♻️AP Environmental Science
1. Wetlands are ecosystems characterized by standing water that supports aquatic plants and diverse communities of organisms. These ecosystems play a critical role in nutrient cycling, particularly nitrogen and phosphorus cycling. In a freshwater wetland, nitrogen enters primarily through atmospheric deposition and runoff from surrounding agricultural lands. Wetland plants absorb nitrogen compounds, and bacteria in the sediment transform nitrogen through various processes.
Describe one characteristic of wetland ecosystems that distinguishes them from terrestrial forest biomes.
Explain how nitrogen-fixing bacteria in wetland sediments contribute to nitrogen availability for primary producers.
Figure 1. Dissolved Nitrogen Concentration (mg/L) and Aquatic Plant Biomass (g/m²) Across One Calendar Year (Jan–Dec) in a Freshwater Wetland
Based on the data in Figure 1, identify the month when dissolved nitrogen concentration was lowest.
Based on the data in Figure 1, describe the relationship between dissolved nitrogen concentration and plant biomass during the period from April through August.
Figure 2. Four-Level Energy Pyramid for a Wetland Food Web (kcal/m²/year)
Based on the data in Figure 2, describe what happens to energy as it moves from one trophic level to the next in the wetland food web.
Treatment | Nitrogen added (mg/L) | Phosphorus added (mg/L) | Algae density after 7 days (cells/mL) |
|---|---|---|---|
Control | 0 | 0 | 2,400 |
Nitrogen only | 5.0 | 0 | 2,600 |
Phosphorus only | 0 | 0.5 | 18,500 |
Both nutrients | 5.0 | 0.5 | 19,200 |
Students investigated whether nitrogen or phosphorus limits algae growth in their local pond. They collected water samples from the pond and divided them into four treatment groups. Each sample received different nutrient additions as shown in the following table. After 7 days under controlled light and temperature conditions, students measured algae density in each sample.
Identify the independent variable in the students' investigation.
Describe the purpose of the control group in this investigation.
Based on the data in the table showing algae growth in water samples with different nutrient additions.
Explain why phosphorus is the limiting nutrient for algae growth in this pond ecosystem.
Explain how increased phosphorus runoff from agricultural lands could affect dissolved oxygen levels in the wetland.
Describe one way that the hydrologic cycle moves phosphorus from terrestrial ecosystems into wetland ecosystems. The hydrologic cycle plays an important role in transporting nutrients through wetland ecosystems. During precipitation events, water moves through the ecosystem carrying dissolved nutrients.
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