Fingerprinting the Origin of Fluvial Suspended Sediment in Larger River Basins: Combining Assessment of Spatial Provenance and Source Type

Investigation of the potential for using sediment fingerprinting to integrate both spatial provenance and source type information for larger drainage basins appears to be desirable. This contribution presents the results of adopting a composite fingerprinting procedure incorporating statistically verified multicomponent signatures and a multivariate mixing model to provide a preliminary integration of spatial provenance and source type information for the upper and middle reaches of the drainage basins of the Rivers Exe (601 km²) and Severn (4325 km²), UK. A nested approach is employed, whereby spatial provenance is addressed in terms of the distinct sub-basin zones constituting each study area as an entirety, and source type is then characterised within each of these distinct spatial zones in terms of surface (woodland, pasture, cultivated) and subsurface (channel bank) materials. The results demonstrate that the fingerprinting approach possesses considerable potential for integrating spatial provenance and source type information, and hence for improving the resolution of existing sediment source information for larger drainage basins.     

Ion microprobe analysis of oxygen isotope ratios in quartz from Skye granite: healed micro-cracks,fluid flow,and hydrothermal exchange

 Quartz grains in hydrothermally altered granites from the Isle of Skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 μm scale. Ion microprobe analysis of one grain shows a gradient of 13‰ over 400 μm and a greater range in δ ¹⁸O than all quartz previously analyzed on the Isle of Skye. Other crystals from the same outcrop are homogeneous. Digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable. The ion probe analysis correlates low δ ¹⁸O values on a micro-scale to one set of healed cracks. Thus, quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures, in contrast to more reactive feldspar that appears to exchange from the grain boundary inward. Macroscopic models of isotope exchange are not realistic for these rocks; the flow of hydrothermal fluids was heterogeneous, anisotropic and crack controlled. Received: 23 October 1995/Accepted: 9 April 1996     

Melting of albite and dehydration of brucite in H2O–NaCl fluids to 9 kbars and 700–900°C: implications for partial melting and water activities during high pressure metamorphism

 The melting reaction: albite_(solid)+ H₂O_(fluid) =albite-H₂O_(melt) has been determined in the presence of H₂O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H₂O–CO₂ fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant pressure is principally determined by water activity. At 5 kbar, the temperature (T)- mole fraction (X _(H2O) ) melting relations in the two systems are almost coincident. By contrast, H₂O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 ^°C higher in H₂O–NaCl brines than in H₂O–CO₂ fluids for X _(H2O) =0.8 and ∼100 ^°C higher for X _(H2O) =0.5. The melting temperature of albite in H₂O–NaCl fluids of X _(H2O)=0.8 is ∼100 ^°C higher than in pure water. The P–T curves for albite melting at constant H₂O–NaCl show a temperature minimum at about 5 kbar. Water activities in H₂O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H₂O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but may be due to the presence of low a _(H2O) brines. Received: 17 March 1995/Accepted: 9 April 1996     

Effects of temperature on strength and compressibility of sand-bentonite buffer

Dense sand-bentonite buffer (γ_d = 1.67Mg/m³) has been proposed in Canada as one of several barriers for isolating nuclear fuel waste. The buffer will be required to function under conditions of high total pressures and elevated temperatures approaching 100°C. Summary results are presented from two test programs: (1) isothermal consolidated undrained triaxial (CIU¯) tests; and (2) isothermal drained constant-p′ (CID) triaxial tests. Specimens were consolidated at effective stresses up to 9.0 MPa and temperatures up to 100°C.

The results indicate parallel hardening lines at systematically lower values of specific volume at elevated temperatures. In shear, increased temperatures produced lower values of maximum deviator stressq_f, and higher pore water pressure changesΔu_f. The net result is curved peak strength envelops in plots ofq_f versusp_f′ that are higher at elevated temperatures, even though the strengths,q_f of individual specimens are lower. The critical state strength envelope is curved inq, p′-planes.

The effect of drained heating on buffer to 100°C is not marked. Compressibilities, stiffnesses, strengths, and pore water pressure generation are all affected, but none of the changes are great.     

Mitigating the Effects of Climate Change on the Water Resources of the Columbia River Basin

The potential effects of climate change on the hydrology and water resources of the Columbia River Basin (CRB) were evaluated using simulations from the U.S. Department of Energy and National Center for Atmospheric Research Parallel Climate Model (DOE/NCAR PCM). This study focuses on three climate projections for the 21st century based on a `business as usual' (BAU) global emissions scenario, evaluated with respect to a control climate scenario based on static 1995 emissions. Time-varying monthly PCM temperature and precipitation changes were statistically downscaled and temporally disaggregated to produce daily forcings that drove a macro-scale hydrologic simulation model of the Columbia River basin at 1/4-degree spatial resolution. For comparison with the direct statistical downscaling approach, a dynamical downscaling approach using a regional climate model (RCM) was also used to derive hydrologic model forcings for 20-year subsets from the PCM control climate (1995–2015) scenario and from the three BAU climate(2040–2060) projections. The statistically downscaled PCM scenario results were assessed for three analysis periods (denoted Periods 1–3: 2010–2039,2040–2069, 2070–2098) in which changes in annual average temperature were +0.5,+1.3 and +2.1 °C, respectively, while critical winter season precipitation changes were –3, +5 and +1 percent. For RCM, the predicted temperature change for the 2040–2060 period was +1.2 °C and the average winter precipitation change was –3 percent, relative to the RCM controlclimate. Due to the modest changes in winter precipitation, temperature changes dominated the simulated hydrologic effects by reducing winter snow accumulation, thus shifting summer streamflow to the winter. The hydrologic changes caused increased competition for reservoir storage between firm hydropower and instream flow targets developed pursuant to the Endangered Species Act listing of Columbia River salmonids. We examined several alternative reservoir operating policies designed to mitigate reservoir system performance losses. In general, the combination of earlier reservoir refill with greater storage allocations for instream flow targets mitigated some of the negative impacts to flow, but only with significant losses in firm hydropower production (ranging from –9 percent in Period1 to –35 percent for RCM). Simulated hydropower revenue changes were lessthan 5 percent for all scenarios, however, primarily due to small changes inannual runoff.     

An experimental study of phase equilibria in the systems H2O–CO2–CaCl2 and H2O–CO2–NaCl at high pressures and temperatures (500–800?°C, 0.5–0.9?GPa): geological and geophysical applications

Phase equilibria in the ternary systems H₂O–CO₂–NaCl and H₂O–CO₂–CaCl₂ have been determined from the study of synthetic fluid inclusions in quartz at 500 and 800 °C, 0.5 and 0.9 GPa. The crystallographic control on rates of quartz overgrowth on synthetic quartz crystals was exploited to prevent trapping of fluid inclusions prior to attainment of run conditions. Two types of fluid inclusion were found with different density or CO₂ homogenisation temperature (T_h(CO₂)): a CO₂-rich phase with low T_h(CO₂), and a brine with relatively high T_h(CO₂). The density of CO₂ was calibrated using inclusions in the binary system H₂O–CO₂. Mass balance calculations constrain tie lines and the miscibility gap between brines and CO₂-rich fluids in the H₂O–CO₂–NaCl and H₂O–CO₂–CaCl₂ systems at 500 and 800 °C, and 0.5 and 0.9 GPa. The miscibility gap in the CaCl₂ system is larger than in the NaCl system, and solubilities of CO₂ are smaller. CaCl₂ demonstrates a larger salting-out effect than NaCl at the same P–T conditions. In ternary systems, homogeneous fluids are H₂O-rich and of extremely low salinity, but at medium to high concentrations of salts and non-polar gases fluids are unlikely to be homogeneous. The two-phase state of crustal fluids should be common. For low fluid-rock ratios the cation compositions of crustal fluids are buffered by major crustal minerals: feldspars and micas in pelites and granitic rocks, calcite (dolomite) in carbonates, and pyroxenes and amphiboles in metabasites. Fluids in pelitic and granitic rocks are Na-K rich, while for carbonate and metabasic rocks fluids are Ca-Mg-Fe rich. On lithological boundaries between silicate and carbonate rocks, or between pelites and metabasites, diffusive cation exchange of the salt components of the fluid will cause the surfaces of immiscibility to intersect, leading to unmixing in the fluid phase. Dispersion of acoustic energy at critical conditions of the fluid may amplify seismic reflections that result from different fluid densities on lithological boundaries.Editorial responsibility: I. Parsons     

Regions and sustainable development: regional planning matters

This paper looks at how the term 'sustainable development' has been used in the process of regional plan making over the past decade. It emphasizes the differing geographies of these debates within England, in terms of how sustainable development has been used to justify different types of approach in different parts of the country. Both drawing on and challenging recent work on state theory, the paper argues the need to see regional planning as a part of a multi-scalar governance system, whose importance should not be underestimated.