Previous Page  11 / 59 Next Page
Show Menu
Previous Page 11 / 59 Next Page
Page Background

Ref. No. [UMCES] CBL 2016-011

ACT VS16-02


equilibrating test instruments at the surface (3m) for ten minutes and then collecting three Niskin

bottle samples at one minute intervals. Following the third sample, the rosette was quickly profiled

into the hypolimnion where samples were collected immediately upon arrival and then each minute

for the next 6 minutes. The second trial was performed in the reverse direction where instruments

were equilibrated for 10 minutes within the hypolimnion, three samples collected, and then

profiled into the surface and sampled at one minute intervals over the next 7 minutes



was then immediately returned to the ship for sample processing. Triplicate BOD bottles were

filled from each Niskin and immediately fixed for Winkler titrations.

Reference Sample Analysis

The Winkler titration for quantifying dissolved oxygen was used as the standard for

comparison. The specific method is described in detail below and is based on the procedures

described in,

Measurement of primary production and community respiration in oligotrophic lakes

using the Winkler method

(Carignan et. al. 1998). All Winkler titrations were done at the

individual laboratory and field sites by trained ACT staff using standardized techniques and


Initial Preparation

The volumes of each BOD bottles (≈ 125 mL) were determined with a precision better than

0.005%. The volume of each bottle was measured gravimetrically (± 0.01 mL) near 20


C, after

filling with degassed (boiled 10 min and cooled) distilled water. Since the procedure’s precision

approaches 1 µg O





, particular care was taken to avoid contamination of the glassware and

working space from any trace amounts of thiosulfate, iodate, I


, and manganese. Reagents

recommended by Carritt and Carpenter (1966) were used and whole bottles titrated to minimize the

loss of volatile I


and the oxidation of iodide to I


at low pH.


(1) Manganous chloride solution (3M Mn


): dissolve 300 g of MnCl




O in 300 mL of distilled

water. Bring to 500 mL.

(2) Alkaline iodide solution (8M OH


, 4M I


): separately dissolve 160 g of NaOH and 300 g of NaI

in ca 160 mL of distilled water. Mix with stirring and bring to 500 mL.

(3) 23N Sulfuric acid solution: slowly add 313 mL of concentrated H




to 175 mL of distilled

water. Carefully mix and cool and bring to 500 mL.

(4) Thiosulfate titrant 0.03N: add 300 mL 0.1N Na








O (Fisher SS368-1) to 700 mL DI.

The thiosulfate is standardized daily with KIO


according to the procedure described below. Note:

The normality of thiosulfate will be adjusted to ensure that a complete sample can be titrated

within one burette volume (less than 10 mLs), but kept as low as possible to maximize precision.

(5) Potassium iodate standard, 0.1000N ±0.005N commercially available stock (Fisher SP232-1).

Sample Fixing Procedures

(1) Samples were fixed immediately after collection into the BOD bottles. Filling order was noted

on log sheets along with bottle and sample IDs. 1.0 ± 0.05 mL of MnCl


was dispensed just below

the water surface, followed by 1.0 ± 0.05 mL of alkaline iodide using positive displacement

pipettors. The pipettors were washed with distilled water every day to prevent valve and plunger

malfunction due to salt crystallization.