Ref. No. [UMCES]CBL 2013-021
ACT VS12-05
Vertical profiling results for all six casts are presented in figures 11-13. Each panel
displays the FLCDRTD response in counts along with a continuous trace of temperature and
salinity for that cast. In addition, total hydrocarbon, CDOM, Turbidity, and Chlorophyll
concentrations from the discrete reference samples are plotted on the same graph. It should be
noted that despite the presence of a visible sheen of oil on the surface of the water above the
leaking barge, all total hydrocarbon concentrations were reported as below detection for all
reference samples collected (stated method of detection limit ≤ 25 ppb). The instrument
response was averaged approximately 80 counts at site 1 and approximately 150 counts at site 2.
These readings are within the range observed for baseline signals observed in DI and ambient
waters monitored in this test, consistent with the analytical non-detects for the reference samples.
Response increased with depth for each of the site two casts ranging from approximately 120 at
the surface to 170 counts at the bottom depth. The FLCDRTD may have been responding to the
general increases in CDOM noted by measurement of discrete reference samples. However, the
instrument response was lower in Terrebonne Bay (site 1) which had significantly higher CDOM
levels. There were two EEM characterizations of the reference samples that revealed some
possible evidence of hydrocarbons, notably the surface sample of site 2, cast 5 and the mid-depth
sample for site 2, cast 3 (Fig. 14), however, even those peaks fell mostly outside the optical
window of the FLCDRTD filter set. Only minimum levels of fluorescent signal was observed
throughout the EEM maps of the other samples. As noted earlier all TPH concentrations were
below detection and therefore it was not possible to evaluate any relationship between instrument
response and hydrocarbon concentrations (Fig. 15, panel A). In addition, there was no consistent
relationship between instrument response and the corresponding EEM
QSE
intensities from the
same reference samples (Fig. 15, panel B).
