250
G.E. Napolitano and D.S. Cicerone
>50 (Johnson et aI., 1989). Using 14C_ and 32P-Iabeled lipids, Sodergren (1979)
also found that the polar lipid classes of the water micro layer of an experimental
microcosm had an enrichment factor greater than that of neutral lipids.
Lipid content and lipid class compositions were recently analyzed in the subsurface water and foam samples from a series of streams in eastern Tennessee
(Napolitano and Richmond, 1995). Concentrations of total lipids were always
greater in the foam than in the subsurface water from the same site. Concentrations of lipids in foam ranged from 10 to 110 mg . L - 1, showing enrichments
factors of up to 100. Eight lipid classes were detected in water and foam samples:
free fatty acids, phospholipids, hydrocarbons, and acetone mobile polar lipids
accounted for >50% of the total lipids. Other detectable components were sterols,
diacylglycerols, fatty alcohols, triacylglycerols, and sterol esters. Relatively large
concentrations of phospholipids (labile celIular lipids that decompose rapidly
after the organism dies) measured in some stream foams, indicating that viable
bacteria, protozoa, and/or algae were probably major contributors to the pool of
particulate organic matter. A more detailed analysis of taxonomicalIy specific
signature lipids (i.e., fatty acids and sterols) by gas chromatography could be used
to identify which of these groups or organisms predominate (Tunlid and White,
1992). The main by-products of the enzymatic hydrolysis of phospholipids are
free fatty acids. Large quantities of free fatty acids coinciding with low levels of
phospholipids were observed in water from some streams (Napolitano and Richmond, 1995), which provides an indication that biological decay of organic matter
was a dominant process in the foam at these sites.
The metabolic processes that can be inferred from the analysis of biochemical
constituents in the foam are not necessarily linked to the conditions in the entire
body of water; instead, they reflect highly localized and specific biological processes that occur within the foams and in the water-surface microlayer. A more
general evaluation of stream condition arises from measurements of hydrocarbons. Biogenic hydrocarbons are commonly extracted from uncontaminated waters or organisms. However, the natural hydrocarbons typicalIy account for only a
smalI proportion (typicalIy <5%) of the total lipids (Nevenzel, 1989). The presence of hydrocarbons at 10-30% oflipids in foams (Johnson et aI., 1989) strongly
suggests petroleum contamination. Hydrocarbons present in foam from smalI
streams in eastern Tennessee (Napolitano and Richmond, 1995) consisted of an
intricate mixture of many compounds, dominated by a series of aliphatic, straightchain alkanes, containing 13-32 carbon atoms, with a maximum at C-25. Also
present were minor amounts of the isoprenoid hydrocarbons pristane (2,6, 10,14tretramethyl-pentahexane), phytane (2,6, 10, 14-tetramethyl-hexadecane), and a
CPI of 2.49. This hydrocarbon profile suggests combined input of two different
sources of organic materials; the presence of a complete series of normal alkanes
and phytane and the large number of hydrocarbon components strongly indicates
petroleum contamination. However, the dominance of compounds containing an
odd number of carbon atoms over compounds containing an even number of
carbon atoms suggested the importance of leaf hydrocarbons originating from
terrestrial vegetation (Johnson and Calder, 1973).
G.E. Napolitano and D.S. Cicerone
>50 (Johnson et aI., 1989). Using 14C_ and 32P-Iabeled lipids, Sodergren (1979)
also found that the polar lipid classes of the water micro layer of an experimental
microcosm had an enrichment factor greater than that of neutral lipids.
Lipid content and lipid class compositions were recently analyzed in the subsurface water and foam samples from a series of streams in eastern Tennessee
(Napolitano and Richmond, 1995). Concentrations of total lipids were always
greater in the foam than in the subsurface water from the same site. Concentrations of lipids in foam ranged from 10 to 110 mg . L - 1, showing enrichments
factors of up to 100. Eight lipid classes were detected in water and foam samples:
free fatty acids, phospholipids, hydrocarbons, and acetone mobile polar lipids
accounted for >50% of the total lipids. Other detectable components were sterols,
diacylglycerols, fatty alcohols, triacylglycerols, and sterol esters. Relatively large
concentrations of phospholipids (labile celIular lipids that decompose rapidly
after the organism dies) measured in some stream foams, indicating that viable
bacteria, protozoa, and/or algae were probably major contributors to the pool of
particulate organic matter. A more detailed analysis of taxonomicalIy specific
signature lipids (i.e., fatty acids and sterols) by gas chromatography could be used
to identify which of these groups or organisms predominate (Tunlid and White,
1992). The main by-products of the enzymatic hydrolysis of phospholipids are
free fatty acids. Large quantities of free fatty acids coinciding with low levels of
phospholipids were observed in water from some streams (Napolitano and Richmond, 1995), which provides an indication that biological decay of organic matter
was a dominant process in the foam at these sites.
The metabolic processes that can be inferred from the analysis of biochemical
constituents in the foam are not necessarily linked to the conditions in the entire
body of water; instead, they reflect highly localized and specific biological processes that occur within the foams and in the water-surface microlayer. A more
general evaluation of stream condition arises from measurements of hydrocarbons. Biogenic hydrocarbons are commonly extracted from uncontaminated waters or organisms. However, the natural hydrocarbons typicalIy account for only a
smalI proportion (typicalIy <5%) of the total lipids (Nevenzel, 1989). The presence of hydrocarbons at 10-30% oflipids in foams (Johnson et aI., 1989) strongly
suggests petroleum contamination. Hydrocarbons present in foam from smalI
streams in eastern Tennessee (Napolitano and Richmond, 1995) consisted of an
intricate mixture of many compounds, dominated by a series of aliphatic, straightchain alkanes, containing 13-32 carbon atoms, with a maximum at C-25. Also
present were minor amounts of the isoprenoid hydrocarbons pristane (2,6, 10,14tretramethyl-pentahexane), phytane (2,6, 10, 14-tetramethyl-hexadecane), and a
CPI of 2.49. This hydrocarbon profile suggests combined input of two different
sources of organic materials; the presence of a complete series of normal alkanes
and phytane and the large number of hydrocarbon components strongly indicates
petroleum contamination. However, the dominance of compounds containing an
odd number of carbon atoms over compounds containing an even number of
carbon atoms suggested the importance of leaf hydrocarbons originating from
terrestrial vegetation (Johnson and Calder, 1973).