Common Indicator 14: Chlorophyll-a concentration in water column

Reporter:: 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:: EO5CI13

GES Definition: Natural levels of algal biomass in line with prevailing physiographic, geographic and weather conditions

GES Targets:

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

Background

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.

Assessment methods

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.

Conclusions

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).

References

Colella, S., Falcini, F., Rinaldi, E., Sammartino, M., Santoleri, R. (2016). Mediterranean Ocean Colour Chlorophyll Trends. PLoS ONE 11(6): e0155756. doi:10.1371/journal.pone.0155756

Coste, B., Le Corre, P., Minas, H. J. (1988). Re-evaluation of nutrient exchanges in the Strait of Gibraltar. Deep-Sea Resarch, 35, 767–775.

EEA (1999). Nutrients in European ecosystems. Environmental assessment report No 4.

Ignatiades, L., Gotsis-Skretas, O., Pagou, K., & Krasakopoulou, E. (2009). Diversification of phytoplankton community struc- ture and related parameters along a large scale longitudinal east–west transect of the Mediterranean Sea. Journal of Plankton Research, 31(4), 411–428.

IMAP (2017). Integrated Monitoring and Assessment Programme of the Mediterranean Sea and Coast and Related Assessment Criteria UNEP, Athens, 52 pp.

Karydis, M., Kitsiou, D. (2016). Eutrophication and environmental policy in the Mediterranean Sea: a review. Environ Monit Assess, 184, 4931–4984.

Krom, M. D., Emeis, K. C., and Van Cappellen, P. (2010). Why is the Mediterranean phosphorus limited? Progress in Oceanography. doi:10.1016/j.pocean.2010.03.003.

Ludwig, W., Dumont, E., Meybeck, M., and Heusser, S. (2009). River discharges of water and nutrients to the Mediterranean and Black Sea: major drivers for ecosystem changes during past and future decades? Progress in Oceanography, 80, 199–217.

Pugnetti, A., Bastianini, M., Acri, F., Bernardi Aubry, F., Bianchi, F., Boldrin, A. and Socal, G. (2007). Comunità fitoplanctonica e climatologia nell'Adriatico Settentrionale. In: Carli B., Gavaretta G., Colacino N., Fuzzi S. (eds), Clima e cambiamenti climatici: le attività di ricerca del CNR. CNR-Roma: pp. 551-556 (in Italian).

Turley, C. M. (1999). The changing Mediterranean Sea: a sensitive ecosystem? Progress in Oceanography, 44, 387–400.

UNEP (1989). State of the Mediterranean Marine Environment. MAP Technical Series No. 28, UNEP, Athens.

UNEP/FAO/WHO (1996). Assessment of the state of eutrophication in the Mediterranean Sea. MAP Technical Report Series No. 106, UNEP, Athens, 455 pp.

UNEP/MAP, 2003. Eutrophication monitoring strategy of MED POL, UNEP(DEC)/MED WG 231/14, 30 April 2003, Athens 24 pp.

UNEP/MAP (2007). Eutrophication Monitoring Strategy for the MED POL (REVISION), UNEP(DEPI)/MED WG.321/Inf. 5, 9 November 2007, Athens.

UNEP/MAP (2012): State of the Mediterranean Marine and Coastal Environment, UNEP/MAP – Barcelona Convention, Athens, 2012.

UNEP/MAP (2016). Decision IG.22/7 - Integrated Monitoring and Assessment Programme (IMAP) of the Mediterranean Sea and Coast and Related Assessment Criteria. COP19, Athens, Greece. United Nations Environment Programme, Mediterranean Action Plan, Athens.

Vollenweider, R.A. (1992). Coastal Marine Eutrophication. In: Vollenweider, R.A., Marchetti, R., Viviani, R. (ed.). Marine Coastal Eutrophication. London: Elsevier, pp. 1-20.

Figure 1. The Mediterranean basin and its chlorophyll a concentration pattern. (A) Geographic regions (B) chlorophyll a concentration (μg L-1) climatology over the Mediterranean Sea relative to 1998–2009 time period. From: Colella et al., 2016.

Figure 2. Stations in the Mediterranean region for which eutrophication parameter were sampled. Also are shown the water types (applicable for phytoplankton; IMAP. 2017) were minimal statistical requirements were satisfied (10 samples in the last 10 years and in the surface layer, <= 10 m)

Figure 3. Stations in the Western Mediterranean Sea sub-region for which eutrophication were assessed. Coastal Water types reference conditions and boundaries in the Mediterranean were applied (applicable for phytoplankton; IMAP. 2017) for were minimal statistical requirements were satisfied (10 samples in the last 10 years and in the surface layer, <= 10 m)

Figure 4. Stations in the Adriatic Sea sub-region for which eutrophication were assessed. Coastal Water types reference conditions and boundaries in the Mediterranean were applied (applicable for phytoplankton; IMAP. 2017) for were minimal statistical requirements were satisfied (10 samples in the last 10 years and in the surface layer, <= 10 m)

Figure 6. Stations in the Ionian Sea and the Central Mediterranean Sea subregion for which eutrophication were assessed. Coastal Water types reference conditions and boundaries in the Mediterranean were applied (applicable for phytoplankton; IMAP. 2017) for were minimal statistical requirements were satisfied (10 samples in the last 10 years and in the surface layer, <= 10 m)

Figure 7. Stations in the Aegean-Levantine Sea sub-region for which eutrophication were assessed. Coastal Water types reference conditions and boundaries in the Mediterranean were applied (applicable for phytoplankton; IMAP. 2017) for were minimal statistical requirements were satisfied (10 samples in the last 10 years and in the surface layer, <= 10 m)

Eutrophication (EO 5)