Abstract
The results of the ecosystem model ERSEM showed, that a reduction in the nutrient load by 50% for N and P cannot be linearly transferred to a similar reduction in primary production in comparison to the standard run for the year 1988. While the reduction scenario results in decreased winter concentrations of nitrogen and phosphorus of up to 40%, the decrease in net primary production reached only up to 20% in small areas in the coastal zone. The phytoplankton groups indicated different reactions to the changed nutrient availability. Generally, there were significant changes in the strength and timing of the nutrient limitation in all phytoplankton groups in the model, but the diatom concentration did not change much. Differences did occur for the flagellates, with sporadically higher flagellate concentration in comparison to the standard run. This result is important, because the increase in algal biomass due to eutrophication was related mainly to an increase in flagellates, which are not decreasing accordingly in the reduction scenario. The reduction scenarios demonstrated that changes in the discharges of the major rivers hardly affect the central North Sea, but lead to significant regional differences in the net primary production. Greatest differences with regard to primary production were found downstream of the river Rhine and Elbe. This leads to changes in the mass flows in the coastal area with an increased importance of the microbial loop. One possible reason for the muted reaction of primary production to decreasing nutrient inputs can be seen in the temporal coincidence of maximum river inputs and the phytoplankton spring bloom. Due to the high nutrient uptake during the spring bloom, inorganic nutrients are bound in the phytoplankton and form a potential for remineralisation. With a more efficient microbial loop, the system becomes less dependent on riverine nutrient inputs in summer.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Aksnes, D. L. (1993): Mathematical models for aquatic populations. — In:Sundnes, G. [Ed.]: Human impact on shelf-recruiting populations: 285–308; Trondheim (Tapir publishers).
Anonymous (1992): Guidance document for the NSTF modelling workshop, 6–8 May 1992. — 41 pp.; Den Haag (Directoraat Generaal Rijkswaterstaat).
Baliño, B. M. (1996): Eutrophication of the North Sea, 1980–1990: An evaluation of anthropogenic nutrient inputs using a 2-D phytoplankton production model. — Dr. scient, thesis Univ. Bergen: 284 pp..
Baretta, J. W. &Ebenhöh, W. &Ruardij, P. (1995): An overview over the European Reginal Sea Ecosystem Model, a complex marine ecosystem model. — Netherl. J. Sea Res.,33 (3/4): 233–246.
Baretta-Bekker, J. G. &Baretta, J. W. &Koch Rasmussen, E. (1995): The microbial food web in the European Regional Seas Ecosystem Model. — Netherl. J. Sea Res.,33 (3/4): 363–379
Baretta-Bekker, J. G. &Baretta, J. W. &Ebenhöh, W. (1997): Microbial dynamics in the marine ecosystem model ERSEM II with decoupled carbon assimilation and nutrient uptake. — J. Sea Res.,38: 195–211.
Behrendt, H. &Huber, P. &Opitz, D. &Schmoll, O. &Scholz, G. &Uebe, R. (1999): Nährstoffbilanzierung der Flußgebiete Deutschlands. — Texte UBA,75/99: 288 pp.
Bennekom, A. J. van &Gieskes, W. W. C. &Tijssen, S. B. (1975): Eutrophication of Dutch coastal waters. — Proc. roy. Soc. London, Ser. B Biol. Sci.,189: 359–374.
Blackford, J. C. (1997): An analysis of benthic biological dynamics in a North Sea ecosystem model. — J. Sea Res.,38: 213–230.
Broekhuizen, N. &Heath, M. R. &Hay, J. S. &Gurney, W. S. (1995). Modelling the dynamics of the North Sea’s mesozooplankton. — Netherl. J. Sea Res.,33 (3/4): 381–406.
Cadée, G. C. &Hegeman, J. (1993): Persisting high levels of primary production at declining phosphate concentrations in the Dutch coastal area (Marsdiep). — Netherl. J. Sea Res.,31 (2): 147–152.
Ebenhöh, W. &Baretta-Bekker, J. G. &Baretta, J. W. (1997): The primary production module in the marine ecosystem model ERSEM II, with emphasis on the light forcing. — J. Sea Res.,38: 173–193.
Hickel, W. &Berg, J. &Treutner, K. (1992): Variability in phytoplankton biomass in the German Bight (North Sea) near Helgoland, 1980 – 1990. — ICES mar. Sci. Symp.,195: 247–257.
Hickel, W. &Mangelsdorf, P. &Berg, J. (1993): The human impact in the German Bight: Eutrophication during three decades (1962–1991). — Helgoländer Meeresunters.,47: 243–263.
Hickel, W. &Eickhoff, M. &Spindler, H. (1995): Langzeit-Untersuchungen von Nährstoffen und Phytoplankton in der Deutschen Bucht. — Dt. Hydrogr. Z. Suppl.,5:297–211.
Joint, I. &Pomroy, A. (1993): Phytoplankton biomass and production in the southern North Sea. — Mar. Ecol. Progr. Ser.,99: 169–182.
Lenhart, H.-J. (1999): Eutrophierung im kontinentalen Küstenbereich der Nordsee, Reduktionsszenarien der Flußeinträge von Nährstoffen mit dem Ökosystem-Modell ERSEM. — Ber. Zentr. Meeres- und Klimaforsch., Reihe B: Ozeanogr.,35: 169 pp.
Lenhart, H.-J. &Radach, G. &Backhaus, J. O. &Pohlmann, T. (1995): Simulations of the North Sea circulation, its variability, and ist implementation as hydro-dynamical forcing in ERSEM. — Netherl. J. Sea Res.,33 (3/4): 271–299.
Lenhart, H.-J. &Pätsch, J. &Radach, G. (1996): Daily nutrient loads for the European continental rivers during 1977–1993. Discharges and loads of rivers entering the North Sea. — Ber. Zentr. Meeres- und Klimaforsch.,22: 159 pp.
Lenhart, H.-J. &Radach, G. &Ruardij, P. (1997): The effects of river input on the ecosystem dynamics in the continental coastal zone of the North Sea using ERSEM. — J. Sea Res.,38: 249–274.
OSPAR (1998): Report of the ASMO Modelling Workshop on Eutrophication Issues, 5–8 November 1996, The Hague. — 86 pp; London (Ospar Comission).
Pätsch, J. (1997): Auswirkungen anhaltender Eutrophierung der Nordsee: Langzeituntersuchungen mit dem Ökosystemmodell ERSEM. — Ber. Zentr. Meeres- und Klimaforsch.,26: 171 pp.
Pätsch, J. &Radach, G. (1997): Long-term simulation of the eutrophication of the North Sea: temporal development of nutrients, chlorophyll and primary production in a comparison to observations. — J. Sea Res.,38: 275–310.
Peeters, J. C. H. &Peperzak, L. (1990): Nutrient limitation in the North Sea: a biomass approach. — Netherl. J. Sea Res.,26: 61–73.
Radach, G. &Berg, J. (1986): Trends in den Konzentrationen der Nährstoffe und des Phytoplanktons in der Helgoländer Bucht (Helgoland Reede Daten). — Ber. Biol. Anst. Helgoland,2: 1–63.
Radach, G. &Lenhart, H.-J. (1995): Nutrient dynamics in the North Sea: Fluxes and budgets in the water derived from ERSEM. — Netherl. J. Sea Res.,33 (3/4): 301–335.
Radach, G. &Berg, J. &Hagmeier, E. (1990): Long-term changes of annual cycles of meteorological, hydro-graphic, nutrient and phytoplankton time series at Helgoland and at FV Elbe in the German Bight. — Com. Shelf Res.,10 (4): 305–328.
Riegmann, R. (1991): Mechanisms behind eutrophication induced novel algal blooms. — NIOZ-Rapp.,1991–9: 52 pp.
Ruardij, P. &Raaphorst, W. van (1995): Benthic nutrient regeneration in the ERSEM ecosystem model of North Sea. — Netherl. J. Sea Res.,33 (3/4): 435–483.
Skogen, M. D. &Svendsen, E. &Berntsen, J. &Asknes, D. &Ulvestad, K. B. (1995): Modelling the primary production in the North Sea using a coupled three-dimensional physical-chemical-biological ocean model. — Estuar. coast. Shelf Sci.,41: 545–565.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Lenhart, HJ. Effects of river nutrient load reduction on the eutrophication of the North Sea, simulated with the ecosystem model ERSEM. Senckenbergiana maritima 31, 299–311 (2001). https://doi.org/10.1007/BF03043038
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF03043038