♻️AP Environmental Science
1. Freshwater streams are dynamic ecosystems where energy flows and nutrients cycle through biotic and abiotic components. Macroinvertebrates are small aquatic organisms without backbones that serve as primary and secondary consumers in stream food webs. A typical stream food web is shown below.
Describe one step in the phosphorus cycle that differs from the nitrogen cycle.
Based on the information provided, explain how increased phosphorus from agricultural runoff could affect the carnivorous macroinvertebrate population through energy transfer in the food web.
Figure 1. Phosphorus Concentration and Algal Biomass in Stream Ecosystems
Based on the data in Figure 1, identify the algal biomass when phosphorus concentration is 0.10 mg/L.
Figure 2. Algal Biomass and Average Macroinvertebrate Abundance
Based on the data in Figure 2, describe the relationship between algal biomass and herbivorous macroinvertebrate abundance.
Scientists hypothesized that carnivorous macroinvertebrate populations would increase as herbivorous macroinvertebrate populations increased. Describe one way that the data in Figure 2 support this hypothesis.
Macroinvertebrate biodiversity is an important indicator of stream ecosystem health. A group of students was interested in studying factors that affect macroinvertebrate diversity in local streams. They selected two study sites: a stream flowing through agricultural land with fertilizer runoff and a stream flowing through a forested watershed. The students used kick nets to collect macroinvertebrates from 10 randomly selected locations at each site. They collected samples during the same time of day and under similar weather conditions. Students identified and counted the different macroinvertebrate species in each sample to determine species richness. They also measured water temperature and recorded the average number of species found at each site.
Identify a likely scientific question for the students' investigation of macroinvertebrate diversity.
Identify the independent variable in the students' investigation.
Site | Species A | Species B | Species C | Species D | Species E | Species F | Species G |
|---|---|---|---|---|---|---|---|
Agricultural stream | X | X | X | ||||
Forested stream | X | X | X | X | X | X |
The data from the student investigation of macroinvertebrate diversity are shown in the following table. An 'X' in the table indicates that the species was present at that site.
Explain why the macroinvertebrate community of the forested stream would be more resilient to environmental disturbances, such as drought or pollution events, than the macroinvertebrate community in the agricultural stream would.
Explain how the results of the investigation could have been altered if students had measured macroinvertebrate biodiversity in a stream receiving untreated sewage discharge rather than in the forested stream.
Describe one effect that excess nitrogen inputs from fertilizer runoff can have on dissolved oxygen levels in stream ecosystems. Nitrogen cycling is essential for aquatic ecosystem function. Excess nitrogen from agricultural runoff can disrupt stream ecosystems.
