Whitehorse Pond – 2.0 METHODS

Crater Lake National Park Whitehorse Pond Limnological and Vascular Plant Study, 1993



2.1 Physical Collection Methods

A Hach One pH meter probe was used to quantify in situ temperature and acid concentration, pH. This probe is used to measure pH in low conductivity waters. It was calibrated with low ionic strength pH buffers following a similar protocol used in the Crater Lake field lab (Salinas, 1992). An Perstorp in situ multiparameter probe was used to measure temperature, pH, and conductivity in addition to the Hach meter.

Pond water samples were collected in a Scott-modified Van Dorn collecting bottle for nutrient chemical concentrations, dissolved oxygen concentration, and phytoplankton. Water was collected in acid rinsed plastic bottles for analyses in the Cooperative Chemical Analytical Laboratory in Corvallis (Jones, 1992). This is the same laboratory used by the Crater Lake monitoring team. Analyses included pH, alkalinity, conductivity, total phosphorus, nitrate/nitrite, sodium, potassium, calcium, magnesium, chloride, and sulfate ions. These ions were only those dissolved in the water since the water was passed through a pre-rinsed glass fiber filter before it was cooled and shipped to Corvallis.

Water samples were preserved in dark plastic bottles for phytoplankton speciation and enumeration. Lugol’s iodine solutions was used for this purpose making the sample one percent iodine before storage.

2.2 Plankton Methods

Each phytoplankton sample was preserved with 1% Lugol’s solution in the field. In the laboratory, each phytoplankton sample was homogenized by shaking and poured into a 1 L graduated cylinder and settled for 72 hours. The sample was concentrated to 100 ml by aspirating off the top and split into 2-50 ml aliquots. One aliquot was put aside for archiving and the other was rinsed into a Hydro-bios Kiel 50 mL settling chamber and allowed to settle for 24 hours. The settled sample was then placed on a Nikon DIAPHOTTMD inverted microscope fitted with a Javelin color camera and Sony color printer and monitor. The first 200 cells encountered were counted and identified at 1500 X oil on phase contrast. A digital photomicrograph was taken of the major algal taxa encountered and are included with this report. The cell density was calculated in cells per liter (cells/L) using the following:

N = [n(A/WL)] / [V/1000] cf,

where      N = the number of cells per liter;

n = the number of cells counted;

A = the area of the chamber (cm2);

W = the field width (cm);

L = the total length of the transect counted (cm);

V = the volume of the chamber (mL);

cf= the volume of the concentrated sample divided by the volume of the original field sample.

Zooplankton were collected with al2-centimeter diameter 64 uM mesh sized zooplankton net. It was towed 9.5 meters through the water for each sample. It was kept between the surface and the pond’s bottom for each tow. No attempt was made to keep the net at the pond’s surface or bottom. All ponds sampled for zooplankton were wide enough and deep enough to accomplish this type of tow. Samples rinsed from the net were preserved with formalin and placed in plastic sample bottles.