Carbonate sedimentation and effects of eutrophication observed at the Kališta subaquatic springs in Lake Ohrid (Macedonia)

To date, little is known about the role of spring waters with respect to authigenic carbonate precipitation in a shallow lacustrine setting. Lake Ohrid, located in Southeastern Europe, is a large lake fed to over 50% by karstic springs of which half enter subaquatically and influence significantly its ecology and species distribution. In order to evaluate how sedimentological processes are influenced by such shallow-water springs, the Kališta subaquatic spring area in the north west of Lake Ohrid was investigated by a sidescan sonar survey and with sediment traps and three transects of gravity short cores. Results indicate that sedimentation in the spring area is dominated by authigenic carbonate precipitation. High sedimentation rates and evidences for bio-induced precipitation processes were observed in the water column and in the sediments. Two distinct stratigraphic units characterize the shallow subsurface, both composed of carbonate silts with high carbonate contents of up to 96%, but differing in color, carbonate content and diatom content. A chronological correlation of the cores by radiocarbon dates and <sup>137</sup>Cs activities places the transition between the two stratigraphic units after ~1955 AD. At that time, coastal sedimentation changed drastically to significantly darker sediments with higher contents of organic matter and more abundant diatoms. This change coincides with the recent human impact of littoral eutrophication

Is Lake Prespa Jeopardizing the Ecosystem of Ancient Lake Ohrid?

Lake Prespa and Lake Ohrid, located in south-eastern Europe, are two lakes of extraordinary ecological value. Although the upstream Lake Prespa has no surface outflow, its waters reach the 160m lower Lake Ohrid through underground hydraulic connections. Substantial conservation efforts concentrate on oligotrophic downstream Lake Ohrid, which is famous for its large number of endemic and relict species. In this paper, we present a system analytical approach to assess the role of the mesotrophic upstream Lake Prespa in the ongoing eutrophication of Lake Ohrid. Almost the entire outflow from Lake Prespa is found to flow into Lake Ohrid through karst channels. However, 65% of the transported phosphorus is retained within the aquifer. Thanks to this natural filter, Lake Prespa does not pose an immediate threat to Lake Ohrid. However, a potential future four-fold increase of the current phosphorus load from Lake Prespa would lead to a 20% increase (+0.9mg P m−3) in the current phosphorus content of Lake Ohrid, which could jeopardize its fragile ecosystem. While being a potential future danger to Lake Ohrid, Lake Prespa itself is substantially endangered by water losses to irrigation, which have been shown to amplify its eutrophicatio

Optimizing the parameterization of deep mixing and internal seiches in one-dimensional hydrodynamic models: a case study with Simstrat v1.3

This paper presents an improvement of a one-dimensional lake hydrodynamic model (Simstrat) to characterize the vertical thermal structure of deep lakes. Using physically based arguments, we refine the transfer of wind energy to basin-scale internal waves (BSIWs). We consider the properties of the basin, the characteristics of the wind time series and the stability of the water column to filter and thereby optimize the magnitude of wind energy transferred to BSIWs. We show that this filtering procedure can significantly improve the accuracy of modelled temperatures, especially in the deep water of lakes such as Lake Geneva, for which the root mean square error between observed and simulated temperatures was reduced by up to 40 %. The modification, tested on four different lakes, increases model accuracy and contributes to a significantly better reproduction of seasonal deep convective mixing, a fundamental parameter for biogeochemical processes such as oxygen depletion. It also improves modelling over long time series for the purpose of climate change studies

Drought-induced building damages from simulations at regional scale

We present a model computing damage costs from drought-induced soil subsidence related to shrinking and swelling soils. The model uses an indicator applicable across different climate regimes. The influence of geology and land use on regional damage levels is taken into account. Simulation results are evaluated at departmental scale, showing a good representation of the regions affected by drought-induced soil subsidence. Substantial differences between simulated and observed damages are however found in some departments

A review on hot cathode ionisation gauges with focus on a suitable design for measurement accuracy and stability

project 16NRM05 'Ion gauge'A literature review starting from 1950 is given on the design and geometry of ionisation gauge types with hot cathodes. Considerations on the material of the electrodes and of surface effects are included. The review focuses on the design issues for measurement accuracy, linearity, repeatability, reproducibility, and stability of sensitivity. Also, the attempts to reduce the lower measurement limit are reviewed to some extent.publishersversionpublishe

Evaluation and metrological performance of a novel ionisation vacuum gauge suitable as reference standard

Funding Information: This work has received funding from the EMPIR programme (projects 16NRM05 and 20SIP01) co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme and the Portuguese National Funding Agency for Science, Research and Technology in the framework of the project UIDB/FIS/ 00068/2020. Publisher Copyright: © 2023 The Author(s)Recently, a new type of ionization vacuum gauge was introduced, which was proposed as a reference and transfer standard in the range of 10-6 Pa to 10-2 Pa because of its excellent stability and linearity. In contrast to present models of ionisation vacuum gauges, all electrons have a well-defined path length through the ionisation space. This even allows one to predict the sensitivity for a gas species provided that the ionisation cross section of the gas molecules for electrons between 50 eV and 200 eV is known. Following the development of this gauge we investigated its metrological performance in terms of linearity, resolution, repeatability, reproducibility, transport and long-term stability, disturbances by magnetic fields, influence of the surrounding earth potential and so on. The gauge demonstrated excellent metrological properties and is indeed suitable as an accurate reference and transfer standard, but can also provide important economic benefits to manufacturers and users.publishersversionpublishe

Heavy Metal and Rock in Space: Cluster RAPID Observations of Fe and Si

Metallic and silicate ions carry essential information about the evolution of the Earth and near-Earth small bodies. Despite this, there has so far been very little focus on ions with atomic masses higher than oxygen in the terrestrial magnetosphere. In this paper, we report on abundances and properties of energetic ions with masses corresponding to that of silicon (Si) and iron (Fe) in Earth's geospace. The results are based on a newly derived data product from the Research with Adaptive Particle Imaging Detectors on Cluster. We find traces of both Si and Fe in all of the regions covered by the spacecraft, with the highest occurrence rates and highest intensities in the inner magnetosphere. We also find that the Fe and Si abundances are modulated by solar activity. During solar maximum, the probability of observing Fe and Si in geospace increases significantly. On the other hand, we find little or no direct correlation between geomagnetic activity and Si and Fe abundance in the magnetosphere. Both Si and Fe in the Earth's magnetosphere are inferred to be primarily of solar wind origin.publishedVersio

Energy input and dissipation in a temperate lake during the spring transition

ADCP and temperature chain measurements have been used to estimate the rate of energy input by wind stress to the water surface in the south basin of Windermere. The energy input from the atmosphere was found to increase markedly as the lake stratified in spring. The efficiency of energy transfer (Eff), defined as the ratio of the rate of working in near-surface waters (RW) to that above the lake surface (P10), increased from ∼0.0013 in vertically homogenous conditions to ∼0.0064 in the first 40 days of the stratified regime. A maximum value of Eff∼0.01 was observed when, with increasing stratification, the first mode internal seiche period decreased to match the diurnal wind period of 24 h. The increase in energy input, following the onset of stratification was reflected in enhancement of the mean depth-varying kinetic energy without a corresponding increase in wind forcing. Parallel estimates of energy dissipation in the bottom boundary layer, based on determination of the structure function show that it accounts for ∼15% of RW in stratified conditions. The evolution of stratification in the lake conforms to a heating stirring model which indicates that mixing accounts for ∼21% of RW. Taken together, these estimates of key energetic parameters point the way to the development of full energy budgets for lakes and shallow seas

Development of a design for an ionisation vacuum gauge suitable as a reference standard

UID/FIS/00068/2019The EURAMET EMPIR project “16NRM05 - Ion gauge” aims to develop an ionisation vacuum gauge suitable as a reference vacuum standard. In such a gauge the electron trajectories and their kinetic energy inside the ionisation volume should be well defined and stable. In the search for a suitable design, a series of simulations on different ionisation gauge concepts that have the potential to meet stringent stability requirements have been carried out. Different software packages were used for this purpose. This paper focuses on the design aspects and the performance of the different ionisation gauge concepts that have been investigated by simulation. Parameters such as ionisation gauge sensitivity, ion collection efficiency and electron transmission efficiency, have been determined as a function of emission current, pressure and electron source alignment.publishersversionpublishe

Type inference in flexible model-driven engineering using classification algorithms

Flexible or bottom-up model-driven engineering (MDE) is an emerging approach to domain and systems modelling. Domain experts, who have detailed domain knowledge, typically lack the technical expertise to transfer this knowledge using traditional MDE tools. Flexible MDE approaches tackle this challenge by promoting the use of simple drawing tools to increase the involvement of domain experts in the language definition process. In such approaches, no metamodel is created upfront, but instead the process starts with the definition of example models that will be used to infer the metamodel. Pre-defined metamodels created by MDE experts may miss important concepts of the domain and thus restrict their expressiveness. However, the lack of a metamodel, that encodes the semantics of conforming models has some drawbacks, among others that of having models with elements that are unintentionally left untyped. In this paper, we propose the use of classification algorithms to help with the inference of such untyped elements. We evaluate the proposed approach in a number of random generated example models from various domains. The correct type prediction varies from 23 to 100% depending on the domain, the proportion of elements that were left untyped and the prediction algorithm used