growth (e.g., salmon and shrimp) (Wilson and Farber,
2009). Because they are biologically productive, estuaries
provide ideal areas for migratory birds to rest and refuel
during their long journeys. Additionally, numerous fish
and invertebrate species rely on the sheltered waters of
estuaries as nursery habitats (Vasconcelos et al., 2011).
Estuaries have important commercial value and their
resources provide economic benefits for fisheries, tourism, and cultural activities.
The protected coastal waters of estuaries also support
important public infrastructure, serving as harbors and
ports vital for shipping and transportation. Estuaries also
perform other valuable services. They are inherently
important to environmental and human health. Estuarine
capacity to filter pollutants not only serves to provide
a healthy environment for marine creatures to thrive, but
it contributes to cleaner coastal waters for beach-going
populations (Kildow, 2009). Wetland plants and soils also
act as natural buffers reducing impacts by moderating the
effects of stormwater runoff including stabilizing soil to
prevent erosion; filtering suspended solids, nutrients, and
harmful or toxic substances; and moderating water-level
fluctuations (Castelle et al., 1992).
Use of estuaries: opportunities and threats
Estuaries are areas with major economic potential because
of their strategic location close to seas and inland waterways. Estuaries also provide some of the world’s most fertile areas for food production. That is why navigation and
port development, as well as agriculture and fisheries,
have always been the engines of economic development
of estuaries. Attracted by these resources, large numbers
of people live in the vicinity of estuaries leading to the
growth of coastal cities and mega cities (Sekovski et al.,
2012). Of the 32 largest cities in the world, 22 are located
on estuaries (Ross, 1995). Five of the ten largest metropolitan areas in the United States are centered along major
estuaries (NOAA, 1998 in Rice et al., 2005). For example,
New York is located at the mouth of the Hudson River
estuary; San Francisco is located on San Francisco Bay
which is an estuary for the Sacramento and San Joaquin
rivers; and New Orleans is on the estuary of the Mississippi River. Unfortunately, this increasing concentration
of people disturbs the natural balance of estuarine ecosystems due to environmental impacts caused by development (Sekovski et al., 2012), which threatens their
integrity, and imposes increased pressures on vital natural
resources that endanger their susceptibility. For example,
along the Hudson River, New York, human presence and
activities have profoundly changed the estuary as a natural
ecosystem (Figure 2).
Trends
Kennish (2002) describes the trends for estuaries until
2025. He suggests that estuaries will be most significantly
impacted by habitat loss and alteration associated with
a burgeoning coastal population, which is expected to
approach 6 billion people. Habitat destruction has
far-reaching ecological consequences, modifying the
structure, function, and controls of estuarine ecosystems
and contributing to the decline of biodiversity. Other anticipated high-priority problems are excessive nutrient and
sewage inputs to estuaries, principally from land-based
sources. These inputs will lead to the greater incidence
of eutrophication as well as hypoxia and anoxia. During
the next 25 years, overfishing is expected to become
a more pervasive and significant anthropogenic factor,
also capable of mediating global-scale change to estuaries.
Chemical contaminants, notably synthetic organic compounds, will remain a serious problem, especially in
heavily industrialized areas. Freshwater diversions appear
to be an emerging global problem as the expanding coastal
population places greater demands on limited freshwater
supplies for agricultural, domestic, and industrial needs.
Altered freshwater flows could significantly affect nutrient loads, biotic community structure, and the
trophodynamics of estuarine systems. Ecological impacts
that will be less threatening, but still damaging, are those
caused by introduced species, sea level rise, coastal subsidence, and debris/litter. Although all of these disturbances
can alter habitats and contribute to shifts in the composition of estuarine biotic communities, the overall effect will
be partial changes to these ecosystem components.
Stevens (2010) also describes trends for estuaries but
focuses on climate change effects (Table 1). With rising
sea levels, estuaries will also be affected, causing changes
in these waterbodies as manifested by the loss of intertidal
area, erosion of shorelines, and increased risk of flooding
of low lying areas (Rossington, 2008 in Stevens, 2010).
Given the above, management strategies must be developed to mitigate future impacts on estuaries.
The future of estuaries: managing, restoring and
monitoring
It is a fact that increasing human activities in the coastal
zone leave a significant human environmental footprint,
leading to multiple stresses on estuaries and causing
declines in water quality and overall ecosystem health.
Included here are the effects of eutrophication, wastewater
inputs, chemical contaminants, freshwater diversions,
draining and ditching of wetlands, hardened shorelines,
sediment/turbidity influx, inlet stabilization, introduced
species, and fisheries overexploitation (Kennish, 2012).
One course of remedial action is habitat restoration.
Restoring habitats involves reestablishing natural ecosystem processes by removing invasive species, reducing
pollution levels, and reintroducing indigenous flora and
fauna. The goal is to rebuild the estuary as an ecosystem
that functions as it once did prior to impacts. Fortunately,
estuarine ecosystems can often be restored, because of
their adaptive and resilient capacity (Most et al., 2009).
Simenstad and Bottom (2002) recommend the following
principles that, although being developed in the context
of estuarine habitat restoration for salmon recovery for
654
SUSTAINABLE USE
2009). Because they are biologically productive, estuaries
provide ideal areas for migratory birds to rest and refuel
during their long journeys. Additionally, numerous fish
and invertebrate species rely on the sheltered waters of
estuaries as nursery habitats (Vasconcelos et al., 2011).
Estuaries have important commercial value and their
resources provide economic benefits for fisheries, tourism, and cultural activities.
The protected coastal waters of estuaries also support
important public infrastructure, serving as harbors and
ports vital for shipping and transportation. Estuaries also
perform other valuable services. They are inherently
important to environmental and human health. Estuarine
capacity to filter pollutants not only serves to provide
a healthy environment for marine creatures to thrive, but
it contributes to cleaner coastal waters for beach-going
populations (Kildow, 2009). Wetland plants and soils also
act as natural buffers reducing impacts by moderating the
effects of stormwater runoff including stabilizing soil to
prevent erosion; filtering suspended solids, nutrients, and
harmful or toxic substances; and moderating water-level
fluctuations (Castelle et al., 1992).
Use of estuaries: opportunities and threats
Estuaries are areas with major economic potential because
of their strategic location close to seas and inland waterways. Estuaries also provide some of the world’s most fertile areas for food production. That is why navigation and
port development, as well as agriculture and fisheries,
have always been the engines of economic development
of estuaries. Attracted by these resources, large numbers
of people live in the vicinity of estuaries leading to the
growth of coastal cities and mega cities (Sekovski et al.,
2012). Of the 32 largest cities in the world, 22 are located
on estuaries (Ross, 1995). Five of the ten largest metropolitan areas in the United States are centered along major
estuaries (NOAA, 1998 in Rice et al., 2005). For example,
New York is located at the mouth of the Hudson River
estuary; San Francisco is located on San Francisco Bay
which is an estuary for the Sacramento and San Joaquin
rivers; and New Orleans is on the estuary of the Mississippi River. Unfortunately, this increasing concentration
of people disturbs the natural balance of estuarine ecosystems due to environmental impacts caused by development (Sekovski et al., 2012), which threatens their
integrity, and imposes increased pressures on vital natural
resources that endanger their susceptibility. For example,
along the Hudson River, New York, human presence and
activities have profoundly changed the estuary as a natural
ecosystem (Figure 2).
Trends
Kennish (2002) describes the trends for estuaries until
2025. He suggests that estuaries will be most significantly
impacted by habitat loss and alteration associated with
a burgeoning coastal population, which is expected to
approach 6 billion people. Habitat destruction has
far-reaching ecological consequences, modifying the
structure, function, and controls of estuarine ecosystems
and contributing to the decline of biodiversity. Other anticipated high-priority problems are excessive nutrient and
sewage inputs to estuaries, principally from land-based
sources. These inputs will lead to the greater incidence
of eutrophication as well as hypoxia and anoxia. During
the next 25 years, overfishing is expected to become
a more pervasive and significant anthropogenic factor,
also capable of mediating global-scale change to estuaries.
Chemical contaminants, notably synthetic organic compounds, will remain a serious problem, especially in
heavily industrialized areas. Freshwater diversions appear
to be an emerging global problem as the expanding coastal
population places greater demands on limited freshwater
supplies for agricultural, domestic, and industrial needs.
Altered freshwater flows could significantly affect nutrient loads, biotic community structure, and the
trophodynamics of estuarine systems. Ecological impacts
that will be less threatening, but still damaging, are those
caused by introduced species, sea level rise, coastal subsidence, and debris/litter. Although all of these disturbances
can alter habitats and contribute to shifts in the composition of estuarine biotic communities, the overall effect will
be partial changes to these ecosystem components.
Stevens (2010) also describes trends for estuaries but
focuses on climate change effects (Table 1). With rising
sea levels, estuaries will also be affected, causing changes
in these waterbodies as manifested by the loss of intertidal
area, erosion of shorelines, and increased risk of flooding
of low lying areas (Rossington, 2008 in Stevens, 2010).
Given the above, management strategies must be developed to mitigate future impacts on estuaries.
The future of estuaries: managing, restoring and
monitoring
It is a fact that increasing human activities in the coastal
zone leave a significant human environmental footprint,
leading to multiple stresses on estuaries and causing
declines in water quality and overall ecosystem health.
Included here are the effects of eutrophication, wastewater
inputs, chemical contaminants, freshwater diversions,
draining and ditching of wetlands, hardened shorelines,
sediment/turbidity influx, inlet stabilization, introduced
species, and fisheries overexploitation (Kennish, 2012).
One course of remedial action is habitat restoration.
Restoring habitats involves reestablishing natural ecosystem processes by removing invasive species, reducing
pollution levels, and reintroducing indigenous flora and
fauna. The goal is to rebuild the estuary as an ecosystem
that functions as it once did prior to impacts. Fortunately,
estuarine ecosystems can often be restored, because of
their adaptive and resilient capacity (Most et al., 2009).
Simenstad and Bottom (2002) recommend the following
principles that, although being developed in the context
of estuarine habitat restoration for salmon recovery for
654
SUSTAINABLE USE