bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natural and Constructed Wetlands
Authors: Craft Christopher B 
Published: April 2006

AbstractWetlands are characterized by periodic to continuous inundation or saturation with water (wetland hydrology), soils that are periodically deficient in oxygen (hydric soils), and vegetation that is adapted to periods of anaerobic or anoxic soil conditions (hydrophytic vegetation). Wetlands include herbaceous marshes and fens, forested swamps, and Sphagnum‐dominated peat bogs. Wetland plants possess morphological adaptations (aerenchyma, buttressed trunks, pneumatophores, hypertrophied lenticels) to facilitate transport of oxygen to the roots and metabolic pathways to respire anaerobically without toxic effects. Duration, depth, and frequency of inundation, water source (precipitation, surface flow, groundwater), and water quality (fresh, saline, oligotrophic, eutrophic) determine the distribution, productivity, and nutrient cycling characteristics of wetland vegetation. Floodplain swamp forests and estuarine marshes and mangroves receive large quantities of water and nutrients during overbank flooding and tidal inundation that enhances plant productivity and sediment, nutrient, and pollutant retention as compared to wetlands that receive most of their water from precipitation. The ability of natural wetlands to filter pollutants has led to construction of artificial wetlands to treat wastewater, stormwater, acid mine drainage, nonpoint runoff and other sources of pollutants. Wetlands also are constructed to replace important ecological functions (water storage, biological productivity, biodiversity) that are lost when natural wetlands are damaged or destroyed by human activities.
Lake Ecosystems (Stratification and Seasonal Mixing Processes, Pelagic and Benthic Coupling)
Authors: Bade Darren L 
Published: April 2006

AbstractSeasonal stratification in lakes is caused by the differential heating of surface waters, causing them to become less dense and buoyant above colder, denser water. Other forces oppose stratification, including wind energy and loss of heat from the surface. Wind imparts many types of motions to lake waters, each having distinct patterns, energy, and scales of mixing. Theoretical considerations are presented in detail on the expected response of lakes to physical forcing. In addition, empirical equations are given for diverse regions of the world to predict epilimnetic and thermocline depth and timing of stratification. Lake morphometry along with climatic conditions determines the depth of epilimnetic mixing. The seasonal patterns of mixing and stratification are observed in a northern temperate lake (Sparkling Lake, Wisconsin, USA). The influence of stratification and mixing on the coupling of benthic and pelagic zones through processes of sedimentation, resuspension, eddy diffusivity, and hypolimnetic entrainment are discussed. Through these mechanisms, the hydrodynamics of lakes directly and indirectly influence the chemical and biological environment of lake ecosystems.
Land Use and Land Cover Effects on Runoff Processes: Agricultural Effects
Authors: Burt Timothy P , Slattery Michael C 
Published: April 2006

Abstract
The impact of agriculture on runoff processes cannot be underestimated. The greatest impact is usually on soil surface conditions, specifically infiltration. Undisturbed soils have much higher infiltration capacity than soils in agricultural land. Once cultivated, soils become easily compacted as they are laid bare to the elements until the next crop develops a protective cover. Infiltration can fall to levels where infiltration‐excess overland flow can occur even in rainfall of modest intensity. Successive rainfall events compact the bare soil further and impermeable crusts often form. Heavy machinery used in agriculture exacerbates soil compaction, particularly at depth, via the development of plough pans. These compacted, dense layers have significantly higher bulk density and lower total soil porosity than the soil directly above or below it and frequently become preferential zones of runoff generation. Temporary saturation of shallow topsoil layers leads to topsoil saturation overland flow that, if connected to the channel network, may become a significant contributor to event response. Linear zones of compaction and reduced hydraulic conductivity that occur as a result of vehicular traffic have similar impacts.
Land Use and Landcover Effects on Runoff Processes: Forest Harvesting and Road Construction
Authors: Sampurno Bruijnzeel L A 
Published: April 2006

AbstractThe hydrologic impacts of various forestry operations are reviewed, notably the effects of thinning, selective harvesting, clear‐cutting with and without roads, and removal of understorey or riparian vegetation. Thinning and selective logging have a relatively modest effect on amounts of rainfall reaching the forest floor unless at least 70% of the standing biomass is removed. The effect on soil water and streamflow is smaller still, mostly because of the increased vigor of the remaining vegetation. Removing understorey vegetation produces a similarly small effect. The annual water yield is invariably increased in proportion to the amount of biomass harvested, with the exception of forests subject to high fog incidence or old‐growth forest of low vigor. Cutting riparian vegetation produces a larger increase in streamflow (compared to cuts away from the streams) under subhumid conditions and shallow water tables only. The largest seasonal increases in flow after clear‐cutting are normally observed at times when water deficits in the undisturbed forest are highest. The gains in streamflow after clear‐cutting gradually disappear when regrowth is allowed, the effect lasting longer where soils are deeper and forest regeneration slower. Mechanized harvesting practices and road building both increase stormflow volumes and peak discharges. The relative effect diminishes with storm size in the case of clear‐cutting only, but increases in the case of roads only. Similarly, effects of forest cutting per se on stormflows are “diluted” at larger scales, but the effect of the associated road network is not. Various measures are discussed to minimize the adverse hydrologic impacts of timber harvesting operations.
Landscape Element Contributions to Storm Runoff
Authors: Seibert Jan , McGlynn Brian 
Published: April 2006

AbstractHydrological conditions and the corresponding land area contributions to streamflow vary across the landscape. Landscapes are mosaics that can be described in varying levels of detail. This document describes the importance of different landscape elements for storm runoff generation. Since topography is often a first‐order control on hydrological processes, topographic indices can be used to describe the spatial variations of hydrological conditions. Another approach is the delineation of landscape elements. We suggest that riparian and hillslope areas are the two most basic landscape elements that need to be considered; however, additional landscape elements including urban areas, floodplains, croplands, wetlands, and so on, can also be important. Landscape elements can be defined through hydrological analysis. This analysis can further define their lateral connections and organization along the stream network, providing valuable interpretation of the dominant controls on hydrological response across the landscape. Additionally, approaches to represent landscape elements in hydrological modeling are reviewed.
Modeling Recession Curves and Low Streamflows
Authors: Kroll Charles 
Published: April 2006

Abstract
Low streamflow events are critical periods for water quantity and water quality management purposes. During most low streamflow events, the stream is comprised solely of groundwater sources. This section focuses on both theoretical and empirical methods for modeling groundwater discharge to a stream and the resulting streamflow recession. A review is provided of solutions to the Boussinesq equation for hillslope discharge, and methods for determining when specific solutions may be most appropriate. In addition, how to estimate baseflow recession constants that aid in the modeling of groundwater discharge to streams, has been discussed. This involves the presentation of numerous methods to parameterize baseflow recession characteristics, how best to represent error in these models, and experiments that have been performed to determine the most appropriate methodology.
Computer Modeling of Overbank Flows
Authors: Ervine Alan , Pender Gareth 
Published: April 2006

Abstract
Computational river models are in widespread use for estimating flood extent and the effectiveness of proposed flood mitigation schemes. This paper investigates the application of commonly used computational models to river floods, highlighting the advantages and shortcomings and current research activity. 1D, quasi‐2D, 2D, and 3D computational models are applied to simulate a large‐scale physical model tested in the Flood Channel Facility (FCF), Wallingford, as well as field data from the River Severn near Shrewsbury. The results reveal that commonly used 1D models give a reasonable representation of flood levels and flood extent but do not include floodplain/main channel interaction losses associated with compound flows and can be in error in their predictions. This deficit can be overcome in a straightforward manner by using a modified conveyance at each cross section based on the depth‐integrated turbulent form of the Navier–Stokes equation. This so‐called Lateral Distribution Method (LDM) has been incorporated into a new Conveyance Estimation System (CES) funded by the EA/Defra Joint Research Programme in Flood and Coastal Defence and developed by HR Wallingford Ltd for use with 1D models. Alternatively, 2D models can be more useful when simulation of flood inundation extent is important. The use of 3D models is becoming more common due to their ability to simulate very complex flow patterns over short river reaches. Initial results indicate that the choice of mesh discretization in a 3D model has a significant influence on the ability of the model to reproduce secondary velocity fields correctly. Problems of data requirements, friction and free surface representation still persist in 3D models in general.
Stochastic Modeling of Flow and Transport in Porous and Fractured Media
Authors: Ezzedine Souheil M 
Published: April 2006

Abstract
Estimation of various flow and mass transport parameters can be seen as a problem of spatial statistics. The definition of the properties of porous and fractured media in space and time using the concept of random functions provides means for (i) studying the inherent heterogeneity, (ii) evaluating the spatiotemporal variability of the properties, and (iii) assessing the uncertainty associated with their estimated values. In this chapter, the fundamentals of stochastic subsurface hydrology are presented. Applications include mapping hydrogeological properties, flow and transport in porous and fractured media, and inverse problems.
Unsaturated Zone Flow Processes
Authors: Nimmo John R 
Published: April 2006

Abstract
Water flow in the unsaturated zone is greatly influenced by unsaturated hydrostatics (water content, energy, pressure, and retention) and by unsaturated hydrodynamics (diffuse flow and preferential flow). Important multiphase processes include the transport of gases, nonaqueous liquids, and solid particles. Numerous means are available for determination of unsaturated conditions and properties, both measurement (of moisture state, water retention, and dynamic characteristics) and through various formulas and models that are mostly empirical in nature, but in some cases incorporating insight into unsaturated‐zone physical processes. Applications to practical problems include models and techniques relating to distributions of water and energy, fluxes at the land surface, inputs, outputs, and fluxes within the unsaturated zone, all of which are frequently complicated by heterogeneity and preferential flow. Further scientific advance requires new measurement techniques and theoretical constructs that more adequately represent the important physical processes within practical modeling schemes.
Modeling Glacier Hydrology
Authors: Hock Regine , Jansson Peter 
Published: April 2006

AbstractModeling glacier hydrology is essential for many aspects of glacier research and water resources planning. Model complexity has developed in parallel with our increasing understanding of the glacier system. Different models can be used depending on the purpose of the modeled results. Stochastic models constitute the first attempts to model glacier discharge. Use of such models has declined because they require extensive site‐specific calibrations and lack a conceptual basis, which makes them cumbersome to use. Conceptual models are the most widely used models for estimating discharge from glacierized basins. Commonly, the concept of linear reservoirs is applied to route melt and rain water through the glacier. Despite the wide variety of models of differing complexity, common to most conceptual models is that they omit many of the physical processes. Therefore attempts have been made to build physically based models that account for all processes in the glacier hydrological system. Because of the complexity of the modeled system and the wide variety of conditions on, in and under glaciers, the first models are relatively site‐specific. However, despite the inherent difficulties, they still yield good results. Physically based models will likely play an increasingly important role in glaciohydrological research while the conceptual models will continue to dominate the monitoring and forecasting modeling in applied hydrology because of their modest data requirements and ease of use.
Observations of the Global Water Cycle – Global Monitoring Networks
Authors: Lettenmaier Dennis P 
Published: April 2006

Abstract
Until the last few decades, in situ networks were the primary source of information for the estimation of the global water cycle. Such networks provide reasonably good climatological estimates of the major terms in the water cycle over the industrialized parts of the world, but are much less adequate in the lesser‐developed countries and in sparsely populated areas. Furthermore, in situ networks have been in the decline over the last several decades. An ongoing trend is toward greater reliance on satellite remote sensing. In some cases (e.g. soil moisture), satellite estimates have characteristics that cannot reasonably be matched by in situ networks. In others, it is less likely that the needs for global observations can be met from remote sensing. Furthermore, there will remain a need for high quality in situ data for algorithm testing and evaluation, and for evaluation of differences between historic in situ‐based, and satellite‐based, observations. The characteristics of in situ and satellite‐based estimates of the dominant fluxes and storages in the land surface and atmospheric branches of the global water cycle are reviewed.
Observations of the Global Water Cycle – Satellites
Authors: Robertson Franklin R 
Published: April 2006

AbstractSatellite observations of Earth's climate system have evolved dramatically since the first crude video images of cloud cover taken over 40 years ago. Today, spaceborne measurements of precipitation, cloud attributes, radiative fluxes, and surface properties make crucial contributions to monitoring key processes and the evolving state of the planet's hydrologic cycle. We illustrate how this maturing capability has enabled study of the hydrologic cycle in a global context that goes beyond consideration of local or regional water balance. Remote sensing has become a key technology for addressing such interdisciplinary questions as whether the global hydrologic cycle is changing and if so how? What key processes linking the atmosphere, biosphere, and hydrosphere are at play, and what are the prospects for predicting extreme hydrologic events of significant societal impact? The discussion is motivated first by considering these key science problems. Following a brief overview of key remote sensing concepts, we then survey existing capabilities to determine various quantities such as precipitation, evaporation, soil moisture, turbulent fluxes, cloud cover, water vapor, and the links to radiative fluxes. Both successes and persisting challenges are discussed. An assessment of where we stand in developing an integrated picture of the hydrologic cycle and climate is presented, along with anticipated improvements in the future measurements.In the context of climate, we demonstrate that in spite of substantial improvements in determining hydrologic variables and processes from space, some key challenges remain. Our examination here of signals in precipitation, evaporation, and radiative fluxes suggests that at present we can detect regional patterns of interannual variability with considerable skill; we can resolve globally integrated signals with only modest certainty; and for the most part, we have little confidence yet in decadal changes or trends. Nevertheless, the situation is encouraging because in many cases these retrievals have been done without regard to intercalibration of sensor data streams, and in the case of operational retrievals, algorithm modifications which result in spurious trends. Careful reprocessing is likely to yield substantial benefits. Future planned missions with active remote sensing at 94 GHz (CloudSat) and interferometric measurements at 1.4 GHz promise to expand our knowledge of hydrologic processes of crucial importance to climate.
Teleconnections in the Earth System
Authors: Chase Thomas N , Pielke Roger A , Avissar Roni 
Published: April 2006

AbstractThis article illustrates the large‐scale connectivity of the atmosphere–ocean coupled system and generalizes the concept to regional scales and to other components of the earth system. Connections at a distance, or teleconnections, can occur by the direct transfer of mass by changes in regular circulations or by propagating waves initiated by a variety of mechanisms. Questions as to what extent recognized teleconnection patterns can be associated with identifiable forcing mechanisms, to what extent these patterns are interrelated and how they might cause, react to, or interact with changing forcing such as changes in atmospheric composition, land cover, or the distribution of sea ice to produce climate changes are examined.
Public Participation in River Basin Planning and Management: Quality‐of‐Life Capital as an Information Aid to Sustainable Decisions
Authors: Newson Malcolm , Chalk Liz 
Published: April 2006

AbstractThe long‐term benefits conveyed by intact ecosystems to human development can be considered as an innate “natural” capital investment. A number of UK environmental management agencies have commissioned a practical realization of this concept, partly as a basis for public participation, successively titled “Environmental Capital” and “Quality of Life Capital”. Hydrological concepts are particularly appropriate to an evaluation of natural goods and services; intact natural systems provide flood and pollution controls which need costly artificial replacement when lost or damaged. There are obvious opportunities, therefore, to incorporate assessments of environmental capital as part of the public participation in river basin planning demanded by the European Water Framework Directive. This contribution examines the effectiveness of “Quality of Life Capital” as an information pool and decision‐support mechanism in two catchment‐scale initiatives (sponsored by the European Union), aimed at community involvement in integrated land and water management. Firstly the conceptual and practical justifications for considering river basins as “multistakeholder platforms” are reviewed, followed by a comparison of the two trial applications in the north of England – to the headwater catchments of the rivers Wharfe and Coquet. What emerges from the comparison and from evaluations of other integrated river basin and coastal zone projects is the importance of information (and its management), continuity and facilitation by project management and a lasting system of monitoring to support adaptive management. The spatial scale of most river basin units defined under the Water Framework Directive is possibly the biggest barrier to widespread adoption of the approach.
Observed Trends in Hydrologic Cycle Components
Authors: Lins Harry F 
Published: April 2006

Abstract
Documentation of change in the Earth's climate is accomplished by assessing the rates, magnitude, and distribution of changes in various elements of the climate system, such as the components of the hydrologic cycle. The present section reviews the general character of changes in precipitation, streamflow, and evaporation as determined using systematically collected data through the end of the twentieth century. Precipitation over global land areas increased about 2% during the century, and streamflow also exhibited widespread increases. There was good agreement regionally between the observed precipitation and streamflow increases. The precipitation increases appear to have occurred most commonly in higher intensity categories (>50 mm per day), while the streamflow increases were overwhelmingly observed in the low to moderate range of flows. No systematic increases were observed in peak streamflows. These findings indicate that a general intensification of the hydrologic cycle occurred during the twentieth century, but that this intensification did not result in increased hydrologic extremes.
Motor Unit
Authors: Enoka Roger M. 
Published: April 2006

Abstract
The activation signal sent by the nervous system to evoke a muscle contraction is discharged by motor neurons in the spinal cord and travels along a peripheral nerve to excite selected muscle fibers. On average, a muscle is innervated by a few hundred motor neurons and each motor neuron connects to several hundred muscle fibers. The functional control element is a single motor neuron and the muscle fibers it innervates, which is known as a motor unit, and all muscle contractions involve grading the amount of motor unit activity. The nervous system can vary muscle force by controlling the number of motor units that are activated and the rate at which each active motor unit discharges an activation signal. Despite considerable diversity in the properties of the both motor neurons and muscle fibers, the activation of a motor unit population proceeds in an orderly sequence from small to large and the discharge pattern of a motor neuron is matched to the mechanical properties of its muscle fibers.