breakthrough curves of chloride measured during the field experiment were modelled with OTIS‐P, a one‐dimensional, surface‐water, solute‐transport model from which we extracted the storage exchange rate α and cross‐sectional area of the storage zone A_s for hyporheic exchange. Along gaining reaches of the stream reach, short‐term hyporheic interactions associated with debris dams were comparable to those associated with severe meanders. In contrast, along the non‐gaining reach, stream water was diverted to the subsurface by debris dams and captured by large‐scale near‐stream flow paths. Overall, hyporheic exchange rates along Red Canyon Creek during snowmelt recession equal or exceed exchange rates observed during baseflow at other streams. Copyright © 2005 John Wiley & Sons, Ltd.     

Moving beyond Component Research in Mountain Regions： Operationalizing Systems Integration .at Farm and Landscape Scales

Introduction Agricultural research continues to face criticism for its shortcomings in reversing current trends toward increased poverty and natural resource degradation. While some of these criticisms would be better attributed to broader structural constraints, shortcomings of the conventional agricultural research paradigm are nevertheless apparent. Researchers continue to frame research objectives, questions and methods with limited consultation of farmers and limited consideration of othe…     

Neogene exhumation of the Marrakech High Atlas (Morocco) recorded by apatite fission-track analysis

Apatite fission-track (AFT) data have been obtained along a traverse across the Marrakech High Atlas to constrain its tectono-thermal evolution. AFT ages vary between 212 ± 15 Ma and 20 ± 4 Ma. An Early Miocene AFT age accompanied by long mean track length from the central part of the chain has been interpreted as the timing of the main inversion of this region with the creation of relief because of the shortening induced by the interplay between the African and Eurasian plates. Thermal modelling of samples collected south of the South Atlas Fault Zone indicates a Middle-Late Miocene or even later cooling that has been attributed to the component of the uplift of the chain related to the thermal anomaly present beneath the Atlas Mountains.     

An approach to estimate Lower Jurassic seawater oxygen‐isotope composition using δ18O and Mg/Ca ratios of belemnite calcites (Early Pliensbachian,northern Spain)

Palaeotemperature estimates from the oxygen‐isotope compositions of belemnites have been hampered by not knowing ancient seawater isotope compositions well enough. We have tackled this problem using Mg/Ca as a proxy for temperature and here, we present a ~2 Ma record of paired Mg/Ca and δ¹⁸O measurements of Jurassic (Early Pliensbachian) belemnites from the Asturian basin as a palaeo‐proxy of seawater oxygen‐isotope composition. From the combined use of the two approaches, we suggest a δ¹⁸O_w composition of about ?0.1‰ for the Jamesoni–Ibex zones. This value may have been increased by about 0.6‰ during the Davoei Zone due to the effect of waters with a different δ¹⁸O_w composition. These findings illustrate the inaccuracy of using a globally homogeneous ice‐free value of δ¹⁸O_w = ?1‰ for δ¹⁸O_carb‐based palaeotemperature reconstructions. Our data suggest that previous palaeotemperatures calculated in the region from δ¹⁸O values of belemnites may have been underestimated as the seawater oxygen isotopic composition could have been higher.     

Observing lingering hyporheic storage using electrical resistivity: variations around stream restoration structures,Crabby Creek,PA

Time‐lapse geophysical surveys can map lingering hyporheic storage by detecting changes in response to saline tracer. Tracer tests were conducted in Crabby Creek, an urban stream outside Philadelphia, to examine the influence of stream restoration structures and variable sediment thickness. We compared electrical resistivity surveys with extensive well sampling (57 wells) in two 13.5‐m‐long reaches, each with a step drop created by a J‐hook. The two step drops varied in tracer behaviour, based on both the well data and the geophysical data. The well data showed more variation in arrival time where the streambed sediment was thick and was more uniform where sediment was thin. The resistivity in the reach with thin sediment showed lingering tracer in the hyporheic zone both upstream and downstream from the J‐hook. In the second reach where the sediment was thicker, the lingering tracer in the hyporheic zone was more extensive downstream from the J‐hook. The contrasting results between the two reaches from both methods suggested that sediments influenced hyporheic exchange more than the step at this location. Resistivity inversion differed from well data in both reaches in that it showed evidence for tracer after well samples had returned to background, mapping lingering tracer either upstream or downstream of a step. We conclude that resistivity surveys may become an important tool for hyporheic zone characterization because they provide information on the extent of slow moving fluids in the hyporheic zone, which have the potential to enhance chemical reactions. Copyright © 2012 John Wiley & Sons, Ltd.