matter regeneration is an indirect indicator of estuarine
water quality.
Impacts: This process can consume dissolved oxygen
(DO) faster than the atmosphere can supply it through
diffusion or the autotrophic community (algae,
cyanobacteria, and macrophytes) can produce it. Decomposition of organic matter may fully deplete oxygen from
the water (Kennish, 1997). Since less dissolved oxygen is
available in the water, fishes and other aquatic organisms
may not survive.
Analytical Method: This method of determination is
based on dissolved oxygen (DO) measurements. In the
first measurement, two or more bottles of water samples
are collected. The oxygen is measured in sample 1 on
the first day, and 5 days later, it is measured in sample
2. Next, the BOD is calculated by subtracting the results.
The BOD may reach 7 mg/l in productive estuaries
compared with values higher than 7 mg/l in polluted estuaries (APHA, 1999).
Estuarine Dynamics: Aquatic plant photosynthesis
raises the DO during the day, and respiration lowers it at
night in estuaries (Day et al., 2013). This leads to a large
diurnal variation in the availability of dissolved oxygen.
Meteorological variations and estuarine dynamics have
a large influence on the dilution and transport of organic
matter. During high tide, more oxygenated coastal waters
are encountered, increasing the availability of dissolved
oxygen. The lower dissolved oxygen levels are generally
found in lower-salinity regions in the upper estuary. When
the runoff is high, more freshwater enters the estuary often
transporting higher loads of organic wastes into the
system.
Limitation: BOD measures the pollution potential. It is
an indirect quantification of the potential impact, not
a direct measurement of such impact. BOD 5, 20 does not
detect nonbiodegradable matter. It does not consider toxicity, nor does it inhibit effects from materials on microbial
activity because it only measures the oxygen consumed
in a standardized test. The BOD is a subset of the chemical
oxygen demand (COD).
Bibliography
APHA, 1999. Standard Methods for the Examination of Water and
Wastewater, 18th edn. Washington, D.C.: American Public
Health Association.
Day, J. W., Kemp, M. W., Yánez-Arancibia, A., and Crump, B. C.,
2012. Estuarine Ecology, 2nd edn. Hoboken: Wiley-Blackwell.
Kennish, M. J., 1997. Practical Handbook of Estuarine and Marine
Pollution. Boca Raton, FL: CRC Press.
Cross-references
Dissolved Oxygen
Eutrophication
Heterotrophic
Nonpoint Source Pollution
Oxygen Depletion
BIOGENIC SEDIMENTARY STRUCTURES
Luca Ragaini
Department of Earth Sciences, University of Pisa, Pisa, Italy
Synonyms
Ichnofossils; Trace fossils
Definition
Biogenic sedimentary structures are evidence of
organism–substrate interactions preserved in rocks and
sediments, including those recorded in estuarine environments. Their study is termed “paleoichnology” (from the
Greek palaios ¼ old, ancient and ichnos ¼ a trace,
a track), whereas similar studies in modern sediments are
referred to as “neoichnology.” Markings that do not reflect
the behavior of organisms (e.g., marks made by the shells
of dead mollusks passively transported on the seafloor by
waves and/or currents) are excluded from the trace fossils.
In addition, biogenic sedimentary structures do not
include body fossils (direct remains, such as shells, bones,
teeth, etc.) or molds of organism bodies.
Introduction
Organisms that have adopted endobenthic or epibenthic
modes of life produce biogenic sedimentary structures
by “disturbing” the substrate. The number of biogenic sedimentary structures is vast, and various authors have proposed subdividing them into component groups to better
define their significance (e.g., Frey, 1971, 1973; Frey
and Pemberton, 1984; Pemberton et al., 1992; Bromley,
1996). Four major categories of structures produced by
the activities of organisms are generally accepted:
– Bioturbation structures, which reflect the disruption by
organisms of biogenic and physical stratification features or sediment fabrics, include tracks, trails, burrows, and similar structures.
– Biostratification structures, which consist of stratification features imparted by organism activities, include
certain stromatolites, biogenic graded bedding, byssal
mats, and similar elements.
– Biodepositional structures, which reflect the production or concentration of sediments, include coprolites,
fecal pellets, pseudofeces, and fecal castings.
– Bioerosion structures, which are mechanically or biochemically produced by organisms in rigid substrates,
include borings, rasps and scrapes, bites, drill holes,
and related traces.
These categories, and others proposed in the literature,
are not exhaustive because the divisions among the various categories are vague. For example, plant–arthropod
interactions may be revealed by biogenic structures
preserved in wood, leaves, and seeds, which are not strictly
rigid substrates comparable to rockgrounds or hardgrounds.
76
BIOGENIC SEDIMENTARY STRUCTURES
water quality.
Impacts: This process can consume dissolved oxygen
(DO) faster than the atmosphere can supply it through
diffusion or the autotrophic community (algae,
cyanobacteria, and macrophytes) can produce it. Decomposition of organic matter may fully deplete oxygen from
the water (Kennish, 1997). Since less dissolved oxygen is
available in the water, fishes and other aquatic organisms
may not survive.
Analytical Method: This method of determination is
based on dissolved oxygen (DO) measurements. In the
first measurement, two or more bottles of water samples
are collected. The oxygen is measured in sample 1 on
the first day, and 5 days later, it is measured in sample
2. Next, the BOD is calculated by subtracting the results.
The BOD may reach 7 mg/l in productive estuaries
compared with values higher than 7 mg/l in polluted estuaries (APHA, 1999).
Estuarine Dynamics: Aquatic plant photosynthesis
raises the DO during the day, and respiration lowers it at
night in estuaries (Day et al., 2013). This leads to a large
diurnal variation in the availability of dissolved oxygen.
Meteorological variations and estuarine dynamics have
a large influence on the dilution and transport of organic
matter. During high tide, more oxygenated coastal waters
are encountered, increasing the availability of dissolved
oxygen. The lower dissolved oxygen levels are generally
found in lower-salinity regions in the upper estuary. When
the runoff is high, more freshwater enters the estuary often
transporting higher loads of organic wastes into the
system.
Limitation: BOD measures the pollution potential. It is
an indirect quantification of the potential impact, not
a direct measurement of such impact. BOD 5, 20 does not
detect nonbiodegradable matter. It does not consider toxicity, nor does it inhibit effects from materials on microbial
activity because it only measures the oxygen consumed
in a standardized test. The BOD is a subset of the chemical
oxygen demand (COD).
Bibliography
APHA, 1999. Standard Methods for the Examination of Water and
Wastewater, 18th edn. Washington, D.C.: American Public
Health Association.
Day, J. W., Kemp, M. W., Yánez-Arancibia, A., and Crump, B. C.,
2012. Estuarine Ecology, 2nd edn. Hoboken: Wiley-Blackwell.
Kennish, M. J., 1997. Practical Handbook of Estuarine and Marine
Pollution. Boca Raton, FL: CRC Press.
Cross-references
Dissolved Oxygen
Eutrophication
Heterotrophic
Nonpoint Source Pollution
Oxygen Depletion
BIOGENIC SEDIMENTARY STRUCTURES
Luca Ragaini
Department of Earth Sciences, University of Pisa, Pisa, Italy
Synonyms
Ichnofossils; Trace fossils
Definition
Biogenic sedimentary structures are evidence of
organism–substrate interactions preserved in rocks and
sediments, including those recorded in estuarine environments. Their study is termed “paleoichnology” (from the
Greek palaios ¼ old, ancient and ichnos ¼ a trace,
a track), whereas similar studies in modern sediments are
referred to as “neoichnology.” Markings that do not reflect
the behavior of organisms (e.g., marks made by the shells
of dead mollusks passively transported on the seafloor by
waves and/or currents) are excluded from the trace fossils.
In addition, biogenic sedimentary structures do not
include body fossils (direct remains, such as shells, bones,
teeth, etc.) or molds of organism bodies.
Introduction
Organisms that have adopted endobenthic or epibenthic
modes of life produce biogenic sedimentary structures
by “disturbing” the substrate. The number of biogenic sedimentary structures is vast, and various authors have proposed subdividing them into component groups to better
define their significance (e.g., Frey, 1971, 1973; Frey
and Pemberton, 1984; Pemberton et al., 1992; Bromley,
1996). Four major categories of structures produced by
the activities of organisms are generally accepted:
– Bioturbation structures, which reflect the disruption by
organisms of biogenic and physical stratification features or sediment fabrics, include tracks, trails, burrows, and similar structures.
– Biostratification structures, which consist of stratification features imparted by organism activities, include
certain stromatolites, biogenic graded bedding, byssal
mats, and similar elements.
– Biodepositional structures, which reflect the production or concentration of sediments, include coprolites,
fecal pellets, pseudofeces, and fecal castings.
– Bioerosion structures, which are mechanically or biochemically produced by organisms in rigid substrates,
include borings, rasps and scrapes, bites, drill holes,
and related traces.
These categories, and others proposed in the literature,
are not exhaustive because the divisions among the various categories are vague. For example, plant–arthropod
interactions may be revealed by biogenic structures
preserved in wood, leaves, and seeds, which are not strictly
rigid substrates comparable to rockgrounds or hardgrounds.
76
BIOGENIC SEDIMENTARY STRUCTURES