May try:
Standard methods for the examination of Water and Wastewater
(16th ed) American Public Health Association, Washington, DC
(1985)
Littler, M and d. Littler 1985. Handbook for Phycological
Methods: Ecological Field Methods: Macroalgae, Cambridge U.
Press (I know you're not dealing with macroalga, but it may
give you some ideas or further tips)
Vollenweider, R.A. (ed) 1969 A manual of Methods for measuring
Primary Productivity in Aquatic Environments. IBP Handbook #12,
Blackwell Scientific Publications, Oxford.
Good luck.
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