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

• DOI: 10.3389/fmars.2021.623714
• Publication Date: 2021-06-04T15:50:59Z
• Authors: Johannes Pein; Annika Eisele; Tina Sanders; Ute Daewel; Emil V. Stanev; Justus E. E. van ...; Joanna Staneva; Corinna Schrum
• Keywords: Biogeochemical Cycle; Stratification (seeds)

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