- UNEP/MAP/MED POL
- Geographical scale of the assessment:
- Regional, Mediterranean Sea
- Contributing countries:
- Albania, Bosnia and Herzegovina, Croatia, Cyprus, Egypt, France, Greece, Israel, Italy, Montenegro, Morocco, Slovenia, Spain, Tunisia, Turkey
- Mid-Term Strategy (MTS) Core Theme:
- 1-Land and Sea Based Pollution
- Ecological Objective:
- EO5. Human-induced eutrophication is prevented, especially adverse effects thereof, such as losses in biodiversity, ecosystem degradation, harmful algal blooms and oxygen deficiency in bottom waters
- IMAP Common Indicator:
- CI14. Chlorophyll-a concentration in water column (EO5)
- Indicator Assessment Factsheet Code:
GES Definition: Natural levels of algal biomass in line with prevailing physiographic, geographic and weather conditions
- State: Chl-a concentrations in high-risk areas below thresholds
- State: Decreasing trend in chl-a concentrations in high risk areas affected by human activities
Eutrophication is a process driven by enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, leading to: increased growth, primary production and biomass of algae; changes in the balance of nutrients causing changes to the balance of organisms; and water quality degradation (IMAP, 2017). Seawaters depending on nutrient loading and phytoplankton growth are classified according to their level of eutrophication. Low nutrient/ phytoplankton levels characterize oligotrophic areas, water enriched in nutrients is characterized as mesotrophic, whereas water rich in nutrients and algal biomass is characterized as eutrophic. The Mediterranean is one of the most oligotrophic seas in the world and most of its biological productivity takes place in the euphotic zone (UNEP, 1989, UNEP/MAP, 2012). The development of nutrient/phytoplankton concentration scales has been a difficult task for marine scientists because of the seasonal fluctuations of nutrient and phytoplankton concentrations, phytoplankton patchiness and small-scale eutrophication phenomena. Although long-term scientific research (UNEP/FAO/WHO1996; Krom et al., 2010) has shown that the main body of the Mediterranean Sea is in good condition, there are coastal areas, especially in enclosed gulfs near big cities in estuarine areas and near ports, where marine eutrophication is a serious threat.
UNEP/MAP’s Pollution Programme (MEDPOL) has a monitoring programme since 1999, based on the contribution of data from Mediterranean countries, including chlorophyll-a. MEDPOL monitoring data was used for this assessment, noting that there are several gaps in the database where there has been inconsistent data reporting from each country over the years.
Coastal Water types reference conditions and boundaries for chlorophyll-a in the Mediterranean were agreed and adopted in the IMAP decision of 2016. (UNEP/MAP, 2016). These criteria were applied for the first time applied on the data available for the Mediterranean through the MED POL Database.
Results and Status, including trends
The trophic status of the Mediterranean Sea is controlled by the highly populated coastal zone and the riverine input from a draining area of 1.5 million km2 (Ludwig et al. 2009) that induce eutrophic trends in coastal areas. The blue offshore waters of the Mediterranean have been characterized as extremely oligotrophic with an increasing tendency for oligotrophy eastwards (Turley 1999). Eutrophication and oligotrophy in the Mediterranean is illustrated as chlorophyll a distribution in remote sensing imagery (Figure 1). This is due to the low nutrient content of EMS; the maximum concentrations recorded for nitrate were about 6 μmol L-1, for phosphate 0.25 μmol L-1, and for silicate 10–12 μmol L-1, with the nitrate to phosphate ratio (N/P) >20 and in deep waters about 28:1, the EMS has been characterized as the largest phosphorus-limited body of water in the global ocean.
The trophic status of the Mediterranean Sea is controlled by the highly populated coastal zone and the riverine input from a draining area. Offshore waters of the Mediterranean have been characterized as extremely oligotrophic with an increasing tendency for oligotrophy eastwards. The Eastern Mediterranean Sea (EMS) is still the most oligotrophic area of the whole Mediterranean basin, and the largest phosphorus-limited body of water in the global ocean.
- Offshore waters of the Mediterranean have been characterized as extremely oligotrophic with an increasing tendency for oligotrophy eastwards.
- The main coastal areas in the Mediterranean which are historically known to be influenced by natural and/or anthropogenic inputs of nutrients are the Alboran Sea, the Gulf of Lions, the Gulf of Gabès, the Adriatic, Northern Aegean and the SE Mediterranean (Nile–Levantine).
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