Evaluating river morphology change with a geomorphic form variation approach

Geomorphic river design strives for natural resilience by encouraging geomorphic form complexity and morphological processes linked to greater habitat diversity. Increasing availability of high-resolution topographic data and spatial feature mapping methods provide advantages for morphological analysis and river restoration planning. We propose and evaluate an approach to quantifying topographic variability of geomorphic form and pixel-level surface roughness resulting from channel planform geometry differences using spatially continuous variety computation applied to component metrics including flow direction, aspect and planform curvature. We define this as the geomorphic form variation (GFV) approach and found it scalable, repeatable and a multi-stage analytical metric for quantifying physical aspects of river-bed topographic variability. GFV may complement process-based morphological feature mapping applications, hydraulic assessment indices and spatial habitat heterogeneity metrics commonly used for ecological quality evaluation and river restoration. The GFV was tested on controlled synthetic channels derived from River Builder software and quasi-controlled sinuous planform flume experiment channels. Component variety metrics respond independently to specific geometric surface changes and are sensitive to multi-scaled morphology change, including coarser-grained sediment distributions of pixel-level surface roughness. GFV showed systematic patterns of change related to the effects of channel geometry, vertical bed feature (pool-bar) frequency and amplitude, and bar size, shape and orientation. Hotspot analysis found that bar margins were major components of topographic complexity, whereas grain-scale variety class maps further supported the multi-stage analytical capability and scalability of the GFV approach. The GFV can provide an overall variety value that may support river restoration decision-making and planning, particularly when geomorphic complexity enhancement is a design objective. Analysing metric variety values with statistically significant hotspot cluster maps and complementary process-based software and mapping applications allows variety correspondence to systematic feature changes to be assessed, providing an analytical approach for river morphology change comparison, channel design and geomorphic process restoration.     

Variations in the geomagnetic dipole moment during the Holocene and the past 50 kyr

All absolute paleointensity data published in peer-reviewed journals were recently compiled in the GEOMAGIA50 database. Based on the information in GEOMAGIA50, we reconstruct variations in the geomagnetic dipole moment over the past 50  kyr, with a focus on the Holocene period. A running-window approach is used to determine the axial dipole moment that provides the optimal least-squares fit to the paleointensity data, whereas associated error estimates are constrained using a bootstrap procedure. We subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment, including those based on cosmogenic radionuclides (¹⁰Be and ¹⁴C). This comparison generally lends support to the axial dipole moments obtained in this study. Our reconstruction shows that the evolution of the dipole moment was highly dynamic, and the recently observed rates of change (5% per century) do not appear unique. We observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment, suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non-dipole field. This study also shows that the Holocene geomagnetic dipole moment was high compared to that of the preceding  40  kyr, and that  4 · 10²²  Am² appears to represent a critical threshold below which geomagnetic excursions and reversals occur.     

Importance of mantle derived fluids during granite associated hydrothermal circulation: He and Ar isotopes of ore minerals from Panasqueira

Helium trapped in arsenopyrite and wolframite from the Panasqueira hydrothermal deposit in central Portugal is overwhelmingly—≈ 75%—derived from the mantle. This is surprising as the W-Cu(Ag)-Sn vein deposits are spatially and temporally associated with an S-type granite. It is difficult to reconcile ³He/⁴He ratios > 5Ra (where Ra is the atmospheric ³He/⁴He ratio) with a granite produced by crustal anatexis, therefore it seems likely that mantle derived fluids unrelated to the granite were the source of the magmatic component in the ore fluids.The mantle appears to transport ³He and heat to the surface in relatively constant proportions (³He/Q = 0.1-1 x10⁻¹² cm³ STP J⁻¹). However, the ³He/heat ratios in the Panasqueira fluids (1-10 x10⁻¹² cm³ STP J⁻¹, calculated using the ³He/³⁶Ar ratio) are considerably higher. Therefore, it does not seem likely that gradual cooling of the pluton supplied heat to the hydrothermal system (as this would result in low ³He/Q ratios). Therefore, both He and heat in this collision related, granite-associated hydrothermal deposit were supplied from the mantle.     

Experiments on the ocean sequestration of fossil fuel CO2: pH measurements and hydrate formation

We have carried out a series of in situ experiments to investigate the formation of a CO₂ hydrate (CO₂:5.75 H₂O) for the purpose of evaluating scenarios for ocean fossil fuel CO₂ disposal with a solid hydrate as the sequestered form. The experiments were carried out with a remotely operated vehicle in Monterey Bay at a depth of 619 m. pH measurements made in close proximity to the hydrate–seawater interface showed a wide range of values, depending upon the method of injection and the surface area of the hydrate formed. Rapid injection of liquid CO₂ into an inverted beaker to form a flocculant mass of hydrate resulted in pH initially as low as 4.5 within a few centimeters of the interface, decaying slowly over 1–2 h towards normal seawater values as dense CO₂ rich brine drained from the hydrate mass. In a second experiment, slower injection of the liquid CO₂ to produce a simple two-layer system with a near planar interface of liquid CO₂ with a thin hydrate film yielded pH values indistinguishable from the in situ ocean background level of 7.6. Both field and laboratory results now show that the dissolution rate of a mass of CO₂ hydrate in seawater is slow but finite.     

Governance and technology transfer in the Clean Development Mechanism in India

Despite significant technological advances in emerging economies, the further development of clean energy technologies in developing countries remains crucial to reducing the greenhouse gas emissions associated with economic development. In this paper we address two significant gaps in the growing body of literature that has assessed the role of the Clean Development Mechanism in promoting the transfer of clean technologies to developing countries. First, we present a qualitative analysis of the governance of the Clean Development Mechanism in India. This provides a basis for understanding the extent to which and the ways in which governance may impact upon the likelihood that projects promote technology transfer. Second, we provide a novel quantification of the level and nature of technology transfer that has occurred in Indian Clean Development Mechanism projects, based on insights from literature on technological capability building. We find that the Clean Development Mechanism in India has produced a negligible number of projects that promote technology transfer if technology transfer is understood as a process of learning about technology. Together these qualitative and quantitative analyses show how politics and governance have contributed to the current form of the Clean Development Mechanism market in India, in which processes of building indigenous technological capabilities have been neglected.     

Tidally incised valleys on tropical carbonate shelves: An example from the northern Great Barrier Reef, Australia

The formation of incised valleys on continental shelves is generally attributed to fluvial erosion under low sea level conditions. However, there are exceptions. A multibeam sonar survey at the northern end of Australia's Great Barrier Reef, adjacent to the southern edge of the Gulf of Papua, mapped a shelf valley system up to 220 m deep that extends for more than 90 km across the continental shelf. This is the deepest shelf valley yet found in the Great Barrier Reef and is well below the maximum depth of fluvial incision that could have occurred under a − 120 m, eustatic sea level low-stand, as what occurred on this margin during the last ice age. These valleys appear to have formed by a combination of reef growth and tidal current scour, probably in relation to a sea level at around 30–50 m below its present position.

Tidally incised depressions in the valley floor exhibit closed bathymetric contours at both ends. Valley floor sediments are mainly calcareous muddy, gravelly sand on the middle shelf, giving way to well-sorted, gravely sand containing a large relict fraction on the outer shelf. The valley extends between broad platform reefs and framework coral growth, which accumulated through the late Quaternary, coincides with tidal current scour to produce steep-sided (locally vertical) valley walls. The deepest segments of the valley were probably the sites of lakes during the last ice age, when Torres Strait formed an emergent land-bridge between Australia and Papua New Guinea. Numerical modeling predicts that the strongest tidal currents occur over the deepest, outer-shelf segment of the valley when sea level is about 40–50 m below its present position. These results are consistent with a Pleistocene age and relict origin of the valley.

Based on these observations, we propose a new conceptual model for the formation of tidally incised shelf valleys. Tidal erosion on meso- to macro-tidal, rimmed carbonate shelves is enhanced during sea level rise and fall when a tidal, hydraulic pressure gradient is established between the shelf-lagoon and the adjacent ocean basin. Tidal flows attain a maximum, and channel incision is greatest, when a large hydraulic pressure gradient coincides with small channel cross sections. Our tidal-incision model may explain the observation of other workers, that sediment is exported from the Great Barrier Reef shelf to the adjacent ocean basins during intermediate (rather than last glacial maximum) low-stand, sea level positions. The model may apply to other rimmed shelves, both modern and ancient.     

Scales and magnitude of hyporheic,river–aquifer and bank storage exchange fluxes

Many studies have investigated the exchange processes that occur between rivers and groundwater systems and have successfully quantified the water fluxes involved. Specifically, these exchange processes include hyporheic exchange, river–aquifer exchange (groundwater discharge and river loss) and bank storage exchange. Remarkably, there are relatively few examples of field studies where more than one exchange process is quantified, and as a consequence, the relationships between them are not well understood. To compare the relative magnitudes of these common exchange processes, we have collected data from 54 studies that have quantified one or more of these exchange flux types. Each flux value is plotted against river discharge at the time of measurement to allow the different exchange flux types to be compared. We show that there are positive relationships between the magnitude of each exchange flux type and increasing river discharge across the different studies. For every one order of magnitude increase in river discharge, the hyporheic, river–aquifer and bank storage exchange fluxes increase by factors of 2.7, 2.9 and 2.5, respectively. On average, hyporheic exchange fluxes are almost an order of magnitude greater than river–aquifer exchange fluxes, which are, in turn, approximately four times greater than bank storage exchange fluxes for the same river discharge. Unless measurement approaches that can distinguish between different types of exchange flux are used, there is potential for hyporheic exchange fluxes to be misinterpreted as river–aquifer exchange fluxes, with possible implications for water resource management decisions. Copyright © 2015 John Wiley & Sons, Ltd.     

Risø 1978: Further investigations into the effects of local terrain irregularities on tower-measured wind profiles

Observations of flow over complex terrain taken at Risø during June–July 1978 and numerical studies confirm earlier findings that small variations in surface elevation have significant effects on mean wind profiles. Measured shear stresses in the nonequilibrium region of the flow are consistent with theory but quite different from those obtained assuming simple flux-profile relationships. These findings imply that flux-profile relationships can be quite complicated over other than simple homogeneous terrain.     

Organochlorine compound and trace metal contaminants in fish near Sydney's ocean outfalls

Sydney's inshore sewage outfalls were significant contributors to organochlorine contamination of inshore sedentary fish such as red morwong. Diversion of the sewage to deepwater outfalls has resulted in marked declines in the concentrations of these compounds in inshore red morwong. Apart from lead, however, similar trends did not occur for concentrations of trace metals. A wide variety of trace metals and organochlorine compounds were found in the flesh and/or livers of a variety of fish species caught at sites associated with the present deepwater ocean outfalls off Sydney. Fish caught at locations remote from Sydney also contained a wide variety of trace metals although organochlorine compounds were usually at lower levels. The mean contaminant levels in all species of offshore fish were generally found to be low when compared to the Australian National Food Authority's Maximum Residue Limit (NFA MRL). No fish analysed was found to have levels of an organochlorine compound above the MRL and no fish was found to have levels of zinc or lead above the MRL. When detected, fish with levels of a trace metal above the MRL appeared to be distributed throughout New South Wales, independent of the deepwater ocean outfalls off Sydney. There is no evidence as yet that the commissioning of the deepwater outfalls has led to an increase in levels of contaminants in the fish examined to the extent that they are of concern relative to the NFA MRLs.     

The influence of natural organic matter on the adsorption properties of mineral particles in lake water

The adsorption characteristics of sediment particles from a prealpine Swiss lake were compared with those of γ-aluminum oxide. Under lake water conditions, i.e. with particle concentration of 2–16 mg/1 and DOC concentrations of 1–4 mg/1 at pH=8, the adsorption of copper, zinc and orthophosphate is reduced significantly by the presence of natural organic matter (NOM). It is postulated that the binding sites of the natural mineral surfaces are occupied almost completely by NOM under natural conditions. A simple ligand exchange model can explain the observed phenomena.