Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary
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...
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| Format: | Article |
| Language: | English |
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Frontiers Media S.A.
2021-06-01
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| Series: | Frontiers in Marine Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fmars.2021.623714/full |
| _version_ | 1819000412604203008 |
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| author | Johannes Pein Annika Eisele Tina Sanders Ute Daewel Emil V. Stanev Justus E. E. van Beusekom Joanna Staneva Corinna Schrum Corinna Schrum |
| author_facet | Johannes Pein Annika Eisele Tina Sanders Ute Daewel Emil V. Stanev Justus E. E. van Beusekom Joanna Staneva Corinna Schrum Corinna Schrum |
| author_sort | Johannes Pein |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-12-20T22:32:55Z |
| format | Article |
| id | doaj.art-dd623a0e7721403289f3b661140174f2 |
| institution | Directory Open Access Journal |
| issn | 2296-7745 |
| language | English |
| last_indexed | 2024-12-20T22:32:55Z |
| publishDate | 2021-06-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Marine Science |
| spelling | doaj.art-dd623a0e7721403289f3b661140174f22022-12-21T19:24:41ZengFrontiers Media S.A.Frontiers in Marine Science2296-77452021-06-01810.3389/fmars.2021.623714623714Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged EstuaryJohannes Pein0Annika Eisele1Tina Sanders2Ute Daewel3Emil V. Stanev4Justus E. E. van Beusekom5Joanna Staneva6Corinna Schrum7Corinna Schrum8Institute of Coastal System Analysis and Modelling, Helmholtz-Zentrum Hereon, Geesthacht, GermanyInstitute of Carbon Cycles, Helmholtz-Zentrum Hereon, Geesthacht, GermanyInstitute of Carbon Cycles, Helmholtz-Zentrum Hereon, Geesthacht, GermanyInstitute of Coastal System Analysis and Modelling, Helmholtz-Zentrum Hereon, Geesthacht, GermanyInstitute of Coastal System Analysis and Modelling, Helmholtz-Zentrum Hereon, Geesthacht, GermanyInstitute of Carbon Cycles, Helmholtz-Zentrum Hereon, Geesthacht, GermanyInstitute of Coastal System Analysis and Modelling, Helmholtz-Zentrum Hereon, Geesthacht, GermanyInstitute of Coastal System Analysis and Modelling, Helmholtz-Zentrum Hereon, Geesthacht, GermanyInstitute of Oceanography, University of Hamburg, Hamburg, GermanyThe 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.https://www.frontiersin.org/articles/10.3389/fmars.2021.623714/fulloxygen depletioneutrophicationtidal pumpingstratificationestuarine management |
| spellingShingle | Johannes Pein Annika Eisele Tina Sanders Ute Daewel Emil V. Stanev Justus E. E. van Beusekom Joanna Staneva Corinna Schrum Corinna Schrum Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary Frontiers in Marine Science oxygen depletion eutrophication tidal pumping stratification estuarine management |
| title | Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary |
| title_full | Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary |
| title_fullStr | Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary |
| title_full_unstemmed | Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary |
| title_short | Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary |
| title_sort | seasonal stratification and biogeochemical turnover in the freshwater reach of a partially mixed dredged estuary |
| topic | oxygen depletion eutrophication tidal pumping stratification estuarine management |
| url | https://www.frontiersin.org/articles/10.3389/fmars.2021.623714/full |
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