Estimating the Effects of Map Error on Habitat Delineation for the California Spotted Owl in Southern California     

Ellen M. Hines  Janet Franklin  John R. Stephenson 《Transactions in GIS》2005,9(4):541-559

The reliability of habitat maps that have been generated using Geographic Information Systems (GIS) and image processing of remotely sensed data can be overestimated. Habitat suitability and spatially explicit population viability models are often based on these products without explicit knowledge of the effects of these mapping errors on model results. While research has considered errors in population modeling assumptions, there is no standardized method for measuring the effects of inaccuracies resulting from errors in landscape classification. Using landscape‐scale maps of existing vegetation developed for the USDA Forest Service in southern California from Landsat Thematic Mapper satellite data and GIS modeling, we performed a sensitivity analysis to estimate how mapping errors in vegetation type, forest canopy cover, and tree crown size might affect delineation of suitable habitat for the California spotted owl (Strix occidentalis occidentalis). The resulting simulated uncertainty maps showed an increase in the estimated area of suitable habitat types. Further analysis measuring the fragmentation of the additional patches showed that they were too small to be useful as habitat areas.  相似文献   

Solar activity levels in 2100     

Mark A Clilverd  Ellen Clarke  Henry Rishbeth  Toby D G Clark  Thomas Ulich 《Astronomy& Geophysics》2003,44(5):5.20-5.22

Mark A Clilverd, Ellen Clarke, Henry Rishbeth, Toby D G Clark and Thomas Ulich look forward to a little less solar activity in 2100, using direct and proxy records of past solar and geomagnetic activity.  相似文献   

Flow hydraulics and geomorphic effects of glacial‐lake outburst floods in the Mount Everest region,Nepal     

Daniel A. Cenderelli  Ellen E. Wohl 《地球表面变化过程与地形》2003,28(4):385-407

Glacial‐lake outburst floods (GLOFs) on 3 September 1977 and 4 August 1985 dramatically modified channels and valleys in the Mount Everest region of Nepal by eroding, transporting, and depositing large quantities of sediment for tens of kilometres along the flood routes. The GLOF discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff, glacier meltwater, and monsoonal precipitation (referred to as seasonal high flow floods, SHFFs). Specific stream power values ranged from as low as 1900 W m^?2 in wide, low‐gradient valley segments to as high as 51 700 W m^?2 in narrow, high‐gradient valley segments bounded by bedrock. Along the upper 16 km of the GLOF routes, the reach‐averaged specific stream power of the GLOFs was 3·2 to 8·0 times greater than the reach‐averaged specific stream power of the SHFFs. The greatest geomorphic change occurred along the upper 10 to 16 km of the GLOF routes, where the ratio between the GLOF specific stream power and the SHFF specific stream power was the greatest, there was an abundant supply of sediment, and channel/valley boundaries consisted primarily of unconsolidated sediment. Below 11 to 16 km from the source area, the geomorphic effects of the GLOFs were reduced because of the lower specific stream power ratio between the GLOFs and SHFFs, more resistant bedrock flow boundaries, reduced sediment supply, and the occurrence of past GLOFs. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Predicting fine sediment dynamics along a pool-riffle mountain channel   总被引：1，自引：0，他引：1  

Sara Rathburn  Ellen Wohl   《Geomorphology》2003,55(1-4):111

Fine sediment dynamics in mountain rivers are of concern because of implications for aquatic habitat, channel stability, and downstream sediment yields. Many mountain river systems have episodic fine sediment transport because of infrequent, point-source sediment inputs from landslides; basin instability triggered by land uses such as logging; or infrequent mobilization of the coarse surface layer in channels. Dam removal, which is now more likely along mountain rivers, may also provide a substantial fine sediment input to downstream channel reaches.Fine sediment storage in the interstices of spawning gravels and within pools along mountain rivers is of particular interest because of impacts to aquatic organisms. In this study we focus on sediment dynamics within pools of the North Fork Poudre River in Colorado as an example of the processes controlling fine sediment deposition, storage, and transport within laterally constricted pools. The 1996 release of 7000 m³ of silt-to gravel-sized sediment from a reservoir on the North Fork provided an opportunity to develop a field data set of fine sediment dynamics and to test the predictions of three different one- or two-dimensional sediment transport and hydraulic models against the field observations.The models were calibrated against quantitative measurements of pool scour and fill. One-dimensional HEC-6 results indicate that robust simulations yield the greatest agreement between predicted and measured pool bed elevation change. Model calibration on two pools and validation on one pool indicate that at least 58% of observed bed changes after the sediment release were predicted by HEC-6. Modeling accuracy using quasi-two-dimensional GSTARS 2.0 was considerably more variable, and no pool-wide trends were obtained. The two-dimensional model RMA2 substantially improved the representation of eddy pool hydraulics within a compound pool of the North Fork. Results from the hydraulic modeling, coupled with bed load and total load computations, delineate areas of scour and deposition which are consistent with observations in the field.A conceptual model of sediment delivery and storage for laterally confined pools suggests that persistent deposition of fine sediment within eddies distal from the sediment source may result from sediment releases. The original loss of channel capacity facilitated additional deposition within eddies as sediment within upstream proximal pools became mobilized. At high discharges, the development of a strong shear zone prevents degradation of sediment deposits within the eddy. Central portions of these proximal pools may clear according to existing models, whereas deposition within recirculating zones may be long-term. Water managers could use these models to estimate minimum pool volume for overwinter habitat and residence time of pool sediment.  相似文献   

Introduction to the themed issue: Wildfire and Geomorphic Systems          下载免费PDF全文

Ellen Wohl 《地球表面变化过程与地形》2018,43(7):1542-1546

Wildfires alter fluxes of water, sediment, solutes, and organic matter in ways that can be transient or persistent. Alterations in material flux then impact geomorphic processes and landforms in a manner that can also be transient or persistent and that can involve complex response. This themed issue includes papers that document distinctive geomorphic responses in the upland and channel components of forested landscapes in southern Europe, northern Australia, and the western United States. Among the themes that emerge from the collected papers are: (i) the importance of ongoing technological developments, including real‐time instrumentation, ground‐based and aerial remote sensing, isotopic ratios, and numerical models of landscape processes, for documenting and predicting fire‐related geomorphic processes; and (ii) the great uncertainties about future landscape change in a global environment of rapidly changing climate and growing human populations that encroach onto remaining wildlands in fire‐susceptible regions. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Historical land use as a driver of alternative states for stream form and function in forested mountain watersheds of the Southern Rocky Mountains          下载免费PDF全文

Bridget Livers  Ellen Wohl  Karen J. Jackson  Nicholas A. Sutfin 《地球表面变化过程与地形》2018,43(3):669-684

We demonstrate how land use can drive mountain streams in the Southern Rockies across a threshold to induce an alternative state of significantly reduced physical complexity of form and reduced ecological function. We evaluate field data from 28 stream reaches in relatively laterally unconfined valleys and unmanaged forest that is either old‐growth forest or naturally disturbed younger forest, and 19 stream reaches in managed forest with past land use. We evaluate potential differences in stream form, as reflected in channel planform, cross‐sectional geometry, and in‐stream wood loads, and stream function, as reflected in pool volume and storage of organic carbon. Field data indicate a threshold of differences in stream form and function between unmanaged and managed stream reaches, regardless of forest stand age, supporting our hypothesis that the legacy effects of past land use result in an alternative state of streams. Because physical complexity that increases stream retentiveness and habitat can maintain aquatic‐riparian ecosystem functions, the alternative physical state of streams in managed watersheds creates a physical template for an alternative ecological state with reduced pool volume, organic carbon storage, and ecosystem productivity. We recommend maintaining riparian forests that can supply large wood to streams as a stream restoration technique in historically forested stream segments. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

How does anisotropy in bedrock river granitic outcrops influence pothole genesis and development?          下载免费PDF全文

Jose Ortega‐Becerril  Miguel Gomez‐Heras  Rafael Fort  Ellen Wohl 《地球表面变化过程与地形》2017,42(6):956-968

Pothole formation and development may be influenced by joint sets and other heterogeneities within bedrock, as well as by hydraulics. Previous research indicates that most potholes found in rivers of the mountainous Spanish Central System exhibit preferred orientations associated with dominant joints and correlate more strongly with variations in substrate resistance than with hydraulics. Weathering and erosion weaken rock surfaces, which leads to decreased mechanical resistance. We start from the hypothesis that different mechanisms of pothole formation may create around the pothole a distinctive signature in terms of ultrasound pulse velocity and surface hardness. We develop a conceptual model and test it using potholes for which we know the mechanism of formation, demonstrating that the spatial and statistical distributions of dynamical mechanical properties and surface hardness of a pothole may provide insight into its genesis. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Effective flood risk visualisation     

Percival  Sarah Ellen  Gaterell  Mark  Hutchinson  David 《Natural Hazards》2020,104(1):375-396

Natural Hazards - The effective communication of flood risk offers the opportunity to ensure communities can adapt and respond appropriately to changing local conditions. At a time of diminishing...  相似文献   

Trends of grain sizes on gravel bars in the Rio Chagres, Panama     

Francis Rengers  Ellen Wohl 《Geomorphology》2007,83(3-4):282-293

We examined the trends of grain sizes along the upper 414 km² of the mountainous Rio Chagres drainage basin in Panama. Gravel bars were sampled along 40 km of the Rio Chagres and five major tributary streams using a transect pebble count of median diameter, lithology, and clast rounding. Although previous investigators have found that downstream fining can be obscured by inputs of colluvial sediment and other local controls in mountain drainages, we decided to examine the trends of grain sizes along a tropical mountain river where rapid weathering and high capability of transport might be capable of overriding the input effects of colluvium. Specifically, we tested the hypotheses that downstream fining would be present as a result of selective sorting, and that weak felsic particles would decrease in size preferentially to strong mafic particles because of abrasion. Statistical analyses reveal a weak downstream decrease of sediment size on gravel bars along the study reach of the Rio Chagres, with a Sternberg diminution coefficient (α) for felsic and mafic grains of − 0.013 and − 0.017, respectively. Felsic clasts have thicker weathering rinds and become rounded downstream faster than mafic particles, but tumbling-mill tests of abrasion show no significant differences in rate of mass loss in relation to lithology, and downstream decreases in grain size are similar between lithologies. Dividing the study reach into six sub-reaches bounded by major tributary junctions, we further tested the hypothesis that downstream trends in fining might be obscured at the basin scale by sediment input from tributaries, but that trends in grain sizes might be more visible at the reach scale between tributaries. We did not find any consistent trends in grain size between tributaries. Stream width appears to assert a local control on grain size; coarse particles are associated with narrow channel reaches, whereas smaller particles are associated with wide channel reaches.  相似文献   

Groundwater chemistry of Al under Dutch sandy soils: Effects of land use and depth     

Ellen P.M.J. Fest  Erwin J.M. Temminghoff  Jasper Griffioen  Bas Van Der Grift  Willem H. Van Riemsdijk 《Applied Geochemistry》2007

Aluminium has received great attention in the second half of the 20th century, mainly in the context of the acid rain problem mostly in forest soils. In this research the effect of land use and depth of the groundwater on Al, pH and DOC concentration in groundwater under Dutch sandy soils has been studied. Both pH and DOC concentration play a major role in the speciation of Al in solution. Furthermore, the equilibrium with mineral phases like gibbsite, amorphous Al(OH)₃ and imogolite, has been considered. Agricultural and natural land use were expected to have different effects on the pH and DOC concentration, which in turn could influence the total Al concentration and the speciation of Al in groundwater at different depths (phreatic, shallow and deep). An extensive dataset (n = 2181) from the national and some provincial monitoring networks on soil and groundwater quality was used. Land use type and groundwater depth did influence the pH, and Al and DOC concentrations in groundwater samples. The Al concentration ranged from <0.4 μmol L⁻¹ at pH > 7 to 1941 μmol L⁻¹ at pH < 4; highest Al concentrations were found for natural-phreatic groundwater. The DOC concentration decreased and the median pH increased with depth of the groundwater. Natural-phreatic groundwater showed lower pH than the agricultural-phreatic groundwater. Highest DOC concentrations were found for the agricultural-phreatic groundwater, induced by the application of organic fertilizers. Besides inorganic complexation, the NICA-Donnan model was used to calculate Al³⁺ concentrations for complexation with DOC. Below pH 4.5 groundwater samples were mainly in disequilibrium with a mineral phase. This disequilibrium is considered to be the result of kinetic constraints or equilibrium with organic matter. Log K values were derived by linear regression and were close to theoretical values for Al(OH)₃ minerals (e.g. gibbsite or amorphous Al(OH)₃), except for natural-phreatic groundwater for which lower log K values were found. Complexation of Al with DOC is shown to be an important factor for the Al concentrations, especially at high DOC concentrations as was found for agricultural-phreatic groundwater.  相似文献