Spatial variations in sedimentary N-transformation rates in the North Sea (German Bight)

Abstract. In this study, we investigate the role of sedimentary N cycling in the southern North Sea. We present a budget of ammonification, nitrification and sedimentary NO3- consumption and denitrification in contrasting sediment types of the German Bight (southern North Sea), including novel net ammonification rates. We incubated sediment cores from four representative locations in the German Bight (permeable, semi-permeable and impermeable sediments) with labeled nitrate and ammonium to calculate benthic fluxes of nitrate and ammonium and gross rates of ammonification and nitrification. Ammonium fluxes generally suggest oxic degradation of organic matter, but elevated fluxes at one sampling site point towards the importance of bioirrigation or short-term accumulation of organic matter. Sedimentary fluxes of dissolved inorganic nitrogen are an important source for primary producers in the water column, supporting ∼7 % to 59 % of the average annual primary production, depending on water depth. We find that ammonification and oxygen penetration depth are the main drivers of sedimentary nitrification, but this nitrification is closely linked to denitrification. One-third of freshly produced nitrate in impermeable sediment and two-thirds in permeable sediment were reduced to N2. The semi-permeable and permeable sediments are responsible for ∼68 % of the total benthic N2 production rates, which, based solely on our data, amounts to ∼1030 t N d−1 in the southern North Sea. Thus, we conclude that semi-permeable and permeable sediments are the main sinks of reactive N, counteracting eutrophication in the southern North Sea (German Bight).

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Spatial variations in sedimentary N-transformation rates in the North Sea (German Bight)

10.5194/bg-2019-295 ◽

2019 ◽

Author(s):

Alexander Bratek ◽

Justus van Beusekom ◽

Andreas Neumann ◽

Tina Sanders ◽

Jana Friedrich ◽

...

Keyword(s):

Water Column ◽

North Sea ◽

German Bight ◽

Inorganic Nitrogen ◽

Permeable Sediments ◽

Southern North Sea ◽

N Transformation ◽

Sediment Types ◽

Transformation Rates ◽

Reactive N

Abstract. In this study, we investigate the role of sedimentary N cycling in the Southern North Sea. We present a budget of ammonification, nitrification and sedimentary NO3− consumption/denitrification in contrasting sediment types of the German Bight (Southern North Sea), including novel net ammonification rates. Dissolved inorganic nitrogen concentration (nitrate, nitrite and ammonium) in the water column showed low levels between 0.2 to 3.2 µmol L−1. We incubated sediment cores with labeled nitrate and ammonium to calculate net and gross N transformation rates. The results show that impermeable sediments are the main site of ammonification (on average 10.2 ± 1.2 mmol m−2 d−1) and that they are an important source for primary producers in the water column, contributing ~ 17 to 61 % of reactive nitrogen in the water column. Ammonification and oxygen penetration depth are the main drivers of sedimentary nitrification. One third of freshly produced nitrate in impermeable sediment and two-thirds in permeable sediment were reduced to N2. The semi-permeable and permeable sediments are responsible for ~ 80 % of the total benthic N2 production rates (~ 890 t N d−1) in the southern North Sea. We conclude that impermeable sediments are important sources of reactive N and that semi-permeable and permeable sediments are the main sinks of reactive N, counteracting eutrophication in the southern North Sea (German Bight).

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The impact of intertidal areas on the carbonate system of the southern North Sea

10.5194/bg-2020-24 ◽

2020 ◽

Author(s):

Fabian Schwichtenberg ◽

Johannes Pätsch ◽

Michael Ernst Böttcher ◽

Helmuth Thomas ◽

Vera Winde ◽

...

Keyword(s):

Organic Matter ◽

North Sea ◽

German Bight ◽

Anaerobic Degradation ◽

Wadden Sea ◽

Total Alkalinity ◽

Carbonate System ◽

Southern North Sea ◽

The North ◽

The North Sea

Abstract. The coastal ocean is strongly affected by ocean acidification because it is shallow and has a low volume. Earlier observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern part of the North Sea and the German Bight, a Northwest-European shelf sea, have revealed lower acidification effects than expected. It has been assumed that anaerobic degradation and subsequent TA release in the adjacent tidal areas (Wadden Sea) in summer time is responsible for this phenomenon. In this study the exchange rates of TA and DIC between the Wadden Sea and the North Sea and the consequences for the carbonate system in the German Bight are estimated using a 3-D ecosystem model. Observed TA and DIC sources in the Wadden Sea were considered as boundary conditions. This procedure is based on the dynamic behaviour of the Wadden Sea as an area of effective production and decomposition of organic material. In addition, modelled tidal water mass exchange was used to transport material between the open North Sea and the Wadden Sea. In the model, 39 Gmol TA yr−1 were exported from the Wadden Sea into the North Sea, which is lower than a previous estimate, but within a comparable range. Furthermore, the interannual variabilities of TA and DIC concentrations, which were mainly driven by hydrodynamic conditions, were examined for the years 2001–2009. Variability in the carbonate system of the German Bight is related to weather in that the occurrence of weak meteorological blocking situations leads to enhanced accumulation of TA there. The results suggest that the Wadden Sea is an important driver of the carbonate system variability in the southern North Sea. According to the model results, on average 63 % of all TA mass changes in the German Bight were caused by net transport, 25 % by Wadden Sea export, 9 % were caused by the internal production of TA and 3 % caused by effective TA river loads (i.e. river load including freshwater dilution). The ratio of exported TA and DIC reflects the dominant underlying biogeochemical processes in the different Wadden Sea areas. Aerobic degradation of organic matter plays a key role in the North Frisian Wadden Sea during all seasons of the year. In the East Frisian Wadden Sea anaerobic degradation of organic matter dominated.

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The impact of intertidal areas on the carbonate system of the southern North Sea

Biogeosciences ◽

10.5194/bg-17-4223-2020 ◽

2020 ◽

Vol 17 (16) ◽

pp. 4223-4245

Author(s):

Fabian Schwichtenberg ◽

Johannes Pätsch ◽

Michael Ernst Böttcher ◽

Helmuth Thomas ◽

Vera Winde ◽

...

Keyword(s):

Organic Matter ◽

North Sea ◽

German Bight ◽

Anaerobic Degradation ◽

Wadden Sea ◽

Total Alkalinity ◽

Carbonate System ◽

Southern North Sea ◽

The North ◽

The North Sea

Abstract. The coastal ocean is strongly affected by ocean acidification because of its shallow water depths, low volume, and the closeness to terrestrial dynamics. Earlier observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern part of the North Sea, a northwest European shelf sea, revealed lower acidification effects than expected. It has been assumed that anaerobic degradation and subsequent TA release in the adjacent back-barrier tidal areas (Wadden Sea) in summertime is responsible for this phenomenon. In this study the exchange rates of TA and DIC between the Wadden Sea tidal basins and the North Sea and the consequences for the carbonate system in the German Bight are estimated using a 3D ecosystem model. The aim of this study is to differentiate the various sources contributing to observed high summer TA in the southern North Sea. Measured TA and DIC in the Wadden Sea are considered as model boundary conditions. This procedure acknowledges the dynamic behaviour of the Wadden Sea as an area of effective production and decomposition of organic material. According to the modelling results, 39 Gmol TA yr−1 were exported from the Wadden Sea into the North Sea, which is less than a previous estimate but within a comparable range. The interannual variabilities in TA and DIC, mainly driven by hydrodynamic conditions, were examined for the years 2001–2009. Dynamics in the carbonate system are found to be related to specific weather conditions. The results suggest that the Wadden Sea is an important driver for the carbonate system in the southern North Sea. On average 41 % of TA inventory changes in the German Bight were caused by riverine input, 37 % by net transport from adjacent North Sea sectors, 16 % by Wadden Sea export, and 6 % were caused by internal net production of TA. The dominant role of river input for the TA inventory disappears when focusing on TA concentration changes due to the corresponding freshwater fluxes diluting the marine TA concentrations. The ratio of exported TA versus DIC reflects the dominant underlying biogeochemical processes in the Wadden Sea. Whereas aerobic degradation of organic matter played a key role in the North Frisian Wadden Sea during all seasons of the year, anaerobic degradation of organic matter dominated in the East Frisian Wadden Sea. Despite the scarcity of high-resolution field data, it is shown that anaerobic degradation in the Wadden Sea is one of the main contributors of elevated summer TA values in the southern North Sea.

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Sediment-water fluxes of inorganic nitrogen compounds along the transport route of organic matter in the North Sea

Ophelia ◽

10.1080/00785236.1995.10422043 ◽

1995 ◽

Vol 41 (1) ◽

pp. 173-197 ◽

Cited By ~ 55

Author(s):

Lutz Lohse ◽

Johannes F. P Malschaert ◽

Caroline P. Slomp ◽

Willem Helder ◽

Wim van Raaphorst

Keyword(s):

Organic Matter ◽

North Sea ◽

Inorganic Nitrogen ◽

Nitrogen Compounds ◽

Water Fluxes ◽

The North ◽

The North Sea

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A cadmium budget for the German Bight in the North Sea

Marine Pollution Bulletin ◽

10.1016/s0025-326x(96)00158-0 ◽

1997 ◽

Vol 34 (6) ◽

pp. 375-381 ◽

Cited By ~ 12

Author(s):

G. Radach ◽

K. Heyer

Keyword(s):

North Sea ◽

German Bight ◽

The North ◽

The North Sea

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The Size of Diatoms II. Further Observations on Rhizosolenia styliformis (Brightwell)

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315400012121 ◽

1946 ◽

Vol 26 (3) ◽

pp. 271-284 ◽

Cited By ~ 15

Author(s):

R. S. Wimpenny

Keyword(s):

North Sea ◽

Indicator Species ◽

Separate Species ◽

Southern North Sea ◽

Auxospore Formation ◽

The North ◽

The North Sea ◽

Set Up ◽

The Antarctic

1. Diameter measurements of Rhizosolenia styliformis from the Antarctic, the subtropical Atlantic and Pacific Oceans and from the North Sea and neighbouring waters have made it appear necessary to set up two varieties, oceanica and semispina, in addition to the type of the species R. styliformis. The type as I describe it has been called var. longispina by Hustedt, but elsewhere it has often been figured as the var. oceanica of this paper. Var. semispina is synonymous with the form represented by Karsten as R. semispina Hensen. It differs from R. semispina as drawn by Hensen and its synonym R. hebetata forma semispina Gran, but is thought likely to be linked by intermediates. If this is so R. hebetata may have to be extended to include and suppress R. styliformis, as var. semispina is linked to the type by intermediates. Var. oceanica has no intermediate forms and, if R. hebetata is to be extended, this variety should be established as a separate species.2. Var. oceanica is absent from the southern North Sea and appears to be an indicator species related to oceanic inflow.3. Auxospore formation was observed for the type in the southern North Sea in 1935 and biometric observations suggest that a period of 3-4 years elapsed between the production of auxospore generations in that area. Outside the southern North Sea for the type, measurements give no indication of auxospore generations occurring at intervals exceeding a year. While auxospore formation has been seen in var. oceanica from the Shetlands area samples of June 1935 and July 1938, this phenomenon has not been observed for var. semispina.

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The impact of sedimentary alkalinity release on the water column CO<sub>2</sub> system in the North Sea

Biogeosciences ◽

10.5194/bg-13-841-2016 ◽

2016 ◽

Vol 13 (3) ◽

pp. 841-863 ◽

Cited By ~ 19

Author(s):

H. Brenner ◽

U. Braeckman ◽

M. Le Guitton ◽

F. J. R. Meysman

Keyword(s):

Coastal Zone ◽

North Sea ◽

Dissolved Inorganic Carbon ◽

Co2 Uptake ◽

Overlying Water ◽

Southern North Sea ◽

The North ◽

Alkalinity Generation ◽

The North Sea ◽

The Impact

Abstract. It has been previously proposed that alkalinity release from sediments can play an important role in the carbonate dynamics on continental shelves, lowering the pCO2 of seawater and hence increasing the CO2 uptake from the atmosphere. To test this hypothesis, sedimentary alkalinity generation was quantified within cohesive and permeable sediments across the North Sea during two cruises in September 2011 (basin-wide) and June 2012 (Dutch coastal zone). Benthic fluxes of oxygen (O2), alkalinity (AT) and dissolved inorganic carbon (DIC) were determined using shipboard closed sediment incubations. Our results show that sediments can form an important source of alkalinity for the overlying water, particularly in the shallow southern North Sea, where high AT and DIC fluxes were recorded in near-shore sediments of the Belgian, Dutch and German coastal zone. In contrast, fluxes of AT and DIC are substantially lower in the deeper, seasonally stratified, northern part of the North Sea. Based on the data collected, we performed a model analysis to constrain the main pathways of alkalinity generation in the sediment, and to quantify how sedimentary alkalinity drives atmospheric CO2 uptake in the southern North Sea. Overall, our results show that sedimentary alkalinity generation should be regarded as a key component in the CO2 dynamics of shallow coastal systems.

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Spatial interactions between saithe (Pollachius virens) and hake (Merluccius merluccius) in the North Sea

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu120 ◽

2014 ◽

Vol 71 (6) ◽

pp. 1342-1355 ◽

Cited By ~ 21

Author(s):

Xochitl Cormon ◽

Christophe Loots ◽

Sandrine Vaz ◽

Youen Vermard ◽

Paul Marchal

Keyword(s):

North Sea ◽

Linear Models ◽

Spatial Dynamics ◽

Distribution Patterns ◽

Trawl Survey ◽

Spatial Interactions ◽

Merluccius Merluccius ◽

The North ◽

Sediment Types ◽

The North Sea

Spatial interactions between saithe (Pollachius virens) and hake (Merluccius merluccius) were investigated in the North Sea. Saithe is a well-established species in the North Sea, while occurrence of the less common hake has recently increased in the area. Spatial dynamics of these two species and their potential spatial interactions were explored using binomial generalized linear models (GLM) applied to the International Bottom Trawl Survey (IBTS) data from 1991 to 2012. Models included different types of variables: (i) abiotic variables including sediment types, temperature, and bathymetry; (ii) biotic variables including potential competitors and potential preys presence; and (iii) spatial variables. The models were reduced and used to predict and map probable habitats of saithe, hake but also, for the first time in the North Sea, the distribution of the spatial overlap between these two species. Changes in distribution patterns of these two species and of their overlap were also investigated by comparing species’ presence and overlap probabilities predicted over an early (1991–1996) and a late period (2007–2012). The results show an increase in the probability over time of the overlap between saithe and hake along with an expansion towards the southwest and Scottish waters. These shifts follow trends observed in temperature data and might be indirectly induced by climate changes. Saithe, hake, and their overlap are positively influenced by potential preys and/or competitors, which confirms spatial co-occurrence of the species concerned and leads to the questions of predator–prey relationships and competition. Finally, the present study provides robust predictions concerning the spatial distribution of saithe, hake, and of their overlap in the North Sea, which may be of interest for fishery managers.

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