Framework for economic cost assessment of land subsidence

Natural Hazards - Land subsidence is increasingly recognised as a complex and costly challenge, especially in urban subsidence-prone areas. Often caused by overextraction of groundwater in order to...     

Sedimentation behavior of flocculant-treated soil slurry

Soil slurry dredged from seabed is becoming more widely used in land reclamation projects. A major problem encountered is that soil slurry is very high in water content and the dewatering process is difficult and time consuming. In this paper, the use of chemical flocculant for the dewatering of soil slurry is proposed and experimentally tested. Polyacrylamide (PAM) with different charge types/charge densities was tested in preliminary slurry dewatering tests. The results showed that the most effective flocculant, cationic PAM (CPAM) with +15 charge density, can reduce the volume of soil slurry (500% water content) by around 60% in 10 minutes. In contrast, the volume of pure soil slurry was almost unchanged. Slurry sedimentation tests on slurries with different flocculant contents and water contents were conducted. It is shown that, by adding flocculant into soil slurry, the rate of settlement under self-weight can be considerably increased in the tested range of water contents (100.7–879.5%). But the water content at the final state increases with flocculant additions. Slurry sedimentation curves displayed different characteristics with different flocculant contents as well as water contents. It is evidenced by particle size analysis that the addition of flocculant into soil slurry can attract soil particles and form large flocs (assemblage of particles), which explains the faster settlement rate in flocculant-treated soil slurry as compared with pure soil slurry. Scanning electron microscopic analysis revealed that flocculant-treated soil particles are more randomly oriented, while soil particles with no flocculant addition deposit in a more paralleled manner. This could explain the higher water content of flocculant-treated soil slurry at the final state.     

Can agricultural groundwater economies collapse? An inquiry into the pathways of four groundwater economies under threat

The aim of this paper is to investigate the notion of collapse of agricultural groundwater economies using the adaptive-cycle analytical framework. This framework was applied to four case studies in southern Europe and North Africa to question and discuss the dynamics of agricultural groundwater economies. In two case studies (Saiss in Morocco and Clain basin in France), the imminent physical or socio-economic collapse was a major concern for stakeholders and the early signs of collapse led to re-organization of the groundwater economy. In the other two cases (Biskra in Algeria and Almeria in Spain), collapse was either not yet a concern or had been temporarily resolved through increased efficiency and access to additional water resources. This comparative analysis shows the importance of taking the early signs of collapse into account. These signs can be either related to resource depletion or to environmental and socio-economic impacts. Beyond these four case studies, the large number of groundwater economies under threat in (semi-)arid areas should present a warning regarding their possible collapse. Collapse can have severe and irreversible consequences in some cases, but it can also mean new opportunities and changes.     

3D structural model and kinematic interpretation of the Panixer Pass Transverse Zone (Infrahelvetic Complex,eastern Switzerland)

The Panixer Pass Transverse Zone in the eastern Swiss Alps is oriented perpendicular to most alpine structures in the area. Its main element is the SSE-trending Crena-Martin Fold, a downward facing fold with Permian Verrucano in its core, which is cut by the Glarus Thrust. Hence Verrucano can be found below the Glarus Thrust in the Infrahelvetic Complex. Across the Panixer Pass Transverse Zone the structural buildup of the Infrahelvetic Complex changes considerably. Multiple published theories of the structural evolution are not satisfying particularly because traditional 2D geological cross-sections are insufficient to understand the 3D complexity. The main result and product of our study is a 3D structural model of the Panixer Pass Transverse Zone providing insight into its geometry. As modeling input, we produced a lithostratigraphic map and collected structural orientation data. The 3D structural model honors the observed surface geology and the expected 3D subsurface geometry. Our field data indicates that the shearing and transport direction was continuously NNW-directed, except for a phase of north-directed shearing during the early movement along the Glarus Thrust (late Calanda Phase) and related foliation development in the Helvetic Nappes. The Panixer Pass Transverse Zone developed prior to the penetrative foliation during a thrust-dominated deformation phase (Cavistrau Phase), for which we created a kinematic block model. According to this model, the Crena-Martin Fold is the result of multiple lateral ramps and related lateral fault-bend folds that all developed in a similar positon. In particular, we do not propose ENE-WSW-directed shortening to form the Crena-Martin Fold. The latter was finally cut at low angle by a dextral strike-slip fault to create the final geometry of the Panixer Pass Transverse Zone. Our kinematic model reproduces the main features of the 3D structural model and embeds well into previously proposed sequences of deformation phases.     

All-cis hentriaconta-9,15,22-triene in microbial mats formed by the phototrophic prokaryote Chloroflexus

All-cis hentriaconta-9,15,22-triene (I) has been isolated from Chloroflexus mats, Yellowstone National Park (USA), and identified by GC–(HR)MS analysis of I and its hydrogenated and DMDS-derivatized products and by ¹H and ¹³C NMR spectroscopy.     

Ridge–hotspot interaction: the Pacific–Antarctic Ridge and the foundation seamounts

The study of different magmatic provinces between the Resolution fracture zone (33°S–131°W) and the Pacific–Antarctic Ridge (PAR) axis (37°S–111°W) suggests that similar processes of interaction between hotspot and spreading axial magmatism occurred 20–25 Ma and 0–5 Ma ago. There is evidence of this process from the changes in composition observed in the lavas erupted near 400–300 km between the present day PAR axis (37°S–111′W) and the eastern tip of the Foundation Seamount (FS) hotspot near 36°20′S–114°W where the last alkali enriched volcanics [K/Ti>0.30, Zr/Y>6 and (Ce/Yb)_N>4] have erupted. This transitional province between the PAR and the FS consists of volcanic cones built on several volcanic ridges (<200 km in length) which have erupted less enriched volcanics such as E-[K/Ti=0.25–0.33, Zr/Y=5–6 and (Ce/Yb)_N=3–4] and T-[K/Ti=0.11–0.25, Zr/Y=2–4 and (Ce/Yb)_N=1–2] MORBs than those from the FS. It is also noticed that there is a general decrease in the degree of the basalt alkalinity (more T-MORBs) towards the PAR axis. The limit of the FS hotspot influence corresponds to the area where the VR intersect the PAR axis for a distance of about 100 km along its strike between 37°10′S and 38°20′S. Indeed, the lava erupted further to the north and to the south of these latitudes contains N-MORBs [K/Ti=0.05–0.11, Zr/Y<3 and (Ce/Yb)_N=<2]. Many Old Pacific Seamounts (OPS, >20 Ma) also built on volcanic ridges are identified west (>1200 km from the PAR axis) of a Failed Rift Propagator (FRP) forming the eastern boundary of the ancient Selkirk microplate. Some of these seamounts made of alkali basalts were built during the initiation of the FS hotspot 20–23 Ma ago. The interaction and the influence (thermal) of mantle plume magmatism with the ancient spreading ridge of the Farallon–Pacific plates was responsible for the eruptions of the T-MORBs and andesitic lavas. This situation is comparable to that presently observed on the PAR axis where silicic lavas are also erupted in association with T-MORBs.     

Effects of discharge,wind, and tide on sedimentation in a recently restored tidal freshwater wetland

Sediment deposition is one of the key mechanisms to counteract the impact of sea level rise in tidal freshwater wetlands (TFWs). However, information about sediment deposition rates in TFWs is limited, especially for those located in the transition zone between the fluvially dominated and tidally dominated sections of a river delta where sedimentation rates are affected by the combined impact of river discharge, wind, and tides. Using a combined hydrodynamic–morphological model, we examined how hydrometeorological boundary conditions control sedimentation rates and patterns in a TFW located in the Rhine–Meuse estuary in the Netherlands. The modelling results show that net sedimentation rate increases with the magnitude of the river discharge, whereas stronger wind increasingly prevents sedimentation. Sediment trapping efficiency decreases for both increasing river discharge and wind magnitude. The impact of wind storms on the trapping efficiency becomes smaller for higher water discharge. The spatial sedimentation patterns are affected by all controls. Our study illustrates the importance of evaluating both the separate and the joint impact of discharge, wind, and tides when estimating sedimentation rates in a TFW affected by these controls. Such insights are relevant to design measures to reactivate the sedimentation process in these areas.     

Interactions between barotropic tides and mesoscale processes in deep ocean and shelf regions

Ocean Dynamics - The interactions between barotropic tides and mesoscale processes were studied using the results of a numerical model in which tidal forcing was turned on and off. The research...     

Comparison between the indirect approach and kriging with samples of different support for estimation using samples of different length

In this paper we compare two estimation methods to deal with samples of different support: (1) the indirect approach using accumulation and (2) kriging with samples of different support. These two methods were tested in a simple example. The estimates of the two methods were compared against a benchmark scenario. The benchmark consisted of kriging using a complete set of samples on the same support. The effects of the nugget effect, variogram range and type on the weight of long samples, the estimate, and the error variance were assessed. Kriging with samples of different support led to lower error variance and to estimates closer to the estimates of the benchmark scenario. Furthermore, in the case of spatially continuous attributes (low nugget effect), the indirect approach assigns greater weight to long samples than kriging with samples of different support. A cross validation study comparing the two methods with a database from a bauxite deposit was performed. The results of the cross validation study showed that kriging with samples of different support resulted in more precise estimates.     

Nickel isotope heterogeneity in the early Solar System

We report small but significant variations in the ⁵⁸Ni/⁶¹Ni-normalised ⁶⁰Ni/⁶¹Ni and ⁶²Ni/⁶¹Ni ratios (expressed as ε⁶⁰Ni and ε⁶²Ni) of bulk iron and chondritic meteorites. Carbonaceous chondrites have variable, positive ε⁶²Ni (0.05 to 0.25), whereas ordinary chondrites have negative ε⁶²Ni (− 0.04 to − 0.09). The Ni isotope compositions of iron meteorites overlap with those of chondrites, and define an array with negative slope in the ε⁶⁰Ni versus ε⁶²Ni diagram. The Ni isotope compositions of the volatile-depleted Group IVB irons are similar to those of the refractory CO, CV carbonaceous chondrites, whereas the other common magmatic iron groups have Ni isotope compositions similar to ordinary chondrites. Only enstatite chondrites have identical Ni isotope compositions to Earth and so appear to represent the most appropriate terrestrial building material. Differences in ε⁶²Ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed, but some of the ε⁶⁰Ni variability could reflect a radiogenic component from the decay of ⁶⁰Fe. Comparison of the ε⁶⁰Ni of iron and chondritic meteorites with the same ε⁶²Ni allows us to place upper limits on the ⁶⁰Fe/⁵⁶Fe of planetesimals during core segregation. We estimate that carbonaceous chondrites had initial ⁶⁰Fe/⁵⁶Fe < 1 × 10^− 7. Our data place less good constraints on initial ⁶⁰Fe/⁵⁶Fe ratios of ordinary chondrites but our results are not incompatible with values as high as 3 × 10^− 7 as determined by in-situ measurements. We suggest that the Ni isotope variations and apparently heterogeneous initial ⁶⁰Fe/⁵⁶Fe results from physical sorting within the protosolar nebula of different phases (silicate, metal and sulphide) that carry different isotopic signatures.