pathways whereby pathogens can invade a host, and
principal pathways have different episodic time frames.
Description
Estuaries form buffer zones between rivers and oceans,
where many anthropogenic inputs and pathogens are
trapped or modified via several mechanisms, including
dispersal within the estuary, burial, wind-induced flushing, or storage in bottom sediments. The range of mechanisms operating in each estuary depends on hydrographic
forcing, but the length of time pathogenic organisms
remain viable and pose a risk to public health is contingent
on their deposition, lifestyle in sediments, and
resuspension. Further, pathogens have the potential to persist or even proliferate in estuaries (Noble and Fries,
2007). This suggests that, once fecal bacteria and other
pathogens enter the aquatic environment, they should be
able to establish long-term reservoirs, depending on their
ability to acclimate and tolerate a range of environmental
conditions (Miller et al., 2006).
Monitoring of microbial contamination of inland waters
and estuaries usually focuses on their inputs during rainfall.
Sediments may represent a significant source of pathogen
populations during resuspension events that can be driven
by wind without rainfall or by wind coincident with rainfall
in shallow systems (Noble and Fries, 2007).
An increase of pathogen bacteria in invertebrates
exposed to human sewage sources suggests that anthropogenic activities can have significant effects on the ecology
of fecal bacteria pathogens at the land–sea interface. Additional research is needed to minimize the impacts of
human and animal pathogens on estuarine and coastal
marine environments for their long-term sustainability
and health (Collins and Rutherford, 2004).
Bibliography
Collins, R., and Rutherford, K., 2004. Modelling bacterial water
quality in streams draining pastoral lands. Water Research, 38,
700–712.
Miller, W. A., Miller, M. A., Gardner, I. A., Atwill, E. R., Byrne,
B. A., Jang, S., Harris, M., Ames, J., Jessup, D., Paradies, D.,
Worcester, D., Melli, A., and Conrad, A. P., 2006. Salmonella
spp., Vibrio spp., Clostridium perfringens, and Plesiomonas
shigelloides in marine and freshwater Invertebrates from Coastal
California Ecosystems. Microbial Ecology: Coastal Invertebrate Bacterial Ecology, 52, 198–206.
Noble, R. T., and Fries, J. S., 2007. Estuarine sediment beds as
a reservoir for human pathogens: monitoring transport of
populations of enterococci and Vibrio sp., in the Neuse River
Estuary. Technical Report. Chapel Hill: University of North
Carolina, UNC-WRRI-368 Project No. 70214.
Cross-references
Microbial Degradation
Microbial Survivability
PEAT
Xavier Comas
Department of Geosciences, Florida Atlantic University,
Boca Raton, FL, USA
Synonyms
Histosol; Humate; Peat soil; Turf
Definition
Peat is the accumulation of partly decomposed vegetable
matter generally containing less than 20 % inorganic
matter.
Introduction
Peat is an organic soil composed of partially to welldecomposed plant remains, which accumulate in a wet
environment. Formation of peat occurs under wetland
conditions, where land is saturated with water and
flooding obstructs the flow of oxygen from the atmosphere which results in slowing down of decomposition
rates (Keddy, 2010). Accumulation therefore occurs only
under anoxic (i.e., no oxygen) conditions. Peat exhibits
very unique physical and chemical properties unlike any
other geological material, particularly in terms of porosity,
water-holding capacity, and organic matter content. Peat
soils are important sources of carbon-based greenhouse
gases such as methane and carbon dioxide; however, the
role of these gases in the global carbon cycle
(particularly in terms of spatial and temporal variability
in production and release to the atmosphere) is currently
unclear. For that reason, the effect of peat-accumulating
environments in future climate and global warming is currently not well understood. Although plant remains in
current peats differ from those found in coals, peat is considered the precursor of coal after diagenetic and metamorphic compressional changes, and it is well accepted
that most coal deposits of economic value formed from
ombrotrophic (or precipitation-fed) peats rather than
rheotrophic/minerotrophic (or groundwater-fed) peat
(Clymo, 1987; Moore and Shearer, 2003).
Physicochemical characteristics of peat
Peat exhibits very unique physical properties when compared to inorganic sediments, including very low bulk
density and a very high water-holding capacity. Bulk density (or dry weight of soil per unit volume) tends to range
between 0.2 and 0.3 g cm
À3 for well-decomposed peat;
however, certain peat types (such as Sphagnum moss)
may go as low as 0.04 g cm
À3
. Total porosity
(or percentage of total pore space per volume) is very high
and ranges between 80 % and 95 % (Hobbs, 1986; Baird
and Waldron, 2003), although effective porosity
(or percentage of interconnected pore space per volume)
tends to be low and ranging from 10 % to 40 %
476
PEAT
principal pathways have different episodic time frames.
Description
Estuaries form buffer zones between rivers and oceans,
where many anthropogenic inputs and pathogens are
trapped or modified via several mechanisms, including
dispersal within the estuary, burial, wind-induced flushing, or storage in bottom sediments. The range of mechanisms operating in each estuary depends on hydrographic
forcing, but the length of time pathogenic organisms
remain viable and pose a risk to public health is contingent
on their deposition, lifestyle in sediments, and
resuspension. Further, pathogens have the potential to persist or even proliferate in estuaries (Noble and Fries,
2007). This suggests that, once fecal bacteria and other
pathogens enter the aquatic environment, they should be
able to establish long-term reservoirs, depending on their
ability to acclimate and tolerate a range of environmental
conditions (Miller et al., 2006).
Monitoring of microbial contamination of inland waters
and estuaries usually focuses on their inputs during rainfall.
Sediments may represent a significant source of pathogen
populations during resuspension events that can be driven
by wind without rainfall or by wind coincident with rainfall
in shallow systems (Noble and Fries, 2007).
An increase of pathogen bacteria in invertebrates
exposed to human sewage sources suggests that anthropogenic activities can have significant effects on the ecology
of fecal bacteria pathogens at the land–sea interface. Additional research is needed to minimize the impacts of
human and animal pathogens on estuarine and coastal
marine environments for their long-term sustainability
and health (Collins and Rutherford, 2004).
Bibliography
Collins, R., and Rutherford, K., 2004. Modelling bacterial water
quality in streams draining pastoral lands. Water Research, 38,
700–712.
Miller, W. A., Miller, M. A., Gardner, I. A., Atwill, E. R., Byrne,
B. A., Jang, S., Harris, M., Ames, J., Jessup, D., Paradies, D.,
Worcester, D., Melli, A., and Conrad, A. P., 2006. Salmonella
spp., Vibrio spp., Clostridium perfringens, and Plesiomonas
shigelloides in marine and freshwater Invertebrates from Coastal
California Ecosystems. Microbial Ecology: Coastal Invertebrate Bacterial Ecology, 52, 198–206.
Noble, R. T., and Fries, J. S., 2007. Estuarine sediment beds as
a reservoir for human pathogens: monitoring transport of
populations of enterococci and Vibrio sp., in the Neuse River
Estuary. Technical Report. Chapel Hill: University of North
Carolina, UNC-WRRI-368 Project No. 70214.
Cross-references
Microbial Degradation
Microbial Survivability
PEAT
Xavier Comas
Department of Geosciences, Florida Atlantic University,
Boca Raton, FL, USA
Synonyms
Histosol; Humate; Peat soil; Turf
Definition
Peat is the accumulation of partly decomposed vegetable
matter generally containing less than 20 % inorganic
matter.
Introduction
Peat is an organic soil composed of partially to welldecomposed plant remains, which accumulate in a wet
environment. Formation of peat occurs under wetland
conditions, where land is saturated with water and
flooding obstructs the flow of oxygen from the atmosphere which results in slowing down of decomposition
rates (Keddy, 2010). Accumulation therefore occurs only
under anoxic (i.e., no oxygen) conditions. Peat exhibits
very unique physical and chemical properties unlike any
other geological material, particularly in terms of porosity,
water-holding capacity, and organic matter content. Peat
soils are important sources of carbon-based greenhouse
gases such as methane and carbon dioxide; however, the
role of these gases in the global carbon cycle
(particularly in terms of spatial and temporal variability
in production and release to the atmosphere) is currently
unclear. For that reason, the effect of peat-accumulating
environments in future climate and global warming is currently not well understood. Although plant remains in
current peats differ from those found in coals, peat is considered the precursor of coal after diagenetic and metamorphic compressional changes, and it is well accepted
that most coal deposits of economic value formed from
ombrotrophic (or precipitation-fed) peats rather than
rheotrophic/minerotrophic (or groundwater-fed) peat
(Clymo, 1987; Moore and Shearer, 2003).
Physicochemical characteristics of peat
Peat exhibits very unique physical properties when compared to inorganic sediments, including very low bulk
density and a very high water-holding capacity. Bulk density (or dry weight of soil per unit volume) tends to range
between 0.2 and 0.3 g cm
À3 for well-decomposed peat;
however, certain peat types (such as Sphagnum moss)
may go as low as 0.04 g cm
À3
. Total porosity
(or percentage of total pore space per volume) is very high
and ranges between 80 % and 95 % (Hobbs, 1986; Baird
and Waldron, 2003), although effective porosity
(or percentage of interconnected pore space per volume)
tends to be low and ranging from 10 % to 40 %
476
PEAT