| A | B |
|---|
| Tributary | A smaller river flowing into a larger one |
| Watershed | The area of land drained by a river and all its tributaries |
| Wetlands | Systems in which the soil is saturated with water and which generally feature shallow standing water with ample vegetation |
| Freshwater marshes | Small-plant-dominated wetlands |
| Bogs | Ponds covered with thick floating mats of vegetation. Habitat for many carnivorous plants |
| Swamps | Tree-dominated wetlands |
| Value of wetlands | They provide ecosystem services by slowing runoff, reducing flooding, recharging aquifers, protect against hurricanes and filtering pollutants. People have drained wetlands for agriculture |
| Lakes | bodies of standing surface water |
| Groundwater | Any precipitation that doesn’t evaporate, flow into waterways or get taken up by organisms is groundwater |
| Aquifers | Porous, sponge-like formations of rock, sand or gravel that hold water. |
| Zone of aeration | Aquifers upper layer that contains pore spaces partly filled with water |
| Zone of saturation | Aquifers lower layer in which the spaces are completely filled with water |
| Water table | The boundary between the zone of aeration and zone of saturation |
| Aquifer recharge zone | Any area where water infiltrates Earth’s surface and reaches an aquifer below |
| Confined vs. Unconfined aquifer | A confined aquifer is water-bearing, porous rocks are trapped between layers of less permeable substrate (i.e., clay). An unconfined aquifer has no impermeable upper layer to confine it, so its water is under less pressure and can be readily recharged by surface water |
| Water unevenly distributed in time and space | Different regions possess vastly different amounts of groundwater, surface water and precipitation. Water is unevenly distributed in time, as some areas can get half of their annual rainfall in a few hours (monsoons). |
| Benefits and drawbacks of dams | Dams prevent floods, provide drinking water, facilitate irrigation and generate electricity. However, dams can alter habitats, displace populations, capture sediment and disrupt flooding. |
| Diversion of rivers and the impact downstream | The river downstream of a dam becomes deprived of sediment and tidal marshes erode away, degrading the costal environment. River water has long been diverted to enable politically strong yet water-poor regions to forcibly appropriate water from communities too weak to keep it for themselves |
| Inefficient irrigation | Crops via “flood and furrow” irrigation absorb only 45% of water. Overirrigation leads to waterlogging, salinization, and lost farming income. Most national governments subsidize irrigation |
| Water mining | Withdrawing water faster than it can be replenished. |
| Freshwater resources | Drinkable water is rare. Only 25% of Earth’s water is fresh. Most fresh water is tied up in glaciers and ice caps |
| Dams | Obstructions placed in a river or stream to block the flow of water so it can be stored in a reservoir |
| How do developed and developing countries use water differently? | Arid (developing) countries use water for agriculture, developed countries use water for industry |
