A new incompatible mode element with selective mass scaling for saturated soil dynamics

It is a well-known fact that addressing hydromechanical problems in saturated soils with the finite element method and equal-order interpolation formulations in displacements and pore pressures produces unstable results. Classically, stabilization has been achieved by increasing the interpolation degree of displacement with respect to pore pressure, hence fulfilling the Babuska–Brezzi condition. However, the use of quadratic elements involves high computational costs. From that point of view, the use of stabilized low-order elements is a more desirable option. Much research has been carried out in different directions in the stabilization of low-order formulations for saturated soils in quasistatic conditions, among others with the technique based on strain field enhancement through internal degrees of freedom. This article presents an alternative displacement–pore pressure formulation for saturated soil dynamics based on the enhancement of the displacement field through incompatible modes.     

Examining the rainfall–topography relationship using non-stationary modelling technique in semi-arid Aseer region,Saudi Arabia

The mountainous region of Aseer, corresponding to the Afromontane phytogeographic region, is an eco-sensitive zone and has complex relationship between topography and rainfall. The region is located inland of the red sea escarpment edge in the west. Therefore, rainfall can occur during any month of the year in the mountain of the high Aseer region when moist air forces up the escarpment from the red sea. Monitoring the rainfall data and its topographical elevation variable in Aseer region is an essential requirement for feasible and accurate rainfall-based data for different applications, such as hydrological and ecological resource management in rugged terrain and remote areas. The relationship of elevation and rainfall are spatially non-stationary, non-linear, scale dependent, and often modelled by conventional regression models. Therefore, a local modelling technique, geographically weighted regression (GWR), was applied to deal with non-stationary, non-linear, scale-dependent problems. The GWR using topoclimatic data (elevation and rainfall) to analyse the cumulative rainfall data for rainy months (March to June) of the 4 years estimated from CHIRPS (Climate Hazards Group InfraRed Precipitation with Stations) product for Aseer region. The bandwidth (scale-size) of the Aseer region rainfall–elevation relationship has stabilised at round off 12 km. By selecting the suitable bandwidth, the spatial pattern of the rainfall–elevation relationship was significantly enhanced by using the GWR than the traditional ordinary least squares (OLS) regression model. GWR local modelling techniques estimated well in terms of accuracy, predictive power and decreased residual autocorrelation. Additionally, GWR assesses the significance of local statistic at each location and identified the location of spatial clusters with local regression coefficients significantly improved as compared with global OLS model, thereby highlighting local variations. Therefore, the GWR, local modelling approach managed to produce more accurate estimates by taking into account local characteristics.     

Conflicts and water governance challenge in irrigated areas of semi-arid regions

Agriculture in arid and semi-arid regions faces two of the principal global challenges: sustainability and water scarcity in the context of climate changes. To overcome the water scarcity constraint, Tunisia adopted different strategies and policies. Since 1989, it has embarked on a policy of decentralization and participatory water management in irrigated areas “IA.” This policy has led to the state disengagement in favor of collective water management. Since then, water management becomes a task of irrigator associations. These associations have experienced a series of transformations ranging from “collective interest associations: CIA” to the current form “Development Agricultural Groups: GDAs.” In spite of these institutional changes, GDAs are suffering from several problems impeding their functioning such as budgetary deficit, conflicts between stakeholders, leaving of irrigated activity by some farmers, and inequality. The current situation of GDA and most IA hypothesizes the existence of local governance problems; these governance problems are causing a performance decrease in IA. The analysis of the interdependence between governance and performance of irrigation water management, in Nadhour IA, is the main aim of this paper. To conduct this analysis, the strategic analysis approach was adopted. Assuming that IA forms a concrete action system, the analysis of structured games between actors allowed assessing their power, convergence, divergence, and ambivalence. Results confirm the hypothesis of a significant effect of governance problems, including political source, on the performance of water management in IA.     

Trace metal contamination by phosphogypsum discharge in surface and core sediments of the Gabes coast area (SE of Tunisia)

The purpose of the present study is to ascertain the extent of the effect that phosphate fertilizer industrial waste has on the surface and bottom sediments of the Ghannouch-Gabes coast, off the Tunisian Mediterranean Sea. To achieve this, 44 surface sediments and 3 core sediments were studied for mineralogy, trace metals (Cd, Cu, Pb, and Zn), F, CaO, and SO₃. For all the analyzed elements, the spatial distribution in surface sediments showed that the area located between the commercial and the fishing port of Gabes is the most polluted zone. The ranking of metal contents was found to be Zn > Cd > Cu > Pb. The vertical distribution of trace metals indicated that the highest levels were found in the uppermost segment of the sediment cores compared to the lower depth subsurface due to a continuous input of phosphogypsum (PG) release and confirmed that the area between the two harbors suffered from several types of pollutants compared to reference core C1, collected from other non-industrialized areas. This spatial and vertical distribution is probably due to the harbor piers which acted as barriers and limited the dispersion of PG discharge. The contamination factor, the geoaccumulation index, and the pollution load index were determined. The results obtained confirm the anthropogenic impact on the levels of metal, on the fluorine, calcium, and sulfate concentrations in the area, located between the commercial harbor of Ghannouch and the fishing harbor of Gabes, whereas the concentrations of elements analyzed tends to decrease on both sides of this sector. Statistical analyses (principal component analysis) showed trace metals, fluoride, sulfate, and a large amount of calcium resulting from the same anthropogenic source.     

Loss on ignition vs. thermogravimetric analysis: a comparative study to determine organic matter and carbonate content in sediments

Journal of Paleolimnology - Mass loss at specified temperatures has been used widely to determine amounts of organic matter and carbonate in sediment samples. The loss on ignition (LOI) method is...     

Persistence of clear-water,shallow-lake ecosystems: the role of protected areas and stable aquatic food webs

The roles of both landscape alteration and in-lake processes need to be considered in conservation strategies for shallow lakes in the prairie regions of North America. Here we focus on shallow lakes in west-central Minnesota, USA, highlighting the long-term ecological history and response to known landscape changes of a clear-water, macrophyte-dominated, shallow lake. Contemporary limnological data suggest the aquatic ecosystem has been very stable and fishless for the last ~15 years. Sediment proxies for primary production and ecological change confirm that a stable ecosystem likely prevailed for the last ~200 years. However, sedimentary indicators of catchment erosion detail a distinct response to land-use change during the conversion of native grassland to agricultural land, and following establishment of a protected waterfowl production area (WPA) around the lake. Post-WPA, the rate of sediment accrual decreased dramatically within 5–10 years and sources of organic matter were similar to those of the pre-settlement period. The aquatic ecosystem has been able to withstand nutrient enrichment and allochthonous inputs because stable trophic interactions have likely been in place for more than 200 years. We conclude that lack of hydrologic connectivity and isolated, small catchments are important factors in the promotion of clear-water shallow lake ecosystems, mainly because they prevent colonization by fish and associated ecological consequences. This study highlights the importance of managing both the landscape and in-lake processes to maintain stable, clear-water, shallow lakes.     

Dynamics of the coupled human–climate system resulting from closed-loop control of solar geoengineering

If solar radiation management (SRM) were ever implemented, feedback of the observed climate state might be used to adjust the radiative forcing of SRM in order to compensate for uncertainty in either the forcing or the climate response. Feedback might also compensate for unexpected changes in the system, e.g. a nonlinear change in climate sensitivity. However, in addition to the intended response to greenhouse-gas induced changes, the use of feedback would also result in a geoengineering response to natural climate variability. We use a box-diffusion dynamic model of the climate system to understand how changing the properties of the feedback control affect the emergent dynamics of this coupled human–climate system, and evaluate these predictions using the HadCM3L general circulation model. In particular, some amplification of natural variability is unavoidable; any time delay (e.g., to average out natural variability, or due to decision-making) exacerbates this amplification, with oscillatory behavior possible if there is a desire for rapid correction (high feedback gain). This is a challenge for policy as a delayed response is needed for decision making. Conversely, the need for feedback to compensate for uncertainty, combined with a desire to avoid excessive amplification of natural variability, results in a limit on how rapidly SRM could respond to changes in the observed state of the climate system.     

Impacts on groundwater recharge areas of megacity pumping: analysis of potential contamination of Kolkata,India, water supply

Abstract

Water supply to the world’s megacities is a problem of quantity and quality that will be a priority in the coming decades. Heavy pumping of groundwater beneath these urban centres, particularly in regions with low natural topographic gradients, such as deltas and floodplains, can fundamentally alter the hydrological system. These changes affect recharge area locations, which may shift closer to the city centre than before development, thereby increasing the potential for contamination. Hydrogeological simulation analysis allows evaluation of the impact on past, present and future pumping for the region of Kolkata, India, on recharge area locations in an aquifer that supplies water to over 13 million people. Relocated recharge areas are compared with known surface contamination sources, with a focus on sustainable management of this urban groundwater resource. The study highlights the impacts of pumping on water sources for long-term development of stressed city aquifers and for future water supply in deltaic and floodplain regions of the world.

Editor D. Koutsoyiannis

Citation Sahu, P., Michael, H.A., Voss, C.I., and Sikdar, P.K., 2013. Impacts on groundwater recharge areas of megacity pumping: analysis of potential contamination of Kolkata, India, water supply. Hydrological Sciences Journal, 58 (6), 1340–1360.     

The O’okiep Copper District, Namaqualand, South Africa: a review of the geology with emphasis on the petrogenesis of the cupriferous Koperberg Suite

The O’okiep Copper District is the oldest formal mining area in South Africa. Between 1852 and 2002, the 2,500 km² area yielded two million tons of copper from 32 mines ranging in ore tonnages from 140,000 to 37 million tons. This paper summarizes the calendar of events from the formation of the first primitive crust 1,700–2,000?Ma ago to early Cambrian times ~500?Ma ago, with particular emphasis on the Namaquan (Grenville) Orogeny, notably: the O’okiepian Episode (1,180–1,210?Ma ago) of alpine-type folding, regional granite plutonism, and granulite facies metamorphism and the Klondikean Episode (1,020–1,040?Ma ago) of open and tight folding and the intrusion of the Rietberg Granite and the Koperberg Suite. Almost all of the copper in the O’okiep District occurs in the Koperberg Suite, of which there are 1,700 small bodies that constitute 0.7% of the outcrop area. The suite comprises jotunite, anorthosite, biotite diorite, and hypersthenic rocks ranging from leuconorite to hypersthenite, and it is one of only two world examples of economic copper mineralization in rocks of the anorthosite–charnockite kindred; the second example is Caraiba, Brazil. High I _Sr and low ε _Nd (for a 1,030 Ma intrusion age), and high μ ₂ of 10.1, for Koperberg rock-types indicate a crustal progenitor for the suite, and the presence of jotunite suggests a (subducted) crustal source at ca. 40–50 km depth. The magmatic sulphide paragenesis in the Koperberg Suite is chalcopyrite?+?pyrrhotite (Narrap-type ore) that, in a number of ore-bodies, has been inverted under upper amphibolite facies conditions to bornite?+?Ti-free magnetite (Carolusberg-type ore). Meteoric fluids resulted in supergene Cu enrichment in Koperberg bodies to ~500?m below the pre-Nama peneplane, and lower greenschist facies metamorphism 500–570?Ma ago is reflected by inter alia Hoits-type ore bearing second-generation bornite?+?chalcopyrite(±?covellite?±?chalcocite).     

Metamorphic re-equilibration and metasomatism of highly chromian,garnet-rich peridotitic xenoliths from South African kimberlites

A history of decompression and metasomatism is preserved in a suite of highly chromian, garnet-rich peridotitic xenoliths from the diamondiferous Newlands and Bobbejaan kimberlites, South Africa. A high proportion of the garnets and chromites in these rocks plot in the diamond-facies fields on Cr₂O₃–CaO and Cr₂O₃–MgO wt% plots, and Cr-rich compositions are found in both the harzburgitic and lherzolitic fields. Petrographic evidence suggests that the earliest known mineralogies were those of olivine-bearing, garnet-rich rocks. These were modified by a decompression event that caused recrystallization of garnets and led to orientated spinel and pyroxene inclusions in garnet. Chemical zonation within garnet is divided into (1) external re-equilibration between garnet and matrix; (2) internal re-equilibration between garnet and its inclusions; and (3) metasomatically induced zoning between garnet core and a metasomatic rim. The compositional trajectories associated with zonations (1) and (2) in Ca–Cr plots may be closely modelled by means of sliding, garnet–spinel transition reactions whose slopes vary with bulk Ca composition; at intermediate Ca compositions, the trajectories closely match the slope of the lherzolite line or harzburgite/lherzolite boundary. The decreasing Cr/(Cr + Al) of the garnet in these zonations is in agreement with the evidence for decompression given by the petrographic recrystallization features, and overall decompression of probably 10–20 kb is indicated. We speculate on the age of these events, and consider the possibility of their association with major orogenic events documented by South African crustal rocks at 2.9–2.7 Ga, and events evidenced by peridotite-xenolith Re–Os model ages at 2.8–2.7 Ga.