Earth and soil 99with excessive organic matter and mineral nutrients. Major industrial centers
with docks and shipping are usually present by coastal cities (Breen and Rigby
1996), resulting in highly polluted deep water that spreads by currents along
thenear-shore coast. The dispersed discarding of solid waste, or dumping in
recognized locations, produces accumulations of debris on the sea bottom. Con-
centrated recreational boating and commercial fish/shellfish boating widely dis-
tribute organic wastes in the water, and significantly affect both fish and bird
populations.
Houses, condominiums, hotels, and other commercial structures often line
thecoasts of urban regions (e.g., Australia’s Gold Coast, Southern Spain, Miami
Beach), especially sandy coastlines. A paucity of protected coastal strips plus
masses of migratory beachgoers and boaters normally results in a coastline with
but shreds of nature. It seems likely that intense human impacts expanding from
cities along coastlines, which are among the world’s most ecologically valuable
habitats, will continue, unless interrupted by rapid sea-level rise and more severe
weather events associated with global climate change.
Earth and soil
Twokeyecological topics are introduced in the context of urban regions:
(1) earth and soil in this section; and (2) microclimate and air pollutants in the
following section.
Earth(orearthen material), resulting from the breakdown of rock to smaller
particles, provides many important functions in urban regions (Costa and Baker
1981, Gilbert 1991 ,Craul1999,Bartels 2000). These include aquifer water sup-
ply, a stormwater drainage system, and a patchy deep structure underlying dif-
ferent soil types on the surface. Porous sand and gravel is extensively used
as fill around buildings and transportation infrastructure, so that water can
readily drain through rather than accumulate in it. However, earthen fill is
inherently unstable on slopes, such as the downslope side of a highway where
the surface of fill is often highly erodible, and thus a sedimentation threat
toawater body below (Lal 1994, Formanet al.2003). Overall, however,erosion
andsedimentationratesincommercial, public, and low-density residential areas
are low (Craul1999). Indeed downstream areas are often scoured out leaving
streams short on sediment. Earth is easily moved, mixed, and smoothed, so
all cities have important sand-and-gravel sources. Usually coastal plains, eskers,
river floodplains, or more-expensive rock-crushing operations provide urban
fill.
The proportions ofsand(relatively coarse material of large particles),silt
(intermediate-sized particles), andclay(fine particles) determine thetextureof