Hydrology and Physiography of Groundwater and Wetland Habitats - Freshwater Ecology: Concepts and Environmental Applications - page 65

et al., 1994). Alligators in the Everglades construct holes that keep the wet-
land from becoming completely dry during times of low precipitation and
serve as refugia for fishes, snails, and turtles.
SUMMARY
1. Freshwater habitats vary in scale from individual sediment particles to
continental watersheds. The appropriate scale of investigation depends
on the question being asked.
2. Water falls unevenly across the earth and evaporates or is transpired
(evapotranspiration) at different rates depending on a variety of
factors, including global weather circulation patterns, geography, and
landscape level influences. The water that is not lost to
evapotranspiration either flows across the surface of the land to
streams and rivers or infiltrates the soil to groundwater.
3. The characteristics of the medium between soil and groundwater
alter the rate at which water flows into the aquifer. Generally, water
flows more slowly through fine-grained sediments. Once water
enters an aquifer, the rate at which it moves through is also
dependent on slope and the materials that make up the aquifer.
Water flows very slowly between the pores of fine-textured
sediments such as silts and clays or those with large amounts of
organic materials and relatively rapidly in coarse gravel or limestone
with large channels and pores.
4. The hydrodynamics of groundwater dictate its use as a water
resource, the ecology of a unique biota, and interactions with other
aquatic habitats. Efforts to clean up groundwater pollution also
depend on knowledge of groundwater and soil characteristics,
particularly flow characteristics.
5. Wetlands are distributed worldwide, provide important habitat for
wildlife, provide vital ecosystem services (such as flood control and
water purification), and are an important source of methane to the
atmosphere. The types of wetlands that have been described are
extremely variable and generally defined by the length of time they
contain water, their vegetation, and the degree of marine influence.
The geology of wetlands varies in different parts of the world, and
there is no dominant process that leads to wetland formation
worldwide.
6. Rice paddies constitute a type of wetland that feeds a large portion of
the world's human population.
7. The hydrology of many wetlands has undergone major changes due
to human activity. Many wetlands have been drained and lost, and
others are compromised severely. Thus, wetlands are among the
most endangered habitats in the United States and throughout the
world.
8. The Everglades in Florida provide a good example of the impact
people can have on wetlands by altering hydrodynamics. Biota such
as beavers and alligators can also alter wetland hydrology.