Anthropogenic impacts on estuarine oxygen dynamics: A model based evaluation

Holzwarth, Ingrid; Wirtz, Kai W.

doi:10.1016/j.ecss.2018.01.020

Cited by 9 publications

(15 citation statements)

References 46 publications

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“…The 3D coupled model simulations reproduced the alongchannel patterns of ecosystem dynamics known from idealised modelling studies of the Elbe estuary (Schroeder, 1997;Geerts et al, 2017;Holzwarth and Wirtz, 2018). The previous studies did not address the vertical variability of hydrodynamics and biogeochemical dynamics.…”

Section: Comparison Of the Results With Other Studiesmentioning

confidence: 82%

“…The organs of certain fish species caught near the port of Hamburg indicate that the animals experienced moderate hypoxia (Tiedke et al, 2014). Previous studies have illustrated the importance of a bathymetric jump, separating the shallow upper reach from the deepened port and mid reaches, for the collapse of primary producers and transition to the heterotrophic regime and associated oxygen depletion (Schroeder, 1997;Holzwarth and Wirtz, 2018). The same bathymetric feature seems to control the position of the estuarine oxygen minimum zone as well as the region of high ammonium remineralisation rates (Sanders et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…Here, we extend the focus of the 3D modelling to the freshwater-dominated reach using a coupled hydrodynamical-biogeochemical model. Earlier coupled modelling made use of Lagrangian (Schroeder, 1997) and idealised depth-averaged models (Holzwarth and Wirtz, 2018) to simulate the dynamics of primary production and oxygen along the estuarine freshwater reach. While these works explained well the transition from autotrophy to heterotrophy in the port region, they did not elucidate why the zones of the oxygen minimum, biogenic particle sedimentation and ammonium accumulation linger close to the bathymetric jump (instead of being flushed downstream by river flow).…”

Section: Introductionmentioning

confidence: 99%

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Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary

et al. 2021

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The Elbe estuary is a substantially engineered tidal water body that receives high loads of organic matter from the eutrophied Elbe river. The organic matter entering the estuary at the tidal weir is dominated by diatom populations that collapse in the deepened freshwater reach. Although the estuary’s freshwater reach is considered to manifest vertically homogenous density distribution (i.e., to be well-mixed), several indicators like trapping of particulate organic matter, near-bottom oxygen depletion and ammonium accumulation suggest that the vertical exchange of organic particles and dissolved oxygen is weakened at least temporarily. To better understand the causal links between the hydrodynamics and the oxygen and nutrient cycling in the deepened freshwater reach of the Elbe estuary, we establish a three-dimensional coupled hydrodynamical-biogeochemical model. The model demonstrates good skill in simulating the variability of the physical and biogeochemical parameters in the focal area. Coupled simulations reveal that this region is a hotspot of the degradation of diatoms and organic matter transported from the shallow productive upper estuary and the tidal weir. In summer, the water column weakly stratifies when at the bathymetric jump warmer water from the shallow upper estuary spreads over the colder water of the deepened mid reaches. Enhanced thermal stratification also occurs also in the narrow port basins and channels. Model results show intensification of the particle trapping due to the thermal gradients. The stratification also reduces the oxygenation of the near-bottom region and sedimentary layer inducing oxygen depletion and accumulation of ammonium. The study highlights that the vertical resolution is important for the understanding and simulation of estuarine ecological processes, because even weak stratification impacts the cycling of nutrients via modulation of the vertical mixing of oxygen, particularly in deepened navigation channels and port areas.

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Section: Comparison Of the Results With Other Studiesmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary

et al. 2021

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“…Given a staggered grid as defined above, Equations (1)-(2) can be conveniently discretized with the semi-implicit method described in the work of Casulli. 13 This method, which has proved to be quite successful in several applications (see, eg, other works [18][19][20][21][22][23][24][25][26] ), is adapted here to simulate shallow water flows with extreme subgrid resolution such as described by a detailed digital elevation model.…”

Section: Finite Difference-finite Volume Approximationmentioning

confidence: 99%

“…Several advantages offered by the subgrid approach have been demonstrated in many applications over the last decade (see, eg, other works [18][19][20][21][22][23][24] ). Essentially, equally acceptable numerical results can be produced at much lower computational cost with a coarser computational grid that contains detailed subgrid specifications.…”

Section: Introductionmentioning

confidence: 99%

Computational grid, subgrid, and pixels

Casulli

2019

Numerical Methods in Fluids

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Summary Free‐surface flows in rivers, estuaries, and coastal areas are strongly dominated by the geometrical details of the study area. Nowadays, accurate bathymetric data are easily available on raster‐based digital elevation models with an impressive spatial resolution. These data are often accessible as large two‐dimensional arrays containing several millions of pixel values. Recent numerical methods are very efficient and rather accurate but far from being able to solve the governing differential equations on a computational grid with such a fine spatial resolution. In the present investigation, the unaltered pixel values from a digital elevation model are clustered to form subgrids of a coarser computational grid. Artificial cross‐flow between disconnected areas is inhibited by introducing cell clones and edge clones. Each clone consists of directly connected pixels. It is shown how the resulting computational grid is able to resolve geometrical details of complex study areas to pixel resolution and for any grid size. As an example, the performance of the proposed algorithm is tested to simulate a typical tidal flow in the San Francisco Bay and the Sacramento‐San Joaquin Delta area by using an extreme subgrid resolution given by a digital elevation model containing 196 000 000 pixels with 10 m pixel size.

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