Hesse, Roland

Holzwarth, Ingrid

Wirtz, Kai

English

Hydraulic Engineering Repository

Conference Poster, Published VersionHolzwarth, Ingrid; Hesse, Roland; Wirtz, KaiDeterminants of biogeochemical cycling in the Elbe - amodel studyVerfügbar unter/Available at: https://hdl.handle.net/20.500.11970/105978Vorgeschlagene Zitierweise/Suggested citation:Holzwarth, Ingrid; Hesse, Roland; Wirtz, Kai (2014): Determinants of biogeochemical cyclingin the Elbe - a model study. Poster präsentiert bei: Estuaries workshop 2014.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.04 - Sep - 2014  ·  Ingrid Holzwarth  ·    ·ingrid.holzwarth@baw.de   BAW   ·   Federal Waterways Engineering and Research Institute - Coastal Department   ·  www.baw.de  MotivationThe Elbe Estuary forms the interface between a major continental river and the Wadden Sea. Its management faces problems of great and recurrent public attention such as oxygen deficits during summer months and siltation in Elbe fairways (see figure 1). These problems supposedly are interlinked in direct and indirect ways.Oxygen consumption is mainly caused by the degradation of high algal loads from upstream. Oxygen depletion increases with dredging and dumping activities which maintain sufficient navigable water depth. Specific forms of organic matter, on the other hand, influence sedimentation and erosion behavior of sediments, and thereby affect water depths.Our work aims to improve the understanding of linkages between sedimentary and biogeochemical processes in the Elbe Estuary and to support estuarine management.- A model studyDeterminants of biogeochemical cycling in the Elbe Ingrid Holzwarth (BAW), Roland Hesse (BAW) and Kai Wirtz (HZG) To describe the tidal hydrodynamic characteristics of the Elbe, we use the numerical model UnTRIM (Casulli and Stelling 2010). To UnTRIM, a tailored configuration of the Deltares-WaterQuality model system (Deltares 2014) is coupled to simulate biogeochemical processes relevant to our problem, see figure 2. The Elbe Estuary is represented by a schematic, funnel shaped model domain resolving the longitudinal estuary direction. The combination of UnTRIM-WaterQualityModel is validated against measurements of dissolved oxygen, nutrient, phytoplankton and detritus concentrations. The model reproduces major trends along the fairway (figure 3) such as a changing summer NO  maximum, a significant decrease in 3chlorophyll-a soon after the tidal barrier, and the formation of an O -minimum. 2Moderate deviations to measurements particularly are likely due to the simple set-up and model geometry, and sparse boundary values.Fig. 1: This year’s headlines in the regional newspaper ‘Hamburger Abendblatt’ on July, 24th.            Upper: Oxygen deficiency - heat wave causes fish kill.            Lower: Oxygen level too low - smelt breeding destroyed.Integrated modelReaeration Global RadiationTurbidityNO3OPALPO4SiOXYDIATGREENSNH4DOCDONDOPMortalityPOC1PON1POP1POC2PON2POP2DissolutionPrimary ProductionNitrificationDegradationSelf-ShadingMineralizationState variable ProcessIdentification of key processesFig. 3: Measurements , marked with single circles,            compared to simulation results, represented by solid lines. (www.fgg-elbe.de., downloaded 25.06.2013)Fig. 4: Measured time series of dissolved oxygen concentration in 2011 at Seemannshoeft            (provided by WGMN Hamburg) compared to simulated values at the corresponding position.Fig. 2: Biogeochemical model configuration with processes highlighted in blue and state variables           in bold letters; Si (free silicate), NH4 (ammonium), NO3 (nitrate), PO4 (ortho-phosphate),            DIAT, GREENS (phytoplankton), OXY (dissolved oxygen), OPAL (opal silicate),            POC1/PON1/POP1 (easily degradable detritus fractions), POC2/PON2/POP2            (less degradable detritus fractions), DOC/DON/DOP (dissolved detritus fractions).Our model analysis revealed dissolved oxygen concentrations to be mostly sensitive to the rate of organic matter mineralization. Changes in other uncertain model parameters such as phytoplankton mortality induce only small variations in simulation results (figure 5). During summer months, the sensitivity with respect to DOC mineralization rates is more pronounced than at late winter conditions. Organic matter quality, apart from quantity, apparently is a key determinant for oxygen concentrations in the Elbe Estuary. Continuous measurements of (dissolved and particulate) organic matter quality and quantity, especially in the upstream freshwater discharge, would be valuable for better modelling and understanding biogeochemical processes in the Elbe Estuary.Fig. 5: Simulated minimum dissolved oxygen concentration at dates of fgg-elbe measurements,            depending on chosen DOC mineralization rate (left) or phytoplankton mortality (right). LiteratureCasulli, V. & Stelling, G. S. (2010): Semi-implicit subgrid modelling of three-dimensional free-surface ?ows. INT. J. NUMER. METH. FLUIDS 67 (4), S. 441–449.Deltares (2014): D-Water Quality Processes Library Description. Technical Reference Manual. Delft, http://oss.deltares.nl/documents/183920/185723/D-Water_Quality_Processes_Technical_Reference_Manual.pdf?version=1.0100200300NO3 [ìmol/l ] ← Measurement   ← Simulation 200400600OXY [ìmol/l ]0100200300Chlfa [ìg/l ]8 MAR 2011100200300NO3 [ ìmol/l ]200400600OXY [ìmol/l ]0100200300Chlfa [ìg/l ]3 MAI 2011100200300NO3 [ìmol/l ]200400600OXY [ìmol/l ]0100200300Chlfa [ìg/l ]4 JUL 2011100200300NO3 [ìmol/l ]200400600OXY [ìmol/l ]0100200300Chlfa [ìg/l ]2 AUG 201120 40 60 80 100 120 140 160100200300km from tidal barrierNO3 [ìmol/l ]200400600OXY [ìmol/l ]0100200300Chlfa [ìg/l ]1 NOV 2011OXY [ìmol/l ]Seemannshoeft / km430 0.1 0.2 0.3062.5125187.5250312.5375437.5rDOC [1/d]O2min [ìmol/l]  08-Mar-201103-May-201104-Jul-20110 0.2 0.4 0.6 0.802468101214mortality [1/d]

Determinants of biogeochemical cycling in the Elbe - a model study

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Determinants of biogeochemical cycling in the Elbe - a model study

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