Nutrient budgets for European seas: A measure of the effectiveness of nutrient reduction policies
Introduction
European marine ecosystems are being degraded as a consequence of continuously increasing pressure from anthropogenic activities. Several EU reports (EEA, 2001b, EEA, 2003a, EEA, 2003b, EEA, 2006) have highlighted the state of the marine environment, its increasing vulnerability and the need for further and stricter regulation of nutrient release. Eutrophication, a product of anthropogenic nutrient enrichment of water bodies, is an important current state change affecting the integrity of European seas (EEA, 2001a, EEA, 2003a). The EU has already adopted several directives and policies intended, directly or indirectly, to combat eutrophication (e.g. Nitrates Directive, Urban Waste Water Treatment Directive, Water Framework Directive, Common Agricultural Policy). The EU’s Water Framework Directive will coordinate much of this action within national and international catchment-scale (“River Basin District”) boundaries. Special measures and interventions (policy and legal reforms, investments in nutrient reduction technology at source) have been planned and partially implemented through coordinated international and national actions by the regional seas conventions and their secretariats (HELCOM in the Baltic, OSPAR in the North Sea, the Barcelona Convention in the Mediterranean and the Bucharest Convention in the Black Sea), together with associated projects and programmes. A new European Marine Strategy Directive is under review and will provide environmental quality targets (Good Environmental Status) that cannot be achieved without tackling eutrophication.
The intensity and spatial extent of eutrophication in European seas varies widely (Fig. 1), from small hot spots in enclosed bays (e.g. Kastela Bay in the Adriatic Sea, or Izmir Bay in the Aegean Sea), to sub-regional areas (e.g. the Wadden and Adriatic Seas) to almost entire seas (e.g. the Baltic Sea). To compare the effectiveness of nutrient regulation in four European regional seas, one case study of an area affected by eutrophication was selected for each sea, viz.: the Northern Adriatic for the Mediterranean Sea (Justic et al., 1987, Vollenweider et al., 1992), the coastal North Sea for the North-East Atlantic (Brockmann et al., 1988, Pätsch and Radach, 1997), the Baltic Proper (Wulff and Stigebrandt, 1989, Wulff and Stigebrandt, 1990) and the North-Western (NW) Black Sea shelf (Lancelot et al., 2002). The large spatial scale addressed in this study responds directly to the needs of policy-makers to guide the integrated management of Europe’s regional seas.
We applied a comparative aggregated mass balance approach on each sub-regional basin for three time periods. Our aim is to assess and to compare changes over past decades in the nutrient budgets (for nitrogen – N and phosphorus – P) of four sub-regional basins of four European seas. These changes reflect the nutrient loading of coastal waters, and changes in loading due to policy that is largely coordinated at the European scale. Finally we draw implications for the further development of nutrient reduction policy.
Section snippets
Case study areas
The main hydromorphologic characteristics of the four selected areas are summarized in Table 1.
The Northern Adriatic is a shallow enclosed basin (average depth 35 m) located between Italy and the Balkans and delimited by the 100 m isobath. The seabed is gently sloping and mostly sandy or muddy. It receives large fresh water discharges (about 80 km3/yr), particularly from Italian rivers (e.g. Po, Adige, Isonzo, Tagliamento) that drain intensely developed catchments where about 50% of Italy’s
Results
Fig. 2, Fig. 3 present the budgets. The Northern Adriatic appears to have the lowest nutrient fluxes (Fig. 2, Fig. 3a). Anthropogenic input of nitrogen from land-based sources is the major N-source and has been increasing steadily since the 1950s. Despite halving TP loads between the eutrophication and contemporary periods, P fluxes from sediments did not significantly change. This is probably indicative of a legacy of past nutrient enrichment or “memory effect”: historic P inputs accumulate in
Comparison of contemporary regional sea budgets
Comparison of contemporary total fluxes normalized to unit basin volume (Table 3) highlights both the physical characteristics of Europe’s regional seas and the socio-economic characteristics of their catchments.
The Northern Adriatic receives the bulk of its nutrients from rivers, although some N derives from atmospheric deposition. This suggests a strong anthropogenic influence on eutrophication. There is net export of nutrients to the Southern Adriatic, but of the four seas, it has the lowest
Final remarks
This study brings together available evidence to compare changes in nutrient budgets in Europe’s regional seas. It highlights the intrinsic differences among the seas in sensitivity to nutrient loading. At one end of the spectrum is the Baltic Proper. With hypoxia and cyanobacteria blooms, it is suffering severely from eutrophication despite receiving the smallest anthropogenic loads. Its sensitivity appears to be caused by limited flushing and climatic events that influence vertical mixing. At
Acknowledgments
The authors want to thank all scientists and institutions that provided data and advice for the implementation of all the budget models. This work has been carried out in the context of the EC-funded FP6 project European Lifestyle and Marine Ecosystems (ELME), contract no. GOCE – CT – 2003 – 505576. A special acknowledgment goes to all colleagues of the ELME project, and in particular to Darius Daunys, Jocelyn de la Cruz, Sven Hille, Olivia Langmead, Christopher Lowe, Sergej Olenin and Rolf
References (72)
- et al.
Point and diffuse load of nutrients to the Baltic Sea by river basins of North East Germany (Mecklenburg-Vorpommern)
Water Sci. Technol.
(1998) - et al.
Long-term ecological changes in Romanian coastal Waters of the Black Sea
Mar. Pollut. Bull.
(1996) - et al.
Benthic nutrient cycling and diagenetic pathways in the North-western Black Sea. Estuarine
Coast. Shelf Sci.
(2002) - et al.
Fine-sediment mass balance in the western Adriatic continental shelf over a century time scale
Mar. Geol.
(2005) - et al.
A box model approach for a long-term assessment of estuarine eutrophication, Szczecin Lagoon, southern Baltic
J. Mar. Syst.
(2000) - et al.
Trends in oxygen content 1911–1984 and occurrence of benthic mortality in the northern Adriatic Sea. Estuarine
Coast. Shelf Sci.
(1987) - et al.
The North-western Black Sea: a pilot site to understand the complex interaction between human activities and the coastal environment
Estuarine, Coast. Shelf Sci.
(2002) - et al.
Simulations of the north sea circulation, its variability, and its implementation as hydrodynamical forcing in ERSEM
Netherlands J. Sea Res.
(1995) - et al.
Abrupt transitions of the top-down controlled Black Sea pelagic ecosystem during 1960–2000: evidence for regime-shifts under strong fishery exploitation and nutrient enrichment modulated by climate-induced variations
Deep Sea Res. Part I: Oceanogr. Res. Pap.
(2007) - et al.
Modelling nutrient emissions from river systems and loads to the coastal zone: Po River case study, Italy
Ecol. Model.
(2005)