Regulate Hydrological Flows
Water flows into, through, and between ecosystems. Because ecosystems need this water for growth and survival, they play an important role in maintaining and regulating hydrological flows. The Earth’s hydrological cycle depends on ecosystems to serve this role, so that water flows to the sea and is evaporated into the air to provide rain. Water is subject to gravity, which carries it down and away from ecosystems. Therefore, ecosystems must slow water to keep it on-site long enough for plants and other organisms to use it. For example, beavers build dams to make ponds where they can store food and travel underwater to avoid predators. These dams slow water, enabling it to seep into the earth surrounding the ponds. A community of plants grows in this moistened soil, supporting other life and transpiring water into the atmosphere.
Modify Pressure
For many living systems, modifying pressure provides extra strength. For others, it provides ways to move air. To use pressure effectively requires a reliable source of pressure, as well as mechanisms to create and release the pressure as needed. Often, modifications in pressure within a living system are created by water, although air can also be a source. An example of a water-facilitated pressure system is wilted leaves that use hydrostatic pressure to stiffen. They do so by bringing solutes (such as salts) into their cells, which causes them to draw in water.
Distribute Liquids
Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.
