Sources and effects of oxygen deficiencies in the south-eastern North Sea

Westernhagen, Hein von; Hickel, Wolfgang; Bauerfeind, Eduard; Niermann, U.; Kröncke, Ingrid

doi:10.1080/00785326.1986.10422006

Cited by 63 publications

(27 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The increase in anthropogenic input has been well documented in the southern North Sea (Hickel et al 1993) and in the Kattegat (Andersson and Rydberg 1988). It is likely to be a general phenomenon along the coasts of northern Europe, In addition, lowered oxygen levels and oxygen deficiency that can be ascribed to eutrophication have been reported from many areas, for instance, in the southern North Sea (Westernhagen et al 1986), the Kattegat (Andersson and Rydberg 1988), and on the west coast of Sweden (Rosen-berg 1990). Richardson and Heilmann (1995) concluded that in the Kattegat, annual primary production probably more than doubled between the 1950s and the 1984-l 993 period and that the most likely underlying cause was eutrophication.…”

Section: Discussionmentioning

confidence: 98%

“…During the last decades, negative trends in oxygen concentrations have been recorded in the deep water of the Kattegat (A.ndcrsson and Rydberg 1988) and in bottom water along the west coast of Sweden (Rosenberg 1990). In the early 198Os, incidents of low oxygen concentrations were recorded in the southeastern North Sea (Westernhagen et al 1986), and through the 198Os, episodes of low oxyg,en concentrations in the Kattegat adversely affected benthic organisms (Rosenberg and Loo 1988) and demersal hsh (Baden et al 1990). Recent studies have revealed that the deep part of the eastern Skagerrak is an important seldiment sink (Weering et al 1987) and total benthic biomass has increased significantly during the last century (Rosenberg et al 1987).…”

Section: Acknowledgmentsmentioning

confidence: 99%

See 1 more Smart Citation

Declines in oxygen concentrations along the Norwegian Skagerrak coast, 1927‐1993: A signal of ecosystem changes due to eutrophication?

Johannesse

Dahl

1996

Limnology & Oceanography

View full text Add to dashboard Cite

Every year since 1927 oxygen concentration, temperature, and salinity have been measured at 3 1 stations along the Norwegian Skagerrak coast during the latter half of September. At all analyzed depths (10 m, 30 m, and bottom water) there have been significant decreases in oxygen saturation all along the coast. In some inner coastal areas, this has led to oxygen deficiency. At intermediate depths (10 and 30 m), there is no trend in oxygen saturation until the middle of the 196Os, after which an almost linear decrease is observed until the 1990s. An explanation for the decreased oxygen saturation in the intermediate layer is increased heterotrophic activity relative to primary productivity. In the bottom water, on the other hand, oxygen saturation did not change until the beginning of the 1970s when it decreased rapidly to a significantly lower level within a few years and then stabilized at this low level after the middle of the 1970s. The higher oxygen consumption in the bottom water may be due to increased sedimentation of phytoplankton and phytodetritus as a result of greater phytoplankton biomass and, in particular, to less grazing by herbivores. No corresponding changes in meteorological or hydrographical variables were found; we therefore conclude that the decreasing oxygen concentrations are most likely caused by increased nutrient load of the coastal waters. The present evidence suggests that the decrease in bottom-water oxygen is due to structural changes in the pelagic community.

show abstract

Section: Discussionmentioning

confidence: 98%

Section: Acknowledgmentsmentioning

confidence: 99%

Declines in oxygen concentrations along the Norwegian Skagerrak coast, 1927‐1993: A signal of ecosystem changes due to eutrophication?

Johannesse

Dahl

1996

Limnology & Oceanography

View full text Add to dashboard Cite

show abstract

“…Biomass may still have increased on muddy sands and sands, but stagnated or episodically recessed on muds due to the repeated occurrences of oxygen deficiencies since the seventies. Such oxygen deficiencies have been demonstrated for larger areas, including sandy stretches (Rachor 1977, Rachor & Albrecht 1983, von Westernhagen et al 1986). Accordingly, the Nuculanitidosa-community exhibited the lowest number of species and individuals, as well as the lowest biomass during this investigation (Fig.…”

Section: Discussionmentioning

confidence: 99%

Macrofauna investigations along a transect from the inner German Bight towards the Dogger Bank

Kröncke¹,

Rachor²

1992

Mar. Ecol. Prog. Ser.

View full text Add to dashboard Cite

During the Bremerhaven Workshop in March 1990 macrofauna san~ples were taken at 9 stations along a transect from the inner German Bight towards the offshore area of the Dogger Bank. Several statistical methods, univariate and multivariate, were applied to identify and describe changes in the communities along this profile. In general, 3 well-described communities were encountered: the Nucula-nitidosa-community in the inner German Bight, the Amphiura-filiforrnis-community from the former Pleistocene valley of the River Elbe and the Tellina-fabula-community from the Dogger Bank. These sediment dependent structures combined with changes due to increasing distance from the shore (including increasing water depth) are superimposed on possible additional changes due to pollution or eutrophication and veil them along the gradient investigated. Thus, indications of impact can only be suggested within the communities. However, even the most offshore Dogger Bank station appears to be disturbed.

show abstract

“…Extended areas of severe oxygen shortage have been found there since the early 'eighties, far away (about 100 km and more) from potential sources of nutrient input (von Westernhagen et al, 1986}. Settlin 9 phytoplankton in the bottom water was found concentrated farther north, in the direction of the residual currents, than blooms of the same species in the surface waters (Hickel et al, 1989) This paper describes the human impact in the German Bight, using nutrient and phytoplankton data from the Helgoland time-series.…”

Section: Discussionmentioning

confidence: 99%

The human impact in the German Bight: Eutrophication during three decades (1962–1991)

Hickel

Mangelsdorf

Berg

1993

Helgolander Meeresunters

131

View full text Add to dashboard Cite

The human impact in the German Bight, in the form of anthropogenic eutrophication, has been documented by a 30-year time-series measurement near the island of Helgoland. Since 1962, the Biologische Anstalt Helgoland has measured inorganic nutrients and phytoplankton abundance from daffy samples at Helgoland Roads, a position 60 km off the main source of eutrophication, the River Elbe. Since the early 'sixties, phosphate concentrations rose for about a decade, levelling off to about twice the former concentrations for another decade, and then decreasing (since 1982) as a result of phosphate-reducing measures. Nitrate concentrations, however, have only increased since 1980/81, following Elbe river flood events. In 1987, three times the former concentrations were reached. A decrease has been observed only since 1991. This different development of phosphorus and nitrogen eutrophication led to a shift of inorganic N/P-ratios in the German Bight. The phosphate increase was more pronounced in the late summer "regeneration mode" conditions, the nitrate increase in the winter months. The eutrophication is not restricted to the inner German Bight and coastal waters of a salinity of < 33, but has also occurred in more saline waters at S > 33 psu (practical salinity unit), as characteristic for the outer German Bight. In this more saline water, phosphate and nitrate maximum levels occurred three years later, compared with the average Helgoland data, which are more representative of the inner German Bight. It is suggested that suspended particulate organic matter, as a long-distance carrier of nutrients, might have caused this delayed eutrophication in the outer German Bight waters. While the human impact is obvious as to nutrient concentrations, it is less obvious in phytoplankton stock enhancement. A general increase in phytoplankton biomass (about 3-4 times) was found, but this was mainly due to unidentified nanoflagellates of unknown trophic state, and subject to methodological errors. The causal relationships of phytoplankton stocks and eutrophication are not clearly understood, as natural variability is large and hydrographical factors possibly dominate. Additional nutrient input by Elbe river floods did not always result in elevated phytoplankton stocks near Helgoland, while extended periods of vertical density stratification of the German Bight water caused large plankton blooms.

show abstract

Sources and effects of oxygen deficiencies in the south-eastern North Sea

Cited by 63 publications

References 23 publications

Declines in oxygen concentrations along the Norwegian Skagerrak coast, 1927‐1993: A signal of ecosystem changes due to eutrophication?

Declines in oxygen concentrations along the Norwegian Skagerrak coast, 1927‐1993: A signal of ecosystem changes due to eutrophication?

Macrofauna investigations along a transect from the inner German Bight towards the Dogger Bank

The human impact in the German Bight: Eutrophication during three decades (1962–1991)

Contact Info

Product

Resources

About