Policy and integrated management Environment

Posted October 1999

Understanding the ecological impact of tideland reclamation
Part 1: The ecological dimension of wetlands

by Nadia Scialabba
Environment Officer
Environment and Natural Resource Service
Research, Extension and Training Division
From "Understanding the ecological impact of tideland reclamation: a step towards Integrated Coastal Resources Management", a paper prepared for the International Symposium on Environment-Friendly Restoration of Coastal Reclaimed Tidelands (Seoul, Republic of Korea, 13-14 September 1999). See also Special: Integrated coastal area management and agriculture, forestry & fisheries


Part I reviews the ecological dimension of wetlands, focusing on energy and nutrient flows that characterize the productivity of tidal flats. Environmental services provided by wetlands such as groundwater recharge and discharge, flood control, retention of nutrients and sediments, shoreline stabilization and erosion control, waste disposal, habitat and aesthetic values, are described. Attention is drawn on the magnitude of environmental, economic and social loss inflicted should wetland's free and public goods be surrended.

Part II introduces the policy and planning dimensions of wetland management in the Republic of Korea. After a brief overview of Korea's wetlands, information and research requirements for tideland reclamation are specifically addressed. Integrated coastal area management is proposed as a framework for informed and coordinated decision-making. The process includes the following steps: inception (to define objectives), performance review (to organize the process), data collection and research (encompassing biophysical, socio-economic and institutional information), analysis (to evaluate problems and causes of concern), strategy formulation (based on negotiated options), plan formulation and plan implementation.

In conclusion, impacts of both reclaimed wetlands and of a restored reclaimed tideland are anticipated along with suggestions to adopt a pro-active and precautionary approach to tideland development at the national level.

1. Ecological systems

The conservation and use of wetlands can only be successful if wetland ecology is understood. Ecology is the study of relationships between individual organisms and the physical and chemical features of their environment. The understanding of ecosystem interactions requires the understanding of energy and nutrient flows.

A very essential aim of ecosystem research is the understanding of the relevant energy flow because nearly all the components of the system are linked together through the transfer of energy. This begins as radiation energy supplied by the sun and is next bound as chemical energy by the primary producers in the form of cell substance and then part of it is passed on via the food chain. A model of a complete ecosystem with energy and nutrient flows is shown in Annex 1.

The energy flow involves the quantity of food energy entering the community through the various trophic levels and the amount leaving it. It involves both the grazing food chain and the detritus food chain. The introduction into the ecosystem of energy above the level that has evolved in nature results in pollution and disruption of nutrient cycles.

The flow of energy drives the carbon, oxygen, nitrogen and phosphorus cycles. Nutrients are pumped through the system by the action of photosynthesis and are again made available for recycling by the action of decomposers (See example of the nitrogen cycle in Annex 2). Nutrients are constantly being removed or added; adding more natural substances or synthetic materials than the ecosystem is able to handle upsets biogeochemical cycles [1].

Information on energy flow guides understanding of ecosystem functioning in terms of net production and efficiencies (of assimilation, growth, and utilization). Understanding the kind and quantity of nutrients available for circulation in the biogeochemical cycle optimizes growth and reproduction of plants and animals, in relation to their various requirements and tolerances for different elements.

2. Ecological services of wetlands

The 1971 Ramsar Convention on Wetlands defines wetlands as "areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres." A classification of wetlands can be found in Annex 3.

While wetland products or "goods" are recognized, the vital environmental functions or "services" they perform are less known. What follows is a brief description of coastal wetland productivity as well as of their main functions.

2.2. Productivity

What characterizes coastal wetlands is the daily tidal cycle and intermediate salinity between salt and fresh water; these characteristics are determining factors that place wetlands among the most naturally fertile habitats in the world. Wetlands are rich in fish, timber, birds, medicinal herbs, etc. and are the natural habitat of one of the world's principal food grains - rice - most strains of which are cultivated in modified wetland habitats.

A coastal salt marsh floods typically twice a day, while also revolving around a monthly pattern of spring and neap tides. As rivers swell with seasonal rainfall, they flow out over neighbouring plains. The annual cycle of inundation and desiccation of floodplains is one of the most important forces governing wetland productivity. The regularity of the flood pattern is important in maintaining the structure and function of wetlands.

Without a regular cycle, the productivity of fisheries, vegetation growth cycles and success of wildlife migrations are seriously affected. In turn, the well-being of human communities is dependent on the flood pattern for the essential goods and services which the wetlands provide.

2.3. Groundwater recharge/discharge and flood control

Wetlands are regulators of water flow and water quality. When water moves from the wetland into an underground aquifer, water is filtered and cleansed for human consumption. When the groundwater table raises to the surface, it discharges in another wetland water with more stable biological communities. By storing rain and releasing runoff evenly, wetlands can diminish the adverse impact of floods downstream.

Preserving natural storage can avoid the costly construction - and maintenance - of dams and reservoirs, save costs incurred by flood damage, and offer a reliable source of water supply for drinking and agricultural purposes [2].

2.4. Retention of nutrients

Wetlands retain nutrients, most importantly nitrogen and phosphorus, by accumulation in the sub-soil, or storage in the vegetation itself, thus improving water quality and preventing eutrophication. By removing nutrients, wetlands can dispense with the need to build water treatment facilities.

When water flows slowly, wetlands accumulate nutrients and when water flows fast, wetlands act as a nutrient "source". Nutrient levels are reduced at a season of the year when added nutrients are likely to cause eutrophic conditions downstream. Release of nutrients occurs when they are less likely to cause eutrophication. This cycle has important implications for algal growth, water quality, fish production and recreation downstream from the wetland area.

Coastal waters also benefit from nutrients that are carried away by surface flow, in streams, or by groundwater discharge. In temperate regions, nutrients stored in growing wetland plants are released when the water cools and the plants die in winter. The value of coastal fisheries is attributable to this vital support function provided by wetlands (i.e. supply of organic material), in addition to their role as breeding or nursery areas for fish [3].

2.5. Shoreline stabilization and erosion control

Wetland vegetation can stabilize shorelines by reducing the energy of waves, currents and other corrosive forces. At the same time, the roots of the plants hold the bottom sediment in place, preventing erosion of valuable land.

Wetlands serve as pools where sediments (and toxic substances that adhere to it, e.g. pesticides) can settle. Settling is further increased if reeds and grasses are present. Sediment retention in headlands can lengthen the lifespan of downstream reservoirs and reduce the need for costly removal of accumulated sediment from dams, power stations and other man-made structures.

2.6. Waste disposal

Wetlands host complete food chains with producers, consumers and decomposers that purify water as it flows to the sea. As in all ecosystems, the succession of micro-organisms that occurs in detritus (involving namely bacteria and fungi as well as detritus-feeding invertebrates) reduces organic material to elemental nutrients. Wetlands, however, are major "sinks" of nutrients and pollutants and are particularly important in the conversion of nitrates to harmless nitrogen gas. This is due to denitrifying bacteria that are especially active in waterlogged anaerobic soils.

Plants have developed a wide range of adaptations in order to survive and exploit their wetland environments. Biochemical adaptations to tolerate flood or waterlogged conditions allow, for some species, oxidization of toxic elements (such as ions of iron, Fe ++) which diffuses into the root from the soil or, for other species, excretes toxic products of anaerobic respiration.

The nutrient-filtering function of wetlands can be compared to that of oxidation ponds of conventional wastewater treatment plants [4]. Ecosystems recycle, detoxify and purify themselves, provided that their carrying capacity is not exceeded by excessive amounts of waste and by the introduction of persistent (synthetic) contaminants.

2.7. Biological diversity

Wetland organisms are uniquely adapted to live in habitats with varying degrees of salt and fresh water and a severe environment dominated by tides. Tides play a significant role in plant segregation. Salt-tolerant grasses and tides prevent harvesting of primary production of tidal marshes by herbivores. Organic matter is carried out to the estuary by tides where it is utilized by bacteria and detritus feeders, to be finally made available as a nutrient to estuaries that are important nursery for marine species.

Many wetlands support great concentrations of individual wildlife species (e.g. waterfowl) and a significant diversity of endemic vertebrates such as fish. Large number of birds and high energy-demanding migratory birds choose wetlands especially because they sustain a great availability of prey populations (e.g. crabs).

Wetlands are namely reservoirs of rice, a common wetland plant that is the staple diet of over half of the world's population. Wild rice in wetlands continues to be an important source of new genetic material used in developing disease-resistance and other desirable traits.

2.8. Habitat

Coastal habitats (mangroves, seagrass systems, coral reefs and lagoons, and estuaries) provide habitat for about 90 percent of the world's fish production, at all or some stages in the lives of the fish. In particular, salt marshes, seagrass beds, and mud flats have enormous biological productivity and are important as nursery grounds for coastal and oceanic marine fish as well as for endemic and migratory birds. Even species not confined to wetlands are dependent on the shelter offered by inaccessible wetlands.

In Korea the share of coastal and off-shore fisheries to total fishery production has fallen from 52% in 1984 to 29.8% in 1995. This decrease is attribuable to a combination of factors such as over-exploitation of fish stocks, decreasing fishing efforts, pollution of coastal waters and tideland reclamation. Although it is difficult to estimate the magnitude of fishery loss due coastal reclamation, the loss of wetland habitats plays a key role in the life cycle of certain economically important marine species: for example, sea eel is a main export product (US$ 110 million in 1995) but this species depends on coastal wetlands during its first stage of development. Reclamation and construction of industrial complexes add a pollution dimension to the conversion of marine habitats and thus threaten the viability of coastal aquaculture areas and future coastal and off-shore fisheries.

In reclaimed wetlands, keeping shrubs and hedgerows on agricultural field margins is important for over-wintering of beneficial arthropods and other organisms useful both as pest enemies and for bird feeding. The latter is particularly important in Korea's coastal wetlands which are visited by migrating birds during the winter, after rice harvest.

2.9. Tourism and recreation

Environmental services such as healthy landscape provides opportunities for eco- or agri-tourism and recreation. The aesthetic value of wetlands is gaining increasing recognition for recreational fishing, boating, bird-watching, and observing the reflection of clouds changing patterns on the landscape.

Ecoparks, especially when equipped with appropriate services for visitors, offer means for income and employment generation.

3. Capitalizing on environmental services

Environmental services are not goods that can be substituted by man-made products but they can be enhanced by human practices. One could replace nutrients exported by agriculture by synthetic fertilizers but there is no possible way by which man-made products could substitute the complex natural "technology" that soil micro-organisms perform to maintain soil fertility [5]. Although we could not survive without environmental services, this contribution of the "natural capital" is often discounted in economics and decision-making for natural resource use.

Wetland development projects concentrate on goods produced by wetlands (agricultural, forestry or fishery yields) without taking into consideration their full value as environmental regulators of land, water and nutrient flows. Consequently, where conversion is attempted, the ability of natural wetlands to sustain alternative development is low.

Wetland development requires major investments of capital, manpower, technology, and input (such as fertilizers), as well as substantial annual investments in maintenance. The limitations of wetland reclamation are becoming obvious, especially as negative consequences can be felt immediately by local people and the economy of the region affected.

"Wise use of wetlands involves maintenance of their ecological character, as a basis not only for nature conservation, but for sustainable development" [6]. If our harvesting of wetland plants and animals respects the annual production rates and regenerative capacity of each species, benefits of wetland productivity can be enjoyed without destroying these important habitats. Where possible, properly managed, natural wetland agriculture can yield substantial benefits [7].

Modern society has much to learn from the many systems of sustainable wetland use which have been practised for centuries by rural communities [8], although traditional practices need to be adjusted to today's conditions.

4. Reclamation: valuating loss

In the past 50 years, the loss of world-wide wetlands has been estimated as being in the order of 70 percent of mangroves that once existed. In the USA, 80 percent of the 870 000 km2 of wetland loss has been to agriculture. Wetlands are destroyed where people envisage putting their land and water to a more productive use. This assumption is not valid if efficiency is measured in terms of profit per unit of water and when the cost of the capital investment is taken into account [9].

The role of wetlands as groundwater recharge and discharge, flood control, water purification, fisheries support and nutrient retention are free goods and public benefits. Costing these services, in addition to ecotourism opportunities, offer attractive alternatives to wetland conversion for other development purposes. The lack of awareness of environmental services or private profit favours wetland drainage, therefore disrupting the normal water supply and compromising long-term viability of investments [10].

Wetlands reclaimed for agriculture release in drainage waters nitrogen, phosphorus and other agro-chemicals that adversely impact ecosystems downstream [11]. Industrial or urban developments totally displace biodiversity and add pressure on ecosystem carrying-capacity (e.g. water supply) or self-purification (e.g. waste disposal). Evaluations of wetland conversion for industrial use should consider this sector capital mobility: when the site will be in a state unfavourable for the enterprise (e.g. water shortage, pollution), the industry will move elsewhere.

In all types of reclaimed land use (agriculture, industry or urban development), taxes and expenses increase to counter-measure flood damage, pollution, siltation of reservoirs and irrigation facilities, and to replace goods or services once provided free by wetlands (e.g. water purification). In societies that rely on wetlands for fish protein, pasture, agricultural products or timber, any reduction in productivity is felt acutely. Decisions on land use options should favour residents dependent on wetland environments and sectors interested in investing in the long-term sustainability of natural resources.

The nutrient cycling pattern of wetlands determines the biodiversity they sustain. The hydrological change brought by reclamation is bound to bring a shift in the composition and concentration of plant and animal species that can only be felt in the longer term. Assessments of the environmental impact of reclamation or restoration should address short-term, medium-term and (most importantly) long-term impacts.

Environmental impact assessments usually identify mitigation measures to potential problems. To this end, it is desirable to identify levels of acceptable risk, or state of biodiversity that is considered undesirable. Such limits could be either expressed in biological terms (e.g. percentage of biomass below which a given species should not be driven) or in economic terms (e.g. minimum profitability from tourism or fisheries). Corrective action should be agreed upon beforehand to curtail problems when and if they arise.

Changes in environmental quality or local elimination of some environmental services lead to quantifiable costs, including:

  • To: Understanding the ecological impact of tideland reclamation, Part 2: Integrated Coastal Area Management

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