Ref. No. [UMCES]CBL 2013-015
ACT VS12-02
Vertical profiling results for all six casts are presented in figures 19-24. Results are
presented sequentially for the CDOM and HC units. Each panel displays the UviLux response in
mV 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). EEM characterizations of the reference samples revealed
some possible evidence of hydrocarbons in the surface sample of site 2, cast 5 and mid-depth
sample for site 2, cast 3 (Fig. 25 and 26), however, even those peaks fell mostly outside the
optical windows of both the UviLux-CDOM (Fig. 25) and the UviLux-HC (Fig. 26)
fluorometers. Only minimum levels of fluorescent signal was observed throughout the EEM
maps of the other samples.
In general, there was very little difference in instrument response between the CDOM
and HC units among all profiles. Minor variability (noise) is seen among different casts at this
fine resolution scaling, but this likely reflects water motion effects as the variance is often
greatest at sampling depths during which the rosette was paused for few minutes to collect a
water sample. Additionally, minimal difference in instrument response was observed between
the nearshore (site 1) and offshore (site 2) sites for both units tested, despite significant
differences in CDOM and chlorophyll levels. Cross plots of instrument response versus TPH
concentration and estimated EEM
QSE
intensity are presented in figure 27 for the UviLux-CDOM
unit and in figure 28 for the UviLux-HC unit. As previously noted there were no detectable
hydrocarbons within the collected reference water samples. Both units showed a similar non-
variant response (approximately 375 mV) to the small range (roughly 1500 cps) of estimated
EEM
QSE
intensity from the reference samples (Fig. 27 and 28, panel B).
SUMMARY of INSTRUMENT RESPONSE ACROSS ALL TEST APPLICATIONS
The CTG UViLux-CDOM and UViLux-HC in situ fluorometers exhibited the expected
linear voltage responses to challenge analyte concentration with the response slope (sensitivity)
mapping to the overlap of the compounds’ fluorescence properties to the optical configuration of
the instrument package (Figs 29 & 30). The UViLux HC detected polyaromatic hydrocarbons
with high sensitivity with detector saturation occurring above 10 ppb carbazole and 100 ppb
NDSA. Chemically dispersed crude oils were detected through 12,000 ppb. The UViLux
CDOM instrument exhibited lower sensitivity to these compounds only exhibiting detector
saturation above 5000 ppb QS and higher thresholds for detection (>30 ppb). This instrument
configuration did reveal differences in source waters and since it shares excitation optical
configuration, may aid in interpretation of refined hydrocarbon detect signals by UViLux HC
instruments. In general
care should be taken in specific interpretation of environmental
fluorescence signals in absence of analytical reference samples.
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