Guest Blog: Ocean Nutrients - Geoscientists Have The Right Balance

Rosalie Tostevin is a PhD student and GfGD Ambassador at University College London (UCL). Her research examines the link between ocean chemistry and the emergence of the first animal life. Rosalie has written for the GfGD blog before, about the terrible situation in central Africa regarding conflict minerals and the negative impact on communities. Today she writes about the health of the oceans, the importance of nutrient balance, and why this is relevant for communities across the world:

The chemical elements carbon, nitrogen and phosphorous are all essential components of DNA, and their availability places major constraints on the oceans’ capacity to nurture life. Nutrient limitation and nutrient pollution are both caused by imbalances in local biogeochemical cycles (cycles in which chemical elements or molecules move through biotic, e.g. biosphere, and abiotic, e.g. atmosphere or lithosphere, parts of the earth). Management of both these very modern problems will require the expertise of the geoscience community.

Nutrient-rich deep water that upwells off the coast of Antarctica is not utilised efficiently by phytoplankton, because their growth is limited by the slow supply of an essential trace element, Iron. Not all of the upwelled carbon is converted to organic matter, as it is in the rest of the ocean, and so the carbon leaks out into the atmosphere. Supplementing the diet of the Southern Ocean with iron could block this leak and help us to offset anthropogenic CO₂ emissions. But before we embark on any geo-engineering missions, we need to appreciate the complex nature of nutrient availability.

Algal Bloom of the coast of Cornwall
(Source: NASA)

In coastal regions we often have the opposite problem: nutrient pollution. Anthropogenic activity elevates nutrient levels in coastal zones, with fertiliser and animal waste being the biggest contributors. High levels of nitrogen and phosphorous can induce algal blooms, leading to oxygen-deprivation (hypoxia) and the collapse of the local ecosystem. Once damage occurs, the system may never fully recover.

Coastal zones are important because they host 25% of global biological productivity, and border more than 70% of the world’s mega-cities. Unlike global warming, this issue affects Europe equally, if not more severely, than developing nations. However, this problem is particularly difficult to manage in developing countries, where legislating against the growing use of fertiliser would stifle development, analogous to attempts to reduce carbon emissions at the expense of industrial growth. The Rio+20 conference identified nutrient pollution and hypoxia as one of the emergent problems of the 21^st century. The UNEP Manila programme recognises that many people depend on the Oceans for their health, food security and economic livelihood. They pledge to:

‘Acknowledge the large increases in the levels of nutrients such as nitrogen and phosphorus entering the world’s environment as a result of human activity, and note the severity of the environmental problems caused by nutrient excess, including eutrophication of coastal waters and oxygen depletion, and the associated damage to ecosystems, biodiversity and coastal water quality’.

Managing nutrient pollution is difficult, because often the source of the nutrients cannot be pinned down to an individual factory or farm. The nutrients enter the atmosphere, plants, groundwater and rivers, where they are cycled many times before they reach the estuary. Input to the ocean is associated with storm activity, and so is sporadic and unpredictable.

Oil Seed Rape
(Source: Petr Kratochvil)

Fertiliser controls brought in in the 1980’s led to a slight decline in nitrogen flux, but the problem has intensified again in recent years. The UK has switched to growing spring wheat, as it is more profitable, but this leaves bare soil in winter, which promotes faster nutrient flow. A surge in the farming of oil seed rape, which needs 3 times more fertiliser than conventional crops, has been driven by a demand for biofuels.

The solutions fall into two categories: damage prevention and damage management. The biggest single change we can make to prevent nutrient pollution is to reduce our meat consumption. Recent research has highlighted the additional benefits of reduced meat consumption; improved health, lower greenhouse emissions and the ability to feed an expanding population, making this a particularly relevant policy focus. In addition, we need to manage coastal systems that have already been damaged. The first step is to understand the complexity of, and coupling between, biogeochemical cycles, something geologists are routinely trained to do. We can also learn from the response of nutrient cycles to past tectonic and climatic events. For example, the effect of increasing bioturbation on nutrient feedbacks during the Cambrian Period (approx. 542-488.3 million years ago) can be assessed using nitrogen and carbon isotopes. The approach must be holistic; geoscientists are particularly adept at working with multiple component systems. This is a problem that calls upon 21^st century geologists to put their knowledge and skills to use for the benefit of coastal communities and shallow marine wildlife.