Cross-taxon responses to elevated nutrients in European streams and lakes

Few studies have compared the response of different taxonomic groups to environmental stress across aquatic ecosystems. We regressed assemblage structure of fish, invertebrates, macrophytes, phytoplankton and benthic diatoms to total phosphorus concentration, after removing the effect of ecosystem size (stream order, lake surface area), using data from 66 streams and 45 lakes across Europe. In streams, the structure of benthic diatom assemblages, measured by nonmetric multidimensional scaling, showed the strongest correlation to elevated nutrient concentrations (adj. R² = 0.495), followed by benthic invertebrates (0.376), fish (0.181) and macrophytes (0.153). For lakes, the patterns were less clear: fish (0.155), macrophytes (0.146) and phytoplankton (0.132). Cross-system comparison showed that stream assemblages were responding more strongly to nutrient concentrations than lake assemblages. Moreover, our results lend some support to the conjecture that response signatures are related to trophic level, with primary producers (benthic diatoms) responding more strongly than consumers (invertebrates, fish). Knowledge of differences in responses among taxonomic groups and between habitats to disturbance can be used to design more cost-effective monitoring programs.     

High-resolution X-Band radar measurements of currents,bathymetry and sea state in highly inhomogeneous coastal areas

In this paper, high-resolution wave, current and water depth fields derived by marine X-Band radar are presented for a coastal region of extreme tidal currents in the presence of inhomogeneous bathymetry at the south coast of New Zealand’s North Island. The current and water depth information for the presented location covers an area of approximately 13 km² with a spatial resolution of 225 m and an update rate of 3 min. The sea state data provides a spatial representation of coastal effects like wave shoaling and refraction forced by bathymetry and current interaction. The near-surface current measurements about 3 km off the coast show expected tidal current pattern with maximum northwest/southeast current of 1.5–2 m/s alongshore. This is in agreement with currents from the RiCOM hydrodynamic model. The spatial resolution of the observed current field exhibits in addition small-scale current features caused by the influence of the local bathymetry. These data demonstrate the insight to be gained in complex, high-energy coastal situations through the use of high-resolution remote sensing techniques.     

Influence of junction angle on three‐dimensional flow structure and bed morphology at confluent meander bends during different hydrological conditions

Recent field and modeling investigations have examined the fluvial dynamics of confluent meander bends where a straight tributary channel enters a meandering river at the apex of a bend with a 90° junction angle. Past work on confluences with asymmetrical and symmetrical planforms has shown that the angle of tributary entry has a strong influence on mutual deflection of confluent flows and the spatial extent of confluence hydrodynamic and morphodynamic features. This paper examines three‐dimensional flow structure and bed morphology for incoming flows with high and low momentum‐flux ratios at two large, natural confluent meander bends that have different tributary entry angles. At the high‐angle (90°) confluent meander bend, mutual deflection of converging flows abruptly turns fluid from the lateral tributary into the downstream channel and flow in the main river is deflected away from the outer bank of the bend by a bar that extends downstream of the junction corner along the inner bank of the tributary. Two counter‐rotating helical cells inherited from upstream flow curvature flank the mixing interface, which overlies a central pool. A large influx of sediment to the confluence from a meander cutoff immediately upstream has produced substantial morphologic change during large, tributary‐dominant discharge events, resulting in displacement of the pool inward and substantial erosion of the point bar in the main channel. In contrast, flow deflection is less pronounced at the low‐angle (36°) confluent meander bend, where the converging flows are nearly parallel to one another upon entering the confluence. A large helical cell imparted from upstream flow curvature in the main river occupies most of the downstream channel for prevailing low momentum‐flux ratio conditions and a weak counter‐rotating cell forms during infrequent tributary‐dominant flow events. Bed morphology remains relatively stable and does not exhibit extensive scour that often occurs at confluences with concordant beds. Copyright © 2014 John Wiley & Sons, Ltd.     

Forecasting Natural Aquifer Discharge Using a Numerical Model and Convolution

If the nature of groundwater sources and sinks can be determined or predicted, the data can be used to forecast natural aquifer discharge. We present a procedure to forecast the relative contribution of individual aquifer sources and sinks to natural aquifer discharge. Using these individual aquifer recharge components, along with observed aquifer heads for each January, we generate a 1‐year, monthly spring discharge forecast for the upcoming year with an existing numerical model and convolution. The results indicate that a forecast of natural aquifer discharge can be developed using only the dominant aquifer recharge sources combined with the effects of aquifer heads (initial conditions) at the time the forecast is generated. We also estimate how our forecast will perform in the future using a jackknife procedure, which indicates that the future performance of the forecast is good (Nash‐Sutcliffe efficiency of 0.81). We develop a forecast and demonstrate important features of the procedure by presenting an application to the Eastern Snake Plain Aquifer in southern Idaho.     

Al decay: Heat production and a revised age for Iapetus

We revisit the appropriate energies to be used for computing heat production from ²⁶Al decay. Due to the complexity of the decay scheme of this radioisotope, previous geophysical studies have used values ranging from 1.2 to 4 MeV per decay. The upper bound corresponds to the difference in mass energy between the ²⁶Al and ²⁶Mg ground states. This includes energy carried away by neutrinos, which does not contribute to heating planetary material. The lower bound does not account for the heating caused by the absorption of the γ rays from the excited ²⁶Mg, or for the annihilation energy deposited in the material if the decay occurs inside even small planetesimals. Based on the calculations described by Schramm et al. [Schramm, D., Tera, F., Wasserburg, G.J., 1970. The isotopic abundance of ²⁶Mg and limits on ²⁶Al in the early Solar System. Earth Planet. Sci. Lett. 10, 44-59] updated with the most recent nuclear constants, we recommend using a heat production value of 3.12 MeV per decay, which is the total energy of disintegration minus the energy carried off by the neutrinos. This heat production value is higher than the value used in the modeling of Iapetus by Castillo-Rogez et al. [Castillo-Rogez, J., Matson, D.L., Sotin, C., Johnson, T.V., Lunine, J.I., Thomas, P.C., 2007. Iapetus’ geophysics: Rotation rate, shape, and equatorial ridge. Icarus 190, 179-202] by about a factor 2.5. The resulting estimate of the time of formation of Iapetus is shifted by about 1 Myr, to between ∼3.4 and 5.4 Myr after the production of the calcium-aluminum inclusions (CAIs).     

A comprehensive program for countermeasures against potentially hazardous objects (PHOs)

At the hundredth anniversary of the Tunguska event in Siberia it is appropriate to discuss measures to avoid such occurrences in the future. Recent discussions about detecting, tracking, cataloguing, and characterizing near-Earth objects (NEOs) center on objects larger than about 140 m in size. However, objects smaller than 100 m are more frequent and can cause significant regional destruction of civil infrastructures and population centers. The cosmic object responsible for the Tunguska event provides a graphic example: although it is thought to have been only about 50 to 60 m in size, it devastated an area of about 2000 km². Ongoing surveys aimed at early detection of a potentially hazardous object (PHO: asteroid or comet nucleus that approaches the Earth’s orbit within 0.05 AU) are only a first step toward applying countermeasures to prevent an impact on Earth. Because “early” may mean only a few weeks or days in the case of a Tunguska-sized object or a longperiod comet, deflecting the object by changing its orbit is beyond the means of current technology, and destruction and dispersal of its fragments may be the only reasonable solution. Highly capable countermeasures- always at the ready—are essential to defending against an object with such short warning time, and therefore short reaction time between discovery and impending impact. We present an outline for a comprehensive plan for countermeasures that includes smaller (Tunguska-sized) objects and long-period comets, focuses on short warning times, uses non-nuclear methods (e.g., hyper-velocity impactor devices and conventional explosives) whenever possible, uses nuclear munitions only when needed, and launches from the ground. The plan calls for international collaboration for action against a truly global threat.     

Geophysical exploration of the Puhipuhi epithermal area, Northland, New Zealand

The Puhipuhi epithermal area, which occurs in a region of graywacke basement partially covered by basalt and lake-bed deposits, is characterized by both large-scale and small-scale geophysical anomalies. Known occurrences of locally intense alteration or silicification are typically associated with strong gravity, resistivity or IP anomalies. Gravity data define a complex negative residual anomaly (up to −50 gu) which has been used to identify and delineate a large area (about 20 km²) of low-density, presumably clay-altered, graywacke basement rocks. This zone, modeled as extending to a few kilometers depth, encompasses, but is more extensive than, the known areas of alteration and has a close spatial association with the basalt cover rocks. Short-wavelength gravity minima and maxima, which indicate that the most intense alteration of the basement rocks occurs below the basalt, correlate, in part, with the inferred location of hydrothermal upflow zones. The control on the location of these zones and their relationship to the location of the basalts is not well known; however, if the basalts acted as a cap rock to the geothermal system, then these areas merit further exploration. High (≥100 ohm-m) and low (≤10 ohm-m) resistivity and high (≥30 mS) IP anomalies occur in association with known silicification, clay alteration and sulfide mineralisation, respectively. In addition, magnetic data help constrain the relative timing of hydrothermal alteration and basaltic volcanism and indicate that mineralisation was broadly synchronous with volcanism.     

A mathematical analysis of the divergence problem in dendroclimatology

Tree rings provide a primary data source for reconstructing past climates, particularly over the past 1,000 years. However, divergence has been observed in twentieth century reconstructions. Divergence occurs when trees show a positive response to warming in the calibration period but a lesser or even negative response in recent decades. The mathematical implications of divergence for reconstructing climate are explored in this study. Divergence results either because of some unique environmental factor in recent decades, because trees reach an asymptotic maximum growth rate at some temperature, or because higher temperatures reduce tree growth. If trees show a nonlinear growth response, the result is to potentially truncate any historical temperatures higher than those in the calibration period, as well as to reduce the mean and range of reconstructed values compared to actual. This produces the divergence effect. This creates a cold bias in the reconstructed record and makes it impossible to make any statements about how warm recent decades are compared to historical periods. Some suggestions are made to overcome these problems.