The extent of soil erosion in upland England and Wales

Following recommendations by the 19th Royal Commission on Environmental Pollution, the area, causes and rates of upland soil erosion in England and Wales were investigated between 1997 and 1999. This paper describes the methods and results of the field survey of 1999 in which the extent of eroded ground was determined. 2. The area of degraded soil and the volume of eroded material were both determined from the dimensions of individual erosion features at 399 field sites located on an orthogonal grid across the uplands. Using measurements of individual erosion features, degraded soil extent in upland England and Wales was estimated at almost 25 000 ha, 2·46 per cent of the total upland area surveyed. Half this eroded area was revegetated and no longer subject to continued accelerated soil loss in 1999. The total volume of eroded material was estimated at 0·284 km³. Although deposition of eroded material occurred within 20 per cent of eroded field sites, the total volume of redeposited material was less than 1 per cent of the total volume of eroded soil. 3. Erosion was more extensive on peat soils than on dry, wet mineral or wet peaty mineral soils. In addition, the higher incidence of erosion at high altitudes and on low slopes reinforced the relationship between erosion and areas of peat formation. Copyright © 2002 John Wiley & Sons, Ltd.     

Towards an integrated environmental assessment for wetland and catchment management

This paper develops a decision support system for evaluation of wetland ecosystem management strategy and examines its, so far partial, application in a case study of an important complex coastal wetland known as the Norfolk and Suffolk Broads, in the east of England, UK. Most managed ecosystems are complex and often poorly understood hierarchically organized systems. Capturing the range of relevant impacts on natural and human systems under different management options will be a formidable challenge. Biodiversity has a hierarchical structure which ranges from the ecosystem and landscape level, through the community level and down to the population and genetic level. There is a need to develop methodologies for the practicable detection of ecosystem change, as well as the evaluation of different ecological functions. What is also required is a set of indicators (environmental, social and economic) which facilitate the detection of change in ecosystems suffering stress and shock and highlight possible drivers of the change process. A hierarchical classification of ecological indicators of sustainability would need to take into account existing interactions between different organization levels, from species to ecosystems. Effects of environmental stress are expressed in different ways at different levels of biological organization and effects at one level can be expected to impact other levels, often in unpredictable ways. The management strategy, evaluation methodologies and indicators adopted should also assess on sustainability grounds whether any given management option is supporting, or reducing, the diversity of functions which are providing stakeholders with the welfare benefits they require.     

Climate variability and ecosystem dynamics of remote alpine and arctic lakes: the MOLAR project

This paper introduces the results of an integrated project designed to compare high resolution analysis of proxy records of climate change in the sediments of seven mountain lakes across Europe with reconstructed instrumental records of climate change over the last 200 years. Palaeolimnological methods used include radiometric dating (²¹⁰Pb, ¹³⁷Cs), mineral magnetics, dry weight, loss-on-ignition, carbon, nitrogen, sulphur, pigments, diatoms, chrysophyte cysts, cladocera and chironomids. Changes in fossil assemblages were summarised using principal components analysis. The stratigraphic data were compared with the instrumental record using linear regression techniques. The dated sediment records for each proxy from each site were treated as the response variables and the various attributes of the instrumental climate record as the predictor variables. The predictor variables were generated for each site for the period 1781 to 1997 using temperature reconstructions based on meteorological records. To harmonise the climatic predictors and the response variables, the climatic variables were smoothed along time with a LOESS regression. The results of the various analyses at the seven sites are presented in the following papers. A synthesis of the project and the relative performance of the different proxy methods are discussed in the final paper.     

Architecture of the evaporite accumulation and salt structures dynamics in Tiddlybanken Basin,southeastern Norwegian Barents Sea

An extensive, reprocessed two‐dimensional (2D) seismic data set was utilized together with available well data to study the Tiddlybanken Basin in the southeastern Norwegian Barents Sea, which is revealed to be an excellent example of base salt rift structures, evaporite accumulations and evolution of salt structures. Late Devonian–early Carboniferous NE‐SW regional extensional stress affected the study area and gave rise to three half‐grabens that are separated by a NW‐SE to NNW‐SSE trending horst and an affiliated interference transfer zone. The arcuate nature of the horst is believed to be the effect of pre‐existing Timanian basement grain, whereas the interference zone formed due to the combined effect of a Timanian (basement) lineament and the geometrical arrangement of the opposing master faults. The interference transfer zone acted as a physical barrier, controlling the facies distribution and sedimentary thickness of three‐layered evaporitic sequences (LES). During the late Triassic, the northwestern part of a salt wall was developed due to passive diapirism and its evolution was influenced by halite lithology between the three‐LES. The central and southeastern parts of the salt wall did not progress beyond the pedestal stage due to lack of halite in the deepest evaporitic sequence. During the Triassic–Jurassic transition, far‐field stresses from the Novaya Zemlya fold‐and‐thrust belt reactivated the pre‐salt Carboniferous rift structures. The reactivation led to the development of the Signalhorn Dome, rejuvenated the northwestern part of the salt wall and affected the sedimentation rates in the southeastern broad basin. The salt wall together with the Signalhorn Dome and the Carboniferous pre‐salt structures were again reactivated during post‐Early Cretaceous, in response to regional compressional stresses. During this main tectonic inversion phase, the northwestern and southeastern parts of the salt wall were rejuvenated; however, salt reactivation was minimized towards the interference transfer zone beneath the centre of the salt wall.     

Meteorological inventory of rain-on-snow events in the Canadian Arctic Archipelago and satellite detection assessment using passive microwave data

The spatial and temporal distributions of rain-on-snow (ROS) events across the Canadian Arctic Archipelago (CAA) remain poorly understood owing to their sporadic nature in time and space. This situation motivated the development of remote sensing detection algorithms. This paper uses a large meteorological dataset across the CAA to adapt an existing ROS-detection algorithm developed in a previous study by our group. Results highlight the spatial distribution and evolution of ROS occurrences reported since 1985 at 14 weather stations across the CAA. Results show that >600 ROS events were inventoried since 1985, for which >70% were classified as pure rain (liquid form) and 30% as mixed precipitation (solid/liquid). Of the pure rain events, 75% occurred during spring, 14% during fall, 8% during summer and <1% during winter. Such events can have significant impacts on ungulate grazing conditions through the creation of ice layers, causing serious problems for caribou calf survival, especially during the migration period. This paper introduces an adaptation for larger scale Arctic application of a detection algorithm (sensitivity analysis on the detection threshold) with an error of ~5%. The validation, however, remains limited due to a short study period and limited number of sites.     

Investigation of Hemispherical Variations of Soft X-Ray Solar Flares during Solar Cycles 21 to 24

Solar System Research - In the current investigation we have studied the distribution as well as the asymmetry of solar X-ray flares during the period 1976–2017 which corresponds to solar...     

An alternative approach in establishing relation between vertical and horizontal gradients of 2D potential field

The relation in which the vertical and horizontal gradients of potential field data measured along a profile across a two‐dimensional source are a Hilbert transform pair is re‐established using complex domain mathematics. In addition, a relation between the measured field and its vertical gradient in terms of a closed‐form formula is also established. The formula is based on hypersingular or Hadamard's finite‐part integral. To estimate the vertical gradient directly from the field data, Linz's algorithm of computing Hadamard's finite‐part integral is implemented. Numerical experiments are conducted on synthetically generated total magnetic intensity data with a mild level of noise contamination. A model of a magnetically polarised vertical thin sheet buried at a finite depth within a non‐magnetic half‐space was considered in generating the synthetic response. The results from numerical experiments on the mildly noise‐contaminated synthetic response are compared with those from using classical Fourier and robust regularised Hilbert transform‐based techniques.     

Freshwater flow to the San Francisco Bay‐Delta estuary over nine decades (Part 1): Trend evaluation

The San Francisco Bay‐Delta estuary and its upstream watershed have been highly modified since exploration and settlement by Europeans in the mid‐18th century. Although these hydrologic alterations supported the growth of California's economy to the eighth largest in the world, they have been accompanied by significant declines in native aquatic species and subsequent efforts to reverse these declines through flow management. To inform ongoing deliberations on management of freshwater flows to the estuary, we examined a recent nine‐decade hydrologic record to evaluate seasonal and annual trends in reported Delta outflow. Statistically significant trends were observed in seasonal outflows, with decreasing trends observed in 4 months (February, April, May, and November) and increasing trends observed in 2 months (July and August). Trend significance in early‐to‐mid autumn (September and October) is ambiguous due to uncertainty associated with in‐Delta agricultural water use. In spite of increasing water use over the period examined, we found no statistically significant annual trend in Delta outflow, a result likely due to large inter‐annual variability. Linkages between outflow trends and changes in upstream flows and coincident developments such as reservoir construction and operation, out‐of‐basin imports and exports, and expansion of irrigated agriculture are discussed. To eliminate inter‐annual variability as a factor, change attribution is explored using modelled flows and fixed climatology in a companion paper.     

Characterization of Mechanisms and Processes Controlling Groundwater Recharge and its Quality in Drought-Prone Region of Central India (Buldhana,Maharashtra) Using Isotope Hydrochemical and End-Member Mixing Modeling

A thorough study on understanding of groundwater recharge sources and mechanisms was attempted by integrating the hydrogeological, geochemical and isotopic information along with groundwater dating and end-member mixing analysis (EMMA). This study was necessitated due to prolonged dryness and unavailability of freshwater in semi arid Deccan trap regions of Central India. In addition, groundwater resources are not characterized well in terms of their geochemical nature and recharge sources. The hydrogeochemical inferences suggest that aquifer I consists of recently recharged water dominated by Ca–Mg–HCO₃ facies, while groundwater in aquifer II shows water–rock interaction and ion exchange processes. Presence of agricultural contaminant, nitrate, in both aquifers infers limited hydraulic interconnection, which is supported by unconfined to semi-confined nature of aquifers. Groundwater in both aquifers is unsaturated with respect to carbonate and sulfate minerals indicating lesser water–rock interaction and shorter residence time. This inference is corroborated by tritium age of groundwater (aquifer I: 0.7–2 years old and aquifer II: 2–4.2 years old). Stable water isotopes (δ²H, δ¹⁸O) suggest that groundwater is a mixture of rainwater and evaporated water (surface water and irrigation return flow). EMMA analysis indicates three groundwater recharge sources with irrigation return flow being the dominant source compared to others (rainwater and surface waters). A conceptual model depicting groundwater chemistry, recharge and dynamics is prepared based on the inferences.

     

Application of satellite — based rainfall products and SRTM DEM in hydrological modelling of Brahmaputra basin

Hydrological modelling of large river catchments is a challenging task for water resources engineers due to its complexity in collecting and handling of both spatial and non-spatial data such as rainfall, gauge discharges, and topographic parameters. In this paper an attempt has been made to use satellite-based rainfall products such as Climatic Prediction Centre (CPC)-National Oceanic and Atmospheric Administration (NOAA) data for hydrological modelling of larger catchment where the limited field rainfall data is available. Digital Elevation Models (DEM) such as Global DEM (1 km resolution) and Shuttle Radar Topography Mission (SRTM) 3-arc second (90 m resolution) DEM have been used to extract topographic parameters of the basin for hydrological modelling of the study area. Various popular distributed models have been used in this study for computing excess rainfall, direct runoff from each sub-basin, and flow routing to the main outlet. The Brahmaputra basin, which is very complex both hydraulically and hydrologically due to its shape, size, and geographical location, has been examined as study area in this study. A landuse map derived from the satellite remote sensing data in conjunction with DEM and soil textural maps have been used to derive various basin and channel characteristics such as each sub-basin and channel slope, roughness coefficients, lag-time. Percentage of residual flows computed between observed flows and simulated flows using Global and SRTM DEMs are discussed. It is found that the topographic parameters computed using SRTM DEM could improve the model accuracy in computing flood hydrograph. Need of using better resolution satellite data products and the use of high-density field discharge observations is discussed.