Nutrient dynamics in a back barrier tidal basin of the Southern North Sea: Time-series, model simulations, and budget estimates

Grunwald, Maik; Dellwig, Olaf; Kohlmeier, Cora; Kowalski, Nicole; Beck, Mélanie; Badewien, Thomas H.; Kotzur, Stephan; Liebezeit, Gerd; Brumsack, Hans‐Jürgen

doi:10.1016/j.seares.2010.02.008

Cited by 53 publications

(48 citation statements)

References 105 publications

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“…2.2.3). Although the earlier replenishment of phosphorus relative to nitrogen in the coastal sites is often reproduced (e.g., Sylt, Noordwijk-2, Noordwijk-10, Terschelling-4), some delays occur in stations such as Norderney, which probably reflects the oversimplification of the benthic processes with respect to the description of oxygen-driven iron-phosphorus complexation kinetics (Appendix A2), which have been suggested to be the main driver for the phenomena in the coastal areas (Jensen et al, 1995;van Beusekom et al, 1999;Grunwald et al, 2010).…”

Section: Discussionmentioning

confidence: 99%

The acclimative biogeochemical model of the southern North Sea

Kerimoglu¹,

Hofmeister²,

Maerz³

et al. 2017

Biogeosciences

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Abstract. Ecosystem models often rely on heuristic descriptions of autotrophic growth that fail to reproduce various stationary and dynamic states of phytoplankton cellular composition observed in laboratory experiments. Here, we present the integration of an advanced phytoplankton growth model within a coupled three-dimensional physicalbiogeochemical model and the application of the model system to the southern North Sea (SNS) defined on a relatively high resolution ( ∼ 1.5-4.5 km) curvilinear grid. The autotrophic growth model, recently introduced by Wirtz and Kerimoglu (2016), is based on a set of novel concepts for the allocation of internal resources and operation of cellular metabolism. The coupled model system consists of the General Estuarine Transport Model (GETM) as the hydrodynamical driver, a lower-trophic-level model and a simple sediment diagenesis model. We force the model system with realistic atmospheric and riverine fluxes, background turbidity caused by suspended particulate matter (SPM) and open ocean boundary conditions. For a simulation for the period 2000-2010, we show that the model system satisfactorily reproduces the physical and biogeochemical states of the system within the German Bight characterized by steep salinity; nutrient and chlorophyll (Chl) gradients, as inferred from comparisons against observation data from long-term monitoring stations; sparse in situ measurements; continuous transects; and satellites. The model also displays skill in capturing the formation of thin chlorophyll layers at the pycnocline, which is frequently observed within the stratified regions during summer. A sensitivity analysis reveals that the vertical distributions of phytoplankton concentrations estimated by the model can be qualitatively sensitive to the description of the light climate and dependence of sinking rates on the internal nutrient reserves. A non-acclimative (fixed-physiology) version of the model predicted entirely different vertical profiles, suggesting that accounting for physiological flexibility might be relevant for a consistent representation of the vertical distribution of phytoplankton biomass. Our results point to significant variability in the cellular chlorophyll-to-carbon ratio (Chl : C) across seasons and the coastal to offshore transition. Up to 3-fold-higher Chl : C at the coastal areas in comparison to those at the offshore areas contribute to the steepness of the chlorophyll gradient. The model also predicts much higher phytoplankton concentrations at the coastal areas in comparison to its non-acclimative equivalent. Hence, findings of this study provide evidence for the relevance of physiological flexibility, here reflected by spatial and seasonal variations in Chl : C, for a realistic description of biogeochemical fluxes, particularly in the environments displaying strong resource gradients.

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Section: Discussionmentioning

confidence: 99%

The acclimative biogeochemical model of the southern North Sea

Kerimoglu¹,

Hofmeister²,

Maerz³

et al. 2017

Biogeosciences

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“…This may be due to a fast recirculation of remineralization products to the water column (Chipman et al, 2010;Ehrenhauss et al, 2004;Seidel et al, 2015). Furthermore, sampling took place several weeks after the main spring phytoplankton bloom, which started at the beginning of March, as reflected in sharply decreasing silicate concentrations at a nearby permanently installed time series station (similar measurements are described in Grunwald et al (2010) and Beck and Brumsack (2012)). Consequently, the OM of the spring phytoplankton bloom had likely already been processed in the upper sediments of the USP.…”

Section: Spatial Differences In Organic Matter Sources and Turnover Rmentioning

confidence: 96%

“…The latter were shown to be of great importance for carbon, nutrient, and trace metal cycles in the large tidal flat area called Wadden Sea stretching from the Netherlands to Denmark, and the frequent water exchange between tidal flat areas and the North Sea transport carbon, nutrient, and trace metals to coastal waters of the North Sea (e.g. Beck et al, 2008;Billerbeck et al, 2006;Grunwald et al, 2010;Marchant et al, 2014;Moore et al, 2011;Riedel et al, 2011;Røy et al, 2008;Santos et al, 2015). Pore water discharge rates calculated for nearby sandy Wadden Sea sediments vary depending on the method applied and the sediment depth considered Moore et al, 2011;Riedel et al, 2010), among which the method most comparable to the model approach applied in our study resulted in lower flux rates (0.97 m −3 per tide and meter of shoreline, which equals~2 m −3 per day and meter of shoreline; Riedel et al, 2010) compared to our study.…”

Section: Pore Water Discharge Influences Phytobenthos and Nearshore Wmentioning

confidence: 99%

“…This zone was estimated to be 56 km long. Based on nutrient discharge rates described previously, the total fluxes (including seawater and freshwater fluxes) from beaches to adjacent nearshore waters are 24 * 10 5 , 11 , and Si(OH) 4 , respectively, from the backbarrier areas to the southern North Sea (Grunwald et al, 2010). Although the extrapolations do not consider the same areas (East-Frisian versus total Wadden Sea), a first comparison shows that the beach zone seems to export less (b 10%) phosphate and silicate than the backbarrier tidal flat areas.…”

Section: Pore Water Discharge Influences Phytobenthos and Nearshore Wmentioning

confidence: 99%

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The drivers of biogeochemistry in beach ecosystems: A cross-shore transect from the dunes to the low-water line

et al. 2017

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This study addresses key processes in high-energy beach systems using an interdisciplinary approach. We assess spatial variations in subsurface pore water residence times, salinity, organic matter (OM) availability, and redox conditions and their effects on nutrient cycles as well as on microbial community patterns and microphytobenthos growth. At the study site on Spiekeroog Island, southern North Sea, beach hydrology is characterized by the classical zonation with an upper saline plume (USP), a saltwater wedge, and a freshwater discharge tube in between. Sediment and pore water samples were taken along a cross-shore transect from the dunes to the low-water line reaching sediment depths down to 5 m below sediment surface. Spatial variations in pore water residence time, salinity, and organic matter availability lead to steep redox and nutrient gradients. Vertical and horizontal differences in the microbial community indicate the influence of these gradients and salinity on the community structure. shoreline. We propose that this nutrient efflux triggers growth of microphytobenthos on sediment surfaces of the discharge zone. A first comparison of nutrient discharge rates of the beach site with a nearby sandy backbarrier tidal flat margin indicates that the beach system might be of less importance in supplying recycled nutrients to nearshore waters than the backbarrier tidal flat area.

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“…This probably causes a net SPM flux into the Wadden Sea (Burchard et al, 2008(Burchard et al, , 2013. The Wadden Sea is hypothesized to act as bioreactor, where organic components of SPM become remineralized and are exported in dissolved form (Postma, 1984;Ebenhöh et al, 2004;Grunwald et al, 2010) by the offshore-directed component of the estuarine circulation. Along this pathway, dissolved nutrients are assimilated by phytoplankton and thus transferred to bio particulates.…”

Section: Implications Of a Cross-coastal Maximum Of Sinking Velocity mentioning

confidence: 99%

Maximum sinking velocities of suspended particulate matter in a coastal transition zone

et al. 2016

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Abstract. Marine coastal ecosystem functioning is crucially linked to the transport and fate of suspended particulate matter (SPM). Transport of SPM is controlled by, amongst other factors, sinking velocity w s . Since the w s of cohesive SPM aggregates varies significantly with size and composition of the mineral and organic origin, w s exhibits large spatial variability along gradients of turbulence, SPM concentration (SPMC) and SPM composition. In this study, we retrieved w s for the German Bight, North Sea, by combining measured vertical turbidity profiles with simulation results for turbulent eddy diffusivity. We analyzed w s with respect to modeled prevailing dissipation rates and found that mean w s were significantly enhanced around log 10 ( (m 2 s −3 )) ≈ −5.5. This region is typically found at water depths of approximately 15 to 20 m along cross-shore transects. Across this zone, SPMC declines towards the offshore waters and a change in particle composition occurs. This characterizes a transition zone with potentially enhanced vertical fluxes. Our findings contribute to the conceptual understanding of nutrient cycling in the coastal region which is as follows. Previous studies identified an estuarine circulation. Its residual landward-oriented bottom currents are loaded with SPM, particularly within the transition zone. This retains and traps fine sediments and particulate-bound nutrients in coastal waters where organic components of SPM become remineralized. Residual surface currents transport dissolved nutrients offshore, where they are again consumed by phytoplankton. Algae excrete extracellular polymeric substances which are known to mediate mineral aggregation and thus sedimentation. This probably takes place particularly in the transition zone and completes the coastal nutrient cycle. The efficiency of the transition zone for retention is thus suggested as an important mechanism that underlies the often observed nutrient gradients towards the coast.

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Nutrient dynamics in a back barrier tidal basin of the Southern North Sea: Time-series, model simulations, and budget estimates

Cited by 53 publications

References 105 publications

The acclimative biogeochemical model of the southern North Sea

The acclimative biogeochemical model of the southern North Sea

The drivers of biogeochemistry in beach ecosystems: A cross-shore transect from the dunes to the low-water line

Maximum sinking velocities of suspended particulate matter in a coastal transition zone

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