Pre- and post-dispersal seed loss and soil seed dynamics of the dominant Bulnesia retama (Zygophyllaceae) shrub in a sandy Monte desert of western Argentina

In deserts and semi-deserts dominant plants seldom rely on a persistent seed bank to ensure their recruitment from sexual reproduction, which is generally based on the seeds produced in the last reproductive event. We studied pre- and post-dispersal seed loss of Bulnesia retama, a dominant shrub of the sandy Monte deserts (western Argentina). We hypothesised that pre- and post-dispersal seed depletion in B. retama regulate soil seed density and in turn decrease soil seed reserves. We also hypothesised that spatial patches induced by standing vegetation and other microsites additionally affect post-dispersal seed loss and soil seed density.We observed that as much as half the total seed production was lost due to pre-dispersal seed predation. Seed dispersal plus predation showed a negative exponential function with 61% of seeds falling during the first 28 days, and 99% after 90 days, when 34% of the seeds remained inside excluded branches. A significant patch effect was observed on soil seed density and seed dynamics, with a greater number of seeds and increased seed depletion rates below B. retama shrubs. However, spatial patches did not affect seed germination although they increased with burial time, from 22% to 70% after 75 and 276 days, respectively. Likewise, a similar trend was found in potential seed germination; seeds collected directly from mother plants had a low germination rate (less than 25%), which increased to 75% after 276 days of soil burial. About 15% of the dispersed seeds should persist to the next rainy season, thus contributing to a low-density but persistent seed bank.The delay in seed germination and temporal decrease in soil seed density that we observed for B. retama suggest that a set of mechanisms have been developed promoting germination events whenever soil water is available, at any moment of the year.     

Photometric Study of the W Uma-Type Eclipsing Binary System GSC 4832.400

We present a photometric analysis of the eclipsing binary systemGSC4832.400 based on 732 photometric observations obtained on sixteen clear nights during 1999–2000 in the V-Johnson and yb-Strömgren filters. The observed times of the minima yielded a linear ephemeris showing that the system has a constant period of 0.313150 ± 0.000002days. The light curve corresponds to a circular orbit for the system and clearly shows that GSC4832.400 has the defining characteristics of a W UMa-type eclipsing binary. It also shows a small O'Connell effect, which could be due to the presence of a hot spot in the primary star. A preliminary photometric solution based on the assumption of an over contact systemsatis factorily reproduced the observed light curve.     

Comparison of two different solutions to Molodensky’s G1 term

The main purpose of this paper is comparison of two different approaches of solution to the Simple Molodensky’s Problem, the Molodensky’s Approach and the Analytical Continuation Approach, based on numerical computation. Although these approaches have been described theoretically by several authors, e.g. Molodensky et al. (1960), Heiskanen and Moritz (1967), Vaníček (1974), Moritz (1980) and Holota (1991, unpublished results) and theoretical proof of equivalence was given by Heiskanen and Moritz (1967), Moritz (1971), Ecker (1971) and Pellinen (1972, unpublished results), only very few practical experiences about the differences between particular solutions and computational efficiency exist. In this paper we compare the above two mentioned approaches in terms of the G₁-effect on quasigeoid. Both quasigeoid solutions are tested by the independent GPS/levelling approach and are also compared with the previous quasigeoid model of Slovakia where the G₁-term has been approximated using the classical terrain correction. The effect of the G₂-term is also numerically estimated, revealing that it might be significant for the precise quasigeoid determination. Some practical comments and recommendations are given at the end of the paper.     

The chemistry of geothermal waters in Iceland. III. Chemical geothermometry in geothermal investigations

New data from geothermal wells in Iceland have permitted empirical calibration of the chalcedony and $\text{Na}\text{K}$ geothermometers in the range of 25–180°C and 25–250°C respectively. The temperature functions are:

$\text{t°C=}\text{1112}\text{4.91?}\text{log SiO}{}_2\text{?273.15}$

$\text{t°C=}\text{933}\text{0.993+}\text{log Na/K}\text{?273.15}$

Concentrations are expressed in ppm. These temperature functions correspond well with the chalcedony solubility data of Fournier (1973) and the thermodynamic data for low-albite/microcline/solution equilibria of Heloeson (1969).A new CO₂ geothermometer is proposed which is considered to be useful in estimating underground temperatures in fumarolic geothermal fields. Its application involves analysis of CO₂ concentrations in the fumarole steam. The temperature function which applies in the range 180?300°C is: logCO₂ = 37.43 + 73192/T- 11829· 10₃/T² + 0.18923T- 86.187·logT where T is in °K and CO₂ in moles per kg of steam.     

Photoreduction of Fe(III) in the Acidic Mine Pit Lake of San Telmo (Iberian Pyrite Belt): Field and Experimental Work

Light-induced reduction of dissolved and particulate Fe(III) has been observed to occur in the surface waters of the acidic mine pit lake of San Telmo (143,600 m², pH 2.8, Fe_total = 2.72 mM). This photochemical production of Fe(II) is directly related to the intensity of solar radiation and competes with biologically catalyzed reactions (i.e., bacterial re-oxidation of Fe(II)) and physical processes (including ionic diffusion, advection, and convection, which tend to homogenize the epilimnetic concentration of Fe(II) at every moment). Therefore, diel cycles of Fe(II) concentration are observed at the lake surface, with minimum values of 10–20 μM Fe(II) (0.35–0.70% Fe_total) at the sunrise and sunset, and maximum values of 90 μM Fe(II) (3.2% Fe_total) at midday in August 2005. Field and experimental work conducted in San Telmo and other pit lakes of the Iberian Pyrite Belt (IPB) (pH 2.3–3.1, Fe_total = 0.34–17 mM) indicate that the kinetics of the photoreductive reaction is zero-order and is independent of the Fe(III) concentration, but highly dependent on the intensity of solar radiation and temperature. Experimental work conducted with natural Fe(III) minerals (schwertmannite, goethite, and lepidocrocite) suggests that dissolved organic matter is an important factor contributing to the photochemical production of Fe(II). The wavelengths involved in the photoreduction of Fe(III) include not only the spectrum of UV-A radiation (315–400 nm), but also part of the photosynthetically active radiation (PAR, 400–700 nm). This finding is of prime importance for the understanding of the photoreduction processes in the pit lakes of the IPB, because the photo-reactive depth is not limited to the penetration depth of UV-A radiation (upper 1–10 cm of the water column depending on the TDS content), but it is approximately equal to the penetration depth of PAR (e.g., first 4–6 m of the water column in San Telmo on July 2007); thus, increasing the importance of photochemical processes in the hydro(bio)geochemistry of pit lakes.     

The Mammoth Peak sheeted complex,Tuolumne batholith,Sierra Nevada,California: a record of initial growth or late thermal contraction in a magma chamber?

The Mammoth Peak sheeted intrusive complex formed in the interior of a ~7–10 km deep magma chamber, specifically in the Half Dome granodiorite of the Tuolumne batholith, central Sierra Nevada, CA (USA). The sheets consist of fractionated melts with accumulated hornblende, biotite, magnetite, titanite, apatite, and zircon. The accumulation, especially of titanite, had a profound effect on minor and trace elements (Nb, Ta, Ti, REE, U, Th, P, Zr, Hf, etc.), increasing their contents up to five to six times. Our thermal–mechanical modeling using the finite element method shows that cooling-generated tensile stresses resulted in the inward propagation of two perpendicular sets of dilational cracks in the host granodiorite. We interpret the sheeted complex to have formed by a crack-seal mechanism in a high strength, crystal-rich mush, whereby outward younging pulses of fractionated magma were injected into these syn-magmatic cracks at the margin of an active magma chamber. Thermal–mechanical instabilities developed after the assembly of the sheeted complex, which was then overprinted by late ~NW–SE magmatic foliation. This case example provides a cautionary note regarding the interpretation that sheeted zones in large granitoid plutons imply a diking mechanism of growth because the sheeted/dike complexes in plutons (1) may display inverse growth directions from the growth of the overall intrusive sequence; (2) need not record initial chamber construction and instead may reflect late pulsing of magma within an already constructed magma chamber; (3) have an overprinting magmatic fabric indicating the continued presence of melt after construction of sheeted complexes and thus a prolonged thermal history as compared to dikes; and (4) because the scale of the observed sheeted complexes may be small (<1%) in comparison to large homogenous parts of plutons, in which there is no evidence for sheeting or diking. Thus, where extensive dike complexes in plutons are absent, such as in much of the Tuolumne batholith, the application of an incremental diking model to explain chamber construction is at best speculative.     

Estimating Runoff Using Hydro-Geodetic Approaches

Given the continuous decline in global runoff data availability over the past decades, alternative approaches for runoff determination are gaining importance. When aiming for global scale runoff at a sufficient temporal resolution and with homogeneous accuracy, the choice to use spaceborne sensors is only a logical step. In this respect, we take water storage changes from Gravity Recovery And Climate Explorer (grace) results and water level measurements from satellite altimetry, and present a comprehensive assessment of five different approaches for river runoff estimation: hydrological balance equation, hydro-meteorological balance equation, satellite altimetry with quantile function-based stage–discharge relationships, a rudimentary instantaneous runoff–precipitation relationship, and a runoff–storage relationship that takes time lag into account. As a common property, these approaches do not rely on hydrological modeling; they are either purely data driven or make additional use of atmospheric reanalyses. Further, these methods, except runoff–precipitation ratio, use geodetic observables as one of their inputs and, therefore, they are termed hydro-geodetic approaches. The runoff prediction skill of these approaches is validated against in situ runoff and compared to hydrological model predictions. Our results show that catchment-specific methods (altimetry and runoff–storage relationship) clearly outperform the global methods (hydrological and hydro-meteorological approaches) in the six study regions we considered. The global methods have the potential to provide runoff over all landmasses, which implies gauged and ungauged basins alike, but are still limited due to inconsistencies in the global hydrological and hydro-meteorological datasets that they use.     

Image analysis applied to quantitative evaluation of chromatic impact generated by open-pit quarries and mines

One of the most important environmental impacts resulting from opencast mining, and especially quarries, is the visual impact. Evaluation of this impact considers two aspects: first, the area occupied by the quarry as seen by an observer from a specific place, and, second, the chromatic contrast existing between landscape and exploitation. In this study we develop a methodology to assess the chromatic impact in an objective and comparable form. To assess this impact we developed a method based on image analysis that allows us to obtain from a picture or image its equivalent as a function of chromatic impact, according to the sensibility of the human eye to different wavelengths. The methodology was applied to the Martinenca limestone quarry (Alcanar, Tarragona) and to Cerro Kori Kollo mine, La Joya district (Bolivia).     

Use of targets to track 3D displacements in highly vegetated areas affected by landslides

Monitoring landslides with terrestrial laser scanning (TLS) is currently a well-known technique. One problem often encountered is the vegetation that produces shadow areas on the scans. Indeed, the points behind a given obstacle are hidden and thus occluded on the point cloud. Thereby, locations monitored with terrestrial laser scanner are mostly rock instabilities and few vegetated landslides, being difficult or even impossible to survey vegetated slopes using this method with its classical non-full wave form. The Peney landslide (Geneva, Switzerland) is partially vegetated by bushes and trees, and in order to monitor its displacements during the drawdown of the Verbois reservoir located at its base, an alternative solution has been found. We combined LiDAR technique with 14 targets made of polystyrene placed at different locations inside and outside the landslide area. The obtained displacements were compared with classical measurement methods (total station and extensometer), showing good resemblance of results, indicating that the use of targets in highly vegetated areas could be an efficient alternative for mass movements monitoring.     

Biases in the diurnal temperature range in Central Europe in an ensemble of regional climate models and their possible causes

The study examines how regional climate models (RCMs) reproduce the diurnal temperature range (DTR) in their control simulations over Central Europe. We evaluate 30-year runs driven by perfect boundary conditions (the ERA40 reanalysis, 1961–1990) and a global climate model (ECHAM5) of an ensemble of RCMs with 25-km resolution from the ENSEMBLES project. The RCMs’ performance is compared against the dataset gridded from a high-density stations network. We find that all RCMs underestimate DTR in all seasons, notwithstanding whether driven by ERA40 or ECHAM5. Underestimation is largest in summer and smallest in winter in most RCMs. The relationship of the models’ errors to indices of atmospheric circulation and cloud cover is discussed to reveal possible causes of the biases. In all seasons and all simulations driven by ERA40 and ECHAM5, underestimation of DTR is larger under anticyclonic circulation and becomes smaller or negligible for cyclonic circulation. In summer and transition seasons, underestimation tends to be largest for the southeast to south flow associated with warm advection, while in winter it does not depend on flow direction. We show that the biases in DTR, which seem common to all examined RCMs, are also related to cloud cover simulation. However, there is no general tendency to overestimate total cloud amount under anticyclonic conditions in the RCMs, which suggests the large negative bias in DTR for anticyclonic circulation cannot be explained by a bias in cloudiness. Errors in simulating heat and moisture fluxes between land surface and atmosphere probably contribute to the biases in DTR as well.