10.7 What issues face coastal wetlands?

Wetlands are ecosystems in which the water table is close to the surface, so they’re typically saturated most of the time. Wetlands can border either freshwater or coastal environments. Coastal wetlands occur along the margins of coastal waters such as estuaries, lagoons, and marginal seas; they include swamps, tidal flats, coastal marshes, and bayous.

Types of Coastal Wetlands

Two most important types, both of which experience intermittent submergence by ocean water and contain salt-adapted plants, oxygen-depleted muds, and accumulations of organic matter called peat deposits.
(1) salt marshes: between approx. 30-65 deg lat, support a variety of salt-tolerant grasses and other low-lying plants that are termed halophytic.

• ex of halophytic grasses: cordgrass, salt-meadow cordgrass ; genus Spartina, have ability to get rid of excess salt by producing exterior salt crystals

• pickleweed: accumulat salts in tissues and dispose of excess salts by breaking off tissues once they become highly salty

well-developed salt marsh habitats found along most coasts of cont. US and Europe, Japan, and eastern S America

(2) mangrove swamps: restricted to tropical regions (below 30 deg lat), support various species of salt-tolerant mangrove trees, shrubs, and palms

• mangroves produce tall tripod-like root systems to stay above salty water, others crystalize excess salt on their leaves

• occur throughout Caribbean and Florida, most extensive mangroves found throughout southeast Asia

Characteristics of Coastal Wetlands

wetlands are home to a diverse assortment of plants and animals and are some of the most highly productive ecosystems on earth. when left undisturbed, provide enormous economic benefits:

• Ex. salt marshes serve as nurseries for >1/2 species of commercially important fishes in SE US

• flounder and bluefish use marshes for feeding and protection during winter

• fisheries of oysters, scallops, clams, eels, and smelt all located in marshes

• mangrove ecosystems important nursery areas and habitats for commercially valuable shrimp, prawn, shellfish, and fish species

• both marshes and mangroves serve as important stopover points for many waterfowl and migrating birds

• wetlands soak up nutrients that run off farmlands and down rivers, which could fuel harmful algal blooms and create marin oxygen-free dead zones if they reached the ocean

  • wetlands amazing at cleansing polluted water = “nature’s kidneys”

• wetlands remove inorganic nitrogen compounds and metals which become attached to clay-sized particles in wetland mud. some nitrogen compounds trapped in sediment are decomposed by bacteria that release the nitrogen to the atmosphere as a gas, and many of the remaining nitrogen compounds fertilize plants, further increasing wetland prodcutivyt

  • as marsh plants die, their remains either accumulate as peat deposits or are broken up to become food for bacteria, fungi, and fish

• wetlands trap carbon in their soils = important sink for atmospheric carbon

• protect shorelines from erosion, serve as a first line of defense against hurricanes and tsunami by dissipating wave energy and absorbing excess water = natural sponge

Serious Loss of Valuable Wetlands

more than half of US’s wetlands have vanished —> filled in and developed for agriculture i.e. rice paddies and palm plantations, fish and shrimp farms, tourism, real-estate projects. many people view wetlands as unproductive, useless land that harbors diseases that would be better served as being developed.

• wetland loss is compounded by lack of fresh sediment from regular river floods. instead, flooding rivers and their sediment are channeled away from wetland areas

Ex. Louisiana

• over time, soil in wetlands naturally compresses under its own weight = subsidence

• normally, growth of plants and infusion of fresh sediment from river floodwaters offset subsidence BUT with these factors reduced or eliminated, many wetlands are sinking into the ocean faster than they’re building up

**scientsist estimate that subsidence of Mississippi River Delta, along with rising sea level, will cause about 10% of Louisiana to sink beneath ocean surface by end of the century

To help prevent loss of remaining wetlands, US Environmental Protection Agency (EPA) established an Office of Wetlands Protection (OWP) in 1986.

• Goal: reduce loss of wetlands in US to zero by actively enforcing regulations against wetland pollution and identifying most valuable wetlands to be protected or restored

overall increase in wetlands in US in 21st century

• gain = small, but due to an increase in freshwater wetlands

• coastal wetlands still decreasing, but at a slower rate then reported

future se leavel rise predicted to exacerbate loss of wetlands

RECAP

coastal wetlands i.e. salt marshes and mangrove swamps are highly productive areas that:

• serve as important nurseries for many marine organisms

• act as filters for polluted runoff

• trap atmospheric carbon in their soils

• help prevent coastal erosion

CONCEPT CHECK 10.7

(1) Name two types of coastal wetland environments and lat ranges where they develop.

• salt marshes: 30-60 deg lat N and S

• mangroves: subtropical (0-30deg N and S)

(2) How do wetlands contribute to the biology of the oceans and the cleansing of polluted river water?

• pollution: soak up nutrients running off farmlands that run down rivers and would create harmful algal blooms that would creat oxygen-free dead zones in the ocean if they went straight into the ocean

  • remove inorganic nitrogen compounds from sewage and fertilizers and metals from polluted groundwater which necome attached to clay-sized particles in wetland mud

• biology: serve as important nurseries for many types of fish who come here to feed, come here for shelter, lay their eggs here, etc.

  • also important stopover point for waterfowl and migrating birds