248
G.E. Napolitano and D.S. Cicerone
of the total organic matter pool between the dissolved and the particulate
fractions. This work, and earlier studies, have shown that the concentration of
lipids in the particulate organic matter of lakes may sometimes be larger and
at other times smaller than the corresponding dissolved fraction (Meyers and
Owen, 1980; Larsson et a!., 1974). These differences highlight the importance of local physicochemical and biological processes in the fractionation of
lipids and other organic constituents between the dissolved and the particulate
fractions.
In general, 40-65% of the lipids of unpolluted surface microlayers are fatty
acids and triacylglycerols, whereas 15-30% are phospholipids and hydrocarbons
(Norkrans, 1980). Structural analysis of these lipids, in particular the examination
of the fatty acid composition, can provide valuable information for elucidating the
major sources of organic matter in the aquatic environment (e.g., algae, zooplankton, terrestrial plants; see below and Napolitano, this volume). Due to their
chemical stability, aliphatic hydrocarbons originating from algae and terrestrial
plant waxes may be an important lipid constituent in pristine environments
(Napolitano and Richmond, 1995; Napolitano et al., 1992; Marty and Choiniere,
1979). Detailed analyses of individual components, however, often reveal a petroleum origin of the hydrocarbons.
Analyses of LlC isotope ratios in hydrophobic and hydrophilic organic compounds in the foam and subsurface water from an eelgrass (Zostera marina) and
macroalgal habitat in the Duckabush River estuary (near Puget Sound, Washington) indicated that a substantial portion of the dissolved organic matter in
foams originated from sea grasses and macroalgal exudates (Wissmar and Simenstard, 1984). Hydrophobic organic compounds comprised between 6-48% of
the total dissolved organic matter of the Duckabush River. The highest concentrations of these compounds were found in the neritic subsurface water (48%),
macroalgal foam (47%), and foam and subsurface waters of the eelgrass habitat
(38%). A crude separation (Leenheer and Huffman, 1976) of the hydrophobic
organic matter of the estuary indicated that they mainly consisted of hydrocarbons
and high-molecular-weight organic acids, possibly fulvic material (Wissmar and
Simenstard, 1984).
Most biogeochemical studies of the lipid, especially those involving fatty acids
and biogenic hydrocarbons, indicate that algal exudates and terrestrial plant
detritus are the major sources of dissolved and particulate lipids in natural waters.
Analysis of the hydrophobic compounds in the surface microlayer (top 440 fLm)
and foam in the St. Lawrence River estuary (Marty and Choiniere, 1979) showed
fatty acids and alkanes as the major lipid components, at concentrations ranging
from 8 to 25 fLg . L -1 and 0.5 to 1.8 fLg . L -1, respectively. Hydrocarbons consisted of a series of n-alkenes, with dominance of odd-carbon numbered chains
over even-carbon numbered chains, where the major components were n-C25 and
n-C27. Petroleum hydrocarbons show no preference between odd-carbon numbered chains and even-carbon numbered chains (Napolitano et al., 1992; and
references therein). Therefore, the hydrocarbon constituents of foam and surface
microlayer materials from the St. Lawrence River pointed to a specific biogenic
G.E. Napolitano and D.S. Cicerone
of the total organic matter pool between the dissolved and the particulate
fractions. This work, and earlier studies, have shown that the concentration of
lipids in the particulate organic matter of lakes may sometimes be larger and
at other times smaller than the corresponding dissolved fraction (Meyers and
Owen, 1980; Larsson et a!., 1974). These differences highlight the importance of local physicochemical and biological processes in the fractionation of
lipids and other organic constituents between the dissolved and the particulate
fractions.
In general, 40-65% of the lipids of unpolluted surface microlayers are fatty
acids and triacylglycerols, whereas 15-30% are phospholipids and hydrocarbons
(Norkrans, 1980). Structural analysis of these lipids, in particular the examination
of the fatty acid composition, can provide valuable information for elucidating the
major sources of organic matter in the aquatic environment (e.g., algae, zooplankton, terrestrial plants; see below and Napolitano, this volume). Due to their
chemical stability, aliphatic hydrocarbons originating from algae and terrestrial
plant waxes may be an important lipid constituent in pristine environments
(Napolitano and Richmond, 1995; Napolitano et al., 1992; Marty and Choiniere,
1979). Detailed analyses of individual components, however, often reveal a petroleum origin of the hydrocarbons.
Analyses of LlC isotope ratios in hydrophobic and hydrophilic organic compounds in the foam and subsurface water from an eelgrass (Zostera marina) and
macroalgal habitat in the Duckabush River estuary (near Puget Sound, Washington) indicated that a substantial portion of the dissolved organic matter in
foams originated from sea grasses and macroalgal exudates (Wissmar and Simenstard, 1984). Hydrophobic organic compounds comprised between 6-48% of
the total dissolved organic matter of the Duckabush River. The highest concentrations of these compounds were found in the neritic subsurface water (48%),
macroalgal foam (47%), and foam and subsurface waters of the eelgrass habitat
(38%). A crude separation (Leenheer and Huffman, 1976) of the hydrophobic
organic matter of the estuary indicated that they mainly consisted of hydrocarbons
and high-molecular-weight organic acids, possibly fulvic material (Wissmar and
Simenstard, 1984).
Most biogeochemical studies of the lipid, especially those involving fatty acids
and biogenic hydrocarbons, indicate that algal exudates and terrestrial plant
detritus are the major sources of dissolved and particulate lipids in natural waters.
Analysis of the hydrophobic compounds in the surface microlayer (top 440 fLm)
and foam in the St. Lawrence River estuary (Marty and Choiniere, 1979) showed
fatty acids and alkanes as the major lipid components, at concentrations ranging
from 8 to 25 fLg . L -1 and 0.5 to 1.8 fLg . L -1, respectively. Hydrocarbons consisted of a series of n-alkenes, with dominance of odd-carbon numbered chains
over even-carbon numbered chains, where the major components were n-C25 and
n-C27. Petroleum hydrocarbons show no preference between odd-carbon numbered chains and even-carbon numbered chains (Napolitano et al., 1992; and
references therein). Therefore, the hydrocarbon constituents of foam and surface
microlayer materials from the St. Lawrence River pointed to a specific biogenic