Bedrock controls on the mineralogy and chemistry of PM<Subscript>10</Subscript> extracted from Australian desert sediments

Given the relevance of desert aerosols to environmental issues such as dust storms, climate change and human health effects, we provide a demonstration of how the bedrock geology of an arid area influences the mineralogy and geochemistry of even the finest particulate matter (i.e., the inhalable fraction <10 μm in size: PM₁₀). PM₁₀ samples extracted from desert sediments at geologically contrasting off-road sites in central and southeastern Australia (granitic, high grade metamorphic, quartzitic sandstone) were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The “granitic” PM₁₀ are highly alkali feldspathic and illitic, with a wide range of accessory minerals including rutile (TiO₂), monazite [(Ce, La, Nd, Th, Y) PO₄], xenotime (YPO₄), apatite [Ca₅(PO₄)₃ (F, OH, Cl)], hematite (Fe₃O₄), zircon (ZrSiO₄) and thorite (ThSiO₄). This mineralogy is reflected in the geochemistry which shows notable enrichments in rare earth elements (REE) and most high field strength elements (both held in the accessory minerals), and higher than normal levels of low (<2.0) ionic potential elements (Na, K, Li, Cs, Rb: held in alkali feldspar and illite). The “metamorphic” resuspended PM₁₀ define a mineralogy clearly influenced by local exposures of pelitic and calc-silicate schists (sillimanite, muscovite, calcite, Ca-amphibole), a dominance of monazite over other REE-bearing phases, and a geochemistry distinguished by enrichments in alkaline earth metals (Ca, Mg, Ba, Sr) and depletion in heavy REE. The “quartzite” PM₁₀, derived from rocks already recycled by Precambrian erosion and sedimentary transport, show a sedimentologically mature mineralogy of mostly quartz and kaolinite, detrital accessory ilmenite, rutile, monazite and hematite, and the strongest geochemical depletion (especially K, Rb, Cs, Na, Ca, Mg, Ba).     

Alteration of fluid properties during the initial operation of a geothermal plant: results from in situ measurements in Groß Schönebeck

Recently, the thermal fluid loop has been established and continuosly operated for 7 days at the geothermal in situ laboratory in Groß Schönebeck (North German Basin). During this initial phase of fluid production, the fluid temperature, measured at the surface, continuously increased until a stable value of about 98 °C was established. Fluid physicochemical properties (pH, redox, density, temperature, and pressure) were measured online and in situ with a newly developed fluid monitoring system (FluMo). Additionally, fluid samples have been collected at various temperatures (in 5–10 °C steps) directly at the production well at about 10 bar pressure. From the pressurized sampling tool, the fluid was directly transferred into a heated autoclave, which allowed filtration (0.2 μm) in the absence of oxygen. Physicochemical parameters [pH, redox, electric conductivity, total dissolved solids (TDS)] as well as acid capacity (K _S 4.3) of these samples have been measured onsite at atmospheric conditions. Concentrations of anions, total organic carbon, and metals were analyzed later in the laboratory. Both, measurements in collected samples or in situ (FluMo) analysis of most the parameters density, electric conductivity, or TDS indicated relatively constant values over the whole production time (1.17–1.18 g · cm^?3, 215–221 mS · cm^?1, 241–260 g · L^?1, respectively). Good correlation was also found for pH values (pH = 6.6–6.9), whereas the redox values varied between ?1 and 46 mV when determined at 25 °C and decreased strongly when measured in situ with increasing temperature (?110 mV at 90 °C). The elemental composition of collected samples remained also relatively constant for most compounds and was clearly higher as compared with samples collected in 2011. Results of this study demonstrate that realistic, comprehensive, and time-resolved physicochemical data can be obtained by FluMo. These detailed data sets can be crucial to understand the complex geochemical processes in a thermal water loop and eventually to take required measures on time.     

Direct evidence of imbalanced seagrass (Posidonia oceanica) shoot population dynamics in the Spanish Mediterranean

Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots m⁻², absolute shoot mortality from 5±0 to 249±53 shoots m⁻² yr⁻¹, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m⁻²yr⁻¹. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot density, varied from 0.015±0.006 to 0.282±0.138 yr⁻¹ and 0.018±0.005 to 0.302±0.093 yr⁻¹, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment. The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass meadows.     

Vertical Distribution of Gelatinous Macroplankton in the North Pacific Observed by Manned Submersibles Mir-1 and Mir-2

The vertical distribution of several medusa species in the Kurile-Kamtchatka region of the Pacific Ocean is described. Animals were observed in the light cone from deep-sea submersibles Mir-1 and Mir-2 throughout the water column, from the surface to 5000–6000 m at four different sites. Bathy- and abyssopelagic species are noted along with the species living in an extremely wide depth range. A faunistic border is revealed at a depth of 3000 m. The contribution of gelatinous animals (medusae, siphonophores, salps) to the total deep-sea plankton biomass was estimated using a wire reference cube during nine dives in the highly productive areas of the northwest Pacific, eastern Pacific (California, Costa-Rica Dome), and subtropical oligotrophic areas. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of environmental factors and predation on benthic communities in headwater streams

Structure and composition of benthic macroinvertebrate assemblages were investigated during three consecutive years in six headwater streams that exhibit a high variation in environmental conditions, habitat structure and predatory pressure. We examined whether the abundance of functional feeding groups could be best predicted by the abundance of predators and some habitat and chemical variables. Mean density and biomass of macroinvertebrate functional feeding groups varied significantly throughout the study area. Stepwise multiple regression analyses revealed that both density and biomass of functional feeding groups was influenced primarily by chemical features of water. Shredder biomass and scraper density were also influenced by habitat features, the abundance of scrapers increasing in deeper localities at lower altitudes and with abundant macrophytes. The abundance of predatory invertebrates was related to the density and biomass of benthic prey. An influence of fish predation on invertebrate communities was not observed in the study streams. The finding that benthic communities in undisturbed headwater streams are mainly affected by water chemistry variables irrespective of fish predation and habitat features clearly highlight the sensitivity of functional feeding groups to changes in chemical features and their role as indicators for bioassessment.     

Life history and temporal distribution of Orchestia sp. cf. cavimana (Amphipoda, Talitridae) on a lake shore in central Italy

The life history of the amphipod Orchestia sp. cf. cavimana (Heller, 1865) was studied throughout the course of a year with monthly samplings and the use of pitfall traps along the shores of Lake Albano in central Italy. The data thus obtained showed two peaks in abundance (the first in June and the second in October) and a minimum capture frequency in February. Egg-bearing females were recorded in spring and late summer, whilst recruitment occurred from spring to autumn, with maximum in June and October. The data collected also indicated the presence of a positive correlation between the abundance of talitrids and both temperature and sediment moisture. Morphological analysis enabled the identification of four different cohorts (with a lifespan of the species of approximately 12–15 months) all four of which remained distinguishable throughout the course of the year. It, moreover, enabled sex determination in individuals of 5 or more millimetres. The subsequent distribution indicated that, when significant, the sex ratio was female biased and that maximum size was greater in males. In particular, maximum sizes were recorded in spring for both males and females and were of 17.5 and 13.0 mm, respectively. Furthermore, the total body length recorded for egg-bearing females was positively correlated with the number of eggs in their brood pouch.     

Numerical experiments on dynamic stiffening of beams and plates

By introducing continuous or discontinuous variations in the thickness of beams, arches and plates, it is possible in many practical situations to raise the value of the fundamental frequency and, at the same time, to lower the weight of the structural element. This is a beneficial situation, especially in those cases where weight reduction and large dynamic stiffness are of interest. The present paper surveys some recent practical accomplishments in this area.The rigorous procedure consists, from a general structural optimization viewpoint, of minimizing an objective function (for instance, total volume) subject to constraints on the geometry and behavior (natural frequencies, buckling loads, etc.). In many instances it is convenient to reverse the problem: one fixes or limits the weight or volume and constructs some quantity which describes the desired behavior of the system e.g. the fundamental frequency.The problems under study in the present paper are considerably more modest in scope, since the procedure is performed by numerical experiments.     

Benthic input rates predict seagrass (Posidonia oceanica) fish farm-induced decline

Fish farms represent a growing source of anthropogenic disturbance to benthic communities, and efficient predictors of such impacts are urgently needed. We explored the effects of fish farm benthic organic and nutrient inputs on the population dynamics of a key seagrass species (Posidonia oceanica) in four Mediterranean deep meadows adjacent to sea bream and sea bass farms. We performed two annual plant censuses on permanent plots at increasing distance from farms and measured benthic sedimentation rates around plots. High shoot mortality rates were recorded near the cages, up to 20 times greater than at control sites. Recruitment rates increased in variability but could not compensate mortality, leading to rapid seagrass decline within the first 100 m from cages. Seagrass mortality increased with total sedimentation rates (K=0.55, p<0.0002), and with organic matter (K=0.50, p=0.001), total nitrogen (K=0.46, p=0.002) and total phosphorus (K=0.56, p<3.10(-5)) inputs. P. oceanica decline accelerated above a phosphorus loading threshold of 50mg m(-2)day(-1). Phosphorus benthic sedimentation rate seems a powerful predictor of seagrass mortality from fish farming. Coupling direct measurements of benthic sedimentation rates with dynamics of key benthic species is proposed as an efficient strategy to predict fish farm impacts to benthic communities.     

Technical paper: FluMo—a mobile fluid–chemical monitoring unit for geothermal plants

A versatile fluid–chemical monitoring unit has been developed in the framework of the geothermal research platform Groß Schönebeck, Germany. It enables selective online and in situ measurements of various physico-chemical parameters at different surface locations of a geothermal fluid loop. Sensors are provided for pressure, temperature, volumetric flow rate, density, pH-value, redox potential, oxygen content, and electrical conductivity. In addition, the apparatus features two fluid samplers to manually collect fluid under in situ conditions and ultimately analyze the solution composition. All devices are mounted on a rack allowing easy transfer of the apparatus to other geothermal plants. The maximum operating pressure and temperature of the unit are 15 bar and 150 °C, respectively. The scientific and technical purpose of the system is to monitor a compositional variability of the produced fluid and chemical processes potentially occurring within the plant. These may result from reactions between the fluid and the surrounding materials, e.g., corrosion. Also, mineral precipitation as a consequence of temperature and/or pressure decrease or oxygen contamination may occur. This information is of paramount importance as so induced reactions might lead to failure of plant components or may damage the geothermal reservoir upon fluid reinjection and thus decrease injectivity.