1. Chapter 7.2 (cont.) Groundwater as precipitation hits the ground, it may either (a) soak into the ground (infiltration) or this water has two alternatives: may be held in soil as capillary water returns to atmosphere by evaporating from soil or by transpiration from plants water may percolate through the soil, eventually accumulating as groundwater (upper surface of groundwater is known as water table) (b) run off the surface runoff flows over the surface of the ground into streams and rivers, which make their way to the ocean or inland seas all the land area that contributes water to a particular stream or river is referred to as the watershed

2. recharge aquifer: layers of porous material through which groundwater moves often difficult to detect location of aquifer groundwater in aquifers may be found at various depths between layers of impervious rock recharge area: area where water enters an aquifer hold 99% of all liquid freshwater

4. purification as water percolates through the soil, debris and bacteria from the surface are generally filtered out however, water may dissolve and leach out certain minerals in most cases, the minerals that leach are harmless— like calcium from limestone groundwater may reach the surface via seeps (water flowing out over a relatively wide area) or springs (water exits the ground from a small opening)

5. pools and fluxes in the cycle the hydrologic cycle consists of four physical processes: (1) evaporation, (2) condensation, (3) precipitation, and (4) gravitational flow three principal loops in cycle: 1. evapotranspiration loop: water evaporates and is returned as precipitation on land, this water is held as capillary water, then returns to the atmosphere via evapotranspiration 2. surface runoff loop: water runs across the ground and becomes part of surface water 3. groundwater loop: water infiltrates, percolates down to join the groundwater, the moves through aquifers

6. human impacts on the hydrologic cycle many of environmental problems stem from direct or indirect impacts on the water cycle: (1) changes to the surface of the Earth as forests are cleared or land is overgrazed, the pathway of the water cycle is shifted from infiltration and groundwater recharge to runoff water runs into streams or rivers sudden influx of water may cause floods and bring increased sediments and pollutants due to surface erosion floods have increased in many parts of the world due to deforestation and overgrazing increased runoff means less infiltration and therefore less evapotranspiration and groundwater runoff

7. human impacts on the hydrologic cycle (2) climate change clear evidence that Earth’s climate is warming because of the rise in greenhouse gases warmer climate means more evaporation wetter means more precipitation and flooding (3) atmospheric pollution aerosol particles form nuclei for condensation more particles lead to formation of more clouds increase in particles from burning coal (sulfates), burning wood (carbon), and dust particle sizes suppress rainfall (4) withdrawing water supplies

8. Chapter 7.3 Water: A Resource to Manage, a Threat to Control uses Americans use less water now than in 1975 most of the water used in homes and industries is for washing and flushing away unwanted materials known as nonconsumptive uses (after treatment, water is again available for human use) irrigation is a consumptive use because the water does not return to its original source (can only percolate into the ground and return via evapotranspiration) 70% of world’s water is used for irrigation; 20% for industry; 10% for direct human use

9. sources in the U.S., 40% of water comes from groundwater sources and 60% comes from surface water in developed countries, the collection, treatment, and distribution of water is highly developed

10. Cleaning Up the Mess ensuring safe drinking water Congress passed the Safe Drinking Water Act (1974) to protect the public from the risk of toxic chemicals contaminating drinking water supplies EPA sets national standards to protect public health, including allowable levels of certain contaminants state and public water agencies are required to monitor drinking water to be sure that it meets the standards

11. groundwater remediation used when dumps, leaking storage tanks, or spills of toxic materials have contaminated groundwater to the point of threatening drinking water techniques involve drilling wells, pumping out the contaminated groundwater, purifying it, and reinjecting the purified water back into the ground or discharging it into surface water