Modeling the effects of environmental variables on short-term spatial changes in phytoplankton biomass in a large shallow lake,Lake Taihu

Understanding the short-term response of phytoplankton biomass on environmental variables is needed for issuing early warnings of harmful algal blooms in aquatic ecosystems. Predicting harmful algal blooms are particularly challenging in large shallow lakes due to their complex mixing patterns. This study used a two-dimensional hydrodynamic–phytoplankton model to evaluate the effects of environmental variables on short-term changes in the horizontal distribution of phytoplankton biomass in a large shallow lake, Lake Taihu, China. Two simulations were performed using daily and hourly average wind condition and water temperature data collected in 2009. Other model inputs were identical for these two simulations. The response of phytoplankton to wind conditions, light intensity, water temperature, and total dissolved phosphorus and nitrogen concentrations were examined based on a sensitivity analysis using the hourly data. Hourly simulation achieved a more realistic distribution of phytoplankton biomass than the daily simulation. This finding implies that data with a higher temporal resolution are more useful for short-term prediction of phytoplankton biomass in this lake. Sensitivity analysis indicated that water temperature and light intensity dominate short-term changes in phytoplankton biomass in this lake. Wind conditions also affect phytoplankton biomass distribution by causing advective water movement.     

Relative pointing offset analysis of calibration targets with repeated observations with Herschel-SPIRE Fourier-transform spectrometer

We present a method to derive the relative pointing offsets for SPIRE Fourier-Transform Spectrometer (FTS) solar system object (SSO) calibration targets, which were observed regularly throughout the Herschel mission. We construct ratios R _obs(ν) of the spectra for all observations of a given source with respect to a reference. The reference observation is selected iteratively to be the one with the highest observed continuum. Assuming that any pointing offset leads to an overall shift of the continuum level, then these R _obs(ν) represent the relative flux loss due to mispointing. The mispointing effects are more pronounced for a smaller beam, so we consider only the FTS short wavelength array (SSW, 958–1546 GHz) to derive a pointing correction. We obtain the relative pointing offset by comparing R _obs(ν) to a grid of expected losses for a model source at different distances from the centre of the beam, under the assumption that the SSW FTS beam can be well approximated by a Gaussian. In order to avoid dependency on the point source flux conversion, which uses a particular observation of Uranus, we use extended source flux calibrated spectra to construct R _obs(ν) for the SSOs. In order to account for continuum variability, due to the changing distance from the Herschel telescope, the SSO ratios are normalised by the expected model ratios for the corresponding observing epoch. We confirm the accuracy of the derived pointing offset by comparing the results with a number of control observations, where the actual pointing of Herschel is known with good precision. Using the method we derived pointing offsets for repeated observations of Uranus (including observations centred on off-axis detectors), Neptune, Ceres and NGC 7027. The results are used to validate and improve the point-source flux calibration of the FTS.     

Semi-active control of the benchmark highway bridge based on seismic early warning systems

Possible interactions between seismic early warning systems and structural control are herein investigated. A SEWS can provide the knowledge of some parameters, ahead of time, of the seismic event that is going to occur in a certain site. Current research activities on SEWS include the estimate of the anticipated peak ground acceleration (PGA) and the acceleration response spectrum (S_a) of an incoming earthquake. This paper proposes the exploitation of this information in the framework of semi-active (SA) control strategies, by using magnetorheological dampers. The latter are time-varying properties devices able to achieve a wide range of physical behaviours using low-power electrical currents. The main idea of this work consists in changing the MR damper behaviour according to the forecasted intensity of an incoming earthquake provided by the SEWS, in order to obtain the optimal seismic response of the hosting structure. This is investigated assuming a case-study problem. It consists in the 91/5 highway bridge located in Orange County of southern California and proposed in literature as a benchmark structure for applications in the field of structural control. The effectiveness of the proposed control strategy is assessed and compared to more consolidated control techniques.     

Fluid flow modeling of a coastal fractured karstic aquifer by means of a lumped parameter approach

Fluid flow and solute transport phenomena in fractured and karstic aquifers remain an open issue that calls the attention of numerous researchers belonging to different disciplinary fields as far as the aspects linked both to shallow and to deep phenomena are concerned. The hydrogeologic knowledge of these phenomena proves to be of high importance especially if considered in relationship with water resource exploitation, with the problems linked to contamination and the ones linked to urban and industrial development of the territory. In the examined area, characterized by a dismissed contaminated site, the realization of the landfill has required the development of a 3D flow model supported by a detailed local scale geologic model in order to evaluate the effects on groundwater flow and subsequently on contaminant propagation. The results of the flow model prove to be coherent with the fractured and karstic nature of the site in that they show at higher depths the presence of a subterranean stream channel that would speed up pollutant propagation. The obtained results represent the fundamental basis to implement a transport model that will permit to achieve a more in depth knowledge of the subsoil transport phenomena, and therefore to optimize any anthropic intervention that can involve the site.     

Event Scenario Analysis for the Design of Rockslide Countermeasures

The Torgiovannetto quarry（Assisi municipality,central Italy） is an example of a site where the natural equilibrium was altered by human activity,causing current slope instability phenomena which threaten two roadways important for the local transportation.The quarry front,having a height of about 140 m,is affected by a 182,000 m3 rockslide developed in intensely fractured limestone and is too large to be stabilized.In 2003 some tension cracks were detected in the vegetated area above the quarry upper sector.From then on,several monitoring campaigns were carried out by means of different instrumentations（topographic total station,extensometers,inclinometers,ground-based interferometric radar,laser scanner and infrared thermal camera）,allowing researchers to accurately define the landslide area and volume.The latter’s major displacements are localized in the eastern sector.The deformational field appears to be related to the seasonal rainfall.The landslide hazard associated with the worst case scenario was evaluated in terms of magnitude,intensity and triggering mechanism.For the definition of the possible runout process the DAN 3D code was employed.The simulation results were used in order to design and construct a retaining embankment.Furthermore,in order to preserve both the safety of the personnelinvolved in its realization and of the roadways users,an early warning system was implemented.The early warning system is based on daily-averaged displacement velocity thresholds.The alarm level is reached if the prediction based on the methods of Saito（1969） and Fukuzono（1985） forecasts an imminent rupture.     

Effects of Compost Addition on Pyrene Removal from Soil Cultivated with Three Selected Plant Species

A greenhouse pot experiment was conducted to investigate the effect of compost addition on the phytoremediation ability of Medicago sativa, Brassica napus, and Lolium perenne in soils contaminated with pyrene. Pyrene concentrations were evaluated after 90 days in contaminated uncultivated amended‐soil, cultivated amended‐soils, and shoots and roots of the three plant species. The addition of compost enhances significantly pyrene dissipation from 16 to 26% in uncultivated soil, whereas in cultivated soils it appears not to have any significant effect on pyrene dissipation, neither pyrene was detectable in shoots and roots of the three species examined. The high partition coefficient of pyrene to compost dissolved organic matter (DOM) and the molar absorptivity values at 280 nm (ε₂₈₀) indicate a high affinity of pyrene to compost DOM molecules, likely due to their aromatic character. These results suggest that compost improves pyrene removal from soil, possibly by promoting its adsorption onto compost DOM. This property is very important in indicating that compost can be used, besides for its amendment capacity, also as a potential tool for remediation of contaminated soils.     

Perfluorinated compounds in blood of Caretta caretta from the Mediterranean Sea

Perfluorinated compounds (PFCs), widely used for their hydro-oil repellent properties, are almost non-degradable in the environment; there is scientific evidence that indicate bioaccumulation. They represent a threat to many organisms, because they are toxic and are endocrine disruptors. Scientific studies have demonstrated the presence of PFCs in blood and liver samples of fish, turtles, birds and mammals of marine ecosystems in different geographical areas. The aim of this study was to determine the distribution of PFOS and PFOA in blood samples of the marine turtle Caretta caretta, using a minimally invasive sampling procedure. 49 blood samples of marine turtle, taken from several Italian marine turtle rescue centers, were analyzed. While PFOA was never detected, measurable concentrations of PFOS were found in 15 blood samples; the values show a range from 1.14 ng/g to 28.51 ng/g (wet wt.). No differences between groups of samples taken from different areas were found.     

Reactive Transport Modeling of ZVI Column Experiments for Nickel Remediation

MIN3P, a multicomponent reactive transport model for variably saturated porous media, is used to simulate the outputs of column tests carried out using zero valent iron (ZVI) for nickel contaminated groundwater remediation. The objective of this study is to investigate the main chemical reactions involved in contaminant removal and the main causes of the reactivity decline of ZVI over time. According to the results of the model the major causes of ZVI reactivity loss is identified in the mineral precipitation of α‐FeOOH on iron surface that probably caused ZVI passivation and led to a decline of the electron transfer rate. An existing empirical relationship between mineral precipitation and the reactivity loss of ZVI, included in the model, reproduced the changes in nickel removal observed during different laboratory column tests.     

Hässeldala – a key site for Last Termination climate events in northern Europe

The Last Termination (19 000–11 000 a BP) with its rapid and distinct climate shifts provides a perfect laboratory to study the nature and regional impact of climate variability. The sedimentary succession from the ancient lake at Hässeldala Port in southern Sweden with its distinct Lateglacial/early Holocene stratigraphy (>14.1–9.5 cal. ka BP) is one of the few chronologically well‐constrained, multi‐proxy sites in Europe that capture a variety of local and regional climatic and environmental signals. Here we present Hässeldala's multi‐proxy records (lithology, geochemistry, pollen, diatoms, chironomids, biomarkers, hydrogen isotopes) in a refined age model and place the observed changes in lake status, catchment vegetation, summer temperatures and hydroclimate in a wider regional context. Reconstructed mean July temperatures increased between c. 14.1 and c. 13.1 cal. ka BP and subsequently declined. This latter cooling coincided with drier hydroclimatic conditions that were probably associated with a freshening of the Nordic Seas and started a few hundred years before the onset of Greenland Stadial 1 (c. 12.9 cal. ka BP). Our proxies suggest a further shift towards colder and drier conditions as late as c. 12.7 cal. ka BP, which was followed by the establishment of a stadial climate regime (c. 12.5–11.8 cal. ka BP). The onset of warmer and wetter conditions preceded the Holocene warming over Greenland by c. 200 years. Hässeldala's proxies thus highlight the complexity of environmental and hydrological responses across abrupt climate transitions in northern Europe.