Wetlands have received a great deal of study over the past 40 years, and have become recognized as ecosystems having many valuable properties. As a result, many wetlands are now protected the world over, or if they are destroyed, replacement wetlands are created. Wetland ecosystem services include provisioning of food, freshwater, and building materials; water filtration and purification; critical habitat for many species of plants, amphibians, fish, and birds; storm abatement, flood control, and erosion control; microclimate regulation; and at larger scales, wetlands are important sites for nutrient cycling and carbon sequestration.
Because of their recognized ecological importance and also their particular vulnerability to development pressures, more attempts at economic valuation of wetlands have been undertaken than at perhaps any other ecosystem. One study from the early 1970s estimated the value of tidal marshes at $2500-$4000 per acre per year (approximately $6200-$9900 per hectare per year), summing up all nonoverlapping services. In India, hurricane damages cost nearly five times as much to villages not protected by mangroves compared to a village in the wind shadow of a mangrove protected area. More recent estimates are lower, but still run high enough to place the value generation of the world's wetlands in the tens of billions of dollars per year.
Although composing a small fraction of the world's surface water, rivers and estuaries are important producers of ecosystem services. Historically, waterways have been critical for transportation, and human settlements often sprung up around the intersection of a river or estuary with another geographic feature (e.g., a natural harbor). Rivers have also been used for drinking water and to remove or dilute waste from populated areas, although often their assimilation capacities, such as to break down organic matter and still provide sufficient dissolved oxygen to support aquatic life, have been exceeded.
Rivers and estuaries are important habitat for fish and shellfish; estuaries, on an areal basis, are some of the most productive ecosystems on Earth. As systems that link continents to the oceans, rivers and estuaries play key roles for many species that use them for all or part of their life cycles. Many commercially important species of fish, for example, use estuaries and rivers as 'nursery' habitat wherein reproduction and early life stages play out. Oysters and other bivalves filter enormous quantities of water as they feed, reducing turbidity, and translocating nutrients to the benthos.
Among the less obvious services of these systems is the connection to land through floodplains and their riparian zones. During flooding, these areas receive silts that increase their fertility, and debris is removed as floodwaters recede. Flooding also connects aquatic and terrestrial food webs, so that fish may literally, as in the Amazon, forage in the trees during flooding. When dry, floodplains are important habitat to many species that are exploited, including large mammals and birds.
Rivers also play a role in the spiritual life of civilizations. For example, the Hindu religion particularly reveres large rivers, which symbolize the washing away of pollution and sin. In the Shinto religion of Japan, springs are thought to be inhabited by deities called Kami. Rivers have been harnessed for a thousand years for irrigation on the island of Bali, through a system of water temples that are managed by priests. Many religions also worshipped water spirits of various forms.
Lakes hold a special place of importance for many people and societies, as they provide freshwater, food fish, and many opportunities for recreation. Lake-shores hold strong attraction for many people, such that real estate values of lakeside are multiplicatively higher than that of adjacent areas without lakes. In a study for the State of Maine, it was found that good water quality increased the collective value of lake-shore homeowners' property by $6 billion over their purchase costs.
Lake productivity can provide recreational fishing opportunities in the billions of dollars. A recent study of sport fishing in New York State found that inland recreational fishing generated $1.2 billion annually in direct expenditures and an additional billion dollars' worth of indirect expenditures (e.g., dining out at local restaurants, motel stays, and so on).
Although not typically occurring inland, coral reefs rank among the most biodiverse ecosystems on Earth, and there is great interest in evaluating their ecosystem goods and services contributions. Reefs form in clear, tropical waters, concentrating biomass and building structure in what are often otherwise nutrient-poor systems. Corals themselves are formed of symbiotic associations of coral polyps and zoox-anthellae, a type of dinoflagellate that provides the corals with photosynthate while receiving protection from the coral. Coral reefs attract many fish and invertebrates, and can also support algae.
Services that coral reefs provide include direct support of fisheries and recreation. Reefs also generate the fine white sands that attract tourists to tropical resorts, and many provide other commercial products such as shells or fish for the aquarium trade. Where reefs are located close to shore, they also play an important role in coastal protection. Studies have shown that this service alone is worth $1-$12 million per kilometer of shoreline. Animals that live on coral reefs but that make excursions to nearby seagrass beds export nutrients to these outlying areas, further enhancing productivity.
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