Topic 8.4 Notes – Human Impacts on Wetlands and Mangroves

What Wetlands and Mangroves Are

A wetland is land where water covers the soil part or all of the time. It does not need standing water all year. Seasonal flooding still counts if the area stays wet long enough to create wetland conditions.

Those conditions usually include:

• the water table at or near the surface
• waterlogged soils
• low oxygen in the soil, because water fills the spaces where air would normally be

That low-oxygen soil is why wetlands have special plants and animals adapted to it. Wetlands also occur along a gradient from open water into drier upland areas, with different plant communities dominating different zones.

Wetland zones from aquatic habitat to upland

Marshes

Marshes are wetlands dominated by grasses and other nonwoody plants.

Swamps

Swamps are wetlands dominated by woody plants such as trees and shrubs.

Mangrove wetlands

Mangroves are coastal wetlands in tropical and subtropical intertidal zones. They have salt-tolerant trees and shrubs growing in soft, muddy, oxygen-poor, salty sediment. Their root systems help them anchor and get oxygen.

Hydrology matters here because the movement, timing, depth, and duration of water determine whether wetland conditions stay in place.

What Services Wetlands and Mangroves Provide

Wetlands matter because they provide water filtration and purification, flood protection, and habitat. Mangroves add major coastal benefits like shoreline stabilization and fishery support.

Water filtration and purification

As water moves through a wetland, it slows down.

• Filtration means sediment settles out and gets physically trapped.
• Pollutants attached to that sediment can also be trapped.
• Wetland plants take up nitrogen and phosphorus.
• Microorganisms can break down or transform some pollutants.

Purification is broader than filtration. It includes trapping plus biological and chemical processing.

Flood protection and water storage

Wetlands act like temporary sponges.

• They store water during storms or floods.
• They release it more slowly.
• This lowers and delays peak discharge downstream.

Mangroves also reduce wave energy and storm surge impacts.

Habitat and biodiversity support

Wetlands provide:

• feeding
• breeding
• spawning
• nursery
• resting
• shelter habitat

Amphibians, birds, fish, invertebrates, reptiles, and mammals use wetlands. Mangrove roots are especially important as nursery habitat for juvenile fish and crustaceans, which connects mangroves directly to commercial and subsistence fisheries.

Shoreline stabilization

Mangrove roots trap sediment and reduce coastal erosion.

Major Human Threats to Wetlands and Mangroves

Commercial development

Development often drains, fills, dredges, clears, or paves wetlands.

• direct habitat loss and fragmentation
• less water storage
• more runoff
• higher flooding risk

Mangroves are often cleared for resorts, ports, marinas, and aquaculture ponds.

Dam construction and altered hydrology

Dams change downstream flooding patterns, sediment delivery, and connectivity.

• wetlands may shrink or dry out
• plant communities may change
• fish migration can be disrupted

The Everglades are a classic example. Canals, levees, drainage, and water diversion changed the natural flow of water.

Overfishing

Overfishing removes organisms faster than they can recover. That disrupts food webs and weakens the mangrove nursery to fishery connection.

Agricultural pollution

This is usually nonpoint source pollution.

Runoff can carry:

• sediment
• fertilizers
• pesticides and herbicides
• animal waste
• pathogens

Sediment raises turbidity and can bury habitat. Excess nitrogen and phosphorus can cause algal growth and then low dissolved oxygen.

Industrial pollution

Industrial pollution can enter through discharge, spills, runoff, atmospheric deposition, or groundwater.

Possible contaminants include:

• acids
• petroleum
• solvents
• heavy metals
• other toxic chemicals

These can cause death, stress, reproductive failure, and long-term contaminated sediment.

How Wetland Loss Causes Environmental Damage

This gets tested as a cause-and-effect chain.

The diagram pulls both chains together, so use it to connect the steps for wetlands and mangroves.

Wetland and mangrove loss cause-and-effect chains

When wetlands are drained or filled:

1. Vegetation and absorbent soil are lost.
2. Filtration and purification decrease.
3. Runoff moves faster.
4. Flood peaks downstream get higher.
5. Habitat is lost and biodiversity drops.

When mangroves are cleared:

1. The root network is removed.
2. Less sediment is trapped.
3. Shorelines erode more easily.
4. Waves and storm impacts get stronger.
5. Nursery habitat is lost.
6. Fishery productivity falls.

Protecting and Restoring Wetlands and Mangroves

The best logic is avoid damage first, then minimize it, then restore.

Limiting direct destruction

Protection can include zoning, protected areas, setbacks, conservation easements, and rules on dredging, filling, and clearing.

Restoring hydrology and vegetation

Restoration may involve removing drainage structures, reconnecting floodplains, restoring tidal flow, and planting native vegetation. Fixing the water conditions first is usually the most important part.

Reducing pollution at the source

Agricultural BMPs include buffer strips, better fertilizer timing and rates, erosion control, and animal waste management. Industrial fixes include wastewater treatment, spill prevention, and discharge limits.

Constructed wetlands can help treat runoff or wastewater, but they do not replace natural wetlands.

Managing dams and fisheries

Managers can use environmental flow releases, limit withdrawals, or sometimes remove dams. Fisheries can be protected with catch limits, size limits, seasonal closures, protected nursery areas, and marine reserves.