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3. Seal the top of each pot with stopper or pencil eraser in silicone adhesive. Mark the petri dish bottoms by batch: Control, N, P, or N&P. and by number: 1,2,3,4… with a permanent marker or pen.
4.
Place pots in plastic tubs for transport to the sites and store in a refrigerator until ready to use. There are (4) four pots for each sample group: Control, Nitrate, Phosphate, and Nitrate & Phosphate, and three sample groups per site.
5. Field tests of the bioassay
6. Select the sites and get a map of the area. If using a topo map, record the name of the quadrangle. On-line maps to help determine Lat/Long of your site are available on the Gazetteer website. (See Resources)
7.
Upon arriving at the site(s), divide the class into sample groups and send three sample groups with pots to each site. Place the three sets of pots (12) in the water, separating the sample sets by a minimum of 1.5 meters. Place the pots about 0.5-1.0 meter away from one other across the directional flow in a lentic site or simply apart in a lotic site, at a depth of 20-30 cm. Anchor pots with loops of nylon cord attached to pegs driven into the bottom. Mark the site location(s) with surveyor tape or stakes. Record the location of each set on the map. (Note degree of sun and shade) Record the air temperature and water temperature at each site.
8. Monitor pots for algae growth or the lack thereof twice a week for the next 14 – 23 days, measuring and recording air and water temperature.
9.
After 14-23 days, take final temperature readings and collect pots. By approaching each site from downstream, one can avoid disturbance of the macroinvertebrates. Cover each pot with a 1-quart Ziploc bag and remove the pegs and cord, lifting it out of the water. Remove surveyor markers.
10. Place the bagged pots back in plastic trays for transport back to the lab.
Lab work and analysis
11. Divide the class back into the sample groups. These groups take note of the algae growth on each pot by nutrient and record the observations.
12. Now arrange the students by site and nutrient, so that for each site three students gather to work on the Control pots, three students work on Phosphate pots, three students work on Nitrate pots and three
students work on Nitrate/Phosphate pots. Next these groups scrape the algae from the pots with a knife blade or scraper, rinsing with distilled water into a petri dish marked with the site number and nutrient.
Compare the amount of algae in each group. Make notes for lab reports.
13. Dry the biomass in separate batches and weigh. Record.
14. Conduct lab analysis for all the class data: temperatures, algae growth and biomass. Plot the date and create graphs for each site:
- Mean of biomass
- Mean of temperature at each site
Clean up
15. Pry off the petri dishes and empty the agar from the pots. The used agar medium should be autoclaved before disposing.
16. Wash pots in hot water and air dry.
17. Mark each set with N, P or N+P notation for future use.
Safety
- Recommend the use of latex gloves in any microbially questionable water sources during fieldwork and lab work.
- Teachers should visit selected field sites before bringing a class to them. It wouldn't hurt to get a weather report too.
- Promote site safety. Brief each class about the use of caution when moving around a water site, whether in or out of the water. Quell all horseplay, it is inappropriate, possibly destructive to the
fieldwork and perhaps even dangerous.
- In the lab, use microbial safety protocol
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