Tackling the Challenge of Nitrogen Pollution in Estuarine and Coastal Waters

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Steve Mustow Member Name

Senior ESIA Practitioner

Nitrogen is a foundational element of life. However, over the last century, we humans have radically shifted the nitrogen balance, creating a nitrogen pollution problem that is now a serious environmental challenge across the world. Estuarine and coastal waters are particularly vulnerable to excess nitrogen, and the ecological impacts can take decades to reverse. It’s a disturbing picture – of fertilisers, manure and sewage creating nutrient overloads, resulting in algal blooms, oxygen depletion, dead zones, fish kills and loss of habitat for migratory waterbirds.

Restoring balance and health to our aquatic environments will require us all – from farmers and developers to regulators, water companies and environmental consultants – to think differently about nitrogen. Many efforts are underway to better understand, manage and reduce the nitrogen pollution problem. By identifying the sources and pathways of the nitrogen and adopting multi-faceted, integrated, and sustainable management approaches, we may begin to reverse the adverse impacts.

Locate the source and trace the path

To tackle the challenge of nitrogen pollution in estuaries and coastal waters, the first step is to determine the sources of nitrogen entering each system and understand the pollutant’s pathways and processes. Some will be point sources, such as discharges from sewage works and storm drains, and others will be diffuse sources, such as run-off from agricultural or urban land. These may enter waters directly or via rivers and groundwater.

In the rush to feed the world we’ve created new problems. The significant increase over the past century in the agricultural use of nitrogen-based fertilisers is the greatest contributor to the total amount of biologically available nitrogen arising from human activities. When fertiliser is used in excessive amounts, nitrogen can migrate to surface waters and groundwater in forms such as nitrate and ammonium, causing ecological problems and reducing water quality. Other common anthropogenic sources of nitrogen pollution include manure from stock farming, fish farm feed and waste, and poorly managed sewage.

Given that a significant proportion of nitrogen pollution in estuarine and coastal waters stems from agriculture, improving farming practices should be a priority. Some of the most effective measures that farmers can adopt to reduce river pollution include knowing the nitrogen content of fertilisers, growing cover crops to reduce nitrogen leaching, calibrating fertiliser spreaders to use only what is necessary, reducing stocking density, or changing from intensively farming the land to less intensive practices such as conversion to managed grassland or woodland. As rivers are a major route for nitrogen to reach the marine environment, any action to improve the quality of rivers is also likely to benefit estuarine and coastal habitats.

Other direct measures that can be taken to reduce nitrogen levels in estuarine and coastal waters include retaining riparian vegetation or creating wetlands and reedbeds, increasing nitrogen removal at sewage treatment works that discharge directly into waters, and imposing greater controls on fish farms. Aquaculture of bivalve molluscs can also remove excess nitrogen and make water clearer.

When a site is threatened by nutrient pollution — including nitrogen — a nutrient management plan can be used to identify sources of nutrients that are entering rivers and the steps that can be taken to manage them. Nutrient management plans provide a mechanism for tackling water pollution where excessive nutrient loading requires a combined approach to address point and diffuse sources. Nutrient management plans have been produced to protect designated ‘special’ areas of conservation in the UK associated with the rivers Avon, Wye, and Clun. In some cases, nutrient management plans have also led to restrictions on development, including house building, where increased development has been expected to lead to more nutrient accumulation and transport.

Apply sustainable, integrated catchment management approaches

Given the diversity of nitrogen pollution sources and processes, it is often necessary to take an ‘integrated catchment management’ approach, which aims to achieve fully integrated management of the land, water, and human activities in a catchment. Integrated management approaches cover the state of the water environment, pressures affecting the quality of the water environment, and actions to protect and improve the water environment. In the UK and Ireland, ‘river basin management plans’ are drawn up by the environmental agencies to identify measures that can bring all water bodies up to a good standard.

‘Catchment partnerships’ can also be effective by coordinating the activities of various stakeholders, such as farmers, water and sewerage companies, and land-owners. For example, in 2018, Thames Water, Yorkshire Water and Anglian Water signed a water catchment declaration aiming to reach and exceed water quality objectives by working with farmers to use fertiliser more efficiently and improve soil quality.

While these are viable approaches it is important to note that in catchments where the groundwater has been polluted by nitrogen from historical farming activities, and feeds into rivers, there is likely to be a significant lag before changes to farming practices reduce nitrogen levels in the rivers. Also, reducing the load source isn’t always enough to solve the problem in the short term, because of complex nitrogen cycling processes between sediments and the water column, and modulating factors such as light and season.

Foster innovation and incentives

To reduce nitrogen pollution nutrient reduction is needed. Because these actions have implications for society and the economy, the long-term environmental and sustainability benefits may not be enough to radically change behaviour in the absence of incentives (“carrots”) or strong regulation (“sticks”). Constraints on development, upgrades to sewage treatment facilities, and altered farming and land-use practices will require cooperation, goodwill, and compromise among the many affected stakeholders.

An example of the “stick” approach can be found when local authorities were considering planning applications in the Solent region. The Solent is a body of water separating the Isle of Wight from the mainland of England, and much of its coastline is designated as conservation areas because of the important coastal and estuarine habitats. Natural England issued an advice note in March 2020[1] to the Solent planning authorities advising that planning permission should not be granted for new development unless nitrogen neutrality could be demonstrated. This was due to increased nutrient levels in the Solent estuary resulting in dense mats of green algae impacting on protected habitats and on birds. Although there was clearly an important environmental problem to be addressed, concern was raised about the impact on housing delivery due to this significant new restriction.

An example of an effective “carrot” is a nitrogen offsetting scheme developed by Wessex Water that uses an online platform called EnTrade. EnTrade allows farmers to sell environmental services to developers, water companies, government agencies and businesses. The services include land use changes like sowing winter cover crops or longer-term changes like woodland creation. This online market for nature-based solutions is reported to have reduced the amount of nitrogen entering Poole Harbour, an ecologically sensitive area threatened by nitrogen pollution. Offsetting systems like EnTrade are likely to gain further impetus in England and Wales with the proposed introduction in 2024 of an environmental land management scheme[2].

Despite the mitigation work undertaken to date, many estuarine and coastal waters continue to exceed nitrogen standards, so there is still a long way to go to address this urgent environmental challenge. Greater recognition of the sources and pathways of nitrogen pollution, increased cooperation in integrated catchment management, and innovation and incentives can work together to create meaningful change. It is time to restore balance, so that future generations can enjoy healthy rivers, estuaries, and oceans, with all the rich biodiversity they support.

[1] https://www.push.gov.uk/wp-content/uploads/2020/03/Advice-on-Achieving-Nutrient-Neutrality-for-New-Deveopment-in-the-Solent-Region-March-2020.pdf
[2] https://www.gov.uk/government/publications/the-environmental-land-management-scheme-an-overview/the-environmental-land-management-scheme-public-money-for-public-goods

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Steve Mustow Member Name

Senior ESIA Practitioner

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