Final answer:
The green water at a Thai beach that Walter encountered is most likely due to the presence of phytoplankton or cyanobacteria, often caused by nutrient pollution resulting in algal blooms. Other factors like sulfate-reducing bacteria may also contribute to the green color. The correct answer is option: B. presence of phytoplankton.
Step-by-step explanation:
When Walter visited Thailand and observed green water at the beach, the most plausible explanation for this phenomenon is the presence of phytoplankton or other microorganisms such as cyanobacteria. These organisms contain chlorophyll, which gives water a green hue when they are present in large quantities.
This can often be due to algal blooms, which can occur as a result of nutrient pollution from sources like agricultural runoff containing fertilizers. Additionally, certain types of bacteria, such as sulfate-reducing bacteria, can lead to the production of hydrogen sulfide, which can also contribute to the green appearance of the water when decomposing algae.
It's less likely that the green color is from high copper content, presence of poisonous gases, or mixing of green sand with water. When considering environmental concerns, phenomena such as eutrophication, which is characterized by a rapid increase in algae due to excess nutrients, may lead to decreased oxygen levels in the water, resulting in adverse effects on aquatic life.
Therefore, to support a positive environmental impact, it is important to manage nutrient input into natural waters, such as cutting down on fertilizer use and preserving wetlands.