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Mangrove coasts: a muddy story (Part 3)

15-May-2013

By Han Winterwerp and Bregje van Wesenbeeck

 

In my first blog, I introduced the term “ecosystem services”, which has become a popular way to refer to the value of ecosystems. This is an important concept as it provides a counter-argument to the often narrow-minded and short-eyed approach of economics.

 

 

The traditional economic focus on “How much can I earn today?” neglects the long-term consequences of short-term profits. For example, the initial earnings from fish ponds erected in pristine mangrove forests are enormous, and apparently much larger than income from, for instance, the production of wood. However, many fish ponds collapse after some time, as they become poisoned by the large quantities of pesticides and antibiotics used in fish farming. Fish ponds also often or breach due to coastal erosion, as frequently happens in Indonesia.

 

Ecosystem services quantify other values besides economic gains, such as coastal protection or carbon sequestration. The term became very popular after the 2005 Millennium Ecosystem Assessment, in which over 3000 ecologists worldwide were asked to identify the status of the world’s ecosystems. These ecologists highlighted the dangers associated with losing the services that we humans gain from the healthy functioning of ecosystems. These services are numerous and vary from food provisioning to recreation and tourism.

 

The ecosystem services concept is helpful to illustrate the costs and benefits of different approaches to natural resource management. Human designs, on the one hand, are often optimized for single functions: for example, a levee is mainly designed to provide flood protection. Ecosystems, on the other hand, naturally provide a whole range of services or functions. For instance, if we decide to conserve ecosystems for coastal protection we get a whole suit of other services for free, such as an attractive area for tourists, increasing fishery yields and possibilities for fire-wood harvesting.

 

A practical example of the diversity of services derived from natural flood defense solutions is constituted by the beach and dune system on the Dutch west coast. Beaches and dunes along this coastline are adaptively managed through artificial sediment nourishment for coastal protection. Additionally, the beach and dune area form the largest natural recreation area for around 10 million people living in the west of the Netherlands. Furthermore, the dunes are used for filtration of drinking water. After purification this water is sold to millions of households. Finally, the beach and dunes directly create jobs and revenue, as yearly around 15 million tourists stay overnight in the Dutch coastal area.

 

Similarly, mangrove-mud coasts also provide a wide range of ecosystem services. Mangrove forests serve as the natural bank accounts and insurance policies of tens of millions of people throughout the tropics. For many centuries they have provided coastal communities with rich fisheries resources: many species, including shellfish, crustaceans and fish, spend critical phases of their life cycle inside the mangrove forest and associated river systems, sea grass beds and coral reefs. Mangroves in South-East Asian countries have been found to support 30 percent of fish catch and almost 100 percent of shrimp catch, while mangroves and associated habitats in QueenslandAustralia, support 75 percent of commercial fisheries species.

 

Mangrove trees are renowned for the high quality fuel wood and timber resources they provide. They have a key role to play in the regulation of atmospheric carbon levels. With living biomass typically ranging between 100-400 tonnes/ha, and significant quantities of organic matter being stored in sediments, mangroves rival the sequestration potential of rainforests. Mangroves offer protection to extreme events, such as storms and more gradual processes such as salt water intrusion and erosion. These regulating services become increasingly important in the face of climate change, specifically increases in sea level.

 

By taking all these factors into account, the ecosystem services approach demonstrated that the annual total economic value of mangroves is substantial. Estimates range between 100 and 22.500 USD per hectare per year. This entails direct values in the form of harvestable products that have a market value, as well as more indirect values such as erosion reduction and storm protection.

 

This is why Deltares and Wetlands International are working together to apply engineering solutions to eroding mangrove mud coasts that simultaneously deliver coastal protection as well as a variety of other ecosystem services. We call this “hybrid engineering” – but we’ll explain more about this approach in a future blog, so watch this space!

Read Blog 2 

Han Winterwerp and Bregje van Wesenbeeck work for the Dutch research institute Deltares. Han is also a professor at the Delft University of Technology, where he teaches and develops instruments to measure and predict the behaviour and properties of mud. He specialises in the behaviour of mud in open waters.  Bregje is a coastal ecologist who has been working on nature-based strategies for flood risk mitigation for several years in several parts of the world. She has experience in ecology and restoration of marshes, mangroves, fresh water wetlands and oyster reefs for flood defense purposes. 

 

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