Earth’s hydrologic cycle Essay

The chemical quality of precipitation in the earth’s hydrologic cycle is significantly altered upon contact with the forest canopy. These chemical changes are traceable to natural biological processes and from polluted airsheds which affects precipitation chemistry. What happens to the water when it reaches solid earth shall be viewed by the chemical changes that occur on the different stages of the hydrologic cycle. Earth’s hydrologic cycle Hydrologic cycle is the process where water moves from and to the earth through the atmosphere over time and space scales powered mainly by the solar energy and gravity. Solar energy drives the evaporation process effectively transforming water from liquid to gas which results to cloud formation through saturation (Davie & Davie 2002). The degree of equilibrium then is the maximum point of saturation in any mixed atmosphere of vapor and air. When the air cools below the dew point, condensation of water vapor begins. The air at higher altitude is less dense producing lesser heat and lesser air pressure giving out cooler air. Condensation is the process through which water vapor changes to its liquid state again in the form of dew, smoke or fog. Precipitation occurs when clouds can no longer hold the heavy water vapor and it falls back to the earth in the form rain or snow and other forms. The distribution of precipitation on earth depends on the patterns of rising and falling air currents. Precipitation fills oceans, river, vegetation, land and other surfaces. Part of the water reaching the ground surface is highly dependent on turbulent transport from the atmosphere to the canopy on its composition, structure and properties. Rainwater picks up dust particles, plant seeds, bacteria, dissolved gases and ionizing radiation as it falls. It also accumulates with chemical substances like sulfur, nitrogen, oxygen, carbon dioxide and ammonia upon hitting the ground. Aerosols, pesticides and fertilizers, sewage and industrial wastes which were introduced into the ground also mix with the infiltrating ground water. If precipitation continues, complete saturation of the soil zone occurs. This allows the water to continue to descend until it merges into a zone of dense rock. Density is directly proportional on its ability to allow penetration of water. Around these rocks are unsaturated and permeable materials called gravel, shale or sand. The boundary between the unsaturated and the water bearing rocks is defined as the water table. Water table could be hundreds of meters below the water surface where sometimes water rises without pumping in the form of springs. Drilling an artesian well will cause the water to gush to the surface until the pressure is equalized. Pumping may be necessary to lift water to the surface. Ground water is largest source of fresh water but is very difficult to track. Ground water well is good if the aquifer water level that supplies it stays the same. Cone of depression occurs when ground water is pumped from an aquifer through a well lowering its water level (Strobel n. d. ). A gradient then occurs producing a flow from the surrounding aquifer into the well decreasing water levels around the well. This results in a conical shaped depression that seems to radiate away from the well continuously expanding in a radial fashion until a point of equilibrium occurs. This plays an important role when planning well placements and deciding pumping rates including distances between wells. References Davie, T. & Davie, T. (2002). Fundamentals of hydrology. New York, NY: Routledge. Strobel, M. (n. d. ). Let’s talk water – cone of depression. Retrieved April 28, 2008 Website: http://nevada. usgs. gov/barcass/articles/Ely27. pdf