Unravelling evapotranspiration controls and components in tropical Andean tussock grasslands

The study of the environmental factors that control evapotranspiration and the components of evapotranspiration leads to a better understanding of the actual evapotranspiration (ET) process that links the functioning of the soil, water and atmosphere. It also improves local, regional and global ET modelling. Globally, few studies so far focussed on the controls and components of ET in alpine grasslands, especially in mountainous sites such as the tussock grasslands located in the páramo biome (above 3300 m a.s.l.). The páramo occupies 35 000 km² and provides water resources for many cities in the Andes. In this article, we unveiled the controls on ET and provided the first insights on the contribution of transpiration to ET. We found that the wet páramo is an energy-limited region and net radiation (Rn) is primarily controlling ET. ET was on average 1.7 mm/day. The monthly average evaporative fraction (ET/Rn) was 0.47 and it remained similar for wet and dry periods. The secondary controls on ET were wind speed, aerodynamic resistance and surface resistance that appeared more important for dry periods, where significantly higher ET rates were found (20% increase). During dry events, transpiration was on average 1.5 mm/day (range 0.7–2.7 mm/day), similar to other tussock grasslands in New Zealand (range 0.6–3.3 mm/day). Evidence showed interception contributes more to ET than transpiration. This study sets a precedent towards a better understanding of the evapotranspiration process and will ultimately lead to a better land-atmosphere fluxes modelling in the tropics.     

Coupled substitutions in the tourmaline group

Statistical analysis of 136 natural tourmaline compositions from the literature reveals the presence and extent of coupled substitutions involving several cations and structural sites. In schorls and dravites these are a dehydroxylation type substitution (1) (OH)^–+R²⁺ = R³⁺+O^2– and an alkali-defect type substitution (2) R⁺+R²⁺ = R³⁺+, Al³⁺ being the predominant R³⁺ action. Substitution (1) which represents solid solution towards a proton-deficient end-member, R⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃ Si₆O₁₈O₃(OH), accounts for three times as much of the observed compositional variability as does (2) which represents substitution toward a hypothetical alkali-free end-member, (R ₂ ²⁺ R³⁺) R ₆ ³⁺ (BO₃)₃Si₆O₁₈(OH)₄. The occurrence of both of these substituions produces intermediates between end-member schorl/ dravite, R⁺ R ₃ ²⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈(OH)₄, and a new series within the tourmaline group, R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x (OH)_1+x.In addition to dehydroxylation type, 2(OH)^–+Li⁺ = R³⁺+20^2–, and possibly alkali-defect type, 2R⁺+Li⁺ = R³⁺+2, substitutions, a third type Li⁺+O^2– = (OH)^–+, occurs in the elbaites giving rise to Li-poor, proton-rich species. All three substitutions serve to reduce the Li-content of natural elbaite which, as a result, does not attain the composition of the ideal end-member, Na(Li_1.5Al_1.5)Al₆(BO₃)₃Si₆O₁₈(OH)₄. Substitution from elbaite and schorl/dravite toward R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x(OH)_1+x is very extensive and may be complete.Substitution toward R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x(OH)_1+x results in improved local charge balance. The mean deviation from oxygen charge saturation is at a maximum in end-member schorl, dravite and elbaite. Substitutions (1) and (2) progressively decrease but substitution (1) does so more effectively, which may explain its predominance in nature. However, alkali-defective end-members appear to be unstable regardless of . Substitution (3) in the elbaites cannot be discussed on the basis of charge balance considerations at present due to the lack of structural information on proton-rich species.     

Fe2+ -F avoidance in silicates

Fe²⁺-F avoidance, reported in the literature in micas and amphiboles, can be accounted for by crystal field theory. The crystal field splitting parameter, Δ_O, of Fe²⁺ octahedrally coordinated to F^? is significantly smaller than its value when (OH)^? is the coordinating anion. Thus, the presence of Fe²⁺ is not favored at sites where F^? substitutes for (OH)^? due to smaller crystal field stabilization energy.     

New procedures for the toxicity testing of oil slick dispersants in the United Kingdom

Under the Dumping at Sea Act 1974 the use of oil slick dispersants requres a licence from the Ministry of Agriculture, Fisheries and Food in England and Wales. These licences are issued or refused on the basis of tests to assess the toxicity of the dispersant when used at sea or on beaches. This paper describes the rationale behind the development of the two toxicity tests used, together with the test methods adopted and the results of the tests.     

An algorithm for the stratigraphic correlation of well logs

This paper describes an algorithm for the semiautomatic shifting and stretching of one well log relative to another until a local maximum correlation coefficient between the two logs is found. The algorithm grew out of a graphical interpretation of the standard shift correlation procedure. The algorithm does not interpolate data and it is as computationally efficient as the standard correlation method using linear interpolation. The algorithm is generalized to the simultaneous stratigraphic correlation of separate sections from two well logs and two examples of its operation are given.     

Abrupt changes in an 8000-year precipitation reconstruction for Nevada, the Western USA

A scanning t-test algorithm for detecting multiple time-scale abrupt changes in the level of a time-series was used to analyze an 8000 year time series of annual precipitation which was reconstructed from tree rings for the Nevada Climate Division 3 in the western USA. The tree ring samples were gathered from eight states in the southwestern USA. Twenty-two change-points were identified by the algorithm and these were used to partition the tree-ring series into twenty-three relatively Wet/Normal/Dry episodes. These twenty-three episodes were collaborated by a coherency analysis of abrupt changes between the precipitation reconstruction series and the TIC/δ18O records from cored sediments of Pyramid Lake in Nevada, and by comparison with published results from related studies. These episodes were also compared with studies of the global climate change and with records of climate change in China during the same periods. The results suggest that the precipitation reconstruction series is quite valuable for climate-change research on multi-centurial time-scales in the western USA, and that the scanning t-test and coherency detection algorithms may have a wide use for detecting multiple time-scale abrupt changes in a long time series.As the TIC and δ18O record series are high resolution with unequal sampling intervals ranging between 3 and 14 years, a new algorithm was developed to deal with the unequal time intervals in the series.     

Estimating the Effects of Map Error on Habitat Delineation for the California Spotted Owl in Southern California

The reliability of habitat maps that have been generated using Geographic Information Systems (GIS) and image processing of remotely sensed data can be overestimated. Habitat suitability and spatially explicit population viability models are often based on these products without explicit knowledge of the effects of these mapping errors on model results. While research has considered errors in population modeling assumptions, there is no standardized method for measuring the effects of inaccuracies resulting from errors in landscape classification. Using landscape‐scale maps of existing vegetation developed for the USDA Forest Service in southern California from Landsat Thematic Mapper satellite data and GIS modeling, we performed a sensitivity analysis to estimate how mapping errors in vegetation type, forest canopy cover, and tree crown size might affect delineation of suitable habitat for the California spotted owl (Strix occidentalis occidentalis). The resulting simulated uncertainty maps showed an increase in the estimated area of suitable habitat types. Further analysis measuring the fragmentation of the additional patches showed that they were too small to be useful as habitat areas.     

On the azimuthal brightness variations of Saturn's rings

We present a simple, semiquantitative explanation that accounts both for the presence of the azimuthal brightness variations in Saturn's ring A and for their absence in ring B. Our explanation avoids any ad hoc reliance on albedo variations and/or synchronous rotation of ring particles. Instead, it requires only some degree of self-gravitation between nearby orbiting bodies. A bias in the particle distribution and corresponding photometric effects are thereby produced—the latter corresponding very closely to the variations observed in ring A. Their absence in ring B is primarily a consequence of the higher optical thickness and decreasing importance of self-gravitation in that ring.