Ref. No. [UMCES] CBL 2013-020
ACT VS12-03
Vertical profiling results for all six casts are presented in figures 27-35. Results are
presented sequentially for the CDOM, Crude Oil and Refined Fuel sensors. Each panel displays
the sensor response in RFU 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 CDOM sensor showed an elevated response in
Terrebonne Bay, with values of approximately 105 (
±
24) RFU (Fig. 27). At site 2, the CDOM
sensor response was significantly lower (4.2 RFU, 0-18 RFU range) and were quite variable with
depth (Figs. 28-29). The sensor response matched elevated CDOM levels measured in the
bottom water reference samples of casts 4 and 5 (Fig. 29). The Crude Oil sensor also showed an
elevated response in Terrebonne Bay (233
±
16 RFU) compared to offshore in the Gulf (5.5
RFU, 0-14 RFU range) (Figs. 30-32). The Crude Oil sensor showed similar variability with
depth and with elevated bottom water levels at site 2, casts 4 and 5 (Fig. 32). The response of
the Refined Fuel sensor was significantly lower than the other two sensors at all sites. The
response in Terrebonne Bay was 14.4 (
±
3) RFU (Fig. 33) and for all casts at site 2 the response
only ranged from 0-4 RFU (average 2 RFU) (Figs. 34-35), similar to the baseline response
observed in deionize water challenges (see Fig 6).
EEM characterizations of the reference samples revealed some possible evidence of
hydrocarbon-like compounds in the surface sample of site 2, cast 5 and mid-depth sample for site
2, cast 3 (Figs. 36-38) but these all yielded non-detect results by our analytical methods. The
observed fluorescence peaks mostly fell outside the optical windows of the CDOM sensor, but
did show overlap with the Crude Oil and Refined Fuel optical windows. Only minimum levels
of fluorescent signal was observed throughout the EEM maps of the other samples.
Cross plots of instrument response versus TPH concentration and estimated EEM
QSE
intensity are presented in figures 39-41 for the CDOM, Crude Oil, and Refined Fuel sensors,
respectively. As previously noted there were no detectable hydrocarbons within the collected
reference water samples, so little or no signal for the sensors to respond to. The CDOM, Crude
Oil and Refined Fuel sensors did show an elevated response to the waters within Terrebonne
Bay, 98, 229 and 13 RFU respectively, well above baseline responses. The corresponding
EEM
QSE
values were 5406 cps, 12635 cps and 944 cps for the CDOM, Crude Oil and Refined
fuel sensors respectively, values lower than observed during the Baltimore Harbor deployment.
Offshore in the Gulf of Mexico predicted EEM
QSE
values were lower ranging 331-579 cps, 1105-
2977 cps and 298-609 cps for the CDOM, Crude Oil and Refined Fuel sensors, respectively.
Corresponding instrument responses were also dampened, ranging from 2.9-4.5 RFU, 4.7-6.3
RFU and 1.6-2.9 RFU for the CDOM, Crude Oil and Refined Fuel sensors, respectively. Only
the CDOM and Crude Oil sensors were noticeably above baseline response levels.
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