Hydrology and Physiography of Groundwater and Wetland Habitats - Freshwater Ecology: Concepts and Environmental Applications - page 48

and spatial variations in movement and distribution of water are called hy-
drodynamics . In order to understand how water moves across the surface
of the continents, the links between terrestrial and aquatic ecosystems, as
well as the links among different aquatic ecosystems, must be examined.
Chapter 1 included a brief description of a global water budget with re-
spect to water availability to humans. This chapter provides a more de-
tailed consideration of the hydrologic cycle and hydrodynamics.
Aquatic habitats can be considered at a variety of spatial and tempo-
ral scales; the organism or process of interest dictates the scale chosen for
study. For example, microbes can be influenced by proximity to a grain of
sand, but ecosystem processes dominated by microbes can be altered by
position in a watershed. Changes in small-scale microbial communities
can occur over periods of hours, but changes in ecosystems can take
decades to millions of years. An indication of the range of habitats and
scales that can be used as a framework to link hydrodynamics to aquatic
ecology is presented in Table 4.1. Basic physical properties of water move-
ment were discussed previously; now I explain how water moves across
the landscape.
Weather patterns result in widely varied quantities of precipitation
around the world (Fig. 4.2). Precipitation, in combination with factors that
influence return of water to the atmosphere, dictates how much water en-
ters aquatic systems (Fig. 4.3). Precipitation can either be intercepted by
vegetation or fall directly on nonvegetated surfaces. Water can return to the
atmosphere by direct evaporation or by transpiration through plants. Tran-

Habitat Classification by Time and Distance Scales a

TABLE 4.1

Habitat Time range Distance range Examples

Microhabitat 1 second-1 year 1 m-1 mm Fine particles of detritus, sand and clay

particles, surfaces of biotic and abiotic
solids in the environment

Macrohabitat 1 day-100 years 1 mm-1 km Riffles and pools in streams, rivers, and

underground rivers; logs; macrophyte beds;
pebbles; boulders; and position on
lakeshore

Local habitat 1 month-1,000 years 1 mm-100 km Lake, regional aquifer, stream or riffle reach,

shallow lake bottom

1-10 6

Watershed years 1-10,000 km Areas feeding small streams to the basins of

large rivers, including lakes, aquifers, and
streams within boundaries

10-10 7

Landscape years 10 -10,000 km A mosaic of local habitats or watersheds

10,000-10 9

Continent years 10,000 km A composite of large drainage basins and

aquifers

a Note that this classification is only one way to divide a natural continuum.