D5C1 Nutrient concentrations (5.1, 5.1.1)

D5C1 Nutrient concentrations (5.1, 5.1.1)

D5C2 Chlorophyll-a concentration (5.2.1)

D5C3 Harmful algal blooms (5.2.4)

D5C5 Dissolved oxygen concentration (5.3.2)

GESOther: BEQI index

LevelPressureOverall

LevelPressureNLoad

LevelPressureNConcentration

LevelPressurePLoad

LevelPressurePConcentration

LevelPressureOLoad

LevelPressureOConcentration

ImpactPressureWaterColumn

ImpactPressureSeabedHabitats

NutrientsOrganicEnrichment5_1

NutrientsNitrogen5_1

NutrientsPhosphorus5_1

NutrientsOrganicMatter5_1

NutrientsEnrichmentWaterColumn5_2or5_3

NutrientsEnrichmentSeabedHabitats5_2or5_3

MarineCoast

ShelfMxdSed

OSPAR and WFD assessment criteria and thresholds are used

OSPAR and WFD assessment criteria and thresholds are used

OSPAR and WFD assessment criteria and thresholds are used

OtherStatus

OtherStatus

NotAssessed

OtherStatus

Improving

Improving

Unknown_NotAssessed

Stable

High

Moderate

NotRelevant

High

Moderate

OSPAR: Eutrophication problem area (coastal waters) WFD: Moderate ecological status

OSPAR: Eutrophication problem area (coastal waters) WFD: moderate ecological status

OSPAR: Eutrophication problem area (coastal waters) WFD: not included (P not a cause of eutrophication in coastal and marine waters)

Organic matter inputs are not assessed in the OSPAR COMPP

OSPAR: Eutrophication problem area (coastal waters) WFD: Moderate ecological status

OSPAR: Oxygen levels in bottom water: non-problem area

Loads of inorganic nutrients (N, P) are the major cause of eutrophication in the Dutch North Sea. Organic matter inputs and concentrations show no trends, and consequently are not assessed in the OSPAR COMPP

Along the south-eastern coast of the North Sea, from northern France to Germany, several large rivers discharge into the sea. The river influence is limited to the coastal waters, and hence the offshore areas of the Dutch part of the North Sea do not show elevated concentrations of nutrients or phytoplankton biomass. The most important source of anthropogenic nutrients in the North Sea is the diffuse load from agriculture within the river basins discharging into the North Sea. Atmospheric deposition is another important source of nitrogen (approximately 1/3 of the total anthropogenic load in the Greater North Sea). Shipping is considered one of the major sources of atmospheric nitrogen deposition. A reduction target of 50% for nitrogen and phosphorus inputs (compared to 1985) was agreed by OSPAR, and laid down in the Rhine Action Plan and the North Sea Action Plan. Progress in achieving the reduction target was reported most recently in the OSPAR Quality Status Report 2010. Source oriented measures have resulted in a 20-40% reduction in riverine nitrogen2) loads in the period 1990-2006. Riverine phosphorus loads have decreased with more than 50%. The reduction target for P has been met but not (yet) for N. The 50% reduction target has been translated into a 15% reduction target for nitrogen (compared to 2006) by the International Commission for the Protection of the Rhine, to achieve WFD targets for coastal waters in the Dutch part of the North Sea.

River discharges are the source of approximately 50% of the total nitrogen input into the southern North Sea. The river discharges are strongly influenced by point and diffuse sources. The other major source is the Atlantic Ocean through the Channel. In Dutch coastal waters the relative contribution of rivers to nitrogen loads is 60-70%. Riverine nitrogen loads have decreased by 20-30% since the 1980s. In 2001 to 2004 an average 15% (range 12-18%) of the total nitrogen input to the Dutch Continental Shelf originated from atmospheric deposition. Several large rivers (e.g. Scheldt, Meuse, Rhine, Ems, Weser, Elbe) discharge into the southern North Sea. Riverine nutrient loads into the Dutch part of the North Sea are dominated by the loads from the river Rhine (>50%), that discharges into the North Sea through the Nieuwe Waterweg at Maassluis and through the Haringvliet, and into the Wadden Sea through Lake IJssel.

Nutrient concentrations in Dutch coastal waters show a strong correlation with riverine nutrient loads, which are dominated by the loads from the Rhine. As a consequence of the strong impact of river discharges on nutrient concentrations, the concentrations are highly correlated with salinity and are high near the coast (in the ‘coastal river’ with salinity <30), and close to natural background concentrations in the offshore areas (with salinity >34.5). Trends in dissolved inorganic nitrogen (DIN) concentrations in Dutch coastal waters are proportional to changes in riverine nitrogen loads. Nitrogen loads have decreased by approximately 20-40% since 1990, and this has resulted in decreased concentrations (winter means) of DIN in coastal waters, too. Nutrient concentrations show a strong seasonal pattern with a distinct peak in winter and a strong decline following the spring phytoplankton bloom. During summer nitrogen can limit primary production, particularly in stratified waters.

River discharges are the source of approximately 30% of the total phosphorus input into the southern North Sea. The river discharges are strongly influenced by point and diffuse sources. The other major source is the Atlantic Ocean through the Channel. In Dutch coastal waters the relative contribution of rivers to phosphorus loads is approximately 40-50%. Riverine phosphorus loads have decreased by more than 50% since the 1980s. Several large rivers (e.g. Scheldt, Meuse, Rhine, Ems, Weser, Elbe) discharge into the southern North Sea. Riverine nutrient loads into the Dutch part of the North Sea are dominated by the loads from the river Rhine (>50%), that discharges into the North Sea through the Nieuwe Waterweg at Maassluis and through the Haringvliet, and into the Wadden Sea through Lake IJssel.

Nutrient concentrations in Dutch coastal waters show a strong correlation with riverine nutrient loads, which are dominated by the loads from the Rhine. As a consequence of the strong impact of river discharges on nutrient concentrations, the concentrations are highly correlated with salinity and are high near the coast (in the ‘coastal river’ with salinity <30), and close to natural background concentrations in the offshore areas (with salinity >34.5). Trends in orthophosphate concentrations in Dutch coastal waters are proportional to changes in riverine phosphorus loads. Phosphorus loads have decreased by more than 50% since 1990, and this has resulted in decreased concentrations (winter means) of phosphate in coastal waters. Nutrient concentrations show a strong seasonal pattern with a distinct peak in winter and a strong decline following the spring phytoplankton bloom. During late spring phosphorus can limit primary production, particularly in stratified waters.

Loads of inorganic nutrients (N, P) are the major cause of eutrophication in the Dutch North Sea. Organic matter inputs and concentrations show no trends, and consequently are not assessed in the OSPAR COMPP

The entire North Sea, except for the Dogger Bank, has long been considered a serious problem area in terms of eutrophication. Although there are still some problems, these are limited (OSPAR Commission, Quality Status Report 2010). Algae blooms and foam on the beach from decaying algal remains are some of the nuisances caused by eutrophication. The quantity of chlorophyll a, which is the indicator for eutrophication, has decreased since 1995. In the 2001-2005 period, however, its concentration in coastal waters was still two to three times above the assessment value formulated by OSPAR (50% above the natural background) (OSPAR Commission, Report on the second application of the OSPAR Comprehensive Procedure to the Dutch marine waters (2008) 14-18). Using the same indicator, the waters up to 1 nautical mile off the coast were assessed for the Water Framework Directive. Between 2006 and 2008, scores fluctuated between 'good' and 'moderate', depending on the body of water; the Zeeland Coast and the Northern Delta Coast have had 'moderate' scores for years. The major variation in the intensity of algae bloom has made it impossible to determine a trend for the 1990-2008 period (OSPAR Commission, Report on the second application, 14-18). In Dutch coastal waters turbidity levels are high as a result of high natural levels of suspended matter. Consequently, the enhanced levels of algal biomass have an insignificant impact on water transparency. Blooms of the nuisance alga Phaeocystis globosa are considered to be one of the most conspicuous symptoms of eutrophication in the Southern Bight of the North Sea, but do not occur further north at the Oyster Grounds or the Dogger Bank. Blooms are characterized by the occurrence of large colonies of cells embedded in a mucus, that cannot be grazed by zooplankton. There is no clear trend in annual levels of Phaeocystis blooms. Causal relations between nutrient enrichment and blooms of other nuisance or harmful species lack evidence.

The low oxygen values that occur in the Oyster Grounds sedimentation area during some summers are mainly caused by the natural decomposition of deposited organic material of dead algae. In the summer months, thermal stratification of seawater occurs in this area. As a result, vertical mixing of the water column does no longer occur and the water on the seabed no longer gets refreshened. The effects of eutrophication on benthos and fish have not been measured in the monitoring programme.

High

Non related GES component

High

Moderate

Decreasing

Unknown_NotAssessed

Decrease

Unknown_NotAssessed

Nearly two-thirds of the nitrogen and a third of the phosphorus discharged to eutrophication problem areas come from agricultural sources. Urban waste water treatment plants and point-sources (industry) are other major sources of nitrogen and phosphorus. In total, these sources make up more than 80% of the total discharges.

• AgricultForestry
• Industry
• Urban