8.4 - Human Impacts on Wetlands and Mangroves

Learning Objectives

I. Wetland Ecosystem Services

• Regulating services: Wetlands provide groundwater recharge, slowly letting water seep into the soil for later use in agriculture or drinking. They also sequester carbon dioxide, which prevents it from entering the atmosphere and mitigates climate change.

• Flood protection (regulating service): Wetlands act like sponges. During heavy rain or storm surges, they soak up and hold floodwater, then release it slowly, which lowers flood peaks downstream and along the coast. During Hurricane Sandy in 2012, coastal wetlands in the northeastern US prevented an estimated $625 million in flood damage.

• Water filtration, pollination, and pest control (also regulating services): Wetlands filter water by trapping pollutants in their roots, which keeps those pollutants from entering the groundwater being recharged by runoff. They're important pollinator habitats, and they provide pest control through organisms like spiders and frogs.

• Supporting services: They aid in nutrient recycling, help build soil, and have very high primary productivity. Supporting services are the background processes that make all the other services possible.

• Provisioning services: They create habitats for plants and animals used as food or raw materials.

• Cultural services: They generate tourism dollars, like fishing licenses, and support educational research.

II. Threats to Wetlands

1. Pollution: Wetlands are harmed by pollutants like sediment, motor oil, and pesticides from urban and agricultural runoff. They’re also impacted by endocrine disruptors, such as medical compounds improperly flushed down the toilet.
• Industrial waste: Factories and mines can release heavy metals like mercury and lead, which settle into wetland and mangrove mud and build up in the plants and animals living there.

2. Development and drainage: Wetlands can be filled in or drained to create stable land for development, including homes, parking lots, stores, or agricultural land. That removes habitats and all the associated ecosystem services.

3. Water diversion: Humans divert water from streams and rivers for agriculture, drinking water, and flood control. That decreases water levels downstream, which can eventually cause wetlands, like the historical Everglades, to dry up completely.

4. Dams and hydroelectric power: Dams block rivers, which dramatically decreases the flow of water downstream. They also block the flow of sediment and nutrients that are vital for the plants living in those wetlands, which alters the soil fertility of downstream habitats.

5. Overfishing: This disrupts the food web and creates predator-prey imbalances, which disrupts the stability of the ecosystem.

III. Mangrove Ecosystems

• Services: Mangroves provide significant economic value. They’re extremely effective at coastal protection: their dense, tangled roots slow down waves and storm surges, which protects the people and property behind them. A 2020 study estimated that mangroves prevent more than $65 billion in flood damage around the world every year, and that without them about 15 million more people would be flooded each year. Protecting mangroves is often cheaper than building and maintaining sea walls. They’re also effective at water filtration and sequestering $\text{CO}_2$ (climate regulation).

• Threats: Mangroves are cleared for logging and deforestation, often because beachfront property is valuable for condos or resorts. They’re also cut down for aquaculture (farming fish or shrimp) and to create rice paddies. Pollutants like sediment can clog their roots, which prevents oxygen uptake, and toxic solutions like heavy metals can kill their roots.

IV. Solutions to Watershed Pollutants

1. Cover crops: Used in agriculture to anchor the soil, which prevents sediment and fertilizer runoff into water bodies.

2. Riparian buffers: Planting vegetation along a body of water to act as a giant sponge or filter. The roots absorb water and trap pollutants, preventing them from making it into the water.

3. Better manure management: Upgrading manure lagoons or converting waste into fertilizer pellets to prevent runoff.

4. Sewage upgrades: Using septic tank upgrades, which allow slower and more natural filtering, or biological waste removal, which uses microbes to eat excess waste.

Big picture: Wetlands and mangroves provide invaluable services, including groundwater recharge, carbon sequestration, and superior coastal protection. But these systems are rapidly threatened by human development, which often involves draining or filling them in, and by water diversion for agriculture and urban use.