Aside from degraded water and sediment quality, aquaculture operations also cause habitat conversion and changes
in hydrological regimes.
Introduced/invasive species
Organisms that are not endemic to an estuary, but are
introduced or invade the water body, can have significant
ecological impacts. Many species are introduced for commercial or recreational interests, an example being the
introduction of the striped bass (Morone saxatilis) to San
Francisco Bay (USA). In fact, the dominant species of
organisms in San Francisco Bay are mainly introduced
forms, with more than 200 nonindigenous species now
inhabiting bay waters and wetland habitat (Kennish,
2000). Some exotic species inhabiting estuaries have been
accidentally introduced via ballast water or some other
means. Nearly all estuaries are affected by introduced or
invasive species (Carlton and Geller, 1993; Kennish,
2002; Kennish et al., 2008)
Introduced and invasive species can be a danger to
the stability and biodiversity of an estuarine ecosystem.
In those cases where native controls are lacking, these species can have a significant competitive advantage, often
rapidly dominating plant or animal communities. The
food web structure is commonly disrupted, and native species may be displaced or greatly reduced in abundance.
Changes in species composition and distribution commonly occur (Cohen and Carlton, 1998). Species diversity
in these systems may drastically decline as well via intense
competition and predation. For instance, the Asian clam
(Potamocorbula amurensis), introduced into Suisun Bay
(USA), has decimated the phytoplankton community and
outcompeted the native shellfish species (Macoma
balthica and Mya arenaria).
The introduction or invasion of exotic species is
expected to increase in the future due to an expanding
world population, the effects of climate change, and
greater shipping and other human activities at sea and in
estuaries. These changes will likely promote additional
ecological disruption. More mariculture ventures, particularly in developing countries, will also add to these effects
(Kennish, 2002).
Human-altered hydrological regimes
As population growth increases in coastal regions, so does
the demand for freshwater to meet domestic, industrial,
and agricultural needs. The urbanization of coastal watersheds also results in greater impervious land cover leading
to accelerated freshwater runoff and higher river discharges. The increase in freshwater flow decreases the
water residence time in estuaries, while increasing their
capacity to dilute, transform, or flush contaminants
(Kennish, 2000). In contrast, dams and reservoirs
constructed upland reduce downstream freshwater flow.
Other changes that can significantly alter water-flow
regimes along coasts include channelization, marsh
impoundment, and wetland habitat destruction which
affect natural water storage capacity (Kennish et al.,
2008). Shifts in water quality and quantity are important
drivers of change in the abundance, distribution, reproductive success, and productivity of estuarine organisms
(Kennish, 2000). Estuarine circulation can also significantly change. The impact of freshwater diversions is perhaps best exemplified by San Francisco Bay (USA),
where 50 % of the freshwater flow has been diverted for
human use, resulting in a modified salinity regime as well
as altered biotic communities in the bay.
Freshwater diversions are used for ecological applications as well, such as coastal wetland restoration. Teal
et al. (2012), for example, discuss diversions of river water
into coastal wetlands as part of plans to mollify the areal loss
of coastal wetlands in Louisiana by reversing or slowing the
rates of degradation. However, freshwater diversions such
as those noted by Teal et al. (2012) can cause major changes
in estuarine water quality, notably large reductions in salinity and increased nutrient availability that affect plant communities, herbivory, and overall marsh stability.
The use of flood control structures has been shown to
completely modify some estuarine ecosystems. For example, acute changes in water inflow to the Haringvliet,
Grevelingenmeer, and Oosterschelde estuaries in southwest Netherlands occurred subsequent to the construction
of dikes to avert flooding problems, such as those incurred
in 1953, resulting in major changes in the physicalchemical conditions and biotic communities of the water
bodies. While the Oosterschelde remained a productive
estuary after these structural changes, the Haringvliet
basin was altered to a highly polluted freshwater body,
and the Grevelingenmeer became a saltwater system.
Tidal marshes and tidal flat habitats also changed considerably (Kennish et al., 2008). Changes such as those
observed in the Haringvliet, Grevelingenmeer, and
Oosterschelde estuaries demonstrate the magnitude of
human influence on coastal environments, particularly in
regard to human-altered hydrologic regimes.
Climate change
An accumulating database indicates that human factors
are important drivers of change of world climate
(Skinner, 2012). Increasing global temperatures, ascribed
in large part to carbon dioxide emissions, have been linked
to greater frequency and severity of damaging storms,
coastal flooding, droughts and fires, and other hazards
projected by climate forecasting models for the twentyfirst century (IPCC, 2007). Extreme climate events and
ongoing sea-level rise will be hazardous to coastal communities worldwide.
During the twentieth century, global sea-level rise
amounted to 0.5–30 cm, being largely attributed to the
increase in global surface temperatures (mean ¼ +0.6 Æ
0.2
C), melting of glaciers and ice sheets, and thermal
expansion of the oceans (IPCC, 2007). Global sea-level rise
during the twenty-first century is projected to increase by
52–98 cm (IPCC, 2013). Relative sea-level rise will be even
32
ANTHROPOGENIC IMPACTS
in hydrological regimes.
Introduced/invasive species
Organisms that are not endemic to an estuary, but are
introduced or invade the water body, can have significant
ecological impacts. Many species are introduced for commercial or recreational interests, an example being the
introduction of the striped bass (Morone saxatilis) to San
Francisco Bay (USA). In fact, the dominant species of
organisms in San Francisco Bay are mainly introduced
forms, with more than 200 nonindigenous species now
inhabiting bay waters and wetland habitat (Kennish,
2000). Some exotic species inhabiting estuaries have been
accidentally introduced via ballast water or some other
means. Nearly all estuaries are affected by introduced or
invasive species (Carlton and Geller, 1993; Kennish,
2002; Kennish et al., 2008)
Introduced and invasive species can be a danger to
the stability and biodiversity of an estuarine ecosystem.
In those cases where native controls are lacking, these species can have a significant competitive advantage, often
rapidly dominating plant or animal communities. The
food web structure is commonly disrupted, and native species may be displaced or greatly reduced in abundance.
Changes in species composition and distribution commonly occur (Cohen and Carlton, 1998). Species diversity
in these systems may drastically decline as well via intense
competition and predation. For instance, the Asian clam
(Potamocorbula amurensis), introduced into Suisun Bay
(USA), has decimated the phytoplankton community and
outcompeted the native shellfish species (Macoma
balthica and Mya arenaria).
The introduction or invasion of exotic species is
expected to increase in the future due to an expanding
world population, the effects of climate change, and
greater shipping and other human activities at sea and in
estuaries. These changes will likely promote additional
ecological disruption. More mariculture ventures, particularly in developing countries, will also add to these effects
(Kennish, 2002).
Human-altered hydrological regimes
As population growth increases in coastal regions, so does
the demand for freshwater to meet domestic, industrial,
and agricultural needs. The urbanization of coastal watersheds also results in greater impervious land cover leading
to accelerated freshwater runoff and higher river discharges. The increase in freshwater flow decreases the
water residence time in estuaries, while increasing their
capacity to dilute, transform, or flush contaminants
(Kennish, 2000). In contrast, dams and reservoirs
constructed upland reduce downstream freshwater flow.
Other changes that can significantly alter water-flow
regimes along coasts include channelization, marsh
impoundment, and wetland habitat destruction which
affect natural water storage capacity (Kennish et al.,
2008). Shifts in water quality and quantity are important
drivers of change in the abundance, distribution, reproductive success, and productivity of estuarine organisms
(Kennish, 2000). Estuarine circulation can also significantly change. The impact of freshwater diversions is perhaps best exemplified by San Francisco Bay (USA),
where 50 % of the freshwater flow has been diverted for
human use, resulting in a modified salinity regime as well
as altered biotic communities in the bay.
Freshwater diversions are used for ecological applications as well, such as coastal wetland restoration. Teal
et al. (2012), for example, discuss diversions of river water
into coastal wetlands as part of plans to mollify the areal loss
of coastal wetlands in Louisiana by reversing or slowing the
rates of degradation. However, freshwater diversions such
as those noted by Teal et al. (2012) can cause major changes
in estuarine water quality, notably large reductions in salinity and increased nutrient availability that affect plant communities, herbivory, and overall marsh stability.
The use of flood control structures has been shown to
completely modify some estuarine ecosystems. For example, acute changes in water inflow to the Haringvliet,
Grevelingenmeer, and Oosterschelde estuaries in southwest Netherlands occurred subsequent to the construction
of dikes to avert flooding problems, such as those incurred
in 1953, resulting in major changes in the physicalchemical conditions and biotic communities of the water
bodies. While the Oosterschelde remained a productive
estuary after these structural changes, the Haringvliet
basin was altered to a highly polluted freshwater body,
and the Grevelingenmeer became a saltwater system.
Tidal marshes and tidal flat habitats also changed considerably (Kennish et al., 2008). Changes such as those
observed in the Haringvliet, Grevelingenmeer, and
Oosterschelde estuaries demonstrate the magnitude of
human influence on coastal environments, particularly in
regard to human-altered hydrologic regimes.
Climate change
An accumulating database indicates that human factors
are important drivers of change of world climate
(Skinner, 2012). Increasing global temperatures, ascribed
in large part to carbon dioxide emissions, have been linked
to greater frequency and severity of damaging storms,
coastal flooding, droughts and fires, and other hazards
projected by climate forecasting models for the twentyfirst century (IPCC, 2007). Extreme climate events and
ongoing sea-level rise will be hazardous to coastal communities worldwide.
During the twentieth century, global sea-level rise
amounted to 0.5–30 cm, being largely attributed to the
increase in global surface temperatures (mean ¼ +0.6 Æ
0.2
C), melting of glaciers and ice sheets, and thermal
expansion of the oceans (IPCC, 2007). Global sea-level rise
during the twenty-first century is projected to increase by
52–98 cm (IPCC, 2013). Relative sea-level rise will be even
32
ANTHROPOGENIC IMPACTS