Which of the following best explains how human activity on land can have a profound influence on marine ecosystems?

• A. Runoff from agriculture can carry fertilizers into rivers, leading to nutrient pollution and algal blooms in marine environments.
• B. Urban development on land decreases the salinity of marine ecosystems.
• C. Mining on land directly increases the population of marine mammals.
• D. Deforestation on land increases the oxygen content of ocean water.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the problem by identifying the key question. The question asks how human activity on land can significantly impact marine ecosystems. This requires understanding the connection between terrestrial activities and aquatic environments.
2. Step 2: Analyze the provided options. Each option describes a potential impact of human activity on marine ecosystems. Evaluate each one based on biological and ecological principles.
3. Step 3: Evaluate the first option: 'Runoff from agriculture can carry fertilizers into rivers, leading to nutrient pollution and algal blooms in marine environments.' This is a well-documented phenomenon known as eutrophication, where excess nutrients (like nitrogen and phosphorus) from fertilizers promote algal blooms, which can deplete oxygen levels in water and harm marine life.
4. Step 4: Evaluate the second option: 'Urban development on land decreases the salinity of marine ecosystems.' While urban development can affect water quality, it does not typically decrease salinity in marine ecosystems. Salinity changes are more often influenced by freshwater inputs or evaporation rates.
5. Step 5: Evaluate the remaining options: 'Mining on land directly increases the population of marine mammals' and 'Deforestation on land increases the oxygen content of ocean water.' Both are biologically inaccurate. Mining does not directly increase marine mammal populations, and deforestation typically reduces oxygen production (due to fewer trees), not increases it in ocean water. Therefore, the first option is the most accurate explanation.