<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="1304" name="water properties" parent="1174" scope="Measurable physical and chemical characteristics of water from different sources."/><bt><term thcode="2" code="1174" name="topics" parent="1" scope="Themes, subjects, and concerns for which USGS information resources are relevant."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><nt><term thcode="2" code="1682" name="dissolved gases" parent="1304" scope="Gases such as ammonia, oxygen, nitrogen, and carbon dioxide in solution measured in a water sample."/><term thcode="2" code="1999" name="dissolved metals" parent="1304" scope="Metal elements in solution, of concern in studies of hazards such as mine drainage and of water resource usability."/><term thcode="2" code="2000" name="dissolved organic compounds" parent="1304" scope="Organic compounds present in water, typically as anthropogenic contaminants including pharmaceuticals, pesticides, and herbicides."/><term thcode="2" code="806" name="nutrient content (water)" parent="1304" scope="Contaminants in water that nourish organisms, especially plants. Includes nitrogen and phosphorus, either of which can lead to the harmful growth of algae and other plants when present to excess in a body of water."/><term thcode="2" code="854" name="oxygen content (water)" parent="1304" scope="Measurement of the concentration of oxygen dissolved in water, which is an important indicator of the condition of a water body."/><term thcode="2" code="1010" name="salinity" parent="1304" scope="Measure of the concentration of salts dissolved in a solution."/><term thcode="2" code="2080" name="sound velocity" parent="1304" scope="Estimates of the velocity of sound in water, indexed by depth at a specific location, usually calculated from other water properties."/><term thcode="2" code="1129" name="suspended material (water)" parent="1304" scope="Sediment or organic material carried in suspension in the water column, in contrast to material that moves on or near the bottom. May be measured directly by sampling, or indirectly by acoustic or optical backscatter or transmission."/><term thcode="2" code="2264" name="water column reflectivity" parent="1304" scope="A measure of the strength of reflection from small particles suspended in water. It is usually measured by sending a pulse of sound or light through the water and measuring the sound or light that is returned. Water column reflectivity can be used to measure the concentration of suspended particles."/><term thcode="2" code="1301" name="water hardness" parent="1304" scope="Indicator of the concentration of alkaline salts in water, mainly calcium and magnesium, as a measure of water quality."/><term thcode="2" code="1302" name="water pH" parent="1304" scope="The negative logarithm of the hydrogen ion concentration or activity of a water solution. Used for expressing both acidity (pH less than 7) and alkalinity (pH greater than 7), with 7 considered neutral."/><term thcode="2" code="1312" name="water temperature" parent="1304" scope="The degrees of heat of water from a given source at a specific time."/></nt><rt><term thcode="2" code="560" name="hydrology" parent="291" scope="Branch of earth science that deals with water as it occurs in the atmosphere, on the surface of the ground, and underground."/><term thcode="2" code="1298" name="water chemistry" parent="437" scope="Branch of chemistry that deals with the elements and compounds in water."/><term thcode="2" code="1306" name="water quality" parent="1174" scope="The chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose."/></rt></descriptor>