Postgraduate prize preparations

While postgrad students complete their PhD theses, supervisors should note the deadline for submissions to the annual Michael Penston and Keith Runcorn Prizes.     

Astronomy in the garden wins RHS prize

The Spaced Out garden, sponsored by the RAS, won a Gold Medal from the Royal Horticultural Society at the Tatton Park Garden Show in August. It also provided a showcase for a model of the Philae Lander, part of ESA's Rosetta mission to comet 67 P/Churyumov-Gerasimenko and an unusual occasion for astronomy outreach.     

Fluid dynamics in volcanology (wager prize lecture)

Fluid motions are important in virtually all volcanic processes. Attempts to understand the mechanism of volcanic activity or the origin of magmas generally require knowledge of fluid dynamics. The use of fluid dynamics is illustrated by considering the Reynolds numbers of some volcanic fluid flow systems. The physics of high Reynolds number buoyant plumes is found to be important in situations ranging from the rise of eruption columns in the atmosphere to the replenishment of basaltic magma chambers. Application of theoretical and experimental work on plumes enables eruption rates to be deduced from eruption column heights and new hypotheses on the origin of some magmatic ores to be put forward. The influence of Reynolds number on the behaviour of lava is also discussed with application to the origin of Archaean komatiite lavas. Komatiite lavas are argued to have flowed in a turbulent manner whereas modern basalt lavas nearly always flow by laminar shear. The turbulent character of komatiites seems to provide an explanation for the origin of associated nickel-sulfide mineralization in komaiites by melting and assimilation of sulfide-rich sediment. This hypothesis depends on komatiite flow having had a high Reynolds number.     

Impact of water withdrawals from groundwater and surface water on continental water storage variations

Humans have strongly impacted the global water cycle, not only water flows but also water storage. We have performed a first global-scale analysis of the impact of water withdrawals on water storage variations, using the global water resources and use model WaterGAP. This required estimation of fractions of total water withdrawals from groundwater, considering five water use sectors. According to our assessment, the source of 35% of the water withdrawn worldwide (4300 km³/year during 1998–2002) is groundwater. Groundwater contributes 42%, 36% and 27% of water used for irrigation, households and manufacturing, respectively, while we assume that only surface water is used for livestock and for cooling of thermal power plants. Consumptive water use was 1400 km³/year during 1998–2002. It is the sum of the net abstraction of 250 km³/year of groundwater (taking into account evapotranspiration and return flows of withdrawn surface water and groundwater) and the net abstraction of 1150 km³/year of surface water. Computed net abstractions indicate, for the first time at the global scale, where and when human water withdrawals decrease or increase groundwater or surface water storage. In regions with extensive surface water irrigation, such as Southern China, net abstractions from groundwater are negative, i.e. groundwater is recharged by irrigation. The opposite is true for areas dominated by groundwater irrigation, such as in the High Plains aquifer of the central USA, where net abstraction of surface water is negative because return flow of withdrawn groundwater recharges the surface water compartments. In intensively irrigated areas, the amplitude of seasonal total water storage variations is generally increased due to human water use; however, in some areas, it is decreased. For the High Plains aquifer and the whole Mississippi basin, modeled groundwater and total water storage variations were compared with estimates of groundwater storage variations based on groundwater table observations, and with estimates of total water storage variations from the GRACE satellites mission. Due to the difficulty in estimating area-averaged seasonal groundwater storage variations from point observations of groundwater levels, it is uncertain whether WaterGAP underestimates actual variations or not. We conclude that WaterGAP possibly overestimates water withdrawals in the High Plains aquifer where impact of human water use on water storage is readily discernible based on WaterGAP calculations and groundwater observations. No final conclusion can be drawn regarding the possibility of monitoring water withdrawals in the High Plains aquifer using GRACE. For the less intensively irrigated Mississippi basin, observed and modeled seasonal groundwater storage reveals a discernible impact of water withdrawals in the basin, but this is not the case for total water storage such that water withdrawals at the scale of the whole Mississippi basin cannot be monitored by GRACE.     

Tree water deficit and dynamic source water partitioning

The stable isotopes of hydrogen and oxygen (δ²H and δ¹⁸O, respectively) have been widely used to investigate tree water source partitioning. These tracers have shed new light on patterns of tree water use in time and space. However, there are several limiting factors to this methodology (e.g., the difficult assessment of isotope fractionation in trees, and the labor-intensity associated with the collection of significant sample sizes) and the use of isotopes alone has not been enough to provide a mechanistic understanding of source water partitioning. Here, we combine isotope data in xylem and soil water with measurements of tree's physiological information including tree water deficit (TWD), fine root distribution, and soil matric potential, to investigate the mechanism driving tree water source partitioning. We used a 2 m³ lysimeter with willow trees (Salix viminalis) planted within, to conduct a high spatial–temporal resolution experiment. TWD provided an integrated response of plant water status to water supply and demand. The combined isotopic and TWD measurement showed that short-term variation (within days) in source water partitioning is determined mainly by plant hydraulic response to changes in soil matric potential. We observed changes in the relationship between soil matric potential and TWD that are matched by shifts in source water partitioning. Our results show that tree water use is a dynamic process on the time scale of days. These findings demonstrate tree's plasticity to water supply over days can be identified with high-resolution measurements of plant water status. Our results further support that root distribution alone is not an indicator of water uptake dynamics. Overall, we show that combining physiological measurements with traditional isotope tracing can reveal mechanistic insights into plant responses to changing environmental conditions.     

Biochemical biomarkers in adult female perch (Perca fluviatilis) in a chronically polluted gradient in the Stockholm recipient (Sweden)

A battery of biochemical biomarkers and the SigmaPCB concentration in adult female perch (Perca fluviatilis) verified an aquatic pollution gradient with the city of Stockholm (Sweden) as a point source of anthropogenic substances. The investigation included both an upstream gradient, 46 km westwards through Lake M?laren, and a downstream gradient, 84 km eastwards through the Stockholm archipelago. Besides the main gradient from Stockholm, there were strong indications of pollution coming from the Baltic Sea. The results indicated a severe pollution situation in central Stockholm, with poor health status of the perch, characterised by increased specific EROD activity in the liver, increased liver EROD somatic index, decreased AChE activity in the muscle, increased amount of DNA adducts in the liver, and a high concentration of biliary 1-pyrenol. In addition, laboratory exposure to common EROD inducers elicited an abnormal response, suggestive of chronic intoxication.     

Statistical assessment of relationships between water flow in a river and water turbidity in water intakes

Probability distributions of water flow and its turbidity after passing through water intake structures are considered. Heavy tails with a power distribution are shown to exist. These distributions are used to find the dependence between water turbidity at the inlet to the water station and water flow in the river. Quantiles of these distributions are estimated to characterize the levels of water flow and turbidity with a given exceedance probability.Translated from Vodnye Resursy, Vol. 32, No. 2, 2005, pp. 196–204.Original Russian Text Copyright © 2005 by Dolgonosov, Korchagin.     

Basic physiological biomarkers in adult female perch (Perca fluviatilis) in a chronically polluted gradient in the Stockholm recipient (Sweden)

By measuring a battery of basic physiological biomarkers and the concentration of SigmaDDT in adult female perch (Perca fluviatilis), an assumed aquatic pollution gradient was confirmed, with the city of Stockholm (Sweden) as a point source of anthropogenic substances. The investigation included an upstream gradient, westwards through Lake M?laren (46 km), and a downstream gradient, eastwards through the Stockholm archipelago (84 km). The results indicated a severe pollution situation in central Stockholm, with poor health status of the perch: retarded growth, increased frequency of sexually immature females, low gonadosomatic index, and disturbed visceral fat metabolism. SigmaDDT, measured as a pollution indicator, was 10-28 times higher than the background in perch from the Baltic Proper. Besides the main gradient other sources of pollution also influenced the response pattern of the measured biomarkers. In particular, there were strong indications of pollution coming from the Baltic Sea.