Asia on the move: research challenges for population geography

This paper "summarises some of the major changes which have occurred in international migration to, from, and within Asia in the last two decades....A number of theoretical challenges are put forward regarding the complex interrelationships between international population movements, economic development and social change. The employment of systems approaches, neoclassical economic theory, social networks and institutional approaches, and the potential role of population geography in developing a more comprehensive explanation of the changing dynamics of international migration in the region, are discussed. Also considered are the gender dimension in migration, remittance flows and their consequences, and policy issues."     

Passage time, viability, and germination of seeds ingested by foxes

Seed passage through the gut of vertebrates is critical for endozoochorus seed dispersal because it may influence seed viability and germination capacity. Foxes are important fruit-eaters and presumed seed dispersers in the Chaco ecoregion. We experimentally assessed the seed passage time (SPT) and its effect on seed viability and germination in two fox species (Pseudalopex gymnocercus and Cerdocyon thous) that occur in the Chaco. Passage time was measured using both artificial seeds of three sizes and wild seeds of four native fleshy-fruit species commonly consumed by foxes (Ziziphus mistol, Acacia aroma, Celtis tala, and Syagrus romanzoffiana). The average SPT was 6.8 h for the Pampa fox and 7.7 h for the crab-eating fox. Passage time did not differ either among seeds of different sizes or between fox species. Passage through digestive tract of both fox species did not affect seed survival, whereas germination rate was slightly improved. Our data suggest that both fox species are legitimate seed dispersers of the four species studied, having a positive effect on both germination rate and dispersal distance from the parent plant.     

Gneiss-Water Interaction and Water Evolution During the Early Stages of Dissolution Experiments at Room Temperature

Gneiss-distilled water interaction at room temperature was investigated with batch-reactors to study water-rock reaction and geochemical evolution of the aqueous phase with time. The ion concentrations in water were controlled not only by the dissolution of primary minerals, but also by the precipitation of secondary minerals. The decreasing fraction sizes of gneiss could favor dissolution and precipitation simultaneously. Ca^2 and K^ were the major cations, and HCO3^- was the major anion in water. All the ions except Ca^2 increased in concentration with time. The Ca^2 release from the rock to the aqueous phase was initially much faster than the release of K^ , Na^2 and Mg^2 . But after about 5 - 24 hours, the Ca^2 concentrations in water decreased very slowly with time and became relatively stable. During the experiment, the water varied from the Ca-( K)-HCO3-type water to the K-Ca-HCO3-type water, and then to the K-(Ca, Na)-HCO3-type water. The water-gneiss interaction was dominated by the dissolution of Kfeldspar in the solution. The remaining secondary minerals were mainly kaolinite, illite and K (Mg) -mica.     

Runoff Scaling in Large Rivers of the World

Runoff and precipitation scaling with respect to drainage area is analyzed for large river basins of the world, those with mean annual runoff in excess of 10 k³/yr. The usefulness of the specific runoff (runoff per unit drainage area, m/yr) to categorize runoff scaling laws across the complete spectrum of climatic and hydrologic conditions is evaluated. It is found that (1) runoff scales with drainage are in those river basins with specific runoff in excess of 0.15 m/yr (r² = 0.88); (2) runoff scaling with drainage area shows remarkably high statistical correlation (r²= 0.97) in river basins with specific runoff equal to or larger than 1.0 m/yr; (3) runoff does not Inc.rease with Inc.reasing drainage area in river basins with specific runoff below 0.15 m/yr, where no discernible statistical association was found between runoff and drainage area; and (4) precipitation depth (m/yr) is inversely proportional to drainage area raised to a fractional exponent in river basins with specific runoff in excess of 0.15 m/yr.     

Managed water levels and the expansion of emergent vegetation along a lakeshore

Water-level fluctuations may be used to promote the expansion of emergent vegetation along lakeshores. We present the case of the lake Volkerak-Zoommeer in the Netherlands, a fresh-water lake created in 1987 after the enclosure of an estuary. Using an experimental area in which the water level could be manipulated, it was shown that partial summer drawdown of the shoreline created suitable conditions for germination and growth of tall emergent species (in particular Phragmites australis). Plant survival and growth depended on subsequent water-level fluctuations and grazing by waterbirds. Based on the experiment and empirical data, a model was developed to predict the effects of the water-level regime on potential reed bed development. The model was applied for four hydrological scenarios that have been considered for the water-level management of the lake.     

Short‐ and long‐term evapotranspiration rates at ecological restoration sites along a large river receiving rare flow events

Many large rivers around the world no longer flow to their deltas, due to ever greater water withdrawals and diversions for human needs. However, the importance of riparian ecosystems is drawing increasing recognition, leading to the allocation of environmental flows to restore river processes. Accurate estimates of riparian plant evapotranspiration (ET) are needed to understand how the riverine system responds to these rare events and achieve the goals of environmental flows. In 2014, historic environmental flows were released into the Lower Colorado River at Morelos Dam (Mexico); this once perennial but now dry reach is the final stretch to the mighty Colorado River Delta. One of the primary goals was to supply native vegetation restoration sites along the reach with water to help seedlings establish and boost groundwater levels to foster the planted saplings. Patterns in ET before, during, and after the flows are useful for evaluating whether this goal was met and understanding the role that ET plays in this now ephemeral river system. Here, diurnal fluctuations in groundwater levels and Moderate Resolution Imaging Spectroradiometer (MODIS) data were used to compare estimates of ET specifically at 3 native vegetation restoration sites during 2014 planned flow events, and MODIS data were used to evaluate long‐term (2002–2016) ET responses to restoration efforts at these sites. Overall, ET was generally 0–10 mm d^?1 across sites, and although daily ET values from groundwater data were highly variable, weekly averaged estimates were highly correlated with MODIS‐derived estimates at most sites. The influence of the 2014 flow events was not immediately apparent in the results, although the process of clearing vegetation and planting native vegetation at the restoration sites was clearly visible in the results.     

Quantifying multiple Permian–Recent exhumation events during the break‐up of eastern Gondwana: sonic transit time analysis of the central and southern Perth Basin

The central and southern Perth Basin in southwestern Australia has a geological history involving multiple regional unconformity‐forming events from the Permian to Recent. This study uses sonic transit time analysis to quantify the magnitudes of net and gross exhumation for four stratigraphic periods from 43 wells. Most importantly, we quantify gross exhumation of the Permian–Triassic, Triassic–Jurassic, Valanginian break‐up and post‐Early Cretaceous events. Post‐Early Cretaceous gross exhumation averages 900‐m offshore and 600‐m onshore. Up to 200 m of this exhumation may be attributed to localized fault block rotation during extension in the Late Cretaceous and/or reverse fault re‐activation due to the compressive stresses in Australia in the last 50 Ma. The remainder is attributed to regional exhumation caused by epeirogenic processes either during the Cenozoic or at the Aptian–Albian boundary. Maximum burial depths prior to the Valanginian unconformity‐forming event were less than those reached subsequently, so that the magnitude of Valanginian break‐up exhumation cannot be accurately quantified. Gross exhumation prior to the break‐up of Gondwana was defined by large magnitude differences (up to 2500 m) between adjoining sub‐basins. At the end of Triassic, exhumation is primarily attributed to reverse re‐activation of faults that were driven by short‐wavelength inversion and exhumation at the end Permian is likely caused by uplift of rotated fault blocks during extension. The evidence from quantitative exhumation analysis indicates a switch in regime, from locally heterogeneous before break‐up to more regionally homogeneous after break‐up.     

Bristen granite: a highly differentiated,fluorite-bearing A-type granite from the Aar massif,Central Alps,Switzerland

Bristen granite is a body of fine-grained leucogranite occurring in the Gotthard rail base tunnel in the Central Alps. During construction of the tunnel, Bristen granite (Brgr) has been drilled along a 600 m long section. The aplite-granite belongs to the suite of Variscan granitoid intrusions of the Aar massif and contains a variety of accessory minerals typical of highly differentiated granites. Rock forming fluorite, partly enriched in yttrium (Y) and rare earth elements (REE), is intergrown with the late Y- and REE-bearing carbonate mineral synchysite. The granite contains a variety of Ti- and Y-REE-niobates, thorite, and zircon. Compared with the calc-alkaline central Aar granite (cAgr), Bristen granite is strongly depleted in Ti, P, Mg, Sr, and Ba and shows a remarkable enrichment in incompatible elements such as Rb, Th, U, Nb, Y, HREE and F. Bristen granite is the most evolved granitoid rock of the Aar massif. The composition of Brgr is typical of post-collisional reduced (ferroan) A-type granites. The Brgr melt formed in the lower crust and crystallized from a highly differentiated melt at the cotectic point in the quartz-feldspar system close to 100 MPa and 700 °C. The Brgr intruded as a small isolated stock pre-Variscan gneisses with sharply discordant contacts. The primary igneous host of Nb, Ta, Y, U, Th and REE is biotite in addition to minor amounts of allanite, and zircon. The presence of Y-REE-fluorite, synchysite, parisite and Y- and Ti-niobates and other REE-minerals can be related to reaction of igneous biotite and primary fluorite with hydrothermal fluids. The reaction is associated with alpine metamorphism, because Y-bearing fluorite and synchysite have been reported from Alpine fissures. The transformation of primary biotite to chlorite and muscovite released the heavy metal oxides under lower greenschist facies conditions that formed the Alpine diagnostic mineral stilpnomelane at about 300 °C.