and marine organisms. Substances such as aromatic and
aliphatic hydrocarbons derived from oil spills and seepages, as well as volatile organic compounds, can be
acutely toxic to biotic communities (Kennish, 1997).
The halogenated hydrocarbons are a ubiquitous group
of environmental contaminants consisting of low- to
high-molecular-weight compounds. Examples are organochlorine biocides (insecticides, herbicides, and fungicides),
low-molecular-weight compounds (chlorofluorocarbons),
and high-molecular-weight chemicals (chlorinated
aromatics and chlorinated paraffins). PCBs and DDT are
two of the most notable halogenated hydrocarbons that
have historically impacted estuarine environments
(Kennish, 2001a).
PAHs consist of a group of chemical carcinogens,
mutagens, and teratogens that originate from both natural
(e.g., volcanic activity and oil seeps) and anthropogenic
sources, although the inputs from anthropogenic sources
(e.g., fossil fuel combustion, waste incineration, municipal and industrial wastewaters, and land runoff)
typically predominate in estuaries (Kennish, 1992).
The low-molecular-weight PAHs are more toxic than the
high-molecular-weight forms. Hepatic neoplasia and
other diseases in aquatic organisms have been attributed
to PAH exposure (Kennish, 1997). A range of biochemical, physiological, behavioral, and other sublethal
responses has also been documented in estuarine organisms that can adversely affect biotic community structure.
Oil spills and leakages from marine vessels and fixed
installations, as well as from nonpoint-source inputs from
coastal watersheds, are hazardous to estuarine organisms
and habitats. The lethal and sublethal effects of polluting
oil on estuarine and marine organisms are well established
(Kennish, 1992, 1997, 2001a). Both aromatic and aliphatic components are problematic as noted above. Benthic organisms are particularly susceptible to oil
accumulation, and contaminated habitats such as salt
marsh systems can be adversely impacted by the oil for
decades due to oil-contaminated sediments which are hazardous to settlement and recruitment of the organisms.
Metals
The literature is replete with pathological responses of
estuarine and marine organisms to toxic levels of metals,
including neurological, digestive, reproductive, and respiratory disorders, tissue inflammation and degeneration,
and developmental abnormalities. Feeding behavior and
growth inhibition are commonly observed. Transition
metals (e.g., copper, cobalt, iron, and manganese), metalloids (e.g., arsenic, cadmium, lead, mercury, selenium,
and tin), and organometals (e.g., methylmercury, tributyltin, and alkylated lead) can be toxic, particularly the
organometals (Kennish, 1997; Kennish, 1998; Kennish
et al., 2008). Metals are persistent in estuarine environments. They tend to bioaccumulate in organisms, and
some metals such as methylmercury undergo biomagnification, with highest levels found in upper-trophic-level
organisms that often serve as a food source for humans.
Hence, the health of humans consuming metalcontaminated seafood can be impaired. There are many
potential sources of metals in estuaries, including industrial activity (e.g., mining, smelting, refining, and
electroplating operations), fossil fuel combustion, landfill
leachates, shipping, marinas, and ash disposal. Delivery
pathways are river discharges, groundwater inputs, and
atmospheric deposition.
Human-induced sediment/particulate inputs
Human activities in coastal watersheds have facilitated
inputs of sediments and other particulates to estuaries.
The removal of natural vegetation and increase in impervious cover with watershed development hasten the delivery
of sediments to estuarine basins. Silviculture operations,
particularly in developing countries, have dramatically
increased sediment loads to coastal areas (Kennish et al.,
2008). One of the adverse effects is altered water and sediment quality. An increase in water column turbidity leads
to the attenuation of light and shading of the estuarine
floor that can reduce primary production and cause
a decline of seagrasses and other essential benthic habitat.
For example, Moore et al. (2012, 2014) correlated dieback
of seagrasses in the Chesapeake Bay system in part to elevated turbidity levels.
Overfishing
Overfishing or overharvesting of finfish and shellfish
populations not only results in depleted stocks but also the
alteration of the food web structure of estuaries. While estuaries historically have had exceptional recreational and
commercial fisheries, overexploitation of the biotic
resources has been a concern through time. In
mid-Atlantic coastal bays, overharvesting of shellfish,
together with disease and predation, has been implicated
in the dramatic decline of oyster and hard clam populations.
Overfishing may have played an important role in the
decline of Chinook salmon (Oncorhynchus tshawytscha),
delta smelt (Hypomesus transpacificus), and striped bass
(Morone saxatilis) fisheries in San Francisco Bay (USA)
after the 1970s. Similarly, overfishing may have been
a factor in the reduction of commercial finfisheries in
Albemarle-Pamlico Sounds, North Carolina, and Sarasota
Bay, Florida (Kennish, 2000).
Intensive aquaculture
A significant amount of the seafood consumed by humans
(>25 %) now derives from aquaculture, which may partially compensate for overfishing (Engelman et al., 2008).
Shellfish aquaculture predominates in countries of the Far
East (e.g., China, Vietnam, and the Philippines). Much finfish aquaculture also occurs in countries of the Far East, but
in many other countries as well. Intensive aquaculture has
caused considerable coastal pollution, water and sediment
quality degradation, and diseases resulting from the feces
and uneaten food of the feedlot operations (New, 2002).
ANTHROPOGENIC IMPACTS
31
aliphatic hydrocarbons derived from oil spills and seepages, as well as volatile organic compounds, can be
acutely toxic to biotic communities (Kennish, 1997).
The halogenated hydrocarbons are a ubiquitous group
of environmental contaminants consisting of low- to
high-molecular-weight compounds. Examples are organochlorine biocides (insecticides, herbicides, and fungicides),
low-molecular-weight compounds (chlorofluorocarbons),
and high-molecular-weight chemicals (chlorinated
aromatics and chlorinated paraffins). PCBs and DDT are
two of the most notable halogenated hydrocarbons that
have historically impacted estuarine environments
(Kennish, 2001a).
PAHs consist of a group of chemical carcinogens,
mutagens, and teratogens that originate from both natural
(e.g., volcanic activity and oil seeps) and anthropogenic
sources, although the inputs from anthropogenic sources
(e.g., fossil fuel combustion, waste incineration, municipal and industrial wastewaters, and land runoff)
typically predominate in estuaries (Kennish, 1992).
The low-molecular-weight PAHs are more toxic than the
high-molecular-weight forms. Hepatic neoplasia and
other diseases in aquatic organisms have been attributed
to PAH exposure (Kennish, 1997). A range of biochemical, physiological, behavioral, and other sublethal
responses has also been documented in estuarine organisms that can adversely affect biotic community structure.
Oil spills and leakages from marine vessels and fixed
installations, as well as from nonpoint-source inputs from
coastal watersheds, are hazardous to estuarine organisms
and habitats. The lethal and sublethal effects of polluting
oil on estuarine and marine organisms are well established
(Kennish, 1992, 1997, 2001a). Both aromatic and aliphatic components are problematic as noted above. Benthic organisms are particularly susceptible to oil
accumulation, and contaminated habitats such as salt
marsh systems can be adversely impacted by the oil for
decades due to oil-contaminated sediments which are hazardous to settlement and recruitment of the organisms.
Metals
The literature is replete with pathological responses of
estuarine and marine organisms to toxic levels of metals,
including neurological, digestive, reproductive, and respiratory disorders, tissue inflammation and degeneration,
and developmental abnormalities. Feeding behavior and
growth inhibition are commonly observed. Transition
metals (e.g., copper, cobalt, iron, and manganese), metalloids (e.g., arsenic, cadmium, lead, mercury, selenium,
and tin), and organometals (e.g., methylmercury, tributyltin, and alkylated lead) can be toxic, particularly the
organometals (Kennish, 1997; Kennish, 1998; Kennish
et al., 2008). Metals are persistent in estuarine environments. They tend to bioaccumulate in organisms, and
some metals such as methylmercury undergo biomagnification, with highest levels found in upper-trophic-level
organisms that often serve as a food source for humans.
Hence, the health of humans consuming metalcontaminated seafood can be impaired. There are many
potential sources of metals in estuaries, including industrial activity (e.g., mining, smelting, refining, and
electroplating operations), fossil fuel combustion, landfill
leachates, shipping, marinas, and ash disposal. Delivery
pathways are river discharges, groundwater inputs, and
atmospheric deposition.
Human-induced sediment/particulate inputs
Human activities in coastal watersheds have facilitated
inputs of sediments and other particulates to estuaries.
The removal of natural vegetation and increase in impervious cover with watershed development hasten the delivery
of sediments to estuarine basins. Silviculture operations,
particularly in developing countries, have dramatically
increased sediment loads to coastal areas (Kennish et al.,
2008). One of the adverse effects is altered water and sediment quality. An increase in water column turbidity leads
to the attenuation of light and shading of the estuarine
floor that can reduce primary production and cause
a decline of seagrasses and other essential benthic habitat.
For example, Moore et al. (2012, 2014) correlated dieback
of seagrasses in the Chesapeake Bay system in part to elevated turbidity levels.
Overfishing
Overfishing or overharvesting of finfish and shellfish
populations not only results in depleted stocks but also the
alteration of the food web structure of estuaries. While estuaries historically have had exceptional recreational and
commercial fisheries, overexploitation of the biotic
resources has been a concern through time. In
mid-Atlantic coastal bays, overharvesting of shellfish,
together with disease and predation, has been implicated
in the dramatic decline of oyster and hard clam populations.
Overfishing may have played an important role in the
decline of Chinook salmon (Oncorhynchus tshawytscha),
delta smelt (Hypomesus transpacificus), and striped bass
(Morone saxatilis) fisheries in San Francisco Bay (USA)
after the 1970s. Similarly, overfishing may have been
a factor in the reduction of commercial finfisheries in
Albemarle-Pamlico Sounds, North Carolina, and Sarasota
Bay, Florida (Kennish, 2000).
Intensive aquaculture
A significant amount of the seafood consumed by humans
(>25 %) now derives from aquaculture, which may partially compensate for overfishing (Engelman et al., 2008).
Shellfish aquaculture predominates in countries of the Far
East (e.g., China, Vietnam, and the Philippines). Much finfish aquaculture also occurs in countries of the Far East, but
in many other countries as well. Intensive aquaculture has
caused considerable coastal pollution, water and sediment
quality degradation, and diseases resulting from the feces
and uneaten food of the feedlot operations (New, 2002).
ANTHROPOGENIC IMPACTS
31