Plankton and Water Quality

Collection

Nitrogen, phosphorus and phytoplankton samples were collected at 1 m below the surface using a Niskin sampling bottle.  Rotifer samples were collected with a 63 micrometer mesh plankton net.  At shallow stations, less than 10 m in depth, vertical tows were made from the bottom to the water surface.  At deeper stations, tows were made from 10 m depth to the surface.  Zooplankton samples were collected with a 202 micrometer mesh net.  At shallow stations, a small diameter (0.11m) net was used and tows were made from the bottom to the water surface.  At deep stations, a 0.5m diameter net was lowered as close to the bottom as feasible and pulled to the surface.  A total of 110 samples were collected for each of the parameters measured during the 2002 growing season.

Analysis

Phytoplankton - Phytoplankton samples were concentrated using Ütermohl settling chambers and counted at 400x with an Olympus CK2 or IX70 inverted microscope equipped with phase contrast.  Organisms were identified to the lowest feasible taxonomic level.  A minimum of 100 individuals of the most abundant taxon was counted or a maximum of 100 fields was examined.

Rotifers - Rotifers were identified using an Olympus CK 2 inverted or Nikon Labphot microscope at 10x.   In general, samples obtained from shallow locations were examined in their entirety while those from deeper locations were subsampled.  If possible, a minimum of 500 organisms from each sample was examined.

Zooplankton - Zooplankton were identified to the lowest feasible taxonomic level using an Olympus CK or CK 2 inverted microscope at 4x, utilizing higher magnifications as needed.  In general, samples obtained from shallow locations were examined in their entirety while those from deeper locations were subsampled.  If possible, a minimum of 200 organisms from each sample was examined.

APHA. 1989. Standard methods for the analysis of water and wastewater. Seventeenth edition. American Public Health Association, Washington, DC.