The influence of leaf litter diversity and soil fauna on initial soil erosion in subtropical forests

Although the protective role of leaf litter cover against soil erosion is known for a long time, little research has been conducted on the processes involved. Moreover, the impact of soil meso‐ and macrofauna within the litter layer on erosion control is not clear. To investigate how leaf litter cover and diversity as well as meso‐ and macrofauna influence sediment discharge in subtropical forest ecosystems, a field experiment has been carried out in Southeast China. A full‐factorial random design with 96 micro‐scale runoff plots and 7 domestic leaf species was established and erosion was triggered by a rainfall simulator. Our results demonstrate that leaf litter cover protects soil from erosion (?82 % sediment discharge on leaf covered plots) by rainfall and this protection is removed as litter decomposes. The protective effect is influenced by the presence or absence of soil meso‐ and macrofauna. Fauna presence increases soil erosion rates significantly by 58 %, while leaf species diversity shows a non‐significant negative trend. We assume that the faunal effect arises from arthropods slackening and processing the soil surface as well as fragmenting and decomposing the protecting leaf litter covers. Even though the diversity level did not show a significant influence, single leaf species in monocultures show rather different impacts on sediment discharge and thus, erosion control. In our experiment, runoff plots with leaf litter from Machilus thunbergii showed the highest sediment discharge (68.0 g m^?2) whereas plots with Cyclobalanopsis glauca showed the smallest rates (7.9 g m^?2). Copyright © 2015 John Wiley & Sons, Ltd.     

A Poroelastic Description of Permeability Evolution

Pore pressure changes in a geothermal reservoir, as a result of injection and/or production of water, result in changes of stress acting on the reservoir rock and, consequently, changes in the mechanical and transport properties of the rock. Bulk modulus and permeability were measured at different pressures and temperatures. An outcropping equivalent of Rotliegend reservoir rock in the North German Basin (Flechtinger sandstone) was used to perform hydrostatic tests and steady state fluid flow tests. Permeability measurements were conducted while cycling confining pressure; the dependence of permeability on stress was determined at a constant downstream pressure of 1 MPa. Also, temperature was increased stepwise from 30 to 140 °C and crack porosity was calculated at different temperatures. Although changes in the volumes of cracks are not significant, the cracks control fluid flow pathways and, consequently, the permeability of the rock. A new model was derived which relates microstructure of porosity, the stress–strain curve, and permeability. Porosity change was described by the first derivative of the stress–strain curve. Permeability evolution was ascribed to crack closure and was related to the second derivative of the stress–strain curve. The porosity and permeability of Flechtinger sandstone were reduced by increasing the effective pressure and decreased after each pressure cycle.     

Laser Ablation (193 nm), Purification and Determination of Very Low Concentrations of Solar Wind Nitrogen Implanted in Targets from the GENESIS Spacecraft

The GENESIS space mission recovered ions emitted by the Sun during a 27 month period. In order to extract, purify and determine the very low quantities of solar nitrogen implanted in the GENESIS targets, a new installation was developed and constructed at the CRPG (Nancy, France). It permitted the simultaneous determination of nitrogen and noble gases extracted from the target by laser ablation. The extraction procedure used a 193 nm excimer laser that allowed for surface contamination in the outer 5 nm to be removed, followed by a step that removed 50 nm of the target material, extracting the solar nitrogen and noble gases implanted in the target. Following purification using Ti and Zr getters for noble gases and a Cu-CuO oxidation cycle for N₂, the extracted gases were analysed by static mode (pumps closed) mass spectrometry using electron multiplier and Faraday cup detectors. The nitrogen blanks from the purification section and the static line (30 minutes) were only 0.46 picomole and 0.47 picomole, respectively.     

FTIR micro-reflectance measurements of the CO3 2– ion content in basanite and leucitite glasses

 Infrared spectroscopy provides a reliable method for rapid, non-destructive quantitative analysis of volatile species in silicate glasses, with applications to geochemistry and volcanology. The technique has been extensively calibrated for transmission measurements, in which the species concentration present is correlated with the height or area of characteristic absorption peaks, for doubly polished samples of known thickness. There are several drawbacks associated with this method, including the need for double polishing of parallel faces on thin samples, the errors associated with sample thickness measurement, and total absorption of the IR beam intensity for samples with high volatile content. We have tested an alternative method for quantitative IR determination of volatile concentrations in silicate glasses, based on analysis of the IR reflectivity signal. The reflectivity method requires preparation of a single polished glass surface, and no thickness measurement of the sample is necessary. The technique is applied easily as a microbeam technique using apertures as small as a few μm in diameter. The method should be particularly useful for volatile analysis of glass inclusions in phenocrystals, or standard samples in thin section. We have developed the methodology for the technique using a series of basanite and leucitite glasses with high carbonate contents (>1 wt% CO₂), which could not be easily analyzed via IR transmission. We have used SIMS to standardize the technique. Two features observed in the reflectance spectra near 1400 cm^–1 and 1500 cm^–1 are due to resonance of the infrared beam with the asymmetric stretching vibrations of carbonate groups. The contribution of these species to the total reflectivity is directly correlated with the carbon abundance in the samples. This forms the basis for an empirical quantitative analysis. The optical constants, including the IR absorption coefficients associated with the CO₃ ^2– stretching vibrations, have been extracted by Kramers-Kronig analysis of the reflectivity data. The molar extinction coefficients are 1119 ± 138 L mol^–1 cm^–1 and 1198 ± 145 L mol^–1 cm^–1 for the 1400 and 1500 cm^–1 bands, respectively, in excellent agreement with results of previous transmission studies, after orientation effects are taken into account. Received: 29 September 1995 / Accepted: 17 May 1996     

Etude de la phase gazeuse occluse dans les laves de «l’Ardoukôba», volcan éphémère d’une dorsale émergée (Afar)

Gases trapped in lavas of three main flows of the Ardoukôba eruption (8 to 15 November, 1978) have been analysed by mass spectrometry. These analyses concern both plagioclase phenocrysts and microcrystalline mesostasis. Fluids are released between 500°C and 1200°C, and consist of H₂O, CO₂, CO, N₂, SO₂, HCl, H₂, CH₄ with traces of hydrocarbons and H₂S. The total content is less than 0.3–0.4 wt. % of samples with about 0.1–0.15 wt % of H₂O. No significant variation among the three flows is observed. Plagioclase phenocrysts are less abundant in fluids than the mesostasis (～2/3). The gases trapped in these phenocrysts are richer in CO and organic compounds, whereas mesostasis contain more H₂O, CO₂ and SO₂. CO is likely produced by reduction of CO₂ and H₂O with carbon during either analyses or eruption itself, or is of primary origin. In the latter case, gas composition suggests an entrapment temperature of about 1200°C ± 75°C. Kinetic study of the water and carbon dioxide release allows to calculate the diffusion characteristics of these fluids. Water and carbon dioxide behave rather similarly. Plagioclase gives a single activation energy value (8 Kcal/mole), while mesostasis gives two values (8 Kcal/mole, 15 Kcal/mole). Diffusion coefficients at 20°C are estimated to fall in the range 10^?13 · 10^?12 cm² · sec^?1.     

Über die Entnahme von Wasserproben in fliessenden Gewässern

Ohne Zusammenfassung     

Zur Methodik der Quantitativen Biologischen Probenahmen in Stark Strömenden Flüssen

Zusammenfassung Es wird eine Technik zur Entnahme quantitativer Organismenproben aus tiefen, schnellfliessenden, steinigen Flüssen beschrieben. Mit Hilfe eines kreisrunden Stechsegmentes wird ein Areal von rund 750 cm² abgegrenzt und dieses sodann mit einem Vakuumschlauch abgesaugt. Das Mundstück des Schlauches wird durch einen Taucher geführt.

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Summary A technique is described for taking quantitative samples of organisms from deep, rapidly flowing rivers with rocky beds. An area of about 750 cm² (0.81 sqft) is confined by a circular sampler, which penetrates the bottom. Organisms in the enclosure are freed from the substrate by hand. Smaller sediment particles, organisms, and water are then pumped out by a vacuum hose. The intake of the vacuum hose is guided by a diver.

     

Buchbesprechungen

Ohne Zusammenfassung     

Ökologische und physiologische Untersuchungen an der planktischen BlaualgeOscillatoria rubescens D.C. unter besonderer Berücksichtigung von Licht und Temperatur

Zusammenfassung Der Vierwaldst?ttersee (Horwer Bucht), Thunersee (H?he Faulensee), Luganersee (Bucht von Lugano) und Mauensee (ein Kleingew?sser im Schweizerischen Mitelland) wurden im Zeitabschnitt 1965 bis 1967 periodisch untersucht. Durch die chemische Analyse wurden die folgenden Komponenten erfasst: Sauerstoff, Nitrat— Stickstoff, Phosphat— Phosphor (PO₄−P), partikul?rer Phosphor (PP), SBV und pH-Wert. Das Phytoplankton wurde im umgekehrten Mikroskop ausgez?hlt, wobei der quantitativen Verteilung vonOscillatoria rubescens D. C. in den verschiedenen Tiefenstufen besondere Beachtung geschenkt wurde. Gleichzeitig wurden Temperatur und subaquatische Ver?nderungen des lichtes gemessen sowie mit der C¹⁴-Methode die Prim?rproduktion bestimmt. In mehr als 80% aller F?lle fielen dieOscillatoria rubescens-Maxima mit jenen Tiefenstufen zusammen, in denen weniger als 14°C gemessen wurde. In diesen Tiefenstufen wurde gleichzeitig in mehr als 65% aller F?lle weniger als 4% der Oberfl?chen-intensit?t des grünen Lichtes (VG 9) beobachtet. Der Einfluss von Licht und Temperatur auf das Wachstum vonOscillatoria rubescens wurde in einem Lichtthermostat experimentell untersucht. Bei temperaturabh?ngigenI _k-Werten zeigte sich, dass sich diese Alge bei einer Lichtintensit?t von 1500 Lux erst im Bereich von 30°C optimal entwickelt. Oberhalb 29°C wirkte sich eine Steigerung über 1500 Lux hinaus wieder hemmend aus. Aus diesen Beobachtungen wurde abgeleitet, dass es sich beiOscillatoria rubescens um eine eurytherme und oligophote Form handelt, und dass das Auftreten vonOscillatoria rubescens-Maxima in der vertikalen Verteilung des Phytoplanktons in einem See durch das Zusammenspiel der beiden Faktoren Licht und Temperatur bedingt wird.

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Summary The Lakes of Lucerne (Horw Bay), Thoune (Faulensee region), Lugano (Lugano Bay) and Lake Mauen, a small lake in central Switzerland, were investigated periodically from 1965 to 1967. The water was analysed in view of determining the following components: oxygen, nitrate-nitrogen, phosphate-phosphorus (PO₄−P), phosphorus incorporated in cell mass (PP), Langlier index. Phytoplankton was counted in an inverted microscope with special consideration to quantitative distribution ofOscillatoria rubescens D. C. at various depths. Temperature and light variations in function of depth were measured simultaneously and the production rate was determined by means of the C-14 method. In over 80% of all cases, theOscillatoria rubescens-maxima coincided with depths showing temperatures under 14°C. In over 65% of all cases, the intensity of green light (VG9) in such depths was less than 4% of the surface intensity. The influence of light and temperature on the growth ofOscillatoria rubescens was tested with a light thermostat. It was shown that maximum growth occurred at temperatures around 30°C and light intensities of 1500 Lux. Increase of light intensities above 1500 Lux had a negative effect on the growth rate at temperatures higher than 29°C. Our investigations lead to the conclusion thatOscillatoria rubescens is a eurythermal, oligophotic species and that the occurrence ofOscillatoria rubescens-maxima in the vertical distribution of the phytoplankton in a lake is caused by the combined effects of light and temperature.

     

Production and nutrient dynamics of aSyringodium filiforme Kütz. Seagrass bed in Indian River Lagoon,Florida

A year-long analysis of the characteristics of the seagrassSyringodium filiforme and the associated dynamics of the nutrient pool in the sediment pore water was done to assess co-variation. Changes in seagrass growth rate and standing stock throughout the year were accompanied by seasonal changes in the nutrient pools. The link between plant production and morphometrics and the sediment nutrient pool was found to be predominantly physiological, with the plant balancing the ability to photosynthesize with the nutrients needed for maintaining production. Measurements of whole plant growth for this seagrass, rather than the more typical leaf growth measurements, show that the production of new shoots and rhizome elongation for these plants represents as substantial amount of growth that usually goes unmeasured. Further, these whole plant growth measures demonstrate the rapid lateral rhizome spread of this species, exceeding one meter per plant per year. The primary cause of seasonal variation in the yearly seagrass cycle was investigated. Correlation analysis supported the hypothesis that the major factor controlling seasonal variation in this seagrass was light. During the peak growing season, however, growth was not regulated by light but by nitrogen. Depletion of the sediment ammonium pool and reduction in pore water ammonium relative to adsorbed ammonium, as well as changes in N content of seagrass leaves, support our hypothesis of peak growing season nitrogen limitation. Our results forSyringodium filiforme in terrigenous sediments are in contrast to our recent findings of phosphorus limitation in this same species occurring in carbonate sediments.