4.1 Because of the direct association of phytoplankton with the water and the water masses that move in response to wind-or-gravity-generated currents, the species composition and abundance of phytoplankton are related to water quality. Moreover, the phytoplankton directly affect water quality, notably dissolved oxygen, pH, concentrations of certain solutes, and optical properties. At times the abundance or presence of particular species of algae result in nuisance conditions ( 2 ).

4.2 Organisms of the phytoplankton communities are collected and studied for many reasons, and the techniques used will vary with the study objectives. In the design of a sampling program and in the selection of techniques, the investigator must take into consideration the uniqueness of each study area and the natural characteristics of phytoplankton communities.

4.3 The principal factors to consider when collecting phytoplankton are the uneven distribution, composition, and abundance of phytoplankton in space and time. Phytoplankton blooms can occur quickly and can be of short duration. Succession of taxa can occur in a matter of 1 to 2 weeks. Furthermore, phytoplankton abundance and composition can change abruptly in the horizontal plane. There also can be remarkable numerical and qualitative differences between depths. The heterogeneous abundance and composition can occur not only over small areas but also over large areas. The uneven distribution makes it difficult to collect a representative sample from a given area and makes replication of samples and, especially, an adequate vertical and horizontal sampling program essential ( 3 ).

1.1 This classification covers both qualitative and quantitative techniques that are used commonly for the collection of phytoplankton. The particular techniques that are used during an investigation are dependent upon the study objectives. Of additional importance in the selection of a technique is the uneven distribution of organisms both temporally and spacially. This classification describes qualitative and quantitative ways of collecting phytoplankton from inland surface waters. Specifically, qualitative samplers include conical tow nets and pumps; quantitative samplers include the Clarke-Bumpus plankton sampler, Juday plankton trap, water sampling bottles, and depth-integrating samplers.