98 Natural systems and greenspaces
cover parts or all of these wetlands. Coastal wetlands, such as those formerly on
theseaward side of New Orleans, are important wave energy absorbers against
major storms (Farber 1987, Danielsenet al.2005, Costanzaet al.2006). Yet coastal
wetlands are particularly subject to loss in urban regions. The wetlands are
drained and filled, sometimes extending the coastline outward to add high-
value city-center real estate for offices, condominiums, parks, and shipping docks
(e.g., Boston; Chicago; Kagoshima, Japan). The fourth terrestrial coastline type,
bays, coves, and harbors,are indentations along the seacoast with concentrated
uses because of their relatively protected low-wave-energy condition. Docks, boat
anchorages, and accompanying functions are located there.
Several of the coastal land types are, in effect,estuaries,the coastal water-
bodies and aquatic ecosystems where river freshwater carrying sediment and
nutrients mixes with saltwater from the sea. Rivers commonly empty into estu-
arine bays, coves, and harbors, which are bordered by coastal wetlands. The com-
bination of environmental resources makes an estuary exceptionally productive,
so normally food chains are long, food webs complex, and fisheries and shell-
fisheries quite productive. Furthermore, the rich resource base combined with
considerable horizontal and vertical heterogeneity usually results in extremely
high biodiversity in estuaries.
Underwater habitats,including seagrass beds, coral reefs, submerged rocky
areas, clear sandy areas, mud bottoms, and, in urban regions, plenty of sunken
ships, boats, and debris used by fish, are equally diverse and important. Seagrass
beds are rich areas for fish and are good indicators of unpolluted water. Coral
reefs, among the Earth’s most species-rich habitats, also require clean water.
Estuarine bays and coves support both dense and diverse fish and shellfish pop-
ulations, as do near-shore areas along the seacoast.
These coastal areas are all highly dynamic. Storms on land produce floodwa-
ters, and storms from the sea bring strong winds and large waves. Big storms
such as hurricanes (cyclones) periodically occur, as well as tsunamis in some
regions. Sand is eroded, transported, and deposited by sea currents along the
coast (Pilkey and Dixon1996). Groundwater and wind arrive from the land. Thus
coasts are in the path of, and shaped by, these forces. Yet coastal areas are also
highly resilient, returning quickly from a disturbance, though often in different
form.Adding to the effect is gradual sea-level rise (Chapter 12 ).
Many other urban effects on these coastal spatial patterns and processes are
evident. A river passing a city receives masses of pollutants which form elongated
plumes in coastal areas. Such pollutants may block light penetration, cause
eutrophication, cover the bottom with sediment, damage tide pools, degrade
estuarine shellfish beds, and diminish near-shore sea fish populations. Sewage
from the city may enter the coastal ecosystems, causing problems associated