Short answers, pulled from the story.
A wetland is a semi-aquatic ecosystem whose ground is flooded or saturated with water, either permanently or seasonally, producing oxygen-poor soils. A simplified definition is an area of land usually saturated with water, where the water table stands at or near the surface long enough each year to support aquatic plants. It is also defined as a community of hydric soil and hydrophytes.
The four main kinds of wetland are marsh, swamp, bog, and fen, with bogs and fens classed as peatlands or mires. Marshes are dominated by emergent herbaceous plants like reeds and cattails, while swamps are dominated by woody trees and shrubs. Mangrove forests are wetlands filled with salt-tolerant woody plants.
The world's largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, and the Sundarbans in the Ganges-Brahmaputra delta. Wetlands exist on every continent except Antarctica.
Wetlands provide ecosystem services including water purification, flood control, shoreline stabilization, storm protection, and groundwater replenishment. One analysis valued the storm protection wetlands provide naturally at US$33,000 per hectare per year, and replacing their services would require enormous spending on purification plants, dams, and levees.
Since 1900, between 65 and 70 percent of the world's wetlands have been lost, often drained for agriculture or real estate or flooded for recreational lakes and hydropower. The Millennium Ecosystem Assessment from 2005 found wetlands more threatened by environmental degradation than any other ecosystem on Earth.
Wetlands can act as a carbon sink or source, storing roughly 44.6 million tonnes of carbon per year globally according to a 2003 estimate, while also emitting methane and nitrous oxide. Peatlands cover only 3% of the world's land area but their degradation produces 7% of all carbon dioxide emissions.