Dynamic patterns of dissolved nitrogen in the Southern Bight of the North Sea

doi:10.1016/0272-7714(84)90086-6

Estuarine, Coastal and Shelf Science

Volume 18, Issue 5, May 1984, Pages 499-510

https://doi.org/10.1016/0272-7714(84)90086-6 Get rights and content

Abstract

Spatial and temporal variations of dissolved inorganic nitrogen (DIN) have been assessed in onshore and offshore areas of the Southern Bight on the basis of several years' measurements. They indicate that both the residual flow lines and DIN isoconcentration lines run parallel with the coast except in the vicinity of important freshwater discharge points such as the Scheldt estuary. Evidence was found that the seasonal DIN oscillations are not created through fluctuations in input conditions at the lateral boundaries, despite considerable fluctuations in these inputs which include the English Channel (from 500 tons(t) N day⁻¹ in June up to approximately 2000 t N day⁻¹ in February) and also rivers such as the Scheldt estuary (up to 50 t N day⁻¹ in January but less than 5 t N day⁻¹ in June–July). In both the onshore and offshore areas the sum of daylight phytoplanktonic nitrogen intake and sediment release of nitrogen corresponds to the observed DIN variations during most of the year. Pelagic N-mineralization from natural or grazing mortality of phytoplankton (220 mg N m⁻² day⁻¹ onshore at its maximum) can account for the differences (200 mg N m⁻² day⁻¹ onshore at its maximum), especially at the end of the phytoplankton spring bloom. Although the causes of DIN oscillations onshore and offshore are the same, the results differ because offshore (1) the vegetative season lasts longer, and (2) DIN is exhausted at the end of the phytoplankton spring bloom.

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Marked changes in diatom and dinoflagellate biomass, composition and seasonality in the Belgian Part of the North Sea between the 1970s and 2000s
2020, Science of the Total Environment
Citation Excerpt :
For some graphs and analyses, a distinction was made between coastal and offshore stations (Fig. 1). This distinction is based on water mass distribution and therefore on gradients in salinity, nutrients and turbidity, as well as differences in mixing regimes (Baeyens et al., 1984; Capuzzo et al., 2015; De Galan et al., 2004; van Leeuwen et al., 2015). The number of coastal vs. offshore samples is very balanced between the two periods.
In the last decades, the North Sea has undergone intense environmental changes which have led to regime shifts that affected all trophic levels. Since the 1970s, both increases and decreases in phytoplankton biomass and production have been reported from different parts of the North Sea. Such conflicting observations may be partly caused by methodological differences, but also reflect regional differences related to bathymetry, hydrodynamics, climate, riverine and Atlantic influence. The Belgian part of the North Sea (BPNS) is a hydrodynamically and bathymetrically complex area under strong human influence, which has been characterized by eutrophication (up to the 1980s) and de-eutrophication (1990s onwards), and pronounced long-term changes in turbidity and water temperature. We used a newly recovered and standardized historic dataset, the Belgian Phytoplankton Database (Nohe et al., 2018), to compare the biomass, composition and seasonality of diatom and dinoflagellate assemblages, two key components of the plankton in the BPNS, between the 1970s and 2000s. Diatoms, especially large-sized taxa, showed an increase from late winter to summer, resulting in a more intense and extended growing season in the 2000s. Dinoflagellates increased year-round but especially in summer. Both diatom and dinoflagellate blooms showed a clear shift towards an earlier bloom start. In addition, while in the 1970s distinct seasonal community types were present, a striking seasonal homogenization in community structure had occurred by the 2000s. Finally, we observed a pronounced increase in the abundance of harmful diatom and dinoflagellate genera. The observed changes are most likely due to an increase in sea surface temperature and water transparency, and changes in nutrient loads and ratios. Our study underscores the importance of recovering previously inaccessible historic data as they can offer unprecedented insights into long-term change in marine ecosystems, which are essential for properly evaluating the impact of human activities on these ecosystems.
Degradation dynamics and bioavailability of land-based dissolved organic nitrogen in the Bohai Sea: Linking experiment with modeling
2017, Marine Pollution Bulletin
Citation Excerpt :
About 48 million tons of N is discharged into the coastal ocean via rivers (Boyer et al., 2006). Most studies focused on dissolved inorganic nitrogen (DIN) (Baeyens et al., 1984; Gentilhomme and Lizon, 1997; Radach et al., 1990; Ramírez et al., 2005; Wafar et al., 1983). Only few studies emphasized the importance of dissolved organic nitrogen (DON) in coastal water (Butler et al., 1979; De Galan et al., 2004; Jurgensone and Aigars, 2012; Pellerin et al., 2006; Zee and Chou, 2004).
Dissolved organic nitrogen (DON) is the major nitrogen form in the Bohai Sea. Land-based DON is released into the nitrogen pool and degraded by planktonic microbiota in coastal ocean. In this study, we evaluated the degradation of land-based DON, particularly its dynamics and bioavailability, in coastal water by linking experiment and modeling. Results showed that the degradation rate constant of DON from sewage treatment plant was significantly faster than those of other land-based sources (P < 0.05). DON was classified into three categories based on dynamics and bioavailability. The supply of dissolved inorganic nitrogen (DIN) pool from the DON pool of Liao River, Hai River, and Yellow River was explored using a 3D hydrodynamic multi-DON biogeochemical model in the Bohai Sea. In the model, large amounts of DIN were supplied from DON of Liao River than the other rivers because of prolonged flushing time in Liaodong Bay.
Geochemical behavior of trace elements in sub-tidal marine sediments of the Belgian coast
2009, Marine Chemistry
High resolution profiles of trace elements (Fe, Mn, Co, As, Cu, Cr, Ni and Pb) were assessed using the DET (Diffusive Equilibrium in Thin films) and DGT (Diffusive Gradients in Thin films) techniques in silty, organically enriched, sub-tidal sediments of the Belgian coast during late winter and spring 2008. The general chemical properties of the sediments such as dissolved oxygen, pH, Eh and sulfide profiles, controlling precipitation/mobilization reactions, were determined with electrodes (pH and Eh) and microelectrodes (oxygen) and AgI-DGT probes (sulfide).
Most trace elements show subsurface maxima and low concentrations beneath 8 cm of depth. The main physicochemical parameters controlling the vertical concentration profiles are dissolved oxygen and redox potential in the surface sediment and sulfide in the deeper sediment layers. Thermodynamic equilibrium calculations have been carried out verifying which solid phases can explain the dissolved trace metal concentrations. Seasonal variations of trace elements have been observed during the sampling period and sedimentation of fresh particulate organic matter (POM) derived from phytoplankton blooms appear to be the main cause of this temporal variability.
Flux calculations based on DGT profiles (these fluxes are minimum ones) show that exchange fluxes of trace metals in February are slightly higher than in April. In addition, “DGT pistons” were deployed at the sediment water interface (SWI) to accumulate labile ions from below. This way all labile ions, binding onto the DGT Chelex resin, are pumped out of the pore waters and the solid sediment phase (only the mobile fraction). These results are a direct estimation of the amount of trace elements that can be released from the upper sediment to the water column (in the range of 4.4·10^− 5 to 0.10 mmol·m^− 2·d^− 1 for Co, Pb, Cr, As, Cu, Ni, Fe and Mn).
Spatial and temporal trends in nutrient concentrations in the Belgian Continental area of the North Sea during the period 1993-2000
2004, Estuarine, Coastal and Shelf Science
Citation Excerpt :
These values also indicate that the winter stock value observed now is still the same as the one at the end of the 1970s. The seasonal changes found for nitrate are in agreement with the traditionally found seasonal cycle for nitrate or nutrients in seas, oceans and estuaries, whereby the primary productivity in spring and summer results in minima in nitrate concentrations, while a minimum in biological activity during winter leads to a maximum in nitrate concentrations (Baeyens et al., 1984; Brockmann et al., 1988; Prandle et al., 1997; Gentilhomme and Lizon, 1998). The significant fall in DIN (Fig. 2) at the start of the phytoplankton bloom in both zones is comparable with the findings of Baeyens et al. (1984).
Statistical analysis of nutrient data obtained during 8 years of monitoring indicated strong seasonal and spatial variability, with highest concentrations in winter and significantly higher concentrations (on average >2 times higher) in the salinity zone S < 33 than in the salinity zone S ≥ 33. In the North Sea ammonium concentrations significantly decreased from 1995 on (47% in zone S < 33 and 64% in zone S ≥ 33), while for nitrate no significant decrease was observed in the zone S ≥ 33. Despite a drastic reduction (50%) in the riverine inputs of phosphorus to the North Sea during the last decade, phosphate concentrations decreased only slightly in the zone S < 33 (<20%). This observation was somewhat similar to what happened with nitrate. Phosphate concentrations were generally low (mean: 0.75 μM; maximum: 2.4 μM) compared to the other dissolved nutrients. Mean nitrate concentrations were about 18 μM but some extreme concentrations, up to 140 μM were observed. Finally, the dissolved organic nitrogen (DON) content represented a major fraction of the total dissolved nitrogen (TDN) (median of 72% for all data), especially in the zone S ≥ 33, but no significant spatial differences in the DON concentrations were found in the Belgian area of the North Sea.
Contrasting nitrogen uptake by diatom and Phaeocystis-dominated phytoplankton assemblages in the North Sea
2003, Journal of Experimental Marine Biology and Ecology
Citation Excerpt :
The pollution problems in this area include, among others, excess nutrient input. This has resulted to subsequent high primary production (Baeyens et al., 1984; Hesse, 1988), and increasing frequency of phytoplankton blooms (Cadée, 1986), dominated by flagellates (Owens et al., 1990). In general, accelerated primary production due to over enrichment of nutrients has occasionally led to oxygen depletion problem in some areas, as was observed in the German Bight (Gerlach, 1984).
This paper documents ambient concentrations of nutrients in the Belgian coastal waters of the North Sea during the spring of 1996 and 1997. The paper elaborates the differences of uptake rates of oxidised nitrogen (NO₃⁻) and reduced nitrogen (NH₄ and urea) by Phaeocystis and diatoms. The nitrogen concentrations were dominated by NO₃⁻ with a maximum concentration of 30 μM (January 1997) and 40 μM (March 1996). In 1996, Phaeocystis dominated the spring biomass with a maximum of 521 μg C l⁻¹, while maximum diatom biomass was 174 μg C l⁻¹. In 1997, the maximum Phaeocystis spring biomass was 1600 μg C l⁻¹ and diatom maximum biomass was below 100 μg C l⁻¹. A maximum bacteria biomass of about 55 μg C l⁻¹ was observed in mid-May 1996. The maximum nitrogen uptake rates were recorded during spring and were dominated by NO₃⁻ (0.005 h⁻¹ in 1996 and 0.032 h⁻¹ in 1997). Maximum specific NH₄ uptake rates were between 0.005 h⁻¹ in May 1996 and 0.006 h⁻¹ in April 1997. The NO₃⁻ uptake rates displayed exponential decrease versus increasing ambient reduced nitrogen concentrations (ammonium and urea), whereas the reduced nitrogen uptake increased but never compensated the decreased nitrate uptake. The NH₄ uptake kinetics of diatoms displayed lower v_max compared to Phaeocystis. Consequently, Phaeocystis showed ability to increase their NH₄ uptake capacity when more NH₄ became available while diatoms failed to do so, after ammonium had exceeded their saturation concentration (>1 μM). Although reduced nitrogen has a negative effect on the uptake of NO₃⁻, Phaeocystis have more advantage than diatoms on the uptake of ammonium. This might be contributing to the biomass domination shown by Phaeocystis over extended periods in spring.
Trace metals at two sites in the southern North Sea: Results from a sediment resuspension study
1998, Continental Shelf Research
Particulate and dissolved trace metals (Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn) have been determined following intensive sampling in January and May 1989 at two sites in the southern North Sea. Site A (52° 39.5′N, 003° 40.0′E) had sandy sediments, a permanently well-mixed water column and salinities >34.5, associated with waters from the English Channel. Particulate trace metal concentrations were higher in January than in May. The concentrations in the dissolved phase were unchanged between the two periods, except for dissolved Mn which had low concentrations in January, as a result of uptake onto particles. Atmospheric inputs to surface waters were evident in January, mainly for particulate Pb. Tidally induced resuspension processes produced temporary changes in the particulate and dissolved trace metal concentrations of the bottom waters for Mn, Pb and Zn. The variation in particulate trace metal concentrations, in May, fitted a two-component particle mixing model. It is argued that a significant source of dissolved metals was from the remineralisation of particulate material held within biological fluff at the sea bed. Site B (54° 35.0′ N, 004° 50.0′ E) had sediments of muddy sand, a seasonally stratified water column and it was influenced mainly by Central North Sea Water, with salinities >34.5. Particulate and dissolved trace metal concentrations did not vary between the cruises, only particulate Pb had higher concentrations in January. The tidal resuspension of particulate metals was negligible and, in May, only the concentrations of dissolved Pb and Zn increased at higher current velocities. The results identify pathways and particle–water interactions that affect trace metal transport in the North Sea.

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Estuarine, Coastal and Shelf Science

Abstract

References (33)

Measurement of upwelling and subsequent biological processes by the Technicon Auto Analyzer and associated equipment

Deep Sea Research

Concentration and microbiological utilization of small organic molecules in the Scheldt estuary, the Belgian Coastal zone of the North Sea and the English Channel

Estuarine and Coastal Marine Science

The effects of vertical stability on phytoplankton distribution in the summer on the northwest European shelf

Deep-Sea Research

Fate of nutrient enrichment of continental shelves as indicated by the C/N content of bottom sediments

Release of photoassimilated carbon as dissolved organic matter by marine phytoplankton

Marine Biology

Mikrobiologische aktiviteiten in de sedimenten

Carbon cycling in the Belgian coastal zone and adjacent areas. Part IV. Utilization of primary products by planktonic and benthic bacteria

Carbon cycling in the Belgian coastal zone and adjacent areas. Part I. General structure of the ecosystems

On the nutrition and metabolism of zooplankton. VII. Seasonal survey of nitrogen and phosphorus excretion by Calanus in the Clyde Sea area

Journal of the Marine biological Association of the United Kingdom

The relationship between inorganic and organic nutrients in sea water

Journal of the Marine Biological Association of the United Kingdom

Mean circulation in shallow seas

Journal of Geophysical Researc

Ecological significance of fronts in the southeastern Bering Sea

Determination of chlorophyll and phaeopigments: spectrophotometric equations

Limnology and Oceanography

The relative importance of nanoplankton in the North Sea primary production

British Phycological Journal

The calculation of particulate primary production in a stratified body of water using a modification of the Vollenweider formula ‘Meteor’

ForschErgebnisse, REIHE-D

Synthesis of research on nutrients in the Southern Bight of the North Sea

Cited by (11)

Marked changes in diatom and dinoflagellate biomass, composition and seasonality in the Belgian Part of the North Sea between the 1970s and 2000s

Degradation dynamics and bioavailability of land-based dissolved organic nitrogen in the Bohai Sea: Linking experiment with modeling

Geochemical behavior of trace elements in sub-tidal marine sediments of the Belgian coast

Spatial and temporal trends in nutrient concentrations in the Belgian Continental area of the North Sea during the period 1993-2000

Contrasting nitrogen uptake by diatom and Phaeocystis-dominated phytoplankton assemblages in the North Sea

Trace metals at two sites in the southern North Sea: Results from a sediment resuspension study