Page 414 - Environment: The Science Behind the Stories

Sunlight
Littoral
zone

Limnetic
zone

Profundal
zone

Benthic
zone

Figure 15.7 In lakes and ponds, emergent plants grow along the shoreline in the littoral zone. The
limnetic zone is the layer of open, sunlit water, where photosynthesis takes place. Sunlight does not reach the
deeper profundal zone. The benthic zone, at the bottom of the water body, often is muddy, rich in detritus and
nutrients, and low in oxygen.

In cypress swamps of the southeastern United States, cypress Bogs are ponds covered with thick floating mats of vegetation
trees grow in standing water (Figure 15.8). In northern forests, and can represent a stage in aquatic succession.
swamps are created when beavers dam streams with limbs Some wetlands are seasonal, being wet only at some
from trees they have cut, flooding wooded areas upstream. times of the year. Vernal pools are an example. In many
parts of North America, these pools form in early spring
Figure 15.8 Freshwater wetlands such as this bald cypress from rain and snowmelt, and then dry up once weather
swamp in Louisiana support biologically diverse and produc- becomes warmer. Numerous animals have evolved to take
tive ecosystems. advantage of the ephemeral time windows in which they
exist each year.
Wetlands are extremely valuable habitat for wildlife. CHAPTER 15 • Fr E shwat E r s yst E m s and rE sour CE s
Louisiana’s coastal wetlands, for example, provide habi-
tat for approximately 1.8 million migratory waterbirds each
year. Wetlands also provide important ecosystem services by
slowing runoff, reducing flooding, recharging aquifers, and
filtering pollutants. Cypress swamps in coastal Louisiana
are home to many rare species that suffer habitat loss when
cypress trees are ground up to produce cypress mulch for land-
scaping. Environmental groups lobbied major home-improve-
ment retailers to cease selling cypress mulch from Louisiana,
and scored major victories in the effort to save these forests
when in 2007 Walmart, Home Depot, and Lowe’s announced
they would no longer buy or sell cypress mulch from southern
Louisiana. 413

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