Human Activities on Wetlands & Mangroves (College Board AP® Environmental Science) : Study Guide

Wetlands are diverse ecosystems and make up 6% of the world’s habitats

They are areas of land which are submerged in water either permanently or seasonally

Wetlands can be inland or coastal

• This means wetland waters can be salt, fresh or brackish

Coastal/tidal wetlands are found in estuaries, making it difficult for most plants to survive the variation in salinity (saltiness)

Mangroves are highly adaptive to changing conditions, making them one of the most successful ecosystems on Earth, covering approximately 25% of tropical coastlines

Mangroves grow in the intertidal zone of the coast and are found in warm tropical waters and coastal swamps within 30° N and S of the equator

• Florida has the largest concentration of mangroves in the US

Salt marshes are found all over the world and are not temperature dependant

• Like mangroves, they are an ecosystem of the intertidal zone 

• They are typically very flat, with numerous channels running through them

• They form in sheltered areas, such as behind spits and artificial sea defences, inlets and estuaries, where fine sediments can be deposited 

  • Salt marshes are found along the Atlantic and Gulf Coasts of the US and are common along the 'Big Bend' area of Florida

Inland/non-tidal wetlands are found near rivers, lakes, streams and ponds

• Swamps are wetlands characterized by trees and shrubs growing in standing water

  • They often have stagnant water with low oxygen levels

  • Okefenokee Swamp, Georgia, is the second largest peat-filled swamp in the U.S.

• Marshes are dominated by grasses, reeds, and other herbaceous plants

  • They typically have shallow standing water that supports diverse plant and animal life

  • The largest freshwater marsh in the U.S. is the Everglades in Florida, which is a slow-moving river that drains from Lake Okeechobee

• Bogs are acidic wetlands characterized by the accumulation of peat moss

  • They get most of their water from precipitation rather than surface runoff or groundwater

  • Hawley Bog in Massachusetts is 65 acres and considered one of the last natural New England bogs

Wetlands provide several crucial ecosystem services

Water purification:

• Wetlands filter pollutants from runoff (like pesticides) before they reach larger bodies of water

Climate change:

• Wetlands trap greenhouse gases and sequester carbon

• Salt marshes store carbon at a rate 50 times greater than forests

Flood protection:

• Wetlands act like sponges, absorbing excess water during heavy rainfall, which prevents flooding

• Mangroves and salt marshes act as natural buffers against storm surges, reducing the impact of hurricanes and tsunamis on coastal communities

Habitat:

• Wetlands are home to many species, including amphibians, fish, and birds, and are considered biodiversity hotspots

• Mangroves are critical nurseries for many marine species, helping to sustain coastal fisheries

The main threats to wetlands come from human activities

Commercial development:

• Wetlands are often filled in to build houses, malls, and other structures

• This destroys habitats and reduces flood protection

• Development can lead to increased noise and light pollution, which may affect wildlife behavior and nesting

• Mangroves are harvested for firewood and construction materials

Dam construction:

• Water is diverted away from wetlands, leading to drained wetlands, loss of habitat, and reduced water purification

Overfishing:

• Fish in wetlands are keystone species, meaning they play a critical role in the ecosystem

• Overfishing can lead to a collapse of the food web and a loss of biodiversity

Pollutant runoff:

• Wetlands are vulnerable to chemical pollutants from runoff that can harm fish and other wildlife

Aquaculture: intense fish and shrimp farms cut down mangroves to make room for temporary pools

• Once the pools have gone, the remaining water is toxic due to the regular use of antibiotics, pesticides, chemicals and shrimp feed

Eutrophication: excess nutrients from pollutants cause algae blooms, disrupting the ecosystem and reducing biodiversity