Final answer:
Reservoirs in the biogeochemical cycle hold water or elements for a long time, with glaciers and ice caps being the largest fresh water reservoirs. Groundwater is the most significant reservoir of usable fresh water. Dams can provide benefits like water storage and electricity, but also impact ecosystems.
Step-by-step explanation:
Reservoirs, or 'pools', are an integral component of the biogeochemical cycle and represent parts of the cycle that hold an element or water for a prolonged duration. The world's largest reservoir of liquid freshwater is glaciers and ice caps, which are mostly found in Antarctica and Greenland. When considering readily accessible freshwater, shallow groundwater represents the most significant reservoir of usable fresh water.
Concepts like residence time are used to understand the average time an element or molecule remains within given reservoirs. Meanwhile, bodies of water such as oceans, lakes, streams, and groundwater sustain ecosystems and human societies by providing water for various needs, but they can also have environmental impacts when altered by human activity, such as the construction of reservoirs behind dams. Dams can offer benefits like hydroelectric power and water storage, yet they can also pose challenges, including affecting aquatic ecosystems and water quality. Examples of reservoirs include oceans, lakes, groundwater, and glaciers and ice caps.