Environmental Assessment > Marine Waters> PSAMP Monitoring > How It Works

How It Works

Sample collection methods are in compliance with the Puget Sound Protocols and Guidelines and are detailed in Janzen (1992b). Major features are summarized below.

Sample Collection

Monitoring From a Float Plane

Long-term monitoring is conducted from a DeHavilland Beaver floatplane, which allows a large geographic area to be sampled in a short amount of time. Four surveys are scheduled in separate weeks each month to complete sampling throughout the Puget Sound and coastal station networks, as weather allows. Approximately 8-10 stations are sampled per survey. Stations are identified by dead-reckoning and verified by a Global Positioning System (GPS) receiver.  

CTD Profiler

A Sea-Bird Electronics, Inc. Seacat® model SBE-19 conductivity-temperature-depth profiler (CTD) is used for collecting continuous water column profile data. The CTD is lowered through an internal opening on the seaplane using a capstan winch and brace outfitted especially for the plane. In addition to measuring conductivity (used to compute salinity and density), temperature, and pressure, the CTD is equipped with sensors to measure pH, dissolved oxygen (DO), and light transmission, all at 0.5 m interval “bins.” Both the conductivity and DO sensors are flushed continuously with sample water by a pump attached to and powered by the CTD. Profiles at each station are conducted from the sea surface (top bin = 0.5 m) to ~100-m depth or the sea bottom when shallower. The CTD sensors are typically lowered to 0.5 - 1 m above the sea bottom, to avoid sensor damage.

Secchi Disk

The Secchi disk depth is used to indicate water clarity and to derive the extinction coefficient of incident light penetration through the water column. Secchi depths (to the nearest 0.1 m) are taken at each station using a solid white, 30-cm disk. Surface water conditions (glare and waves) are the main source of inaccuracy in Secchi depth readings. To help reduce sources of error, all field crew are trained to conduct Secchi depth readings using the same procedure. If surface conditions are not optimal, the reading is not recorded or is recorded as an estimate.

Niskin Bottle Sampling

A 1.2-L Niskin® bottle is used to collect seawater at 0.5, 10, and 30 m. For stations shallower than either 10 or 30 m, a sample at the near-bottom depth (0.5-1 m above the seabed) is taken. Discrete water samples are taken from the Niskin bottle for dissolved nutrients (ammonium-N, nitrate+nitrite-N, and orthophosphate-P), and pigments (chlorophyll a and phaeopigment) and stored on ice. Discrete samples for DO and salinity are drawn periodically for comparison with the in situ sensor values. Samples for DO are fixed with powdered reagents for the azide-modified Winkler titration analysis, stored at ambient temperature. Samples for salinity are capped tightly and stored at ambient temperature. Samples for fecal coliform bacteria are collected just below the surface (0.1-m) using sterile glass sample bottles and stored on ice.

Laboratory Procedures

Nutrients

Analyses for dissolved nutrients were conducted by Manchester Environmental Laboratory (MEL) for ammonium, nitrate+nitrite, and orthophosphate for samples collected 1 October 1997 through 18 February 1999. All nutrient samples were filtered through Nalgene® 0.45 μm pore cellulose acetate filters in the field at the time of collection and maintained at 4ºC. Samples were frozen upon return to Ecology (roughly 2-7 hours after sampling). Nutrient samples were analyzed using an Alpkem® series 300 autoanalyzer at MEL. Results are reported in mg/L units. For samples collected 19 February 1999 through 31 December 2000, sample collection, filtration, and storage procedures were the same but analyses for dissolved nutrients were conducted by the University of Washington Marine Chemistry Lab for nitrate, nitrite, ammonium, orthophosphate, and silicate. Nutrient samples were analyzed using Technicon AutoAnalyzer II at UW. Results are reported as micromolar (μM).

Chlorophyll a 

Samples for chlorophyll a (chl a) and phaeopigment (phaeo) from 0.5 and 10 m depths were filtered through Whatman® GF/F glass fiber filters (0.70 μm nominal pore size) at the end of the sampling day by Ecology staff. The filters were immersed in 90% acetone and stored frozen in glass centrifuge tubes. For samples collected October 1997 through 30 June 1999, frozen samples were transferred to MEL for analysis. Determination of chl a and phaeopigment concentrations was made by MEL using fluorometric detection with a Sequoia-Turner model 112 fluorometer and the APHA et al. (1989) protocol. For samples collected 1 July 1999 through 31 December 2000, frozen samples were analyzed for chl a and phaeopigment by Ecology staff using a Turner 10 fluorometer according to the United States Joint Global Ocean Flux Study protocol. The two procedures do not differ substantially.

Fecal Coliform

Fecal coliform bacteria samples were stored refrigerated and transferred to MEL within 24 hours of collection. Upon arrival, samples were incubated and analyzed using the membrane filter method.

Dissolved Oxygen

The discrete samples for DO analysis were analyzed by Ecology staff using the azidemodified Winkler method and powdered reagents. The powdered reagents have the capability to accurately bind oxygen for DO concentrations up to 10 mg/L. Results from the Winkler DO analyses were compared with the in situ DO results obtained with the CTD's Beckman oxygen sensor. The comparison allows for monitoring of sensor calibration drift or sensor failure; however because discrete samples were collected following the CTD cast, and could not obtained at the same time of sensor measurement, these results cannot be used for calibration of the in situ sensor.

Salinity

Discrete salinity samples were analyzed by University of Washington Marine Chemistry Laboratory with a Guildline Instruments, Inc. Autosal® salinometer, using standard
seawater as a reference.