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Modelling nutrients in the Mediterranean Sea

Wastewater from urban coastal areas contributes to rising nutrient pollution of the Mediterranean Sea.
Apr 02 2019

A recently published JRC article describes a new modelling framework for quantifying and identifying the human causes of nutrient pollution in the Mediterranean Sea and provides possible solutions for its control.

Pollution from agriculture and wastewater treatment plants will have to be controlled in order to protect the water resources and coastal and marine ecosystems, and to ensure the long-term sustainability of the economic activities and ecosystem services in the region.

These controls are especially urgent in light of the major challenges that the Mediterranean region will face in future years as a result of intensification of economic activities, population rise, urban sprawl and climate change.

Eutrophication of the Mediterranean Sea

Human activities and consequent pollution have put the freshwater and marine ecosystems of the Mediterranean region under pressure over the past 50 years. Future expansion, population growth and the effects of climate change in the region are likely to exacerbate this pressure, unless counteracting measures are put in place.

In excess, nutrients (including nitrogen and phosphorus) degrade water quality. Too much nitrogen and phosphorus leads to eutrophication and causes algae to grow faster than ecosystems can handle. Algal blooms can severely reduce oxygen in the water, killing water-dwelling organisms such as fish, and can produce toxins and bacterial growth that are harmful to humans.

Eutrophication due to nutrient inputs from land-based pollution sources is a major environmental problem for the Mediterranean Sea, particularly in densely populated areas. To plan management strategies for the protection of coastal ecosystems and their services, we need to understand how much nitrogen and phosphorus is discharged into the sea, and where they are coming from, and how much are lost or retained in the river basin.

A simple conceptual water quality model

This paper presents a robust modelling framework for assessing water nutrient pollution in the Mediterranean and evaluating the impact of management strategies on water quality.

Using readily available data and the linkages between crop, water, and nutrient management impacts on water quality, it quantifies recent nitrogen and phosphorus fluxes to determine the relative importance of different nitrogen and phosphorus sources and to identify hotspot areas of higher pollution where priority actions should focus.

The study shows that, during the period 2003 to 2007, 1.87 Tg of nitrogen, 1.22 Tg of nitrates, 0.11 Tg of phosphorus and 0.03 Tg of orthophosphate were discharged into the Mediterranean Sea every year, mainly through the Nile, Po, Rhone and Ebro Rivers.

Agriculture is identified as the main source of nitrogen and nitrate inputs, while the main sources of phosphorus include wastewater and scattered dwellings.

Two management scenarios are presented in the study, showing the potential effectiveness and trade-offs of mitigation measures on the various forms of nitrogen and phosphorus.

The scenarios show that a 50% reduction in nitrogen surplus leads to a significant reduction in nitrogen emissions in regions characterised by high intensity agriculture, while the upgrading of wastewater treatment plants to tertiary level could reduce phosphorus discharge by 10%, and by as much as 30% in northern African coastal cities.

Such measures are necessary to protect the water resources and coastal and marine ecosystems in the Mediterranean basin, and to ensure the long-term sustainability of the economic activities and ecosystem services in the region, particularly in view of the future climatic and demographic challenges the region will face regarding nutrients in the agriculture-water nexus.

The new assessment and modelling tool offers a robust framework for overcoming the limited availability of water-quality monitoring data in the southern part of the Mediterranean Sea, and for evaluating alternative scenarios of nutrient reduction.

It shows how the interlinkages between water and agriculture can be explored, integrating the basin-coastal relationship and nutrient sources and sinks from different sectors. This makes it a valuable tool not only for the Mediterranean area but also for other seas.

Further information