Final answer:
The answer to the student's question about freshwater ecosystems is that a kelp forest is not a freshwater ecosystem but a marine one. Kelp forests are found in oceanic neritic zones, whereas freshwater ecosystems include rivers, lakes, streams, and swamps.
Step-by-step explanation:
The correct answer to the question of which of the following is not a freshwater ecosystem is kelp forest. A kelp forest is a marine ecosystem, typically found in oceanic, neritic zones along coastlines and is characterized by high concentrations of kelp, which are large brown algae. Freshwater ecosystems, on the other hand, include rivers, lakes, streams, and swamps, and are defined by their low salt concentration, usually less than 1%. Freshwater ecosystems like rivers and swamps may have varying water flow, with marshes and swamps often characterized by slow water flow. Phytoplankton are photosynthetic organisms more likely to grow in lakes as opposed to rivers due to the stable water conditions that favor their development.