I am taking my students to collect water samples from different bodies of water. These bodies of water include the local river, a park pond, and water accumulation from recent rain. Once we gather the samples students will be analyzing the samples under standard light microscopes. I was wondering what is the best way to preserve any life that may be found in the samples in case there is no immediate opportunity to analyze the samples under the microscopes? Is there a specific time frame to analyze the samples before they have to be replaced? Also if they are kept in a bottle/jar does the container have to be unsealed or with perforations to allow air flow? Thank you.
Depending on what you are trying to look at, for zooplankton you can take water samples and filter them through a 100-200um mesh and store them in glass or plastic bottles. For my research we used mason jars that were cleaned thoroughly. After filtering just submerge the biomass in 70-90% ethanol and they can be stored in a fridge for quite some time.
If you want to look at phytoplankton, you can look into using Lugols Solution for preserving your samples. The nice thing about using lugols is that it will stain the phytoplankton as well. Your best bet for these is to store in amber bottles and keep in cool dark place. Here is a decent guide on how to collect the samples and prep the solution.