For each type of these species in the simulation, list the type of organism it is (Phytoplankton, Zooplankton, and primary producer, primary consumer, or secondary consumer)

Green Algae phytoplankton , producer

Cyanobacteria phytoplankton , producer

Bosmina zooplankton , primary consumer

Daphnia zooplankton , primary consumer

Trout Fish vertebrate , secondary consumer

Table 1. Phosphorus input simulation (set Nitrogen at 1X)

Phosphorus input	Green Algae	Cyanobacteria	Daphnia	Bosmina	Trout	Dissolved O2 (mg/L)
1X	38	150	4	2	5	7.3
2X	15	343	16	1	4	4.0
3x	12	436	22	3	0	1.9

Draw a line graph of your green algae population size data to show how green algae relate to phosphorus input levels.

1. Explain if the relationship in the above graph indicates whether phosphorus is a limiting nutrient for green algae.

   Phosphorus seems to be a limiting nutrient for Cyanobacteria. When P concentration increases: Cyanobacteria population size increases, dissolved oxygen decreases, and trout population crashes.

   Draw a line graph of the relationship of phosphorus input levels to dissolved oxygen in the water.

2. Explain the relationship between phosphorus and dissolved oxygen concentrations in the graph above.

   As P increases, O₂ decreases.

3. Based on your two graphs and your background readings, provide a biological explanation for the relationship between green algae population size and dissolved oxygen in the lake.

   As phytoplankton populations increase, their eventual death and decomposition leads to decreased dissolved oxygen levels.

4. Explain how the presence of consumers influenced producer population sizes and dissolved oxygen levels.

   Primary consumers and decomposers feed on producers, use up oxygen.

TOXIN ANALYSIS DATA: Time = 52 weeks

Organism	Population Size	Mercury (ng/g)
Green Algae	93	26
Cyanobacteria	10	20
Daphnia	10	28
Bosmina	18	29
Trout	6	27

TOXIN ANALYSIS DATA: Time = 104 weeks

Organism	Population Size	Mercury (ng/g)
Green Algae	126	30
Cyanobacteria	11	20
Daphnia	5	67
Bosmina	16	55
Trout	7	133

TOXIN ANALYSIS DATA: Time = 156 weeks

Organism	Population Size	Mercury (ng/g)
Green Algae	131	32
Cyanobacteria	4	10
Daphnia	3	35
Bosmina	10	53
Trout	6	244

Create a line graph showing mercury concentration over a three-year interval in each species. Your graph will include 5 lines, one for each species; be sure to label which line is for which species.

1. Explain the relative amounts of mercury in phytoplankton, zooplankton, and trout over time.

   Mercury in phytoplankton increases slowly, due to bioaccumulation. Mercury in zooplankton increases a little more, due to biomagnification as primary consumers. Mercury in trout increases much more, due to biomagnification as a higher level consumers

2. Did your results indicate whether biomagniication of mercury occurred in the aquatic ecosystem over time? Explain.

   Biomagnification occurred in the consumers: zooplankton and trout.

Hypothesis: Cyanobacteria are capable of nitrogen fixation, so should not need Nitrogen. Both Green Algae Cyanobacteria need Phosphorus as input.

Table 3. Testing the effects of phosphorus and nitrogen levels on green algae and cyanobacteria population sizes.

Phosphorus input	Nitrogen input	Green Algae	Cyanobacteria
0x	0x	19	35
1x	1x	20	152
1x	3x	186	69
3x	1x	29	515
3x	3x	9	452
3x	0x	13	465

Conclusion:

Green Algae grow best when there is abundant Nitrogen. Cyanobacteria grow best when there is abundant Phosphorus. When both N and P are abundant, Cyanobacteria outcompete Green Algae.