Wetlands

An overview

[The first post since returning from my holiday in Sicily. I’m not going to bore you with ALL my holiday snaps, but I had to go somewhere geographically significant, and stunning, didn’t I?

Taormina, with Mount Etna puffing smoke in the background.

Photo: David Redfern

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Introduction

Coastal wetlands are extremely important for society and the natural world. They are also among the most threatened environments. Approximately 40% of the global population live within 100 km of the coast. As population has increased, so too have the economic incentives to convert coastal wetlands into different land uses, for example farming and aquaculture, industry, shipping, housing and tourism.

Furthermore, about 10% of the global population now lives less than 10m above sea level. Therefore, as climate change continues, large numbers of people, in both developed and developing countries, will be impacted to even greater degrees by sea level rise and its consequences.

The loss of coastal wetlands exacerbates these problems by removing a natural defence between coastal settlements and the sea. Although coastal wetlands will not prevent sea-level rise, they can reduce its local impacts.

What is a wetland?

The US Environmental Protection Agency defines wetland as ‘areas where water covers the soil or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season’. There are two main types of wetlands:

■ inland, including nontidal marshes, swamps, fens and bogs

■ coastal, including tidal marshes (saltmarsh), mangrove swamps and seagrass beds.

The formation of a coastal wetland ecosystem requires deposition of fine sediment (clay and silt-sized particles) to provide a substrate for plant growth, and therefore these environments are found along ‘low-energy coasts’ where erosion is more limited due to weaker currents and wave action.

The main type of coastal wetland found in the temperate to high latitudes is saltmarsh. This develops in the intertidal zone from mudflats colonised and stabilised by ‘halophytic’ (salt tolerant) plants such as cord grasses and glassworts. As mud and decomposing organic material build up, plants characteristic of higher elevations of saltmarsh (less frequently inundated by tides) follow, such as sea purslane, sea lavender and sea rush.

Closer to the equator, where the mean annual temperatures of the coldest months are above 20°C, mangrove swamps are more common.

Ramsar

The Ramsar Convention on Wetlands of International Importance (also called the ‘Convention on Wetlands’), formulated in 1971 in the Iranian city of Ramsar, is an international treaty promoting the ‘conservation and wise use’ of wetlands. It came into force in 1975, and it is the oldest intergovernmental environmental agreement.

To date, the convention includes 172 countries, and it has designated nearly 2,500 wetlands across the world as being of international importance, hence requiring protection. The convention uses a broad definition of what constitutes a wetland, with initial classification into marine/coastal, inland and human-made (for example, fishponds and rice paddies).

Details of each designated wetland can be searched by country on the Ramsar Sites Information Service website here. :

Ecosystem services of wetlands

Recognition of the importance of wetlands has grown internationally, especially since the United Nations Millennium Ecosystem Assessment in 2005 that focused on ecosystem services and their link to human wellbeing. We are currently in the UN Decade on Ecosystem Restoration, running alongside the UN’s Sustainable Development Goals (SDGs) to 2030. Conserving and restoring coastal wetlands plays a key part in achieving several SDGs.

Their ecosystem services include:

■ Coastal protection - absorbing wave energy, slowing tidal flows and storm surges, storing excess water from coastal and/or river flooding and protecting against coastal erosion.

■ Habitat for aquatic life - about 75% of commercially valuable fish and shellfish rely in some way on coastal wetlands, for example for food or as a nursery.

■ Biodiversity gain - coastal wetlands provide essential habitats for many species of birds, fish, amphibians, reptiles and a wide range of uniquely adapted plants.

■ Pollution control – acting as a buffer for agricultural, industrial or domestic pollution running off the land, for example absorbing heavy metals and preventing excess nutrients from entering coastal water bodies, causing algal blooms.

■ Carbon sequestration - saltmarshes, mangrove swamps and seagrass meadows are very productive ecosystems and have an average annual carbon sequestration rate of over 100 g per m², 50 times higher than forests. Preservation and enhancement of this ‘blue carbon sink’ is essential for achieving net-zero carbon emissions.

■ Recreation – an aesthetic value for human wellbeing and opportunities for outdoor tourist activities that can bring jobs and other benefits to local communities.

■ Cultural - coastal wetlands have supported human civilisations for millennia and are the founding locations of many of our great cities and cultures.

Despite their value, coastal wetlands continue to be lost or degraded. Reasons include land reclamation (draining and infilling) for agriculture and other uses, dredging for shipping, and hard engineering along the coast, which cuts off places further inland that could potentially become new wetland as the sea-level rises. Today, the area of saltmarsh globally is thought to be 25% smaller than the historic average in pre-industrial times.

Case studies.

Based on the urgent need to protect and restore coastal wetlands, several large-scale restoration projects have been initiated around the world.

Two case studies of wetlands can be better examined online – one in the EU, and the other in the USA.

(a) The WaterLANDS Project

The European Union (EU) WaterLANDS project is one of the largest and focuses not only on coastal wetlands but also on terrestrial wetlands including peatlands and marshes. Spanning 32 partner organisations across 14 countries, and with a budget of almost €24 million, the project’s goals are broad and ambitious, with an overall aim of upscaling the restoration of wetlands across Europe.

You can read more about this European project here.

(b) The Louisiana Wetlands

NASA have produced a fascinating outline of the changes affecting the wetlands in coastal Louisiana, including satellite images contrasting 40 years, and some time lapse imagery. You can find the piece here.

Coastal saltmarsh in the Norfolk Broads, UK

Photo: David Redfern