♻️AP Environmental Science
1. A freshwater lake ecosystem supports multiple trophic levels. Phytoplankton are photosynthetic organisms that form the base of the food web. Zooplankton are small animals that consume phytoplankton. Small fish consume zooplankton, and large fish consume small fish, as shown in the following food chain: Phytoplankton → Zooplankton → Small fish → Large fish. Scientists studied how nutrient availability affects primary productivity and energy transfer through the food web.
Describe one step in the phosphorus cycle that occurs in aquatic ecosystems.
Based on the food chain provided (Phytoplankton → Zooplankton → Small fish → Large fish), explain how an increase in phytoplankton biomass would affect the small fish population.
Figure 1. Phosphorus Concentration vs. Phytoplankton Biomass and Zooplankton Abundance (same vertical scale)
Based on the data in Figure 1, identify the zooplankton abundance at a phosphorus concentration of 20 μg/L.
Based on the data in Figure 1, describe the relationship between phosphorus concentration and phytoplankton biomass.
Figure 2. Energy Transfer Efficiency vs. Phosphorus Concentration with 10% Reference Line
Scientists hypothesized that energy transfer efficiency would be greater than 10% when phosphorus concentration exceeds 30 μg/L. Describe how the data in Figure 2 support this hypothesis.
Aquatic invertebrate biodiversity is an important indicator of stream health. A group of students was interested in learning about factors that affect aquatic invertebrate diversity. They selected two study sites: a stream flowing through a forested area and a stream flowing through agricultural land. The students used kick nets to collect invertebrates from 10 randomly selected locations at each site. They identified the different invertebrate species collected to determine species richness.
Identify a likely scientific question for the students' investigation of aquatic invertebrate diversity.
Identify the independent variable in the students' investigation.
Site | Species A | Species B | Species C | Species D | Species E | Species F |
|---|---|---|---|---|---|---|
Forested stream | X | X | X | X | X | X |
Agricultural stream | X | X |
The data from the student investigation of aquatic invertebrate diversity are shown in the following table. An 'X' in the table indicates that the species was present at that site.
Explain why the invertebrate community of the forested stream would be more resilient to environmental stress, such as a drought or pollution event, than the invertebrate community in the agricultural stream would.
Explain how the results of the investigation could have been altered if students had measured invertebrate biodiversity in a stream receiving treated wastewater discharge rather than in the forested stream.
Describe one negative effect that eutrophication can have on dissolved oxygen levels in the lake ecosystem. Agricultural runoff can introduce excess nutrients into aquatic ecosystems, leading to eutrophication.
