What it is
Wetlands are wet ground that stays wet. Marshes, fens, bogs, floodplain forests, mangrove swamps.
They cover less than 6% of the land. They do far more than their share.
One hectare of healthy wetland filters millions of litres a year. It traps sediment, eats nutrients, breaks down pollutants. Peat locks carbon away for thousands of years, faster than any rainforest.
Why they matter
Wetlands are biodiversity engines. The wet-dry edge stacks niches: amphibians, dragonflies, water beetles, waterbirds, spawning fish.
Plenty of upland birds are obligate wetland breeders. Drain the marsh and they vanish from the whole region. Habitat math doesn't save them.
Then there's flood control. A working floodplain stores millions of cubic metres at peak flow, then releases it slowly. Drain it and the flood doesn't disappear. It moves downstream onto someone else.
How they were lost
Globally, 64% of the wetlands present in 1900 are gone. In heavily developed regions, the loss tops 90%.
The recipe was always the same. Dig ditches. Install tile drains. Lower the water table. Plough the black earth.
Wetland soils are some of the most fertile on earth, built over millennia of slow accumulation under water. Once drained, yields are exceptional. That paid for the destruction.
The carbon bill. Drained peat oxidises. Worldwide, drained peatlands emit roughly 2 billion tonnes of CO2 per year. That's about 5% of all human greenhouse emissions, from a sliver of land.
River engineering finishes the job. Straighten, deepen, embank, and you cut the river off from its floodplain. A river in a concrete channel is a pipe.
Put the water back
The rule is one line. Reverse the drainage.
Block the ditches. Plug drains with dams of compacted peat, clay, or plastic sheet piling. On a big bog you might install hundreds of blocks. Work downstream to upstream so you don't drown the work below. Water tables rise within weeks. Sedges and rushes show up the first growing season.
Dig ponds and scrapes. Vary the depth. Shallow seasonal pools serve different species than 2 m permanent pools. Use the spoil to build islands and banks for ground-nesting birds. Feed in surface runoff with rain gardens and swales around the edge.
Reconnect the floodplain. This is the ambitious one. Breach old embankments. Lower the bank. Cut a secondary channel so the river spreads at high flow. Given time, you get wet woodland, reed bed, open water, and wet grassland in one mosaic.
What recovery looks like
Water quality shifts inside a year. Sediment drops out, nutrients get pulled by new vegetation.
Birds follow on a two to five year timeline. Invertebrates and amphibians take longer, especially on isolated sites cut off from source populations. Get the hydrology right and the trajectory holds.
Great Fen, eastern England. Over 3,700 hectares of restored fenland linking two reserves. Within ten years, breeding bitterns, marsh harriers, and water voles were back on land that had been arable for generations.
Mississippi basin. Restored wetlands on former farmland strip 20 to 40 kg of nitrogen per hectare per year through denitrification. Bacteria turn dissolved nitrate into nitrogen gas. That's the same trick the soil food web runs in every healthy handful of dirt, scaled to a continent.
See also
- Rain Gardens for small-scale wetland features that catch and filter runoff
- Swales on Contour for earthworks that feed restoration sites
- Mangroves for coastal wetland forests with outsized value
- Wildlife Corridors for tying wetlands into the wider landscape
- Rainwater Harvesting Basics for managing water inputs