Gschwend%20thesis.pdf

-l98-
average year-round sample data most closely resembled the distribution
found in gasoline and auto-exhaust -dissolved-in-seawa ter. The larges t
deviations of the average year-round isomer distribition from these
laboratory-determined distributions was for peaks containing para-
substituted benzenes. These particular isomers may be preferentially
degraded, for example by microorganisms,
Cz- and C3-benzenes were not homogeneously distributed in surface
seawa ter collected near CD in the fall, spring, or summer. Rain samples
from June and November contained lower or equal concentrations of these aromatic
. _... ,-. _.......
hydrocarbons than seawater. Oys ter Pond, a 'nearby::freshwa ter pon:d - on:
which
motor boats are not allowed, had lower concentrations of C2- and C3-benzenes
than seawater samples from CD collected at the same time in August and
September. Atmospheric levels of these compounds measured at CD in August
and September were also below those expected for equilibrium with coastal
seawater. All of these results are consistent with the hypothesis that
the atmosphere was not a source of Cz- and C3-benzenes at CD from the
spring through the faii.
Low concentrations of C2- and C3-benzenes in samples from inland
sites showed that runoff through these relatively undeveloped regions
dilutes seawater with respect to these compounds.
Hydrocarbons and Halomethanes from Benthic Algae and Seagrass
Algae released hydrocarbons and halomethanes to seawater during
day long incubations. Pentadecane, heptadecane, and bromoform were
produced at rates which may support the observed coastal seawater levels.
The other compounds were not identified in the year-round study and release
ra tes sugges t that they would appear at only trace levels.