Form Civ Gp 130 Request Preliminary Conference New York City
Form Civ Gp 130 Request Preliminary Conference New York City – Suspended particulate matter drives the spatial segregation of the nitrogen cycle along the highly turbid Ems estuary.
Gesa Schulz1, 2, Tina Sanders2, Justus E.E. van Beusekom2, 3, Yoana G. Voynova2, Andreas Schöl4, and Kirstin Dähnke2 Gesa Schulz et al. Gesa Schulz1, 2, Tina Sanders2, Justus E.E. van Beusekom2, 3, Yoana G. Voynova2, Andreas Schöl4 and Kirstin Dähnke2
Form Civ Gp 130 Request Preliminary Conference New York City
Received: Nov 29, 2021 – Thread Started: Dec 2, 2021 – Revised: Mar 15, 2022 – Accepted: Mar 15, 2022 – Published: Apr 11, 2022
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Estuaries are nutrient filters and change the nutrient load of rivers before they reach the coastal oceans. Their morphology has been extensively modified by anthropogenic activities such as dredging, dredging and dredging to meet economic and social demand, causing significant regime changes such as tidal intensification and, in some cases, extremely turbid conditions. In addition, the increased nutrient load, especially nitrogen, mainly from agriculture, causes coastal eutrophication. Estuaries can act as a sink or as a source of nitrate, depending on environmental and geomorphological conditions. These factors vary along the estuary and change the nitrogen cycle in the system. Here we investigate the factors controlling nitrogen turnover in the highly turbid Ems estuary (Northern Germany), which has been strongly influenced by human activity. During two research trips in August 2014 and June 2020, we measured water column properties, dissolved inorganic nitrogen, double stable isotopes of nitrate and dissolved nitrous oxide concentrations in the estuary. We found that the estuary has three distinct biogeochemical zones. Strong fractionation of nitrate stable isotopes (∼26 ‰) suggests removal of nitrate by denitrification of the water column in a highly turbid tidal river caused by anoxic conditions in deeper aquifers. In the middle of the estuary, nitrification becomes important, making this part a net source of nitrate. Mixing dominates outdoor running, nitrate intake will be in 2020.
We find that the overall control of biogeochemical nitrogen cycling, zoning and NO production in the Ems estuary is exerted by suspended matter concentrations and the associated oxygen deficiency.
Schulz, G., Sanders, T., van Beusekom, J.E.E., Voynova, Y.G., Schöl, A., and Dähnke, K.: Suspended particles drive the spatial segregation of nitrogen turnover along the hyperturbid Emsi estuary, Biogeosciences, Biogeosciences, 19 , 2007-2024, https://doi.org/10.5194/-19-2007-2022, 2022.
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Estuaries can significantly alter the nutrient load of rivers before they reach adjacent coastal seas (Bouwman et al., 2013; Crossland et al., 2005). Humans and human activities have profoundly altered the morphology of estuaries to meet economic and social needs. Land drainage, expansion, damming, dredging and dredging lead to significant regime changes including tidal strengthening, highly turbid conditions and habitat loss (e.g. Kennish, 2005; Winterwerp et al., 2013; De Jonge et al., 2014). High nutrient loads from agriculture, sewage and urban runoff have led to eutrophication (Galloway et al., 2003; Howarth, 2008; Van Beusekom et al., 2019), posing one of the greatest threats to coastal ecosystems worldwide (e.g. Howarth and Marinus ). , 2006; Voss et al., 2011).
Depending on the dominant microbial processes, environmental conditions and geomorphological features, estuaries can act as a sink or as an additional source of nitrate (Dähnke et al., 2008; Middelburg and Nieuwenhuize, 2001). In particular, the balance of remineralization, nitrification and denitrification determines the net role of a particular estuary. Previous studies have shown that biogeochemical changes in dissolved oxygen saturation, residence time or light penetration influence this balance of nutrient uptake and removal (Thornton et al., 2007; Diaz and Rosenberg, 2008; Voss et al., 2011; Carstensen et al. . ., 2014). .
To disentangle the role of nitrate production and removal processes, stable isotopes are a common tool, as nitrogen cycle processes secrete heavier isotopes leading to enrichment of the remaining substrate pool. The magnitude of the enrichment, the so-called isotope effect, is process specific (e.g. Granger et al., 2004; Deutsch et al., 2006; Sigman et al., 2009).
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Nitrification and denitrification also produce nitrous oxide (N2O) (Knowles, 1982; Tiedje, 1988; Wrage et al., 2001; Francis et al., 2007), a potent greenhouse gas that contributes to global warming (IPCC, 2007 ). Estuaries are potential sources of nitrous oxide (Bange, 2006) and together with coastal wetlands contribute approximately 0.17–0.95 Tg N2O-N yr−1 to the global nitrous oxide budget of 16.9 Tg alray urray et al.. , 2015; Tian et al., 2020). Estuarine emissions from nitrous oxide are regulated by several factors. Depletion of oxygen, nutrient levels and possibly the composition of organic matter trigger the production of nitrous oxide. Therefore, nitrogen oxide emissions are associated with eutrophication (e.g. de Wilde and de Bie, 2000; Galloway et al., 2003; Murray et al., 2015; Quick et al., 2019). The role of nitrous oxide production may vary in the estuary depending on environmental and geomorphological characteristics.
Although individual processes of nitrogen cycles are well understood, the interplay of multiple stressors in the nitrogen cycle requires further investigation (e.g., Billen et al., 2011; Giblin et al., 2013; Sanders and Laanbroek, 2018). Therefore, we investigate how biogeochemical properties of the water column can alter nitrogen conversion, emergent eutrophication and nitrous oxide production in an estuary.
We conducted two summer research trips along the Ems estuary, a heavily managed estuary in Germany that is under anthropogenic pressure from fertilization, dredging and channel dredging (De Jonge, 1983; Talke and de Swart, 2006; Johannsen et al., 2008). . Since the 1950s, this has led to sharp increases in particulate matter concentrations in the estuary (De Jonge et al., 2014). We investigated the nutrient and stable isotope composition of the water column and the suspended matter concentration in the Ems estuary to investigate the spatial dynamics of nitrogen removal, nitrogen cycle processes and their relationship to nitrous oxide production. We (1) assessed the biogeochemical zoning of nitrogen cycle along the estuary, (2) identified dominant nitrogen cycle pathways within individual zones, and (3) discussed factors controlling nitrogen cycle and emerging NO production. Ultimately, with this study we provide a better insight into the impact of biogeochemical properties of the water column and biogeochemistry on estuarine nutrient turnover.
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The Eems estuary is located on the Dutch-German border (Figure 1). The estuary is about 100 km long and extends from the Herbrum dam to the island of Borkum. The Ems flows into the Wadden Sea, which is part of the southern North Sea (Van Beusekom and de Jonge, 1994). The catchment area of Ems is 17,934 km2 (Krebs and Weilbeer, 2008). The catchment area is dominated by agricultural land use (80%), and urban land use represents 8% of the catchment area (FGG Ems, 2015a), with a population density of ~200km−2 (FGG Ems, 2015b). The Ems is also an important waterway with ports in Delfzijl and Emden and is used to transport large ships from the Papenburg shipyard to the North Sea (Talke and de Swart, 2006).
The Ems is characterized by high salinity and tidal gradients (Compton et al., 2017). It has an average discharge of 80.8 m3 s−1, with low freshwater flow in summer and highest discharge from January to April. The Ems is a very turbid estuary with high floating sediment concentrations (De Jonge et al., 2014; Van Maren et al., 2015b), with values of 30–40 g L−1 and more in liquid silt layers (Winterwerp et al., 2014; Van Maren et al., 2015b). al., 2013). The dredging of channels has resulted in tidal reinforcement and increased sediment transport in the upstream tidal Ems (De Jonge et al., 2014). The increase in suspended solids has led to reduced light penetration and a decrease in oxygen concentration (Bos et al., 2012). Bos et al. (2012) classified the Ems estuary as a degraded ecosystem with a high nutrient load.
Based on geomorphological features, the Ems can be divided into four sections: tidal river (kilometre 14-35), Dollar Range (kilometre 35-43), middle course (kilometre 43-75) and outer course (downstream from kilometre 75). (Figure 1).
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Figure 1 Map of the Ems estuary with sampling stations in two summer periods. Red triangles represent cruise stations in 2014, green in 2020 and crosses represent stations with oxygen readings. The gray figures show flow kilometers calculated according to the German federal waterways (https://www.gdws.wsv.bund.de/DE/startseite/startseite_node.html, last access: April 6, 2022). Background map: © OpenStreetMap Contributors 2021. Distributed under the Open Data Commons Open Database License (ODbL) v1.0.
During two research cruises, water samples were taken by the research vessel Ludwig Prandtl in August 2014 and June 2020. Nutrient concentrations and particulate matter concentrations from the 2014 cruise have been published in Sanders and Laanbroek (2018). A built-in diaphragm pump supplied the on-situ FerryBox system with water from a depth of 2 m below the surface. The FerryBox system continuously measures dissolved oxygen, water temperature, pH, salinity, fluorescence and turbidity (Petersen et al., 2011). In 2014, FerryBox dissolved oxygen measurements were about 32 µmol L−1 lower than Winkler titrations for two separate samples collected in July 2014. This offset was used to correct FerryBox optode measurements. Salinity readings were verified using an Optimare Precision Salinometer (Bremerhaven, Germany) and FerryBox readings were within 0.01 salinity units.
Discrete water samples were taken from the FerryBox system bypass. Samples for nutrient and isotope analysis were immediately filtered through burned, pre-weighed GF/F filters (4 hr, 450 ∘C) and stored frozen in acid-washed (10% HCl, overnight) PE bottles at -20 ∘C. to the analyses. Filters were saved at
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