How does the National Pollution Discharge Elimination System program address point-source pollution ...

(Answer to question 1 )  The NPDES program addresses point-source pollution and issues permits that regulate discharges from wastewater treatment plants and industrial sources.

(Answer to question 2 )  Water evaporates from surface water when it is heated, and condenses when it cools. Water is pure at this point because only water molecules evaporate. When enough water condenses, precipitation occurs. As precipitation moves through the atmosphere it may pick up water soluble pollutants but it may also be fairly pure if not many water soluble compounds are encountered. When precipitation reaches the ground, some of the water infiltrates the soil and some runs off to streams, lakes, and the oceans. This water will pick up solutes from the soil. The water that soaks into the ground may either be capillary water or gravitational water. Gravitational water will percolate through the ground and collect as groundwater in an aquifer and may be released to the surface through seeps and springs. The height of the water table will determine if springs or seeps are flowing or dry. The recharge area for an aquifer may be over a fairly large surface of land. Capillary water will be picked up by plants or evaporate from the soil. Water is transpired through plants, and evapotranspiration is the process by which water is evaporated and transpired from plants.
There are three principal loops in the cycle: (1) In the evapotranspiration loop (consisting of green water), the water evaporates and is returned by precipitation. On land, this water, the main source for natural ecosystems and rain-fed agriculture, is held as capillary water and then returns to the atmosphere by way of evapotranspiration. (2) In the surface runoff loop (containing blue water), the water runs across the ground surface and becomes part of the surface water system. (3) In the groundwater loop (also containing blue water), the water infiltrates, percolates down to join the groundwater, and then moves through aquifers, finally exiting through seeps, springs, or wells, where it rejoins the surface water.

(Answer to question 3 )  Precipitation: any form of water (snow, sleet, hail, rain) that falls from the atmosphere;
Infiltration: water that soaks into the ground;
Runoff: water the runs off the surface; a blue water flow;
Capillary water: water that returns to the atmosphere either by way of evaporation from the soil or by transpiration through plants;
Transpiration: the green flow of water through plants;
Evapotranspiration: the combination of evaporation and transpiration;
Percolation: water that infiltrates into the ground and trickles through the pores or cracks;
Gravitational water: water that is not held in the soil and moves downward under the pull of gravity;
Groundwater: the accumulated water from gravitational water that has encountered an impervious layer of rock or dense clay;
Water table: the upper surface of groundwater;
Aquifer: layers of porous material through which groundwater moves;
Recharge area: the area where water enters an aquifer;
Seep: a natural exit from groundwater where the water flows out over a relative wide area;
Spring: water exits the ground as a significant flow from a relatively small opening.

(Answer to question 4 )  Beginning in 2001, the EPA began publishing water quality nutrient criteria aimed at preventing and reducing the eutrophication that impacts so many bodies of water. The agency listed its recommended criteria for causative factorsnitrogen and phosphorusand criteria for response factors: chlorophyll as a measure of phytoplankton density and a measure of water clarity. The EPA divided the country into ecoregions and determined criteria levels deemed appropriate for the specific region. Like the other water quality criteria, the nutrient criteria are provided as targets for the states as they address their water pollution (and especially eutrophication) problems.

(Answer to question 5 )  In nature, apart from human impacts, eutrophication is part of the process of aquatic succession, discussed in Chapter 4 . Over periods of hundreds of thousands of years, bodies of water are subject to gradual enrichment with nutrients. Thus, natural eutrophication is a normal process. Wherever nutrients come from sewage-treatment plants, poor farming practices, urban runoff, and certain other human activities, humans have inadvertently managed to vastly accelerate the process of nutrient enrichment. The accelerated eutrophication caused by humans is called cultural eutrophication.

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