Oxygen Consumption of Resuspended Sediments of the Upper Elbe Estuary: Process Identification and Prognosis

Abstract

The resuspension of sediment leads to an increased release of nutrients and organic substances into the overlying water column, which can have a negative effect on the oxygen budget. Especially in the warmer months with a lower oxygen saturation and higher biological activity, the oxygen content can reach critical thresholds in estuaries like the upper Elbe estuary. Many studies have dealt with the nutrient fluxes that occur during a resuspension event. However, the sediment properties that influence the oxygen consumption potential (OCP) and the different biochemical processes have not been examined in detail. To fill this gap, we investigated the biogeochemical composition, texture, and OCP of sediments at 21 locations as well as the temporal variability within one location for a period of 2 years (monthly sampling) in the upper Elbe estuary. The OCP of sediments during a seven-day resuspension event can be described by the processes of sulphate formation, nitrification, and mineralisation. Chlorophyll, total nitrogen (Ntotal), and total organic carbon showed the highest correlations with the OCP. Based on these correlations, we developed a prognosis model to calculate the OCP for the upper Elbe estuary with a single sediment parameter (Ntotal). The model is well suited to calculate the oxygen consumption of resuspended sediments in the Hamburg port area during the relevant warmer months and shows a normalised root mean squared error of < 0.11 ± 0.13. Thus, the effect of maintenance measures such as water injection dredging and ship-induced wave on the oxygen budget of the water can be calculated.

Organic matter pools in sediments of the tidal Elbe river

“…It was assumed that the input of fresh SOM in March from upstream was still low due to high winter discharge, in combination with still low irradiation (Kamjunke et al, 2021), low water and sediment temperatures. A similar seasonal pattern was also described for the sediment oxygen consumption potential in the investigation area (Spieckermann et al, 2021) with highest oxygen consumption values for the summer months due to a larger of easily degradable biomass. Independent of this seasonally varying input of phytoplankton-derived, easily degradable organic matter, SOM mineralization rates are strongly controlled by in situ temperature, as also shown by Gudasz et al (2010) for sediments of boreal lakes.…”

“…They based their clusters on element fingerprinting and isotopic tracer approaches. These findings are corroborated by higher upstream oxygen consumption rates (Spieckermann et al, 2021) and higher upstream shares of organic carbon bound in the low density fraction and lower δ 13 C values (Zander et al, 2020). Further it was indicated by increased values of parameters representing phytoplankton biomass such as chlorophyll a and silicic acid (Table 1).…”

Role of Particle Resuspension in Maintaining Hypoxic Level in the Pearl River Estuary

“…Previous studies in some hypoxic zones have also found that particle resuspension can effectively increase the oxygen consumption rate in the bottom water, such as the Gulf of Mexico (Bianucci et al., 2018; Moriarty et al., 2018) and the Chesapeake Bay (Moriarty et al., 2021). The particle resuspension leads to an increased release of nutrients and organic substances into the overlying water column, which can have a negative effect on the oxygen budget (Spieckermann et al., 2022). In summary, particle resuspension plays a non‐negligible role in the coastal hypoxic level.…”

“…Particle resuspension has gained an increasing attention because it is highly involved with oxygen dynamics. An enhancement of oxygen consumption due to particle resuspension was investigated in coastal oceans and lakes through observations and numerical models (Almroth et al, 2009;Bianucci et al, 2018;Moriarty et al, 2017Moriarty et al, , 2018Moriarty et al, , 2021Spieckermann et al, 2022). Moreover, particle resuspension can indirectly affect dissolved oxygen processes by changing biogeochemical cycles, such as the rate of photosynthesis and nitrification (Gloor et al, 1994;Lou et al, 2000;Valipour et al, 2017).…”

Metabolic alkalinity release from large port facilities (Hamburg, Germany) and impact on coastal carbon storage

“…from agricultural fertilizers and wastewater) can cause large phytoplankton blooms both in rivers and in the coastal zone (Hardenbicker et al, 2016). Whose decay increases oxygen consumption (Spieckermann et al, 2021;Schöl et al, 2014), and may lead to declining oxygen levels in bottom water, and possibly hypoxia in estuaries and coastal zones (Große et al, 2016;Howarth et al, 2011;Mucci et al, 2011;Thomas et al, 2009;Frankignoulle et al, 1996;Nixon, 1995). Just upstream of the port of Hamburg, dredging activities have increased the depth from around 5 m to about 20 m to guarantee accessibility of large seagoing vessels.…”