| Abstract: | The chemical composition of natural water is derived
from many different sources of solutes, including gases and
aerosols from the atmosphere, weathering and erosion of
rocks and soil, solution or precipitation reactions occurring
below the land surface, and cultural effects resulting from
human activities. Broad interrelationships among these
processes and their effects can be discerned by application
of principles of chemical thermodynamics. Some of the
processes of solution or precipitation of minerals can be
closely evaluated by means of principles of chemical equilibrium,
including the law of mass action and the Nernst
equation. Other processes are irreversible and require consideration
of reaction mechanisms and rates. The chemical
composition of the crustal rocks of the Earth and the composition
of the ocean and the atmosphere are significant in
evaluating sources of solutes in natural freshwater.
The ways in which solutes are taken up or precipitated
and the amounts present in solution are influenced by
many environmental factors, especially climate, structure
and position of rock strata, and biochemical effects associated
with life cycles of plants and animals, both microscopic
and macroscopic. Taken together and in application with
the further influence of the general circulation of all water
in the hydrologic cycle, the chemical principles and environmental
factors form a basis for the developing science
of natural-water chemistry.
Fundamental data used in the determination of water
quality are obtained by the chemical analysis of water samples
in the laboratory or onsite sensing of chemical properties
in the field. Sampling is complicated by changes in the
composition of moving water and by the effects of particulate
suspended material. Some constituents are unstable
and require onsite determination or sample preservation.
Most of the constituents determined are reported in gravimetric
units, usually milligrams per liter or milliequivalents
per liter.
More than 60 constituents and properties are included
in water analyses frequently enough to provide a basis for
consideration of the sources from which each is generally
derived, the most probable forms of elements and ions in
solution, solubilitycontrols, expected concentration ranges,
and other chemical factors. Mechanisms that control concentrations
of elements commonly present in amounts less
than a few tens of micrograms per liter cannot always be
easily ascertained, but present information suggests that
many are controlled by solubility of their hydroxides or
carbonates or by sorption on solid particles. Many dissolved
organic compounds can now be specifically determined.
Chemical analyses may be grouped and statistically
evaluated by means, medians, frequency distributions, or
ion correlations to summarize large volumes of data. Graphing
of analyses or of groups of analyses aids in showing
chemical relationships among water, probable sources of
solutes, areal water-quality regimen, temporal and spatial
variation, and water-resources evaluation. Graphs may show
water type based on chemical composition, relationships
among ions, or groups of ions in individual waters or many
waters considered simultaneously. The relationships of water
quality to hydrogeologic characteristics, such as stream
discharge rate or ground-water flow patterns, can be shown
by mathematical equations, graphs, and maps.
About 80 water analyses selected from the literature
are tabulated to illustrate the relationships described, and
some of these, along with many others that are not tabulated,
are also used in demonstrating graphing and mapping
techniques.
Relationships of water composition to source rock type
are illustrated by graphs of some of the tabulated analyses.
Human activities may modify water composition extensively
through direct effects of pollution and indirect results of
water development, such as intrusion |
| Genre: | USGS Numbered Series |
| ProdID: | 1842 |
| Citation Author: | Hem, John David |
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| Citation Edition: | 3rd ed. |
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| Citation Language: | ENGLISH |
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| Citation Phsyical Description: | xii, 264 p. :ill., maps ;28 cm.; 3 plates in pocket |
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| Citation Publisher: | U.S. Geological Survey ;
For sale by the Distribution Branch, Text Products Section, |
| Citation Series: | Water Supply Paper |
| Citation Series Code: | WSP |
| Citation Series Number: | 2254 |
| Citation Search Results Text: | Study and interpretation of the chemical characteristics of natural water; 1985; WSP; 2254; Hem, John David |
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| Citation Year: | 1985 |
| Type: | citation/reference |
| Text: | Study and interpretation of the chemical characteristics of natural water; 1985; WSP; 2254; Hem, John David |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/usgs_thumb.jpg |
| URL (INDEX PAGE): | http://pubs.water.usgs.gov/wsp2254 |
| Date Other: | Sat, 1 Jan 1994 00:00 -0600 |
| Publisher: | U.S. Geological Survey ;
For sale by the Distribution Branch, Text Products Section, |
