Ocean pollution: Addressing root causes of nutrient over-enrichment

Human activities, notably food production, fossil fuel burning and wastewater from people and industry, have led in recent decades to very large increases in the amount of nutrients such as nitrogen and phosphorous in our environment, notably in the marine environment. In the case of coastal waters this excess is leading to nutrient over-enrichment, which in turn produces eutrophication and hypoxia leading to declining coastal water quality and associated human health impacts, damage to biodiversity such as sea-grasses and coral reefs, and fish kills.

Low oxygen (hypoxic) areas known as dead zones, where most marine life cannot survive, can result in the collapse of some ecosystems. There are now close to 500 dead zones with a total global surface area of over 245,000 km², roughly equivalent to that of the United Kingdom. The overall effect is to undermine the resilience of marine and coastal ecosystems, affecting in turn their ability to support coastal livelihoods such as fishing and tourism and their potential role in climate change adaptation and mitigation.

The cost to countries of nutrient over-enrichment from the degradation of their marine and coastal natural resource base, and the services and livelihoods it provides, will increase without improved policy responses. A Global Environment Facility (GEF) project entitled “Global Foundations for reducing nutrient enrichment and oxygen depletion from land based pollution in support of global nutrient cycle” aims to provide the foundations for governments and other stakeholders to initiate comprehensive, effective and sustained programmes addressing nutrient over-enrichment and oxygen depletion from land based pollution of coastal waters in Large Marine Ecosystems. A paper recently published within the framework of the project proposes a new integrated model approach.

In river basins, soils, groundwater, riparian zones, streams, rivers, lakes and reservoirs act as successive filters in which the hydrology, ecology and biogeochemical processing are strongly coupled and together act to retain a significant fraction of the nutrients transported. The paper compares existing river ecology concepts with current approaches to describe river biogeochemistry, and assesses the value of these concepts and approaches for understanding the impacts of interacting global change disturbances on river biogeochemistry. Through merging perspectives, concepts, modelling techniques, it proposes integrated model approaches that encompass both aquatic and terrestrial components in heterogeneous landscapes. In this model framework, existing ecological and biogeochemistry concepts are extended with a balanced approach for assessing nutrient and sediment delivery on the one hand, and nutrient in-stream retention on the other hand.

The paper “Nutrient dynamics, transfer and retention along the aquatic continuum from land to ocean: towards integration of ecological and biogeochemical models” was published in Biogeosciences, an interactive open access journal of the European Geosciences Union, on 2 January 2013. The Intergovernmental Oceanographic Commission of UNESCO (IOC/UNESCO) is an executing partner of this GEF project, coordinated by the United Nations Environment Programme (UNEP).

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