Wind Tunnel And Field Measurements Of Turbulent Flow In Forests. Part I: Uniformly Thinned Stands

Many forest management methods alterstand density uniformly. The effectsof such a change on the wind andturbulence regimes in the forest arecritical to a number of processes governingthe stability of the stand and itsmicroclimate. We measured wind speed andturbulence statistics with a Dantec tri-axialhot-film probe in model forests of variousdensities (31–333 trees m^-2), created byremoving whole trees in a regular pattern in awind tunnel, and compared them with similarmeasurements made with propeller anemometers insimilarly thinned plots (156–625 trees ha^-1)within a Sitka spruce stand in Scotland. The results agree well, in general, with measurements made inother such studies with diverse canopy types.The systematic variations with density and verticalleaf-area distribution (which differed betweenwind-tunnel and field trees) in our work can explainmuch of the variability shown in scaled profiles ofbasic turbulence statistics reported in theliterature. The wind tunnel and field results are shown to be in good agreement overalldespite the difference in vertical leaf-areadistribution. Within-canopy and isolated-treedrag coefficients in the wind tunnel showthat tree-scale shelter effects increase astree density increases. The measurements indicatethat turbulence in the canopy is dominated bylarge-scale structures with dimensions of the sameorder as the height of the canopy as found inother studies but suggest that inter-tree spacing also modulates the size of these structures. These structures are associated with the sweeps that dominatemomentum exchange in the canopy and it is thisfact that allows the tri-axial probe to operate sowell despite the relatively narrow range of anglesin which the wind vector is correctly measured. Theratio of streamwise periodicity of these structuresto vorticity thickness varies systematically withtree density in the range 2.7–5.1, which spans theexpected range of 3.5–5 found in a laboratorymixing-layer, suggesting that tree spacing imposes another relevant length scale. This test andothers show that the results are in agreement withthe idea that canopy turbulence resembles that of a mixing layer even though they disagree with, and challenge the linear relationship between, streamwise periodicity andshear length scale presented recently in theliterature. The measurements are also in goodoverall agreement with simple drag models presented recently by other researchers.     

Composition and processes of the mantle lithosphere in northeastern Brazil and Fernando de Noronha: evidence from mantle xenoliths

Spinel–peridotite facies mantle xenoliths in Cenozoic alkali basalts of the Pico Cabuji volcano (Rio Grande do Norte State, Northeast Brazil) and the adjacent South Atlantic oceanic island of Fernando de Noronha are studied for: (1) the information they provide on the composition of the lithospheric component in the erupted basalt geochemistry, and (2) to check the effects of the Fernando de Noronha plume track on the mantle lithosphere. Xenoliths from Pico Cabuji are protogranular lherzolites and porphyroclastic harzburgites recording average equilibrium temperatures of 825 ± 116 and 1248 ± 19 °C, respectively. Pressure in the porphyroclastic xenoliths ranges from 1.9 to 2.7 GPa (Ca-in-olivine geobarometer). Both groups show major element chemical variation trends in whole-rock and Ti and HREE (Er, Yb) variations in clinopyroxene consistent with fractional melting and basalt extraction. REE (rare earth element) profiles of clinopyroxenes vary from LREE (La, Ce) enriched (spoon shaped) to LREE depleted in the protogranular group, whereas they are slightly convex upward in most porphyroclastic clinopyroxenes. HFSE (Ti and Zr) negative anomalies are in general modest in the clinopyroxenes of both groups. Xenoliths from Fernando de Noronha have textural variations similar to those of Pico Cabuji. Protogranular and porphyroclastic samples have similar temperature (1035 ± 80 °C) and the pressure is 1–1.9 and 2.3 GPa, respectively. Whole-rock chemical variation trends overlap and extend further than those of Pico Cabuji. The trace element profiles of the clinopyroxenes of the porphyroclastic xenoliths are enriched in La up to 30 × PM and are smoothly fractionated from LREE to HREE, with deep, negative, Zr and Ti anomalies. The geochemical heterogeneities of the xenoliths from both localities are interpreted in terms of reactive porous percolation. The porphyroclastic xenoliths from Pico Cabuji represent the lower part of a mantle column (the head of a mantle diapir, at the transition conductive–adiabatic mantle), where OIB infiltration triggers melting, and the protogranular xenoliths the top of the mantle column, chromatographically enriched by percolation at a low melt/rock ratio. This interpretation may also apply for Fernando de Noronha, but the different geochemical signature recorded by the clinopyroxenes requires a different composition of the infiltrated melt. Nd and Sr isotopes of the Pico Cabuji porphyroclastic clinopyroxenes (¹⁴³Nd/¹⁴⁴Nd= 0.51339–0.51255, ⁸⁷Sr/⁸⁶Sr=0.70275–0.70319) and of Fernando de Noronha (¹⁴³Nd/¹⁴⁴Nd=0.51323–0.51285, ⁸⁷Sr/⁸⁶Sr=0.70323–0.70465) plot on distinct arrays originating from a similar, isotopically depleted composition and trending to low Nd–low Sr (EMI) and low Nd–high Sr (EMII), respectively. Correlation of the isotope variation with geochemical parameters indicates that the isotopic variation was induced by the metasomatic component, of EMI type at Pico Cabuji and of EMII type at Fernando de Noronha. These different components enriched a lithosphere isotopically similar to DMM (depleted MORB mantle) at both localities. At Fernando de Noronha, the isotopic signature of the metasomatic component is similar to that of the ∼ 8 Ma old lavas of the Remedios Formation, suggesting that this is the age of metasomatism. At Pico Cabuji, the mantle xenoliths do not record the high ⁸⁷Sr/⁸⁶Sr component present in the basalts. We speculate that the EMII component derives from a lithospheric reservoir, which was not thermally affected during mantle metasomatism at Pico Cabuji, but was mobilized by the hotspot thermal influence at Fernando de Noronha. This interpretation provides a plausible explanation for the presence of distinct metasomatic components at the two localities, which would be difficult to reconcile with their genetic relationship with the same plume. Received: 12 June 1999 / Accepted: 13 December 1999     

A note on the polarographic behavior of the Cu(II) ion selective electrode in seawater

The non-Nernstian behavior of a solid-state cupric ion-selective electrode in seawater is attributed to a reduction of Cu²⁺ at the surface in accordance with a suggestion made in the literature. This ‘polarographic’ behaviour was demonstrated by showing that the electrode potential is affected by molecular oxygen in solution.     

Multivariate models for landslide hazard evaluation

As part of a long-term project aimed at a better understanding of the geological and geomorphological factors that control slope instability phenomena in Southern Italy, multivariate models for assessing landslide incidence hazard were developed and tested in two Calabrian sample areas characterized by different geological-geomorphological conditions. Discriminant analysis, based on a large set of mappable geological and geomorphical variables, is able to discriminate rather successfully between stable and unstable areas or slope units. Multiple regression analysis has also proved to be a useful tool in predicting actual and potential landslide hazard. Consequently, geomathematical models may provide a feasible approach to environmental hazard assessment, particularly when applied within the framework of a wider multidisciplinary project for land evaluation and planning.     

Recent advances in the chemistry and properties of atmospheric nucleants: a review

Summary A survey is carried out of recent progress in the investigation of weather-active atmospheric nucleants. Emphasis is placed on the work date during the last decade, and some resulting implications are discussed.     

Distribution of macrobenthic assemblages along a marine gradient in Mediterranean eutrophic coastal lagoons

Coastal lagoons can be characterised by strong environmental changes along the outer marine‐inner brackish gradient, which are reflected in the patterns of distribution of organisms and composition of assemblages. Close to the sea the assemblages are dominated by marine animals, while in the innermost confined areas, there would be estuarine taxa and organisms typical of organically‐enriched areas. During the last decades, human impact has been severe in these habitats and has often profoundly altered the distribution of animals and plants along the gradient. In this study we have analysed the distribution of macrofauna along the outer marine‐inner brackish gradient in five Italian lagoons, affected by severe human disturbance on the Adriatic, Tyrrhenian and Sardinian coasts. We aimed to measure changes in the composition of assemblages according to the distance from the sea, consistent among lagoons and time, after the occurrence of eutrophication, repeated distrophic crisis and other human interventions. We considered existing data from campaigns done during 1994, 1995 and 1999. We arranged different datasets according to the available data, in order to measure the spatial distribution of macrofauna genera with distance from the sea and through time. Analyses showed differences among assemblages related to the gradient. Nevertheless, the species characterizing the assemblages were all typical of organically‐enriched areas, which testified to an impoverishment of diversity and functioning of all these systems.     

Body size–abundance distributions of nano- and micro-phytoplankton guilds in coastal marine ecosystems

This study focuses on body size–abundance distributions of nano- and micro-phytoplankton guilds in coastal marine areas of the Southern Adriatic–Ionian region. The aim of the study was to evaluate the occurrence of common patterns of body size–abundance distributions in relation to physical, chemical and biological environmental forcing factors and to taxonomic composition of phytoplankton guilds. This paper is based on data collected during four oceanographic cruises carried out seasonally along the Southern Apulian coast (Adriatic and Ionian Seas, SE Italy) as a part of the INTERREG II Italy–Greece Program. The study was performed at 21 stations located on 7 transects perpendicular to the coastline, with 3 stations per transect at a distance of 3, 9 and 15 NM from the coastline. At each station, profiles of the major physical features of the water were determined and water samples were collected for phytoplankton and nutrient analysis. Overall, 320 nano- and micro-phytoplankton taxa were identified, 76% of which at species level, with phytoplankton cells ranging in size from 0.008 to 4697.54 ng. Body size–abundance distributions showed some common features: they were relatively invariant (average similarity 65%) with respect to taxonomic composition (average similarity 32%), right skewed (90%), leptokurtic (77%) and log normal (76%). Moreover, abiotic, biotic and spatial ecosystem components accounted for up to 75% of body size–abundance distribution variation. The results of this study suggest that body size–abundance distributions are an intrinsic property of marine phytoplankton communities, emphasising functional dependence on ecological constraints related to trophic factors and intra-guild coexistence relationships.     

Morphology and downslope sediment displacement in a deep-sea valley,the Valencia Valley (Northwestern Mediterranean)

The Valencia Valley is a Quaternary, 200 km long deep-sea valley in the Valencia Trough, Western Mediterranean Sea. A swathmapping survey approximately mid-way along the valley length, where the floor has an average gradient of 1:250 (0.2°), shows valley walls that rise 200 to 350 m above the valley floor, with slopes of 2 to 18°. Sediment forming the walls is undergoing retrogressive, upslope-directed slumping with increasing bedding disruption along steeper walls. The valley exhibits a winding course with steep outer and gentler inner walls around bends, and bedforms on the valley floor. Lateral migration around bends is less than 5 km and the valley is deeply entrenched into Quaternary-bedded sediments.