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At least 397 records · Page 22Linked to original sources
USGS1996

Triggering mechanisms and depositional rates of postglacial slope-movement processes in the Yosemite Valley, California

We examined information collected from 395 reports of slope-movement events during about the past 150 years in Yosemite National Park, central Sierra Nevada, California, to identify the most prevalent types of slope movements and their triggering mechanisms. Rock slides and rock falls have been more numerous than debris slides, debris flows, and miscellaneous slumps. Rock falls have produced the largest cumulative volume of deposits. About half of slope movements had unreported or unrecognized triggering events. Earthquakes and rain storms individually accounted for the greatest cumulative volumes of deposits from recognized triggers of all types of historical slope movements; snowmelt, human activities and freeze-thaw conditions accounted for only a small proportion of the volumes from reported triggers. A comparison of the historical and postglacial average annual rates of deposition from slope-movement processes in a portion of the Yosemite Valley indicates that, during the period 1851-1992, slope-movement processes have been producing about half the average rate of deposits than during the past 15,000 years.

Geomorphology↗
USGS1992

Sampling design for spatially distributed hydrogeologic and environmental processes

A methodology for the design of sampling networks over space is proposed. The methodology is based on spatial random field representations of nonhomogeneous natural processes, and on optimal spatial estimation techniques. One of the most important results of random field theory for physical sciences is its rationalization of correlations in spatial variability of natural processes. This correlation is extremely important both for interpreting spatially distributed observations and for predictive performance. The extent of site sampling and the types of data to be collected will depend on the relationship of subsurface variability to predictive uncertainty. While hypothesis formulation and initial identification of spatial variability characteristics are based on scientific understanding (such as knowledge of the physics of the underlying phenomena, geological interpretations, intuition and experience), the support offered by field data is statistically modelled. This model is not limited by the geometric nature of sampling and covers a wide range in subsurface uncertainties. A factorization scheme of the sampling error variance is derived, which possesses certain atttactive properties allowing significant savings in computations. By means of this scheme, a practical sampling design procedure providing suitable indices of the sampling error variance is established. These indices can be used by way of multiobjective decision criteria to obtain the best sampling strategy. Neither the actual implementation of the in-situ sampling nor the solution of the large spatial estimation systems of equations are necessary. The required values of the accuracy parameters involved in the network design are derived using reference charts (readily available for various combinations of data configurations and spatial variability parameters) and certain simple yet accurate analytical formulas. Insight is gained by applying the proposed sampling procedure to realistic examples related to sampling problems in two dimensions.

Advances in Water Resources↗
USGS2020

Wildfire and landscape change

Wildfire is a worldwide phenomenon that is expected to increase in extent and severity in the future, due to fuel accumulations, shifting land management practices, and climate change. It immediately affects the landscape by removing vegetation, depositing ash, influencing water-repellent soil formation, and physically weathering boulders and bedrock. These changes typically lead to increased erosion through sheetwash, rilling, dry ravel, and increased mass movement in the form of floods, debris flow, rockfall, and landslides. These process changes bring about landform changes as hillslopes are lowered and stream channels aggrade or incise at increased rates. Furthermore, development of alluvial fans, debris fans, and talus cones are enhanced. The window of disturbance to the landscape caused by wildfire is typically on the order of 3–4 years, with some effects persisting up to 30 years.

Book chapter↗
USGS2004

Effects of phase-feeding dietary phosphorus on survival, growth, and processing characteristics of rainbow trout Oncorhynchus mykiss

A factorial experiment involving eight diets and three feeding periods was conducted to determine the minimal level of dietary phosphorus required to maintain survival, growth, and processing characteristics of post-juvenile rainbow trout. Trout were reared to an average size of 200, 300, or 400 g using a commercial feed (1.20% P), then allotted by triplicate groups of nine fish to one of seven experimental diets containing logarithmic increments of dietary phosphorus (0.15%%, 0.21%, 0.30%, 0.42%, 0.60%, 0.85%, and 1.20% P) or a commercial trout feed (1.20% P). At an average weight of 550 g, fish were transported to a commercial processing plant, mechanically filleted, and evaluated for quality. Fish survival and weight gain increased quadratically with increased dietary phosphorus for fish started on treatment at 200 and 300 g, but were similar among all fish started at 400 g. Phosphorus retention decreased with increasing dietary phosphorus level, from approximately 88% in groups fed diets containing 0.21% phosphorus to between 23% and 32% in groups fed diets containing 0.85% phosphorus. Calculated phosphorus losses increased as dietary phosphorus levels increased, from a low of approximately 0.4 g phosphorus kg-1 fish weight gain to between 9.5 and 13 g phosphorus kg-1 fish weight gain at the highest dietary phosphorus level. Dietary phosphorus did not affect carcass moisture, protein, lipid, or ash, but carcass phosphorus increased with increased dietary phosphorus among fish started on treatment at 200 and 300 g. There were no differences among any treatment group in carcass dressing or finishing percentage, or visual or textural appeal. The results indicate that available phosphorus levels can be reduced in rainbow trout diets to 0.60% at 200 g, to 0.30% at 300 g, or to 0.15% at 400 g live weight without loss in production or product quality in fish harvested at 550 g. Using these phase-feeding strategies would reduce the amount of phosphorus fed to the fish over the production cycle by 25%, and the amount lost to the environment by 12.5% for fish starting at 300 or 400 g. ?? 2004 Elsevier B.V. All rights reserved.

Aquaculture↗
USGS2010

Ecological hierarchies and self-organisation - Pattern analysis, modelling and process integration across scales

A continuing discussion in applied and theoretical ecology focuses on the relationship of different organisational levels and on how ecological systems interact across scales. We address principal approaches to cope with complex across-level issues in ecology by applying elements of hierarchy theory and the theory of complex adaptive systems. A top-down approach, often characterised by the use of statistical techniques, can be applied to analyse large-scale dynamics and identify constraints exerted on lower levels. Current developments are illustrated with examples from the analysis of within-community spatial patterns and large-scale vegetation patterns. A bottom-up approach allows one to elucidate how interactions of individuals shape dynamics at higher levels in a self-organisation process; e.g., population development and community composition. This may be facilitated by various modelling tools, which provide the distinction between focal levels and resulting properties. For instance, resilience in grassland communities has been analysed with a cellular automaton approach, and the driving forces in rodent population oscillations have been identified with an agent-based model. Both modelling tools illustrate the principles of analysing higher level processes by representing the interactions of basic components.The focus of most ecological investigations on either top-down or bottom-up approaches may not be appropriate, if strong cross-scale relationships predominate. Here, we propose an 'across-scale-approach', closely interweaving the inherent potentials of both approaches. This combination of analytical and synthesising approaches will enable ecologists to establish a more coherent access to cross-level interactions in ecological systems. ?? 2010 Gesellschaft f??r ??kologie.

Basic and Applied Ecology↗
USGS2022

Coupling process-based and empirical models to assess management options to meet conservation goals

Conservation lands face a mounting threat of ecosystem transformation and the loss of biodiversity from the invasion of fire-prone perennial and annual grasses. Managers must make difficult decisions to find efficient ways to expend limited resources to manage large and complex landscapes amidst substantial uncertainty regarding effective treatment strategies, climates, and invader-induced novel processes. We developed a state-and-transition simulation model coupled with a fire behavior model to study impacts to native biodiversity and fire regimes in a national park invaded by a perennial grass. We evaluated resources required to meet management objectives, and how to spatially allocate available resources efficiently and effectively. Management strategies and ecological scenarios strongly influenced the ability to minimize potential impacts; the inclusion of a new management strategy, aerial precision spot spraying targeting low cover levels in remote regions, was needed to supplement current treatments that can only target large, dense patches. Adding this new treatment method may be enough to conserve the desert ecosystem from small scale transformation through invasive competition and from broad functional transformations through invasive-induced fire regime changes. Spot spraying may also be highly beneficial if wetter monsoonal conditions create faster growth rates, decreasing the ability to contain the invasion even with unlimited management resources. Given current annual budgets for control, and the new treatment option, invasion control and preservation of native biodiversity may be possible regardless of spatial prioritization. Coupled empirical and process-based models efficiently simulated the effects of management activities, quantifying potential management costs and ecological impacts, while considering a wide range of possible future uncertainties associated with climate, spread rates, and wildfires lacking historical precedent. These techniques could be applied to other situations to evaluate the feasibility of conservation goals and to determine actions that would be most efficient and effective in meeting those goals.

Arizona↗
USGS2020

Acoustic Sediment Estimation Toolbox (ASET): A software package for calibrating and processing TRDI ADCP data to compute suspended-sediment transport in sandy rivers

Quantifying suspended-sediment transport is critical for a variety of disciplines related to the management of water resources. However, the number of gauging stations and monitoring networks in most rivers around the world is insufficient to improve understanding of river dynamics and support water resource management decisions. This is mainly due to the high operational costs and intensive labor involved in traditional sediment measurement techniques, especially in sand bed rivers where coarse material varies spatially in the river cross section. Recently, the acoustic surrogate method has received attention as a potentially accurate surrogate technology for estimating suspended-sediment concentrations. In addition, the acoustic surrogate method, through use of acoustic Doppler current profilers (ADCPs), has the advantage of being able to simultaneously measure the flow velocity field and cross-sectional area when moving-boat measurements are performed. In spite of the important advances made in the implementation of this technique, there are no widely-available, free tools for processing the ADCP acoustic signal cross section measurements which include options to extrapolate velocity and sediment in unmeasured ADCP zones and develop calibrations with physical samples. This paper presents a new software called Acoustic Sediment Estimation Toolbox (ASET), which enables the user to develop a calibration between the acoustic signal collected with a down-looking Teledyne RD Instruments ADCP and sediment concentrations determined using traditional sediment sampling techniques. Moreover, ASET software uses dynamic ADCP measurements to estimate the total suspended-sediment transport through a river cross section. The theoretical framework and data processing routines applied by each module in ASET are presented. Finally, a comparison is made between the results obtained by ASET and by traditional methodologies for computing suspended-sediment transport in a large river system (Paraná River, Argentina).

Computers & Geosciences↗
USGS2011

Prediction and assimilation of surf-zone processes using a Bayesian network: Part I: Forward models

Prediction of coastal processes, including waves, currents, and sediment transport, can be obtained from a variety of detailed geophysical-process models with many simulations showing significant skill. This capability supports a wide range of research and applied efforts that can benefit from accurate numerical predictions. However, the predictions are only as accurate as the data used to drive the models and, given the large temporal and spatial variability of the surf zone, inaccuracies in data are unavoidable such that useful predictions require corresponding estimates of uncertainty. We demonstrate how a Bayesian-network model can be used to provide accurate predictions of wave-height evolution in the surf zone given very sparse and/or inaccurate boundary-condition data. The approach is based on a formal treatment of a data-assimilation problem that takes advantage of significant reduction of the dimensionality of the model system. We demonstrate that predictions of a detailed geophysical model of the wave evolution are reproduced accurately using a Bayesian approach. In this surf-zone application, forward prediction skill was 83%, and uncertainties in the model inputs were accurately transferred to uncertainty in output variables. We also demonstrate that if modeling uncertainties were not conveyed to the Bayesian network (i.e., perfect data or model were assumed), then overly optimistic prediction uncertainties were computed. More consistent predictions and uncertainties were obtained by including model-parameter errors as a source of input uncertainty. Improved predictions (skill of 90%) were achieved because the Bayesian network simultaneously estimated optimal parameters while predicting wave heights.

Coastal Engineering↗
USGS2013

Current research issues related to post-wildfire runoff and erosion processes

Research into post-wildfire effects began in the United States more than 70 years ago and only later extended to other parts of the world. Post-wildfire responses are typically transient, episodic, variable in space and time, dependent on thresholds, and involve multiple processes measured by different methods. These characteristics tend to hinder research progress, but the large empirical knowledge base amassed in different regions of the world suggests that it should now be possible to synthesize the data and make a substantial improvement in the understanding of post-wildfire runoff and erosion response. Thus, it is important to identify and prioritize the research issues related to post-wildfire runoff and erosion. Priority research issues are the need to: (1) organize and synthesize similarities and differences in post-wildfire responses between different fire-prone regions of the world in order to determine common patterns and generalities that can explain cause and effect relations; (2) identify and quantify functional relations between metrics of fire effects and soil hydraulic properties that will better represent the dynamic and transient conditions after a wildfire; (3) determine the interaction between burned landscapes and temporally and spatially variable meso-scale precipitation, which is often the primary driver of post-wildfire runoff and erosion responses; (4) determine functional relations between precipitation, basin morphology, runoff connectivity, contributing area, surface roughness, depression storage, and soil characteristics required to predict the timing, magnitudes, and duration of floods and debris flows from ungaged burned basins; and (5) develop standard measurement methods that will ensure the collection of uniform and comparable runoff and erosion data. Resolution of these issues will help to improve conceptual and computer models of post-wildfire runoff and erosion processes.

Earth-Science Reviews↗
USGS2026

Watershed Continuum Monitoring Approach: Combining multiple water quality patterns along stream and river flowpaths to track sources, pathways, and processing of pollutants

There is a growing need to improve and expand water quality monitoring approaches to more accurately track the sources, fate, and transport of multiple chemicals and pollutants holistically and quantify the effects of best management practices (BMPs) at the watershed scale. An overarching question raised by scientists, environmental managers, and the general public is: how far can water quality impacts from disturbances or benefits from watershed management and restoration propagate along stream and river flowpaths? Many studies using the classic watershed approach focus on analyzing changes in water quality over time at one or a few sampling stations, whereas theories such as the River Continuum Concept focus on predicting shifts in energy sources and biological communities along rivers but have not been directly applied to water quality. We propose to merge these concepts to create a Watershed Continuum Monitoring Approach (WCMA) that combines both spatial and temporal monitoring in order to better detect and quantify trends and transitions in multiple water quality indicators along flowpaths. Specifically, an array of multiple water quality indicators are analyzed at multiple downstream points along a watershed flowpath over time. These multiple water quality indicators are analyzed together for making comparisons to infer hydrological, biological, and geochemical processes controlling sources, transport, and attenuation of pollutants ( e.g. , analagous to stream tracer studies at the watershed scale). The WCMA leverages the natural expansion of watershed areas along a flowpath, which reflect transitions in land use, land cover, and environmental management across spatial and temporal dimensions for making direct comparisons across different stream reaches and spatial trend analysis. WCMA facilitates monitoring of multiple water quality indicators together, and identifcation of hot spots in sources and attenuation of pollutants or mixtures of pollutants. We illustrate practical applications of the WCMA to analyze water quality trends, transitions, and tradeoffs ( i.e. , a tradeoff occurs when one pollutant is reduced but another is directly or indirectly increased downstream). We explore case studies that quantify: (1) downstream reductions in concentrations of multiple pollutants along a stream flowing to a major drinking water source due to engineered and nature-based solutions, (2) downstream reductions in multiple pollutants and water quality tradeoffs along streams experiencing stormwater BMPs and stream restoration, (3) comparisons in downstream reductions of multiple pollutants and nutrient uptake along streams draining into major drinking water sources based on types of stream restoration, (4) comparisons of downstream pollutant reductions along streams experiencing riparian forest conservation vs. stream restoration, and (5) mapping and visualizing hot spots of increasing water quality problems such as hypoxia, contaminant mobilization, and freshwater salinization that extend downstream to tidal rivers of the Chesapeake Bay. We explore future applications of WCMA for tracking decreasing trends in salinity, E. coli , and other pollutants of emerging concern. WCMA can holistically inform progress towards achieving multiple water quality goals and also be used as a screening tool for selecting monitoring sites and targeting management in strategic locations. Overall, WCMA enables the simultaneous quantification and comparison of sources and transport and attenuation rates for different chemicals and pollutants across a broader range of watershed sizes and flowpath lengths, which is critical for understanding ecological, hydrological, geochemical, and biogeochemical processes along human-impacted streams and rivers.

Ecological Engineering↗
USGS2014

Comparing cropland net primary production estimates from inventory, a satellite-based model, and a process-based model in the Midwest of the United States

Accurately quantifying the spatial and temporal variability of net primary production (NPP) for croplands is essential to understand regional cropland carbon dynamics. We compared three NPP estimates for croplands in the Midwestern United States: inventory-based estimates using crop yield data from the U.S. Department of Agriculture (USDA) National Agricultural Statistics Service (NASS); estimates from the satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) NPP product; and estimates from the General Ensemble biogeochemical Modeling System (GEMS) process-based model. The three methods estimated mean NPP in the range of 469–687 g C m −2 yr −1 and total NPP in the range of 318–490 Tg C yr −1 for croplands in the Midwest in 2007 and 2008. The NPP estimates from crop yield data and the GEMS model showed the mean NPP for croplands was over 650 g C m −2 yr −1 while the MODIS NPP product estimated the mean NPP was less than 500 g C m −2 yr −1 . MODIS NPP also showed very different spatial variability of the cropland NPP from the other two methods. We found these differences were mainly caused by the difference in the land cover data and the crop specific information used in the methods. Our study demonstrated that the detailed mapping of the temporal and spatial change of crop species is critical for estimating the spatial and temporal variability of cropland NPP. We suggest that high resolution land cover data with species–specific crop information should be used in satellite-based and process-based models to improve carbon estimates for croplands.

Illinois, Indiana, Iowa, Kansas, Michigan, Minneso↗
USGS2004

Bioturbation depths, rates and processes in Massachusetts Bay sediments inferred from modeling of 210Pb and 239 + 240Pu profiles

Profiles of 210 Pb and 239 + <240 Pu from sediment cores collected throughout Massachusetts Bay (water depths of 36-192 m) are interpreted with the aid of a numerical sediment-mixing model to infer bioturbation depths, rates and processes. The nuclide data suggest extensive bioturbation to depths of 25-35 cm. Roughly half the cores have 210 Pb and 239 + 240 Pu profiles that decrease monotonically from the surface and are consistent with biodiffusive mixing. Bioturbation rates are reasonably well constrained by these profiles and vary from ~0.7 to ~40 cm 2 yr -1 . As a result of this extensive reworking, however, sediment ages cannot be accurately determined from these radionuclides and only upper limits on sedimentation rates (of ~0.3 cm yr -1 ) can be inferred. The other half of the radionuclide profiles are characterized by subsurface maxima in each nuclide, which cannot be reproduced by biodiffusive mixing models. A numerical model is used to demonstrate that mixing caused by organisms that feed at the sediment surface and defecate below the surface can cause the subsurface maxima, as suggested by previous work. The deep penetration depths of excess 210 Pb and 239 + 240 Pu suggest either that the organisms release material over a range of >15 cm depth or that biodiffusive mixing mediated by other organisms is occurring at depth. Additional constraints from surficial sediment 234 Th data suggest that in this half of the cores, the vast majority of the present-day flux of recent, nuclide-bearing material to these core sites is transported over a timescale of a month or more to a depth of a few centimeters below the sediment surface. As a consequence of the complex mixing processes, surface sediments include material spanning a range of ages and will not accurately record recent changes in contaminant deposition.

Massachusetts↗
USGS2020

Small mammals and ungulates respond to and interact with revegetation processes following dam removal

Terrestrial wildlife communities are often overlooked as components of ecosystem restoration following dam removal. However, a diverse mammalian fauna colonizes habitat on dewatered reservoirs and may influence restoration processes. We studied mammalian colonization and ungulate herbivory from 2014 to 2018 following the removal of two large dams on the Elwha River in Washington, USA. Specifically, we examined (1) small mammal colonization and (2) Roosevelt elk ( Cervus elaphus roosevelti ) and Columbian black-tailed deer ( Odocoileus hemionus columbianus ) distribution and browsing pressure in association with revegetation efforts. We live-trapped small mammals on two former reservoir beds and monitored deer and elk use by conducting pellet group counts and quantifying ungulate herbivory at plots throughout the former reservoir beds and an adjacent reference site. We found that the proportion of deciduous riparian species on plots best predicted occupancy for mice, shrews, and voles. Small mammal species diversity was best explained by the proportion of logs and conifers on study plots. Roosevelt elk presence and browsing intensity on willows ( Salix spp.) and black cottonwood ( Populus balsamifera ssp. trichocarpa ) varied both spatially and temporally, affecting the stature and potentially the growth trajectories of these species. Early seral restoration of these terrestrial habitats has included the presence of a diversity of granivores, insectivores, and herbivores, with elk demonstrating the strongest influence over portions of the study area. Small mammal colonization complements revegetation succession and demonstrates restoration of ecological processes, while large ungulates may be playing a more substantial role in shaping revegetation.

Washington↗
USGS2017

The waterfall paradox: How knickpoints disconnect hillslope and channel processes, isolating salmonid populations in ideal habitats

Waterfalls create barriers to fish migration, yet hundreds of isolated salmonid populations exist above barriers and have persisted for thousands of years in steep mountainous terrain. Ecological theory indicates that small isolated populations in disturbance-prone landscapes are at greatest risk of extirpation because immigration and recolonization are not possible. On the contrary, many above-barrier populations are currently thriving while their downstream counterparts are dwindling. This quandary led us to explore geomorphic knickpoints as a mechanism for disconnecting hillslope and channel processes by limiting channel incision and decreasing the pace of base-level lowering. Using LiDAR from the Oregon Coast Range, we found gentler channel gradients, wider valleys, lower gradient hillslopes, and less shallow landslide potential in an above-barrier catchment compared to a neighboring catchment devoid of persistent knickpoints. Based on this unique geomorphic template, above-barrier channel networks are less prone to debris flows and other episodic sediment fluxes. These above-barrier catchments also have greater resiliency to flooding, owing to wider valleys with greater floodplain connectivity. Habitat preference models further indicate that salmonid habitat is present in greater quantity and quality in these above-barrier networks. Therefore the paradox of the persistence of small isolated fish populations may be facilitated by a geomorphic mechanism that both limits their connectivity to larger fish populations yet dampens the effect of disturbance by decreasing connections between hillslope and channel processes above geomorphic knickpoints.

Geomorphology↗
USGS2018

Post-wildfire landscape change and erosional processes from repeat terrestrial lidar in a steep headwater catchment, Chiricahua Mountains, Arizona, USA

Flooding and erosion after wildfires present increasing hazard as climate warms, semi-arid lands become drier, population increases, and the urban interface encroaches farther into wildlands. We quantify post-wildfire erosion in a steep, initially unchannelized, 7.5 ha headwater catchment following the 2011 Horseshoe 2 Fire in the Chiricahua Mountains of southeastern Arizona. Using time-lapse cameras, rain gauges, and repeat surveys by terrestrial laser scanner, we quantify the response of a burned landscape to subsequent precipitation events. Repeat surveys provide detailed pre-and post-rainfall measurements of landscape form associated with a range of weather events. The first post-fire precipitation led to sediment delivery equivalent to 0.017 m of erosion from hillslopes and 0.12 m of erosion from colluvial hollows. Volumetrically, 69% of sediment yield was generated from hillslope erosion and 31% was generated from gully channel establishment in colluvial hollows. Processes on hillslopes included erosion by extensive shallow overland flow, formation of rills and gullies, and generation of sediment-laden flows and possibly debris flows. Subsequent smaller rain events caused ongoing hillslope erosion and local deposition and erosion in gullies. Winter freeze-thaw led to soil expansion, likely related to frost-heaving, causing a net centimeter-scale elevation increase across soil-mantled slopes. By characterizing landscape form, the properties of near-surface materials, and measuring both precipitation and landscape change, we can improve our empirical understanding of landscape response to environmental forcing. This detailed approach to studying landscape response to wildfires may be useful in the improvement of predictive models of flood, debris flow and sedimentation hazards used in post-wildfire response assessments and land management, and may help improve process-based models of landscape evolution.

Arizona↗
USGS2012

Effects of future climate change, CO 2 enrichment, and vegetation structure variation on hydrological processes in China

Investigating the relationship between factors (climate change, atmospheric CO 2 concentrations enrichment, and vegetation structure) and hydrological processes is important for understanding and predicting the interaction between the hydrosphere and biosphere. The Integrated Biosphere Simulator (IBIS) was used to evaluate the effects of climate change, rising CO 2 , and vegetation structure on hydrological processes in China at the end of the 21st century. Seven simulations were implemented using the assemblage of the IPCC climate and CO 2 concentration scenarios, SRES A2 and SRES B1. Analysis results suggest that (1) climate change will have increasing effects on runoff, evapotranspiration (ET), transpiration (T), and transpiration ratio (transpiration/evapotranspiration, T/E) in most hydrological regions of China except in the southernmost regions; (2) elevated CO 2 concentrations will have increasing effects on runoff at the national scale, but at the hydrological region scale, the physiology effects induced by elevated CO 2 concentration will depend on the vegetation types, climate conditions, and geographical background information with noticeable decreasing effects shown in the arid Inland region of China; (3) leaf area index (LAI) compensation effect and stomatal closure effect are the dominant factors on runoff in the arid Inland region and southern moist hydrological regions, respectively; (4) the magnitudes of climate change (especially the changing precipitation pattern) effects on the water cycle are much larger than those of the elevated CO 2 concentration effects; however, increasing CO 2 concentration will be one of the most important modifiers to the water cycle; (5) the water resource condition will be improved in northern China but depressed in southernmost China under the IPCC climate change scenarios, SRES A2 and SRES B1.

Global and Planetary Change↗
USGS2008

Fluvial erosion and post-erosional processes on Titan

The surface of Titan has been revealed by Cassini observations in the infrared and radar wavelength ranges as well as locally by the Huygens lander instruments. Sand seas, recently discovered lakes, distinct landscapes and dendritic erosion patterns indicate dynamic surface processes. This study focus on erosional and depositional features that can be used to constrain the amount of liquids involved in the erosional process as well as on the compositional characteristics of depositional areas. Fluvial erosion channels on Titan as identified at the Huygens landing site and in RADAR and Visible and Infrared Mapping Spectrometer (VIMS) observations have been compared to analogous channel widths on Earth yielding average discharges of up to 1600 m3/s for short recurrence intervals that are sufficient to move centimeter-sized sediment and significantly higher discharges for long intervals. With respect to the associated drainage areas, this roughly translates to 1-150 cm/day runoff production rates with 10 years recurrence intervals and by assuming precipitation this implies 0.6-60 mm/h rainfall rates. Thus the observed surface erosion fits with the methane convective storm models as well as with the rates needed to transport sediment. During Cassini's T20 fly-by, the VIMS observed an extremely eroded area at 30?? W, 7?? S with resolutions of up to 500 m/pixel that extends over thousands of square kilometers. The spectral characteristics of this area change systematically, reflecting continuous compositional and/or particle size variations indicative of transported sediment settling out while flow capacities cease. To account for the estimated runoff production and widespread alluvial deposits of fine-grained material, release of area-dependent large fluid volumes are required. Only frequent storms with heavy rainfall or cryovolcanic induced melting can explain these erosional features. ?? 2008 Elsevier Inc.

Icarus↗
USGS2019

Europa’s ice tectonics: New insights from physical wax experiments with implications for subduction initiation and global resurfacing processes

Jupiter's Moon Europa has one of the youngest geological surfaces in our solar system with an age of 40–90 Ma, implying an intense history of resurfacing. The surface of Europa indeed shows abundant evidence of tectonic deformation related to extension, strike-slip, and shortening. However, observed features related to shortening are scarce compared with pervasive extensive extensional features such as dilational bands, and do not suffice as the sole mechanism for recycling aging terranes. Recently, evidence for potential plate tectonics, associated with subduction zones , has been discovered on Europa; this could be responsible for recycling most of Europa's surface. However, basic physical parameters needed to initiate subduction on Europa, such as thickness of the brittle layer, deformation rates, and orientation of pre-existing zones of weakness at which subduction could start, are not well understood. Here, we aim to better understand the process and the conditions that could lead to initiation of subduction on Europa through physical experiments, using wax to simulate Europa's two-layered (i.e. convective) icy crust. By deforming the wax, strain on Europa's surface—possibly caused by diurnal tides or its nonsynchronous rotation—is simulated. Our results indicate that subduction could initiate over a broad range of surface thicknesses and deformation rates above a minimum conductive layer thickness, but is strongly dependent on the orientation of the pre-existing zones of weakness. Very thin conductive layer experiments, however, result in a previously undescribed process that we term ductile rolldown, which creates surface features similar to double ridges observed on Europa. Thus, subduction and ductile rolldown represent physically plausible mechanisms that could play a critical role in resurfacing Europa throughout its geologic history. These results could yield significant implications for Europa's thermal history and evolution, habitability, and future spacecraft missions.

Icarus↗