Suspended Sediment Transport and Fluid Mud Dynamics in Tidal Estuaries

Cohesive sediments transport has been systematically studied for more than a century from field studies, laboratory experiments, and mathematical models. During the past decades, the accumulation of flocculated cohesive sediments and the formation of weakly consolidated mud deposits, including fluid mud, gained increased attention. Despite extensive research efforts, the governing processes of fluid mud formation are far from being fully understood. The primary objective of this study is to investigate tide-driven dynamics of fluid mud in estuaries. State of the art hydroacoustic subbottom (SES) and current velocity profilers (ADCP) are used, to measure fluid mud dynamics on appropriate temporal and spatial scales. Connected fields of research are to be taken into account, such as bedload transport and the influence of subaqueous dunes on the turbulent flow field. Technical aspects are considered, in particular the detection of suspended cohesive sediments. Measurements are conducted in the Ems and the Weser estuary, located along the North Sea coast of Germany. Other study sites in the North Sea are the Jade Bay in Germany and the Grådyb tidal inlet in Denmark. Not only the combined deployment of different hydroacoustic profiling devices but also the combined processing of collected data allows fluid mud dynamics to be studied in great detail. Combined processing is implemented in a software tool, programmed in MATLABTM. The software facilitates the acoustic backscatter calibration with respect to suspended sediment concentration (SSC) and thus joins information on hydrodynamic, near-bed density stratification and SSC in the water column. A large data set is collected in the Weser estuary and analysed regarding tide-driven dynamics of fluid mud. Fluid mud does not appear in the suggested form of a contiguous layer, but is deposited in depressions, in troughs of subaqueous dunes, as well as in the form of mud drapes during slack water. Entrainment is controlled by local production of turbulence, which is, in turn, influenced by local morphology. Fluid mud deposits in dune troughs are rapidly entrained, induced by strong turbulent stresses which are generated at the dune crest and advected in direction of the lutocline, i.e. the density gradient between fluid mud and the water column. Mobile mud layers are significantly resistant to entrainment and partly survive half a tidal cycle. Continuous feeding by slack water deposition induces a positive feedback of increasing concentrations and increased damping of turbulence, which inevitably leads to the formation of erosion-resistant estuarine mud deposits. A new method for the detection of density stratification is introduced, based on the backscatter gradient of acoustic current profiles. Furthermore, the gradient Richardson stability criterion is also expressed in terms of the backscatter gradient and proved to be applicable in order to assess lutocline stability under intricate hydrodynamic conditions in the Ems estuary. In the heavily engineered Ems estuary, weir closure during flood slack water and the subsequent release of captured water masses induce the flushing of the estuary and catastrophic downstream advection of fluid mud. By the time the estuary returns to flood-dominated conditions, fluid mud is rapidly advected upstream and re-established in the upper part of the estuary. In the Grådyb tidal inlet channel bedload transport in presence of large dunes is determined on the basis of highly accurate multibeam measurements. Bathymetrical changes are converted into bedload transport rates, which are not predicted by classical bedload transport formulae due to variations in grain-size composition of the mobilised sediment. Results from this study are applied to the Weser estuary to infer that lee-side deposition occurs simultaneously to the entrainment of fluid mud in dune troughs. An instrumental study conducted in the Jade Bay concerning suspended sediment dynamics reveals that suspended sediment is transported in form of turbidity clouds. Thereby, acoustic methods underestimate SSC when large aggregates are present. Several floc populations coexist in the water column, covering a wide range of sizes from a few microns to millimetre size

Wochenbericht L19-09

01.07. - 12.07.201

EST analysis of the scaly green flagellate Mesostigma viride (Streptophyta): Implications for the evolution of green plants (Viridiplantae)

BACKGROUND: The Viridiplantae (land plants and green algae) consist of two monophyletic lineages, the Chlorophyta and the Streptophyta. The Streptophyta include all embryophytes and a small but diverse group of freshwater algae traditionally known as the Charophyceae (e.g. Charales, Coleochaete and the Zygnematales). The only flagellate currently included in the Streptophyta is Mesostigma viride Lauterborn. To gain insight into the genome evolution in streptophytes, we have sequenced 10,395 ESTs from Mesostigma representing 3,300 independent contigs and compared the ESTs of Mesostigma with available plant genomes (Arabidopsis, Oryza, Chlamydomonas), with ESTs from the bryophyte Physcomitrella, the genome of the rhodophyte Cyanidioschyzon, the ESTs from the rhodophyte Porphyra, and the genome of the diatom Thalassiosira. RESULTS: The number of expressed genes shared by Mesostigma with the embryophytes (90.3 % of the expressed genes showing similarity to known proteins) is higher than with Chlamydomonas (76.1 %). In general, cytosolic metabolic pathways, and proteins involved in vesicular transport, transcription, regulation, DNA-structure and replication, cell cycle control, and RNA-metabolism are more conserved between Mesostigma and the embryophytes than between Mesostigma and Chlamydomonas. However, plastidic and mitochondrial metabolic pathways, cytoskeletal proteins and proteins involved in protein folding are more conserved between Mesostigma and Chlamydomonas than between Mesostigma and the embryophytes. CONCLUSION: Our EST-analysis of Mesostigma supports the notion that this organism should be a suitable unicellular model for the last flagellate common ancestor of the streptophytes. Mesostigma shares more genes with the embryophytes than with the chlorophyte Chlamydomonas reinhardtii, although both organisms are flagellate unicells. Thus, it seems likely that several major physiological changes (e.g. in the regulation of photosynthesis and photorespiration) took place early during the evolution of streptophytes, i.e. before the transition to land

Software design patterns for ai-systems

Well-established design patterns offer the possibility of standardized construction of software systems and can be used in various ways. The systematic use of design patterns in the field of Artificial Intelligence (AI) Systems however, has received little attention so far, despite AI being a popular research area in recent years. AI systems can be used for a wide variety of applications and play an increasingly important role in business and everyday life. AI systems are becoming more complex however, the actual machine learning (ML) task comprises only a small part of the total source code of a system. In order to maintain a clear and structured architecture for such systems and to allow easy maintenance, standardized elements should be reused in the design. This paper describes possible applications of well-known design patterns in AI systems to improve traceability of the system design