7170 - Laserfiche WebLink

Home Browse Search

I 40 JOSEPH B. HUNN AND ROSALIE A. SCHNICK presence or absence and whether living or dead is sufficient. Zooplankton samples can also be used to document the nature of the cause and the extent of the kill. The presence or absence of live animals can be useful information in determining the cause of the kill (see Chapter 3). The choice of sampling gear used to collect the zooplankton depends on the types of organisms present and the body of water to be in- vestigated. To collect zooplankton, 30 liters of water are filtered through an 80-micron mesh plankton net. For a discussion of sampling techniques, see APHA et al. (1985) or Weber (1973). To preserve zooplankton, use 7007o isopropyl alcohol or 5% buf- fered formalin. Do not store the sample in formalin longer than 48 hours before transferring it to 70% isopropyl alcohol. Plant Samples Phytoplankton and macrophyte samples are not normally used for residue analyses. However, in cer- tain situations, for example, petroleum hydrocarbon contamination, residues can be rinsed from the plant surfaces and used to document the presence of par- ticular hydrocarbons. Phytoplankton Samples of phytoplankton should be examined for the presence and abundance of live algae. Closing samplers, pumps and filters, or fine-mesh plankton nets can be used to collect samples. For quan- titative determinations, the volume of water filtered must be recorded. If live samples are wanted for analysis, the samples should be refrig- erated after collection or kept chilled at 4° C. For fixing and preserving samples, Lugol's solution is recommended (Weber 1973; Vollenweider 1974; APHA et al. 1985). (See Appendix E for the for- mula for Lugol's solution.) Macrophytes The distribution, abundance, and general physical condition of macrophytes should be noted if it is suspected that the plants are causing a decrease in the dissolved oxygen concentration, especially in early morning hours.