Impacts of mariculture practices on the temporal distribution of macrobenthos in Sandu Bay,South China

Sandu Bay is located in the East China Sea and is characterized by high-density fish farming and kelp culture. Despite this, little is known about the impacts of these different mariculture practices on the local environment. We investigated the temporal variation in macrobenthos and environmental conditions at three sites in the bay (fish farming site, kelp culture site, and a control site). We collected water and sediment samples during nine cruises between May 2009 and February 2010. The density of macrobenthos peaked at the fish farming site in July (655 ind./m2) whereas density did not fluctuate as widely at the other two sites. Biomass varied significantly at both the control and kelp culture sites, but had only a single peak at the fish farming site in June (21.90 g/m2). The dominant species varied throughout the study period at the control and kelp culture sites, whereas a single terebellid species (Lysilla pacifica) dominated the macrobenthos at the fish farming site. The diversity index H’ increased at the control site beginning in February then decreased after May, whereas H’ was low at the other sites in December. The mean dissolved oxygen level was highest at the control site (6.59 mg/L) and lowest at the fish farming site (5.54 mg/L). DO levels were lowest at all sites in summer (July and August). The sediment acid volatile sulfide content was higher at the fish farming site (1.46 mg/g dry weight) than those at the kelp culture and control sites (1.22 and 0.14 mg/g, respectively). Our results suggest that mariculture practices have a clear impact on the benthic environment/ community in Sandu Bay.     

Pigment characterization for the 2011 bloom in Qinhuangdao implicated "brown tide" events in China

A large-scale bloom occurred from May to June in 2011 in sea area near Qinhuangdao of the Bohai Sea, leading to huge damage of the scallop culture industry. Similar blooms have been observed in this region for three years. The causative species of the bloom, which dominated the phytoplankton community with the maximum cell density around 109 cell/L, could not be identified with morphological features due to the small cell size (~2 mm). A pigment analytical method was then adopted to analyze the pigment profile of the phytoplankton samples collected from the blooming sea area. It was found that pico-sized (<2 mm), nano-sized (2-20 mm), and bulk phytoplankton samples had similar pigment profile, representing the pigment signature of the bloom-causative species. The major pigments detected included 19-butanoyloxyfucoxanthin (But-fuco), fucoxanthin (Fuco), diadinoxanthin (Diad) and chlorophyll a (Chl a), and high content of But-fuco was the most significant characteristics of the phytoplankton samples. Based on the pigment composition and content, the bloom-causative species could be tentatively identified as pelagophyte, "type 8" group of haptophyte, or silicoflagellate. Some unique features of the bloom, such as the extremely high cell density, small-sized and But-fuco containing cells, occurring in early summer, and the feeding-cessation effects on scallops, suggest it be a "brown tide" event similar to those reported in the east coast of the United States of America. The recurrent "brown tide" events and their dramatic impacts on the shellfish mariculture industry in Qinhuangdao need close attention in the coming years.     

GIS-based assessment of landslide susceptibility on the base of the Weights-of-Evidence model

The major scope of the study is the assessment of landslide susceptibility of Flysch areas including the Penninic Klippen in the Vienna Forest (Lower Austria) by means of Geographical Information System (GIS)-based modelling. A statistical/probabilistic method, referred to as Weights-of-Evidence (WofE), is applied in a GIS environment in order to derive quantitative spatial information on the predisposition to landslides. While previous research in this area concentrated on local geomorphological, pedological and slope stability analyses, the present study is carried out at a regional level. The results of the modelling emphasise the relevance of clay shale zones within the Flysch formations for the occurrence of landslides. Moreover, the distribution of mass movements is closely connected to the fault system and nappe boundaries. An increased frequency of landslides is observed in the proximity to drainage lines, which can change to torrential conditions after heavy rainfall. Furthermore, landslide susceptibility is enhanced on N-W facing slopes, which are exposed to the prevailing direction of wind and rainfall. Both of the latter geofactors indirectly show the major importance of the hydrological conditions, in particular, of precipitation and surface runoff, for the occurrence of mass movements in the study area. Model performance was checked with an independent validation set of landslides, which are not used in the model. An area of 15% of the susceptibility map, classified as highly susceptible, “predicted” 40% of the landslides.     

Depositional mechanics of turbulent nuées ardentes (surges) from their grain sizes

The ability of turbulent nuées ardentes (surges) to transport coarse pyroclasts has been questioned on the basis that settling velocities of coarse fragments in the deposits are much too high for them to have been supported by turbulence in a dilute gas suspension. A computer model is used to evaluate the settling velocity of pyroclasts in suspensions of varying concentration and temperature. Since suspension of grains in low-concentration surges occurs if the shear velocity exceeds the settling velocity, the shear velocities related to the 16th and 84th percentiles, and the mean of the grain-size distribution are compared in surge deposits of the Vulsini, with the shear velocity necessary to move the coarsest grain on the bed surface (the Shields criterion). The results show that the settling velocities do not vary significantly in gaseous suspensions having volume concentrations lower than 15%, and that an increase in concentration to 25% is not sufficient to decrease the settling velocity of the coarser fraction, if it represents flow shear velocity. It is shown that the settling velocity of the mean grain size (M _z ) best depicts the shear velocity of a dilute turbulent suspension. Applying the results to the May 1902 paroxysmal nuées ardentes of Mount Pelée shows that the estimated mean velocities are well within the observed velocities, and sufficient to support all the clasts in dilute, turbulent suspensions.     

Present limitations of accurate satellite Doppler positioning for tectonics. An example: Djibouti

One of the possibilities of the Doppler positioning from satellite is to provide geodetic measurements continuous in time without the need for reference stations. If measurements of sufficient accuracy can be achieved they may be used to study local surface displacements in relation to tectonic activity. A Doppler receiver of the MEDOC network is located near Djibouti in the Ghoubhat-Asal rift region which corresponds to the accreting plate boundary between the Arabian and African plates. In November 1978, a seismic and volcanic crisis occured in this area. Surface geodetic measurements and levellings performed in 1973 and 1978–79, just after the crisis, reveal a 60–80 cm sinking of the graben floor and a lateral extension of about 2 meters. Here we analyse Doppler measurements for the period January 1977 to November 1980. Point positions are computed for 7 to 10 day intervals using a precise ephemeris, and a moving window analysis is applied to the data. An apparent 2 meter uplift preceding the November 1978 seismic crisis is detected at Djibouti, whereas no similar phenomenon is observed at the two closest stations, Pretoria and Uccle-Brussels. However, field observations rule out a tectonic origin for this uplift. In Djibouti, the correlation between the apparent vertical station position and the electron density in the ionospheric F-layer reveals that a bias may be induced by the third order term of the ionospheric refractive index not previously taken into account, or more probably by the ray curvature through the ionosphere. This bias is particularly strong for our data set, from a station located close to the magnetic equator, and related to a period of rapid increase in the solar activity. Although our analysis fails to detect any tectonic displacement related to the rift seismic activity, it shows that similar tectonic studies by the Doppler method will be possible once the residual ionospheric errors are removed, for example by use of higher radio frequencies.     

Element Mobility During Incipient Granulite Formation at Kabbaldurga, Southern India

At Kabbaldurga, infiltration of carbonic fluids along a systemof ductile shears and foliation planes has led to partial transformationof Archaean grey biotite–hornblende gneiss to coarse-grainedmassive charnockite at about 2.5 b.y. ago. The dehydration ofthe gneiss assemblage was induced by a marked metasomatic changeof the reacting system from granodioritic to granitic, and obviouslytook place under conditions of an open system at 700–750?C and 5–7 kb. Extensive replacement of plagioclase (An_16–30)by K-feldspar through Na, Ca–K exchange reactions withthe ascending carbonic fluids led to strong enrichment in K,Rb, Ba, and SiO₂, and to a depletion in Ca. Progressive dissolutionof hornblende, biotite, magnetite, and the accessory mineralsapatite and zircon resulted in a marked depletion in Fe, Mg,Ti, Zn, V, P, and Zr. Most important is the recognition of REEmobility: with advancing charnockitization, the moderately fractionatedREE distribution patterns of the grey gneisses (La_N270; La_N/Yb_N= 5–20; Eu_N27; Eu/Eu^* = 0.6–0.3) give way to stronglyfractionated REE patterns with a positive Eu-anomaly (La_N200;La_N/Yb_N = 20–80; Eu_N22; Eu/Eu^* = 0.6–1.8). The systematicdepletion especially in the HREE is due to the progressive dissolutionof zircon, apatite (and monazite), which strongly concentratethe REE. Stable isotope data (¹⁸O of 6.9–8.0 per mille for gneissesand charnockites; ¹³C of –8.5 and –6.5 per millefor late carbonate) indicate a magmatogenic source for the carbonicfluids. In contrast to the currently favoured derivation ofcarbonic fluids by decarbonation of the upper mantle or degassingof underplated basaltic intrusions, it is discussed here thatabundant fluid inclusions in lower crustal charnockites providedan extensive reservoir of ‘fossil’ carbonic fluids.Shear deformation has tapped this reservoir and generated thechannel-ways for fluid ascent. Charnockitization of the Kabbaldurgatypethus appears to be a metasomatic process which is tectonicallycontrolled and restricted to the crustal level of the amphiboliteto granulite transition.