Search results for "Macro"
showing 10 items of 3471 documents
Structural characterization and chemical composition of aragonite and vaterite in freshwater cultured pearls
2008
AbstractVaterite and aragonite polymorphs in freshwater cultured pearls from mussels of the genus Hyriopsis (Unionidae) were structurally and compositionally characterized by Raman spectroscopy, Micro computer tomography, high resolution field emission scanning electron microscopy, electron microprobe analysis and laser ablation inductively coupled plasma mass spectrometry. The appearance of vaterite in pearls is related to the initial stages of biomineralization, although we demonstrate that vaterite can not be a precursor to aragonite. It is not related to a particular crystal habit and therefore does not have a structural functionality in the pearls. Larger contents of elements typically…
Modelling the Effects of Climate Change on the Supply of Inorganic Nitrogen
2009
Human-induced changes in the nitrogen cycle due to the increased use of artificial fertilisers, the cultivation of nitrogen-fixing crops and atmospheric deposition have made nitrogen pollution to surface waters a long-standing cause for concern. In Europe, legislation has been introduced to minimise the risk of water quality degradation from excessive nitrogen inputs e.g., the European Union Nitrates Directive (EU, 1991), Drinking Water Directive (EU, 1998) and Water Framework Directive (EU, 2000). Coastal regions in particular have been an important focus, since coastal eutrophication has been attributed to increased fluxes of nitrogen from the landscape (Howarth et al., 1996; Boesch et al…
Melange: A viscoelastic lattice-particle model applicable to the lithosphere
2012
[1] This article introduces the software Melange, a 3D lattice-particle hybrid model. The software was specifically designed in order to simulate ductile visco-elasto-plastic deformation and can be used to study tectonic processes in the lithosphere from the micro to the macro scale. Melange is under an open source license. The code takes both relevant yield mechanisms for the deformation of lithospheric material into account: dynamic brittle failure and ductile creep, where ductile creep is modeled as viscoelasticity. The software considers effects of the local geology, of the inherent disorder of geomaterials, of rheological layering of the lithosphere and applies repulsion when the mater…
Responses of aquatic plants to eutrophication in rivers:a revised conceptual model
2018
Compared to research on eutrophication in lakes, there has been significantly less work carried out on rivers despite the importance of the topic. However, over the last decade, there has been a surge of interest in the response of aquatic plants to eutrophication in rivers. This is an area of applied research and the work has been driven by the widespread nature of the impacts and the significant opportunities for system remediation. A conceptual model has been put forward to describe how aquatic plants respond to eutrophication. Since the model was created, there have been substantial increases in our understanding of a number of the underlying processes. For example, we now know the thre…
Climate variability and lake ecosystem responses in western Scandinavia (Norway) during the last Millennium
2017
This paper provides a high-resolution temperature reconstruction for the last Millennium from Lake Atnsjøen, SE Norway (61°52′31″N, 10°10′37″E). The sedimentary record reveals strong influence of the large-scale global climate patterns on the local climate in southern part of Eastern Norway. We reconstructed mean July air temperature using Chironomidae-based transfer function and fossil Chironomidae assemblages. The reconstruction was supported by a selection of climate-sensitive geochemical and paleoecological sedimentary proxies of terrestrial and aquatic origin, including Cladocera, pollen and macrofossils. Presented results revealed that summer temperatures were 1–2 °C warmer than the m…
The response of flood-plain ecosystems to the Late Glacial and Early Holocene hydrological changes: A case study from a small Central European river …
2016
Abstract We use a range of environmental variables to explore the possible drivers influencing the biota, especially the composition of aquatic invertebrates, during the Younger Dryas (YD) and Early Holocene (EH) in different river valley sites: a well-developed meandering river and the confluence zone of headwater streams. Using pollen, macrofossil, cladoceran, and chironomid as well as geochemical and lithological data as proxies for environmental factors (i.e., water depth and temperature), we attempt to show that these different sites display similar hydroclimatic signals (especially floods). The geochemical records in the studied valley are correlated with environmental factors, such a…
Response of the aquatic plants and mollusc communities in Lake Kojle (central Europe) to climatic changes between 250 BCE and 1550 CE
2018
Abstract Sediments of Lake Kojle, located in the transition zone between the nemoral and boreal biogeographic zones in NE Poland, were analysed to verify the response of the aquatic ecosystem to major environmental changes. High-resolution plant macrofossil, mollusc and pollen data were derived from two replicate parallel cores and revealed several shifts in the biota composition within the littoral zone between 250 BCE and 1550 CE. The reaction of the aquatic ecosystem to temperature changes was found to be minor, which is ascribed to the mitigating influence of water and the wide ecological tolerance of most of the taxa. Najas marina, considered as an indicator of warmer conditions, was t…
The response of a shallow lake and its catchment to Late Glacial climate changes — A case study from eastern Poland
2015
In this study we investigate how climate fluctuation in the Late Glacial period influenced the development of a lake and its catchment located in the East European Plain. We analyzed the sediments of the lake for pollen, subfossil Cladocera, macrofossils and chemical composition. We aimed at disentangling: (1) the climate changes and their limno-ecological responses, (2) temperature dynamics with the use of Cladocera-based transfer function (MJT) and macrofossil-based reconstruction of mean minimum July temperature (MMJT), (3) timing of the response of different proxies to environmental changes. The results of multiproxy analyses explicitly suggest that the main driver for changes in aquati…
Dating Bulk Sediments from Limnic Deposits Using a Grain-Size Approach
2013
Radiocarbon measurements on bulk subaqueous sediments typically provide ages significantly older than actual time of deposition. This is generally caused by the presence of reworked organic compounds, which are depleted in 14C. To explore this issue of age heterogeneity, we collected 4 organic-rich samples from varying depths in a lake sediment core at the Gemündener Maar (Eifel, Germany), a lake of volcanic origin. We divided each sample into 5 standard grain-size fractions: gravel, sand, silt, clay, and 1 fraction smaller than 0.45 μm. These were cleaned separately using a standard acid-alkali-acid treatment. The highly organic gravel-size fraction provided the youngest 14C ages of all gr…
Priedaine: A Neolithic Site at the Head of the Gulf of Riga
2016
The Neolithic site of Priedaine in Jūrmala was excavated on a small scale in 2007–2008, yielding an assemblage of Comb Ceramics, along with unique wooden implements and fragments of pine-lath fishing structures. The environment and subsistence resources are indicated by plant macrofossil remains and a small faunal collection. Located by a palaeolake and also very close to the sea, the site, dated to c. 3700–3500 cal BC, would have been oriented towards aquatic resource exploitation. However, it had a wider range of functions, as indicated by the evidence of flint and amber processing. Key words: Neolithic, pottery, fishing gear, plant macro-remains, faunal remains, lake, coastal settlement.…