What Counts as a Wetland
The term covers natural and some human-made systems with permanent or seasonal flooding or water-saturated soils — floodplains, lake shallows, marshes, peatlands, estuaries, mangroves, salt marshes, rice fields, and ponds. Wetland boundaries can shift seasonally; a seasonally dry area may remain part of a wetland system when hydrology determines its soils, vegetation, and functions.
How Wetlands Affect Floods and Drought
Floodplains and marshes can receive excess water, spread it over a wider area, and slow a flood wave. Vegetation and uneven terrain reduce flow velocity and retain sediment. However, not every wetland can fully protect a city from a major flood — effects depend on location, area, condition, catchment development, and event magnitude. Nature-based measures must form part of integrated risk management. Healthy wetlands also store water in soils, peat, and shallow basins and release it gradually to rivers or groundwater, supporting baseflow and soil moisture during dry periods.
Filtering Runoff and Carbon Storage
Slow water movement allows particles to settle, while plants and microorganisms absorb or transform some nutrients. Wetlands can reduce loads of nitrogen, phosphorus, and suspended solids — but they are not unlimited treatment systems. Excessive wastewater or sediment can exceed natural capacity and trigger eutrophication. Peatlands accumulate organic carbon over long periods because decomposition is slow under waterlogged conditions. Drainage exposes peat to oxygen, accelerates decay, and can increase fire risk. Rewetting reduces further carbon loss, though the greenhouse-gas balance — including CO₂, methane, and nitrous oxide — depends on wetland type and time since restoration.
Biodiversity, Migration Routes, and Threats
Wetlands provide spawning, feeding, breeding, and resting areas for fish, amphibians, insects, mammals, and waterbirds. A chain of sites along a migration route may be essential even where each site is small. Major threats include drainage, river channelisation, dams, floodplain development, peat extraction, pollution, invasive species, and climate change. Wetland loss often occurs gradually through small channels, embankments, and roads. Building on a natural floodplain destroys habitat and can shift flood risk elsewhere — planning should assess the entire catchment.
Restoring Natural Hydrology
Restoration may block drainage channels, reconnect rivers with floodplains, remove unnecessary embankments, adjust grazing, control invasive species, and restore native vegetation. The causes of degradation and the water balance must be identified first. After intervention, monitoring covers water levels, vegetation, peat, water quality, birds, and other indicator groups. Rapid flooding or an unsuitable water level can damage infrastructure — adaptive management is essential.
Wetlands are natural water infrastructure, but their functions depend on an intact hydrological regime. The strongest approach is to conserve healthy systems, avoid floodplain development, and restore hydrological connections across the catchment.