10. Lipids in Water-Surface Microlayers and Foams - 247
(Blanchard and Syzdek, 1972). The material collected in the surface film is
subject to photochemical processes driven by ultraviolet light, which promotes the
decomposition of nitrate, iodine compounds, peptides, esters, and organic acids
(Zepp et aI., 1975; Antia and Landymore, 1974; Zafiriou, 1974; Bennett-Corriea
et aI., 1970; Miyake and Tsunogai, 1963).
Atmospheric wet and dry deposition provide dust particles to the surface microlayer (Hardy, 1982), which interact with the surface material (heavy metals,
organic compounds, and bacteria). Sinking of these particles and injection of
bubbles to the subsurface waters are the major mechanisms of material transport
out of the surface microlayer.
The relative importance of each of these factors varies widely and depends on
the particular environment factors and the prevailing meteorological and hydrological conditions. In addition, biologically driven processes, such as photosynthesis, respiration, bioaccumulation, and biodegradation, can alter the concentration and speciation of compounds present at the interface (Norkrans, 1980).
10.6. Lipids in the Water-Surface Microlayers and Foams
10.6.1. Total Lipids and Major Lipid Classes
Lipids, polysaccharides, and polypeptides are the major organic constituents of
the surface microlayers and foams (Velimirov, 1982; Barger and Garret, 1976).
Total dissolved organic carbon in the surface microlayer is estimated to range
from 0.5 to 2 g . L -1 (Stumm and Morgan, 1981), whereas the concentrations of
fatty acids (often the main dissolved lipid) may vary from about 10 to 90 f.Lg . L - 1
in the microlayer of lakes (Meyers and Owen, 1980) and from about 1 to 20
mg . L -1 in the microlayer of streams (Napolitano and Richmond, 1995). Many
studies have demonstrated that the concentration of lipids in the surface microlayers and foams is consistently higher than in the subsurface waters (Napolitano
and Richmond, 1995; Johnson et aI., 1989; Kattner and Brockmann, 1978;
Larsson et aI., 1974; Garrett, 1967; Harvey, 1966). The enrichment oflipids in the
surface microlayer is a consequence of their hydrophobicity, a low relative density (0.8-0.9), low vapor pressure, the presence of natural and anthropogenic
surfactants, and the special characteristics of the water microlayer as a solvent for
hydrophobic substances. Lipids in the surface microlayers are normally not only
more concentrated than in the subsurface water, but the chain length and saturation pattern of their fatty acid constituents are different (Meyers and Owen, 1980).
This observation implies that fatty acids in the microlayer and those from subsurface waters have a different origin, or alternatively, the observed differences arise
from physicochemical and biological processes that alter the lipid composition
during transport and accumulation into the microlayer.
Lipid contents and compositions of the surface micro layers and subsurface
waters of Lake Michigan were measured in an attempt to evaluate the relative importance of fluvial and autochthonous sources of organic matter (Meyers
and Owen, 1980). In this study, lipids were also used to investigate the partition
(Blanchard and Syzdek, 1972). The material collected in the surface film is
subject to photochemical processes driven by ultraviolet light, which promotes the
decomposition of nitrate, iodine compounds, peptides, esters, and organic acids
(Zepp et aI., 1975; Antia and Landymore, 1974; Zafiriou, 1974; Bennett-Corriea
et aI., 1970; Miyake and Tsunogai, 1963).
Atmospheric wet and dry deposition provide dust particles to the surface microlayer (Hardy, 1982), which interact with the surface material (heavy metals,
organic compounds, and bacteria). Sinking of these particles and injection of
bubbles to the subsurface waters are the major mechanisms of material transport
out of the surface microlayer.
The relative importance of each of these factors varies widely and depends on
the particular environment factors and the prevailing meteorological and hydrological conditions. In addition, biologically driven processes, such as photosynthesis, respiration, bioaccumulation, and biodegradation, can alter the concentration and speciation of compounds present at the interface (Norkrans, 1980).
10.6. Lipids in the Water-Surface Microlayers and Foams
10.6.1. Total Lipids and Major Lipid Classes
Lipids, polysaccharides, and polypeptides are the major organic constituents of
the surface microlayers and foams (Velimirov, 1982; Barger and Garret, 1976).
Total dissolved organic carbon in the surface microlayer is estimated to range
from 0.5 to 2 g . L -1 (Stumm and Morgan, 1981), whereas the concentrations of
fatty acids (often the main dissolved lipid) may vary from about 10 to 90 f.Lg . L - 1
in the microlayer of lakes (Meyers and Owen, 1980) and from about 1 to 20
mg . L -1 in the microlayer of streams (Napolitano and Richmond, 1995). Many
studies have demonstrated that the concentration of lipids in the surface microlayers and foams is consistently higher than in the subsurface waters (Napolitano
and Richmond, 1995; Johnson et aI., 1989; Kattner and Brockmann, 1978;
Larsson et aI., 1974; Garrett, 1967; Harvey, 1966). The enrichment oflipids in the
surface microlayer is a consequence of their hydrophobicity, a low relative density (0.8-0.9), low vapor pressure, the presence of natural and anthropogenic
surfactants, and the special characteristics of the water microlayer as a solvent for
hydrophobic substances. Lipids in the surface microlayers are normally not only
more concentrated than in the subsurface water, but the chain length and saturation pattern of their fatty acid constituents are different (Meyers and Owen, 1980).
This observation implies that fatty acids in the microlayer and those from subsurface waters have a different origin, or alternatively, the observed differences arise
from physicochemical and biological processes that alter the lipid composition
during transport and accumulation into the microlayer.
Lipid contents and compositions of the surface micro layers and subsurface
waters of Lake Michigan were measured in an attempt to evaluate the relative importance of fluvial and autochthonous sources of organic matter (Meyers
and Owen, 1980). In this study, lipids were also used to investigate the partition