The document discusses key concepts about ecosystems and water resources. It defines the water cycle as the continuous process by which water circulates between the Earth's surface and atmosphere. It also explains groundwater as water stored underground and runoff as water flowing downhill towards oceans. Finally, it distinguishes between renewable resources like water that can be replenished versus nonrenewable resources that cannot be renewed.
![Water cycle ,[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)