Intertidal samples were collected on an alongshore transect at
increasing distances (650 m, 950 m) from the original disposal
site on the west end of the beach. For intertidal sampling, four
replicate sediment cores were collected using 5 x 20 cm hand
corers, stoppered on either end, placed in a cooler on ice, and
transported immediately back to the laboratory at the University
of California Santa Barbara (UCSB). Subtidal marine sediment
samples were collected along two longitudinal transects, at 5 m,
10 m, and 20 m water depths perpendicularly offshore of the
disposal site in west Goleta Bay and at 10 m and 20 m water depths
offshore of the mouth of Goleta Slough in east Goleta Bay. At each
subtidal location, four replicate sediment cores were collected by
SCUBA divers using the same 5 x 20 cm hand corers, stoppered on
either end, and transported back to the laboratory in a cooler on
ice. All samples were stored frozen (-20°C) until sample
processing. Intertidal cores were stored intact, since their size
varied between 10 and 20 cm, and all subtidal cores were sectioned
into 0-10 cm and 10-20 cm horizons prior to freezing.
To prepare samples for analyses, two replicate cores from each
site were selected, thawed, and 100 g of sediment from each core
was weighed into clean aluminum tins. Samples were dried at 60°C
for 48 hours, ground by hand using a mortar and pestle, and passed
through a 2 mm sieve prior to being placed into combusted glass
vials with a Teflon cap for storage.
Measurement of bulk stable organic carbon isotope signatures was
done at the Department of Geological Sciences, University of
Florida (UF) following Mays et al. (2017). To remove inorganic C,
approximately 200 mg of sediment was weighed into in a container
with ~250 ml 1 N HCl. After 48 h, the material was passed through
a glass fiber filter with the aid of a vacuum pump. Decarbonated
samples were then rinsed with deionized water to remove excess
acid and chloride. The remaining sediment was oven-dried,
separated from the filter, and stored in 20 mL glass scintillation
vials. Ratios of 12C and
13C were then determined on a Thermo
Finnigan Delta Plus XL isotope ratio mass spectrometer with a
ConFlo III interface linked to a Costech ECS 4010 Elemental
Combustion System. Carbon stable isotope results are reported as
per mil (‰) in standard delta notation relative to Vienna PeeDee
Belemnite (VPDB). Precision for δ13C
was ±0.21‰ based on nine analyses of UFCS, an internal laboratory
standard. Total organic carbon (TOC) contents of the original
sample after HCl acidification and in the digested samples were
analyzed in duplicate (or additional times until <5% relative
error) on a Carlo-Erba NA-1500 CHS Elemental Analyzer.
Samples were also processed for pyrogenic carbon content using the
Kurth-Mackenzie-Deluca method (Kurth et al., 2006), in which 1 g
of sample was ground to <0.76 μm, and digested using 20 mL of
30% peroxide (H2O2)
and 10 mL of 1M nitric acid (1M HNO3) at
100 °C for 16 h to remove non-charcoal carbon. After cooling and
filtering with Whatman #2 filter paper, the sediment-laden filters
were dried at 60 oC. Samples were
carefully scraped from the filters, weighed, and analyzed for C
content. It is assumed that all C that remained was pyrogenic
carbon (Kurth et al., 2006). Pyrogenic carbon content (%PyC) was
then calculated as the product of the C content in the digested
sample and the ratio of pre- to post-digestion weight of the
sample.
Lignin phenol analyses were used to determine the presence of
terrestrial OM in sediment samples and the extent of diagenetic
processing or degradation. A separate subsample from each
replicate core was analyzed for lignin content using a modified
alkaline cupric (CuO) oxidation method (Goñi and Montgomery, 2000)
and a Varian 3800/Saturn 2000TM coupled gas chromatograph – mass
spectrometer with a fused capillary column (DB-1 from J&W,
60m, 320µm) housed by Geotop at the Université du Québec à
Montréal (UQAM) (Moingt et al., 2016). A standard reference
material of estuarine sediment (SAG 05) was analyzed, and results
were consistent with previously published values (Louchouarn et
al., 2000; Moingt et al., 2016).
References
Goñi, M.A., Montgomery, S., 2000. Alkaline CuO oxidation with a
microwave digestion system: Lignin analyses of geochemical
samples. Analytical Chemistry 72, 3116–3121.
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