Experimental Manipulation of Model Ecosystems
307
2. Each group measures the pH and temperature of a water sample from the outlet
(about 30ml).
3. Half of each group: (a) Collects a 200-ml sample from the outflow tube and processes
it to settle phytoplankton. (b) Counts the phytoplankton sample that was collected
and preserved during the previous week. Handle the sample very carefully so as not
to resuspend any of the settled organisms.
4. Half of each group should perform pigment analyses on a chemostat sample
following the procedure given in Exercise 10.
5. At the end of the laboratory period add the N- and/or P-enrichment solution to one
of the medium reservoirs labeled "Enriched." Refill both of the reservoirs to the 20-1
mark with autoclaved water prior to adding the nutrients.
Enrichment procedure: Using NH 4 N0 3 and/or K 2 HP04, enrich the culture
medium concentrations of Nand P by about tenfold.
Sections B, C and D (Days 10, 12 and 14)
1. Complete Parts 1 through 4 given under the second week for Section A. In Part 3,
you will be processing the 200-ml sample taken the previous week.
2. Check the nutrient reservoirs to see if they need refilling. If so, be careful to create the
proper nutrient concentration.
Third Week
All Sections (2-Day Intervals)
1. Complete Parts 1 through 4 from the second week's schedule. Process the 200-ml
sample, which your section (group) collected from the chemostat during the previous
week.
2. Section D will turn off and clean the chemostat.
Fourth Week
All Sections
1. Run analyses for NH 4 -N, N0 3 -N, and P0 4 -P on any frozen samples. Follow the
procedures given in Exercise 7.
2. Complete all counts of phytoplankton samples.
3. Check all records and data for possible errors and omissions.
Data Analysis
1. Record all of your data on the sheets provided on pp. 310 and 311. Also fill in the
data collected by the other sections. Answer the questions in items 4 and 5 below.
2. Determine the growth rates for the two dominant species for the interval between
the time of initiation of the experiment and the first collection, and thereafter
between successive collection periods.
3. Calculate the theoretical nitrogen and phosphorus concentrations in the culture
chamber for 2, 4, 6, 8, and 10 days after the beginning of enrichment. Compare these
values with the actual concentrations as determined from the water samples.
Determine the uptake of Nand P per unit volume of ChI a or cells for each of the
above days.
307
2. Each group measures the pH and temperature of a water sample from the outlet
(about 30ml).
3. Half of each group: (a) Collects a 200-ml sample from the outflow tube and processes
it to settle phytoplankton. (b) Counts the phytoplankton sample that was collected
and preserved during the previous week. Handle the sample very carefully so as not
to resuspend any of the settled organisms.
4. Half of each group should perform pigment analyses on a chemostat sample
following the procedure given in Exercise 10.
5. At the end of the laboratory period add the N- and/or P-enrichment solution to one
of the medium reservoirs labeled "Enriched." Refill both of the reservoirs to the 20-1
mark with autoclaved water prior to adding the nutrients.
Enrichment procedure: Using NH 4 N0 3 and/or K 2 HP04, enrich the culture
medium concentrations of Nand P by about tenfold.
Sections B, C and D (Days 10, 12 and 14)
1. Complete Parts 1 through 4 given under the second week for Section A. In Part 3,
you will be processing the 200-ml sample taken the previous week.
2. Check the nutrient reservoirs to see if they need refilling. If so, be careful to create the
proper nutrient concentration.
Third Week
All Sections (2-Day Intervals)
1. Complete Parts 1 through 4 from the second week's schedule. Process the 200-ml
sample, which your section (group) collected from the chemostat during the previous
week.
2. Section D will turn off and clean the chemostat.
Fourth Week
All Sections
1. Run analyses for NH 4 -N, N0 3 -N, and P0 4 -P on any frozen samples. Follow the
procedures given in Exercise 7.
2. Complete all counts of phytoplankton samples.
3. Check all records and data for possible errors and omissions.
Data Analysis
1. Record all of your data on the sheets provided on pp. 310 and 311. Also fill in the
data collected by the other sections. Answer the questions in items 4 and 5 below.
2. Determine the growth rates for the two dominant species for the interval between
the time of initiation of the experiment and the first collection, and thereafter
between successive collection periods.
3. Calculate the theoretical nitrogen and phosphorus concentrations in the culture
chamber for 2, 4, 6, 8, and 10 days after the beginning of enrichment. Compare these
values with the actual concentrations as determined from the water samples.
Determine the uptake of Nand P per unit volume of ChI a or cells for each of the
above days.