Page 3 - NutrientsReadMe

Methods and Evaluation of Data

Quality

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Dissolved macronutrients include: nitrate NO3 (actually
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nitrate plus nitrite NO2 is measured, although nitrite
concentrations are generally much lower than those for
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nitrate in the ocean), phosphate PO4 , and silicic acid
Si(OH)4 (sometimes assumed to have the chemical form
of silicate or silica, a solid with formula SiO2), all required
for the growth of phytoplankton.

At selected stations, water samples in the CitSci program
are collected at depths of 0 and 20 m for nutrient
analysis. Water is obtained from a ‘Niskin’-type sampling
bottle, attached to a rope marked at various depths and
kept vertical by both a weight at the bottom and
maneuvering of the boat in the direction of any tilt.
These bottles are lowered in an open position, and then
closed to trap a water sample using a mechanism
Deploying the Niskin Sampling Bottle. triggered by the descent of a weighted “messenger” on
the sampling rope.

For nutrient analysis, water from the Niskin is
subsampled and (from 2016 onwards) filtered
through a glass-fibre filter of nominal pore size
0.7 µm to remove all organic matter. The
filtered water samples are frozen for storage,
and then thawed and analyzed for the
concentration of dissolved macronutrients in a
laboratory.

Several different laboratories (and different
analysts) have been used over the years to
analyze samples in the CitSci program. In most
Subsampling from the Niskin into nutrient vials.
years an autoanalyzer is used to allow for the
consistent analysis of a large set of samples.