Water sampling was performed over three 36-hour sampling periods in
August 2018 with samples collected every four hours. A vertical
profile of the entire water column was obtained using a SBE 19plus
V2 SeaCAT Profiler sampling at 4Hz (4 scans
sec-1). Temperature readings are accurate
to 0.01ºC, and conductivity readings are accurate to 0.001 S
m-1. Water samples were collected using a
5L Okeanus GO-FLO Sampler at 1, 3, and 5 m depths, one deployment
for each depth. Seawater sample collection followed SBC LTER
protocol, with all HDPE sample vials acid washed (10% HCl) and
several rinses of seawater performed prior to collection.
Immediately upon collection, samples were placed on ice, transported
to the laboratory, and filtered through GF/F filters (0.7 µm,
Whatman) for dissolved nutrient analyses and MCE filters (0.45 µm,
Millipore) for chlorophyll analyses. A subset of GF/F-filtered
samples was analyzed immediately for ammonium
(NH4
+) using the
ortho-phthaldialdehyde method (Holmes et al.
1999, Taylor et al. 2007). Duplicates were measured using a Turner
Trilogy Laboratory Fluorometer (limit of detection, 0.05 µM).
Another subset of GF/F-filtered samples was stored frozen (-20 ºC)
and measured later for combined nitrate
(NO3
-) and nitrite
(NO2
-)
concentrations by flow injection analysis on a Lachat QuickChem 8500
Series 2 Analyzer (Hach Company) (limit of detection, 0.2 µM). A
third subset of the GF/F-filtered samples was acidified with 4N HCl
and refrigerated (4 ºC) until analyzed for dissolved organic carbon
(DOC) by high temperature combustion on a Shimadzu TOC-V Analyzer
(limit of detection, 25 µM). One DOC sample (collected at 6AM from
3m water depth on August 4th) was removed
from the final dataset due to concerns about sample contamination.
The MCE filters were folded into vials and stored frozen (-20 ºC)
until they were analyzed for chlorophyll a and phaeopigments by
extraction in 90% acetone (Strickland & Parsons 1968, Smith et
al. 1981) and measurement on a Turner 10AU Field and Laboratory
Fluorometer (limit of detection, 0.02 µg
L-1). Samples below the limit of
detection for any analyses are reported as equal to the limit of
detection.
CTD profiles were processed and converted to .mat file formats using
SBE data processing software (v 7.26.7). Profiles were edited to
remove the horizontal sections, suggesting spiking occurring in
surficial or benthic waters. Remaining organization and analyses
were performed using Excel (v 16.24), MATLAB (v R2018b 9.5), and R
(v 4.0.2). All data formatting was performed using the
tidyverse package (Wickham et al. 2019).
Holmes, R.M., et al. 1999. A simple and precise method for measuring
ammonium in marine and freshwater ecosystems. Can J Fish Aquat Sci
56, 1801–1808.Smith, R.C., Baker, K.S., Dustan, P., 1981.
Fluorometric Techniques for the Measurement of Oceanic Chlorophyll
in the Support of Remote Sensing. Visibility Laboratory, Scripps
Insitution of Oceanography, University of California, San Diego, La
Jolla 81–17.Strickland, J.D.H., Parsons, T.R., 1968. A Practical
Handbook of Seawater Analysis. Fisheries Research Board of Canada,
Ottawa.Taylor, B.W., et al. 2007. Improving the fluorometric
ammonium method: matrix effects, background fluorescence, and
standard additions. J N Am Benthol Soc 26, 167–177.Wickham, H., et
al. 2019. Welcome to the Tidyverse. J Op Sour Soft 4, 1686.
