Use of stream response functions to determine impacts of replacing surface-water use with groundwater withdrawals

A regional-scale numerical groundwater model is used to study the impacts of replacing surface-water use with groundwater wells to improve low-flow stream conditions for endangered species within the Bertrand and Fishtrap watersheds, southern British Columbia, Canada and Washington, USA. Stream response functions ranging from 0 to 1.0 were calculated for individual wells placed within a steady-state groundwater flow model at varying distances from the streams to determine the impact that these replacement wells, operating under sustained pumping rates, would have on summer instream flows. Lower response ratios indicate groundwater pumping will have less of an impact on streamflow than taking an equivalent amount of water directly from a surface-water source. Results show that replacing surface-water use with groundwater withdrawals may be a viable alternative for increasing summer streamflows. Assuming combined response factors should be ≤0.5 for irrigators to undergo the expense of installing new wells, ~57% of the land area within 0.8 km of Bertrand Creek would be suitable for replacement wells. Similarly, 70% of the land area within 0.8 km of Fishtrap Creek was found to be appropriate. A visual analysis tool was developed using STELLA to allow stakeholders to quickly evaluate the impact associated with moving their water right.     

Future changes in Central Europe heat waves expected to mostly follow summer mean warming

Daily output from the PRUDENCE ensemble of regional climate simulations for the end of the twentieth and twenty-first centuries over Europe is used to show that the increasing intensity of the most damaging summer heat waves over Central Europe is mostly due to higher base summer temperatures. In this context, base temperature is defined as the mean of the seasonal cycle component for those calendar days when regional heat waves occur and is close, albeit not identical, to the mean temperature for July–August. Although 36–47% of future Central Europe July and August days at the end of the twenty-first century are projected to be extreme according to the present day climatology, specific changes in deseasonalized heat wave anomalies are projected to be relatively small. Instead, changes in summer base temperatures appear much larger, clearly identifiable and of the same order of magnitude as changes in the whole magnitude of heat waves. Our results bear important consequences for the predictability of central European heat wave intensity under global warming conditions.     

GEOEssential – mainstreaming workflows from data sources to environment policy indicators with essential variables

ABSTRACT

When defining indicators on the environment, the use of existing initiatives should be a priority rather than redefining indicators each time. From an Information, Communication and Technology perspective, data interoperability and standardization are critical to improve data access and exchange as promoted by the Group on Earth Observations. GEOEssential is following an end-user driven approach by defining Essential Variables (EVs), as an intermediate value between environmental policy indicators and their appropriate data sources. From international to local scales, environmental policies and indicators are increasingly percolating down from the global to the local agendas. The scientific business processes for the generation of EVs and related indicators can be formalized in workflows specifying the necessary logical steps. To this aim, GEOEssential is developing a Virtual Laboratory the main objective of which is to instantiate conceptual workflows, which are stored in a dedicated knowledge base, generating executable workflows. To interpret and present the relevant outputs/results carried out by the different thematic workflows considered in GEOEssential (i.e. biodiversity, ecosystems, extractives, night light, and food-water-energy nexus), a Dashboard is built as a visual front-end. This is a valuable instrument to track progresses towards environmental policies.     

Effects of aging on silica solubility: A laboratory study

In three separate experiments, one using a bicarbonate buffered aqueous NaCl solution and two using natural seawater. the solubility of chemically pure X-ray amorphous precipitated silica decreased by approximately 20‰ after aging in contact with solution for several months. The specific surface area of the silica decreased by approximately half during the same experimental time periods. The solubility decrease in buffered NaCl solution occurred at both 2 and 22°C and over the pressure range from 1.01 × 10⁵ to 7.45 × 10⁷ Pa (1–740 atm). The aging process which causes the solubility and surface area decreases may be caused by the formation of a smooth surface silica layer that is more dense than the original surface. No change in the bulk chemistry of the silica could be defined after aging. This short term aging process contributes to the scatter in published solubilities for amorphous silica in seawater.     

High-resolution grain-size characterisation of gravel bars using imagery analysis and geo-statistics

The scarcity of grain-size data from gravel-bed rivers has traditionally hindered hydraulic, sediment transport and river habitat studies. A new remote sensing methodology to estimate grain-size distribution is presented. It combines textural digital images of the riverbed at 1 : 1000 and 1 : 40 scales with grain-size sampling. It was applied to a 12-km reach of the Isábena River (Central Pyrenees NE Spain). First, textural patterns for each grain-size range were obtained, selecting the most closely related texture variables, including the use of semivariograms. Second, multiple linear regression equations were derived from the textural variables to estimate each value of the grain-size distribution. The highest correlation values (r²) were obtained from the central part of the distribution (D₅₀ with a RMS error of 12.7%). Finally, new multiple linear regression equations to estimate the D₅₀ and D₈₄ were obtained from 1 : 1000 images and four textural variables. These were used to derive D₅₀ and D₈₄ maps of the riverbed, re-sampled at a resolution of 1.5 m pixels, with RMS estimation errors of 26% and 32%, respectively. Downstream change in grain-size is also well reproduced by the method. The mean D₅₀ of 72 and 32 mm were estimated in the upper and the lower reaches of the river, respectively. The methodology shows great potential for application, the relation between the spatial resolution of the images and the mean grain-size of the riverbed sediment being the main issue for future development.     

History of sedimentary infilling and faulting in Subic Bay, Philippines revealed in high-resolution seismic reflection profiles

Subic Bay sediments and faults identified in seismic-reflection profiles were dated using sea-level curves. The oldest sedimentary packages are marine sediments subaerially exposed and eroded 20 ka. Fluvio-marine to wholly marine sediments were deposited during the ensuing transgression, and prograding units were deposited during stillstands or minor sea-level falls. Faults within the bay have three age ranges. The oldest set cuts through the pre-δ¹⁸O Stage 2 rock units, >18 ka; a second disrupts 10.2–11.3 ka sediments; and the youngest, which cut the uppermost sedimentary package, show that movements occurred about every 2 ky, most recently about 3 ka. Northwest–southeast faults that parallel onshore structures associated with Paleogene emplacement of the Zambales Ophiolite Complex to the west and north likely represent rejuvenated tectonism. The northern coastline and north–south-trending axial bay islands appear related to a lineament that dissects Mt Pinatubo farther northeast. A breach in the caldera of Mt Natib is the most likely source of a presumed pyroclastic deposit in the eastern bay that is associated with sediments about 11.3–18 ka, indicating that a Natib eruption occurred much more recently than previously documented for this volcano.     

Assessing burn severity and comparing soil water repellency,Hayman Fire,Colorado

An important element of evaluating a large wildfire is to assess its effects on the soil in order to predict the potential watershed response. After the 55 000 ha Hayman Fire on the Colorado Front Range, 24 soil and vegetation variables were measured to determine the key variables that could be used for a rapid field assessment of burn severity. The percentage of exposed mineral soil and litter cover proved to be the best predictors of burn severity in this environment. Two burn severity classifications, one from a statistical classification tree and the other a Burned Area Emergency Response (BAER) burn severity map, were compared with measured ‘ground truth’ burn severity at 183 plots and were 56% and 69% accurate, respectively. This study also compared water repellency measurements made with the water drop penetration time (WDPT) test and a mini‐disk infiltrometer (MDI) test. At the soil surface, the moderate and highly burned sites had the strongest water repellency, yet were not significantly different from each other. Areas burned at moderate severity had 1·5 times more plots that were strongly water repellent at the surface than the areas burned at high severity. However, the high severity plots most likely had a deeper water repellent layer that was not detected with our surface tests. The WDPT and MDI values had an overall correlation of r = ?0·64(p < 0·0001) and appeared to be compatible methods for assessing soil water repellency in the field. Both tests represent point measurements of a soil characteristic that has large spatial variability; hence, results from both tests reflect that variability, accounting for much of the remaining variance. The MDI is easier to use, takes about 1 min to assess a strongly water repellent soil and provides two indicators of water repellency: the time to start of infiltration and a relative infiltration rate. Copyright © 2005 John Wiley & Sons, Ltd.     

Evolution of bulk composition, mineralogy, strain style and fluid flow during an HT–LP metamorphic event: sillimanite zone of the Catalan Coastal Ranges Variscan basement, NE Iberia

Metamorphic rocks in the Osor complex (Guilleries massif, NE Iberian Peninsula) show the following structural and compositional features: strong differentiation into quartz-rich gneissic semipelitic and quartz-absent, mica-rich schistose bands, higher density of igneous (both basic and leucogranitic) and quartz veins in the schistose domains and strong strain partitioning in the pelitic bands. Garnet is present in both kinds of lithologies, showing also differential textural and chemical features interpreted to be dependent on bulk composition, deformation and fluid interaction histories. Textures, mineral composition and thermobarometry suggest the operation of concurrent mechanical, mass transfer and thermal phenomena such as: (1) variations in strain style, (2) fluid infiltration, (3) magmatic injection and (4) HT–LP metamorphic and metasomatic episodes. The following sequence of events is suggested: initially the cooling of syntectonic high-T basic quartz diorite sheets promoted high strain rates, low dP/dT thermobaric evolution, incipient anatexis in the pelitic bands and devolatilization through a pervasive to vein-channelized prograde fluid flow. The prograde flow enhanced an ongoing compositional tectono-metamorphic differentiation and produced metasomatism through depletion of the Osor rocks in alkalis and calcium. Later injection and cooling of peraluminous leucogranitoid sheets, preferentially along pelitic bands, increased the ratio of magmatic/metamorphic components in the fluids and strongly enriched them in alkalis producing a second metasomatic episode. During crystallization of quartz and leucogranitoid veins, the pelitic bands were strongly enriched back again in alkalis, promoting the blastesis of big crystals of post-peak muscovite and albite as well as the retrogression of garnet. The metasomatic mica-rich levels must have been the preferred locus for development of a new deformation style dominated by shear band fabrics in metapelites and related to a release of the gravitational instability originated previously due to crustal thickening. The increasing decompressional component of the retrograde P–T path also suggests that this style of deformation was prevalent during, if not responsible for, a phase of exhumation of the metamorphic complex. It is suggested that similar patterns of thermomechanical and mass transfer phenomena could well be a fundamental characteristic common to all HT–LP metamorphic belts.