Hydrodynamic-phytoplankton model for short-term forecasts of phytoplankton in Lake Taihu, China

Phytoplankton biomass is an important factor for short-term forecasts of algal blooms. Our new hydrodynamic-phytoplankton model is primarily intended for simulating the spatial and temporal distribution of phytoplankton in Lake Taihu within a time frame of 1-5 days. The model combines two modules: a simple phytoplankton kinetics module for growth and loss; and a mass-transport module, which defines phytoplankton transport horizontally with a two dimensional hydrodynamic model. To adapt field data for model input and calibration, we introduce two simplifications: (a) exclusion of some processes related to phytoplankton dynamics like nutrient dynamics, sediment resuspension, mineralization and nitrification, and (b) use of monthly measured data of the nutrient state. Chlorophyll-α concentration, representing phytoplankton biomass, is the only state variable in the model. A sensitivity analysis was carried out to identify the most sensitive parameter set in the phytoplankton kinetics module. The model was calibrated with field data collected in 2008 and validated with additional data obtained in 2009. A comparison of simulated and observed chlorophyll-α concentration for 33 grid cells achieved an accuracy of 78.7%. However, mean percent error and mean absolute percent error were 13.4% and 58.2%, respectively, which implies that further improvement is necessary, e.g. by reducing uncertainty of the model input and by an improved parameter calibration.     

The influence of well hydraulics on the spatial distribution of well incrustations

In many cases, the operation of wells is hampered by the formation of mineral incrustations. From field studies, it is known that the distribution of incrustations in wells is quite inhomogeneous. Flow models were calculated to assess the hydraulic background of this phenomenon. For horizontal flow, the screen section facing the natural flow direction receives the majority of the total inflow. This phenomenon increases with increasing natural gradients of flow. The vertical distribution of water intake is also quite inhomogeneous. In partially penetrating wells, the uppermost part of the screen receives much more inflow than the deeper screen sections. These flow inhomogenities involve elevated flow velocities and may cause increased influx of shallow, oxygenated water, all conditions favorable for incrustation growth. Field investigations on incrusting wells clearly show that the identified screen areas of elevated flow are indeed much more prone to incrustation deposition. Such sections require more attention during rehabilitations. A suction flow control device can help to homogenize the inflow but can cause elevated entrance loss when affected by incrustation buildup itself.     

Simulating the mobile barrier (MOSE) operation in the Venice Lagoon, Italy: global sea level rise and its implication for navigation

Three years of mobile barrier operations have been simulated with a hydrodynamic model to check the efficiency of the barriers in defending the city of Venice from flooding. The simulations have been carried out in the actual situation and with a sea-level rise of 30 and 50 cm. Moreover, the interference of the barrier operations with the ship traffic has been studied. It is found that without a security increment for the forecasted water levels, the mobile barriers cannot defend completely Venice from flooding due to the uncertainty in the forecast. With a security increment of 10 cm, the barriers work well in actual conditions but still cannot avoid flooding with a global sea-level rise. The interference with the ship traffic is acceptable under actual conditions but becomes prohibitive with a sea-level rise of 50 cm, when nearly two-thirds of the ship passages are blocked or delayed.     

Analysis of Wellbore Skin Samples—Typology,Composition, and Hydraulic Properties

The presence of a wellbore skin layer, formed during the drilling process, is a major impediment for the energy‐efficient use of water wells. Many models exist that predict its potential impacts on well hydraulics, but so far its relevant hydraulic parameters were only estimates or, at best, model results. Here, we present data on the typology, thickness, composition, and hydraulic properties obtained from the sampling of excavated dewatering wells in lignite surface mines and from inclined core drilling into the annulus of an abandoned water well. Despite the limited number of samples, several types of skin were identified. Both surface cake filtration and particle straining in the aquifer occur. The presence of microcracks may be a determining feature for the hydraulic conductivity of skin layers. In the case of the well‐developed water supply well, no skin layer was detected. The observed types and properties of wellbore skin samples can be used to test the many mathematical skin models.     

Holocene relative sea-level change, isostatic subsidence and the radial viscosity structure of the mantle of northwest Europe (Belgium, the Netherlands, Germany, southern North Sea)

A comprehensive observational database of Holocene relative sea-level (RSL) index points from northwest Europe (Belgium, the Netherlands, northwest Germany, southern North Sea) has been compiled in order to compare and reassess the data collected from the different countries/regions and by different workers on a common time–depth scale. RSL rise varies in magnitude and form between these regions, revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity. It clearly contains a non-linear, glacio- and/or hydro-isostatic subsidence component, which is only small on the Belgian coastal plain but increases significantly to a value of ca 7.5 m relative to Belgium since 8 cal. ka BP along the northwest German coast. The subsidence is at least in part related to the Post-Glacial collapse of the so-called peripheral forebulge which developed around the Fennoscandian centre of ice loading during the Last Glacial Maximum. The RSL data have been compared to geodynamic Earth models in order to infer the radial viscosity structure of the Earth's mantle underneath NW Europe (lithosphere thickness, upper- and lower-mantle viscosity), and conversely to predict RSL in regions where we have only few observational data (e.g. in the southern North Sea). A very broad range of Earth parameters fit the Belgian RSL data, suggesting that glacial isostatic adjustment (GIA) only had a minor effect on Belgian crustal dynamics during and after the Last Ice Age. In contrast, a narrow range of Earth parameters define the southern North Sea region, reflecting the greater influence of GIA on these deeper/older samples. Modelled RSL data suggest that the zone of maximum forebulge subsidence runs in a relatively narrow, WNW–ESE trending band connecting the German federal state of Lower Saxony with the Dogger Bank area in the southern North Sea. Identification of the effects of local-scale factors such as past changes in tidal range or tectonic activity on the spatial and temporal variations of sea-level index points based on model-data comparisons is possible but is still complicated by the relatively large range of Earth model parameters fitting each RSL curve, emphasising the need for more high-quality observational data.     

Beobachtungen in der libyschen Sahara

Zusammenfassung Vom Westrand der Großen Syrte zieht sich eine grabenartige tektonische Senke in SSO-Richtung bis zu den Djofra-Oasen, die in einer Ausweitung dieses Systems liegen. Begleitender Vulkanismus liefert neben Einzelvulkanen auf tektonischen Linien vom Eozän bis ins Alluvium ausgedehnte Deckenergüsse. Diese gehören genetisch zum Graben und liegen südlich der Senke der Djofra-Oasen. Noch weiter südlich verläuft die Störungszone parallel zum Graben des Roten Meeres bis zu dem vulkanbesetzten Tibestigebirge. Auf halbem Wege liegen alluviale Einzelvulkane. Die klimatische Entwicklung zeigt seit dem Tertiär mindestens fünf deutliche Pluvialzeiten, deren jüngste wahrscheinlich dem Capsien, die zweitjüngste vielleicht etwa dem Acheul entspricht. Die Grundwässer liegen in zwei Stockwerken und stammen teils aus dem Tibestigebirge, teils aus örtlichen Niederschlägen (des letzten Pluvials). Das heutige Grundwasser ist ein Rest.Die Beobachtungen stammen aus Wüstenfahrten in den Jahren 1941 und 1942. Da durch die Zeitumstände ein großer Teil der Bilder, Gesteine und Fossilien sowie viele Aufzeichnungen verloren gegangen sind, bleibt die Darstellung etwas skizzenhaft.     

Discrete element model for quasi‐brittle rupture under tensile and compressive loading

In the absence of initial cracks, the material behavior is limited by its strength, usually defined in homogeneous conditions (of stress and strain). Beyond this limit, in quasi‐brittle case, cracks may propagate and the material behavior tends to be well described by fracture mechanics. Discrete element approaches show consistent results dealing with this transition during rupture. However, the calibration of the parameters of the numerical models (i.e., stiffness, strength, and toughness) may be quite complex and sometimes only approximative. Based on a brittle rupture criterion, we analyze the biaxial response of uncracked samples. Thus, tensile and compressive strengths are analytically identified and become direct parameters of our discrete model. Furthermore, a physically reliable crack initiation (and subsequent propagation) is shown to be induced during rupture and verified by the simulation of three‐point bending and diametral compression tests. Copyright © 2016 John Wiley & Sons, Ltd.     

What are the climate controls on δD in precipitation in the Zongo Valley (Bolivia)? Implications for the Illimani ice core interpretation

Controversy has surrounded the interpretation of the water isotopic composition (δD or δ¹⁸O) in tropical and subtropical ice cores in South America. Although recent modeling studies using AGCM have provided useful constraints at interannual time scales, no direct calibration based on modern observations has been achieved. In the context of the recent ice core drilling at Nevado Illimani (16°39′S-67°47′W) in Bolivia, we examine the climatic controls on the modern isotopic composition of precipitation in the Zongo Valley, located on the northeast side of the Cordillera Real, at about 55 km from Nevado Illimani. Monthly precipitation samples were collected from September 1999 to August 2004 at various altitudes along this valley. First we examine the local and regional controls on the common δD signal measured along this valley. We show that (1) local temperature has definitely no control on δD variations, and (2) local rainout is a poor factor to explain δD variations. We thus seek regional controls upstream the Valley potentially affecting air masses distillation. Based on backtrajectory calculations and using satellite data (TRMM precipitation, NOAA OLR) and direct observations of precipitation (IAEA/GNIP), we show that moisture transport history and the degree of rainout upstream are more important factors explaining seasonal δD variations. Analysis of a 92-yr simulation from the ECHAM-4 model (T30 version) implemented with water stable isotopes confirms our observations at seasonal time scale and emphasize the role of air masses distillation upstream as a prominent factor controlling interannual δD variations. Lastly, we focus on the isotopic depletion along the valley when air masses are lifted up. Our results suggest that, if the temperature gradient between the base and the top of the Andes was higher by a few degrees during the Last Glacial Maximum (LGM), less than 10% of the glacial to interglacial isotopic variation recorded in the Illimani ice core could be accounted for by this temperature change. It implies that the rest of the variation would originate from wetter conditions along air masses trajectory during LGM.