The Movement of Water
Hydrology is the study of the movement, distribution, and quality of water throughout the Earth, including the hydrologic cycle, water resources and environmental relationships.
“The hydrologic cycle is the water cycle, including precipitation of water from the atmosphere as rain or snow, flow of water over or through the earth, and evaporation or transpiration to water vapor in the atmosphere. Water evaporates from the earth and rises into the atmosphere where it forms clouds. In nature, this is where water is in its purest form. However, it does not stay that way for long. Its stay in the air is short. Water droplets forming in clouds, absorb particles and impurities found floating in the air.”
Before launching into the individual water quality parameters and interactions, some discussion is needed to put the Earth’s water systems or hydrologic cycle into perspective. A wide variety of representations of the hydrologic cycle exist.
The water cycle is subject to various water processes of condensation, precipitation, evaporation, transpiration, interception, infiltration, percolation, storage, and runoff.
Although the work of circulating water and transporting non-aqueous material are major aspects, by no means are these the only water processes to be considered. There are many different paths that continuous water circulation can occur, or places where water can be stored for periods of time.
Conditions for aquatic life in lakes and rivers are largely determined by the physical and chemical properties of water including its stability and solvent powers. Since aquatic life and organism communities can exist only within a narrow range of environmental conditions, the properties of water help maintain the boundaries of the aquatic environment.
Each organism that lives in water or otherwise uses it, influences to some degree the energy and materials the water carries. Many changes that organisms bring about in water are essential to the existence of their own and other kinds. Man is no exception.
A major impact on the environmental factors influencing the composition of the water results from the land use activities of man. The power of man to alter his environment is awesome and is evident by the many changes which civilization can bring about in the water resources. Solutes may be directly added to water by disposal of various wastes. The ecology of whole drainage basins may be profoundly altered by bringing land into cultivated agriculture and urbanization.
For example: This is a river in India that is flowing trash, plastics and garbage.
Studies have estimated that rivers of North America carry an average natural load of 85 metric tons per year in solution for each square mile of drainage basin. Imagine what this river must be carrying. Plus, water movement rates and solute circulation rates can be altered by water diversions, structures, and paved surfaces that replace open land.
However, by practicing careful management and use of fresh water, man can maintain the conditions necessary for aquatic life and also provide for his drinking water, aesthetic and material needs associated with water.