Collocation of hydrological and biological attenuation of nitrate in an urban stream

The hydrologic and biogeochemical processes that control nutrient export in urban streams are not well understood. Attenuation can occur by tributary dilution, groundwater discharge, and biological processing both in the water column and the hyporheic zone. A wastewater treatment plant on Pennypack Creek, an urban stream near Philadelphia, PA, provided high nitrate concentrations for analysis of downstream attenuation processes. Longitudinal sampling for an 8‐km reach revealed decreases in nitrate concentration of 2 mg l^?1 at high flow and 4.5 mg l^?1 during low flow. During high flow, δ¹⁵N‐NO₃ increased from 9.5 to 10.5‰ and during low flow increased from 10.1 to 11.1‰. Two reaches were sampled at fine spatial intervals (approximately 200 m) to better identify attenuation processes. Mixing analysis indicated that groundwater discharge and biological processing both control nitrate concentration and isotope signatures. However, fine‐scaled sampling did not reveal spatially discrete zones; instead, these processes were occurring simultaneously. While both processes attenuate nitrate, they have opposite isotope signatures, which may have muted changes in δ¹⁵N‐NO₃. At high flow, a decrease in Cl/NO₃ ratios helped distinguish groundwater discharge occurring along both finely sampled reaches. At low flow, biological processing seemed to be occurring more extensively, but the δ¹⁵N‐NO₃ signature was not consistent with either a single process or a sequential combination of groundwater dilution and biological nitrate attenuation. The collocation of processes makes it more difficult to assess biological processing hot spots and predict how urbanization and subsequent stream restoration influence nitrate attenuation. Copyright © 2016 John Wiley & Sons, Ltd.     

An assessment of the climate change impacts on groundwater recharge at a continental scale using a probabilistic approach with an ensemble of GCMs

This study used 16 Global Climate Models and three global warming scenarios to make projections of recharge under a 2050 climate for the entire Australian continent at a 0.05° grid resolution. The results from these 48 future climate variants have been fitted to a probability distribution to enable the results to be summarised and uncertainty quantified. The median results project a reduction in recharge across the west, centre and south of Australia and an increase in recharge across the north and a small area in the east of the continent. The range of results is quite large and for large parts of the continent encompasses both increases and decreases in recharge. This makes it difficult to utilise for water resources management so the results have been analysed with a risk analysis framework; this enables the future projections for groundwater recharge to be communicated to water managers in terms of likelihood and consequence of a reduction in recharge. This highlights an important message for water resource managers that in most areas of Australia they will be making decisions on water allocations under considerable uncertainty as to the direction and magnitude of recharge change under a future climate and that this uncertainty may be irreducible.     

Future climate of the Caribbean from a super-high-resolution atmospheric general circulation model

Present-day (1979–2003) and future (2075–2099) simulations of mean and extreme rainfall and temperature are examined using data from the Meteorological Research Institute super-high-resolution atmospheric general circulation model. Analyses are performed over the 20-km model grid for (1) a main Caribbean basin, (2) sub-regional zones, and (3) specific Caribbean islands. Though the model’s topography underestimates heights over the eastern Caribbean, it captures well the present-day spatial and temporal variations of seasonal and annual climates. Temperature underestimations range from 0.1 °C to 2 °C with respect to the Japanese Reanalysis and the Climatic Research Unit datasets. The model also captures fairly well sub-regional scale variations in the rainfall climatology. End-of-century projections under the Intergovernmental Panel on Climate Change SRES A1B scenario indicate declines in rainfall amounts by 10–20 % for most of the Caribbean during the early (May–July) and late (August–October) rainy seasons relative to the 1979–2003 baselines. The early dry season (November–January) is also projected to get wetter in the far north and south Caribbean by approximately 10 %. The model also projects a warming of 2–3 °C over the Caribbean region. Analysis of future climate extremes indicate a 5–10 % decrease in the simple daily precipitation intensity but no significant change in the number of consecutive dry days for Cuba, Jamaica, southern Bahamas, and Haiti. There is also indication that the number of hot days and nights will significantly increase over the main Caribbean basin.     

Core Density Profile Survival in Dissipationless Mergers

We use N-body experiments to study the survival of power-law density cusps in mergers of spherical galaxy models. Steep cusps (e.g. ρ∝r ^-2) are preserved during mergers of equal-mass models; this may be viewed as a general consequence of the incomplete violent relaxation observed in such mergers. Progenitor profile has a strong effect on remnant shape; steep cusps produce oblate remnants. If bright ellipticals form by hierarchical mergers of faint ones, the lack of steep cusps in these galaxies is somewhat surprising. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tenerife – the big pyramid

There is nothing like a good controversy in geology, when vehemently held conflicting opinions set the adrenaline running. The debate over hot spots or mantle plumes is developing in this way; as such it is pertinent to look at the Canary Islands archipelago where hot spot ideas have been in place for some time.     

The X-ray emission in post-merger ellipticals

The evolution in X-ray properties of early-type galaxies is largely unconstrained. In particular, little is known about how, and if, remnants of mergers generate hot gas haloes. Here we examine the relationship between X-ray luminosity and galaxy age for a sample of early-type galaxies. Comparing normalized X-ray luminosity to three different age indicators, we find that L _X L _B increases with age, suggesting an increase in X-ray halo mass with time after the last major star formation episode of a galaxy. The long-term nature of this trend, which appears to continue across the full age range of our sample, poses a challenge for many models of hot halo formation. We conclude that models involving a declining rate of type Ia supernovae, and a transition from outflow to inflow of the gas originally lost by galactic stars, offer the most promising explanation for the observed evolution in X-ray luminosity.     

Experimental constraints on hydrogen diffusion in garnet

The incorporation mechanisms and diffusional loss of hydrogen in garnet have been experimentally investigated. A suite of gem-quality hydrous spessartine- and grossular-rich garnets were analysed by Fourier transform infrared spectroscopy (FTIR) and by ion microprobe (SHRIMP-SI) to determine the calibration coefficients for quantification of FTIR data. The excellent agreement between measured absorption and OH/O indicates that the same molar extinction coefficient can be used for spessartine and grossular. The coefficient of 14400 l mol^??1 cm^??2 proposed by Maldener et al. (Phys Chem Miner 30:337–344, 2003) seems the most appropriate for both minerals. A grossular with 6.4% andradite and 1.6% almandine containing 834 ppm H₂O, and an almost pure spessartine with 282 ppm H₂O, were selected for diffusion experiments. 1.5-mm cubes of garnets were heated between 12 h and 10 days at 1 atm under various temperature (750–1050 °C) and oxygen fugacity (\({f_{{{\text{O}}_2}}}\)) conditions, (ΔQFM +?15.2 to ??3.0). Diffusion profiles were acquired from sections through the cubes using FTIR, with a deconvolution algorithm developed to assess peak-specific behaviour. Different families of peaks have been identified based on their diffusive behaviour, representing hydrogen incorporated in different H-bearing defects. A dominant, fast, strongly \({f_{{{\text{O}}_2}}}\)-dependent oxidation-related diffusion mechanism is proposed \(\left( {\{ {{\text{M}}^{2+}}+{{\text{H}}^+}\} +\frac{1}{4}{{\text{O}}_2}={{\text{M}}^{3+}}+\frac{1}{2}{{\text{H}}_2}{\text{O}}} \right)\) (M=Fe, Mn) with a relatively low activation energy (158?±?19 kJ mol^??1). This diffusion mechanism is likely restricted by availability of ferrous iron in grossular. At low oxygen fugacity, this diffusion mechanism is shut off and the diffusivity decreased by more than three orders of magnitude. A second, slower hydrogen diffusion mechanism has been observed in minor bands, where charge balance might be maintained by diffusion of cation vacancies, with much higher activation energy (≈?200–270 kJ mol^??1). Spessartine shows clear differences in peak retentivity suggesting that up to four different H sites might exist. This opens exciting opportunities to use hydrogen diffusion in garnet as speedometer. However, it is essential to constrain the main diffusion mechanisms and the oxygen fugacity in the rocks investigated to obtain timescales for metamorphic or igneous processes.     

Chemical speciation and fate of tripolyphosphate after application to a calcareous soil

Adsorption and precipitation reactions often dictate the availability of phosphorus in soil environments. Tripolyphosphate (TPP) is considered a form of slow release P fertilizer in P limited soils, however, investigations of the chemical fate of TPP in soils are limited. It has been proposed that TPP rapidly hydrolyzes in the soil solution before adsorbing or precipitating with soil surfaces, but in model systems, TPP also adsorbs rapidly onto mineral surfaces. To study the adsorption behavior of TPP in calcareous soils, a short-term (48 h) TPP spike was performed under laboratory conditions. To determine the fate of TPP under field conditions, two different liquid TPP amendments were applied to a P limited subsurface field site via an in-ground injection system. Phosphorus speciation was assessed using X-ray absorption spectroscopy, total and labile extractable P, and X-ray diffraction. Adsorption of TPP to soil mineral surfaces was rapid (< 48 h) and persisted without fully hydrolyzing to ortho-P. Linear combination fitting of XAS data indicated that the distribution of adsorbed P was highest (~ 30–40%) throughout the site after the first TPP amendment application (high water volume and low TPP concentrations). In contrast, lower water volumes with more concentrated TPP resulted in lower relative fractions of adsorbed P (15–25%), but a significant increase in total P concentrations (~ 3000 mg P kg soil) and adsorbed P (60%) directly adjacent to the injection system. This demonstrates that TPP application increases the adsorbed P fraction of calcareous soils through rapid adsorption reactions with soil mineral surfaces.