GeoData Center Project: Nenana RiverWater Basics
The Phase Diagram of Fresh Water
A phase diagram is a graphical way to depict the effects of pressure and temperature on the phase of a substance. This water phase diagram shows whether a substance exists as a vapor, liquid, or solid at a given temperature and pressure.
The curves indicate the conditions of temperature and pressure under which equilibrium between different phases of a substance can exist. The triple point occurs where the three lines intersect in a phase diagram and indicates the pressure and temperature where solid, liquid, and vapor all exist in equlibrium.
The critical point is the thermodynamic state in which liquid and gas phases of a substance coexist in equilibrium at the highest possible temperature. At higher temperatures than the critical no liquid phase can exist.
For water the critical point is:
es = 2.21 x 105 mb
T = 647°K
α = 3.1 gm cm-3
where es is the saturation vapor pressure of the water vapor, T is the Kelvin temperature, and α the specific volume. (The specific volume is the volume per unit mass of a substance, and hence the reciprocal of density.)
A torr is a non-SI unit of pressure and is the pressure exerted by 1mm of mercury (Hg). A standard atmosphere of pressure equals 760 torr or 1 torr equals 0.001316 atmospheres.
QUESTION: At what temperatures do ice and liquid water and liquid water and water vapor exist in equilibrium?
The Hydrological Cycle
The hydrological cycle is powered by solar energy and is the continuous circulation of water from the atmosphere to earth and oceans and back again. It involves changes in the physical state of water between liquid, solid, and gas phases. The amount of water never changes but its state and position in the cycle does change.
Source: United Nations Environment Program (UNEP)
QUESTIONS: Where are the ice and snow in the water cycle?
What is their impact on the cycle?
See animations of some of these processes.
Click here to learn more about the world's water cycle
Hydrological Cycle Definitions
Condensation: The process of water changing from a vapor to a liquid. Water vapor in the air rises mostly by convection. This means that warm, humid air will rise, while cooler air will flow downward. As the warmer air rises, the water vapor will lose energy, causing its temperature to drop. The water vapor then has a change of state into liquid or ice.
Evaporation: The process by which water changes from a liquid to a gas and is transferred from the earth’s surface to the atmosphere. Radiant energy from the sun heats water causes water molecules to become so active that some of them rise into the atmosphere as vapor. Approximately 80% of all evaporation is from the oceans, with the remaining 20% coming from inland water and vegetation.
Groundwater: The underground water trapped between layers of rock or clay. Water that infiltrates the soil flows downward until it encounters impermeable rock and then travels laterally. The locations where water moves laterally are called ‘aquifers’. Groundwater returns to the surface through these aquifers , which empty into lakes, rivers and the oceans. The flow of groundwater is much slower than run-off with speeds usually measured in centimetres per day, metres per year or even centimetres per year.
Infiltration: The portion of the precipitation that reaches the Earth's surface and seeps into the ground. The amount of water that infiltrates the soil varies with the degree of land slope, the amount and type of vegetation, soil type and rock type, and whether the soil is already saturated by water. The more openings in the surface (cracks, pores, joints), the more infiltration occurs. Water that doesn't infiltrate the soil flows on the surface as runoff.
Percolation: The gravity flow of water within soil from the surface or surface groundwater into the groundwater table. In general, water flow in which gravitational forces predominate.
Precipitation: The primary mechanism for transporting water from the atmosphere to the surface of the earth. Precipitation begins after water vapor, which has condensed in the atmosphere, becomes too heavy to remain in atmospheric air currents and falls from clouds as rain, sleet, snow, or hail. A proportion of atmospheric precipitation evaporates.
Surface Runoff: Precipitation that reaches the surface of the Earth but does not infiltrate the soil. Runoff can also come from melted snow and ice. When there is a lot of precipitation, soils become saturated with water. Additional rainfall can no longer enter it. Runoff will eventually drain into creeks, streams, and rivers, adding a large amount of water to the flow. Surface water always travels towards the lowest point possible, usually the oceans. Along the way some water evaporates, percolates into the ground, or is used for agricultural, residential, or industrial purposes.
Transpiration: The process by which water absorbed by plants, usually through the roots, is transferred as water vapor to the atmosphere from a single leaf, or the amount of water so transferred.
Transport: The movement of water through the atmosphere, specifically from over the oceans to over land. Most water is transported in the form of water vapour, which is actually the third most abundant gas in the atmosphere. Some of the earth’s moisture transport is visible as clouds, which themselves consist of ice crystals and/or tiny water droplets. Clouds are propelled from one place to another by either the jet stream, surface-based circulations like land and sea breezes or other mechanisms. However, a typical cloud 1 km thick contains only enough water for a millimetre of rainfall, whereas the amount of moisture in the atmosphere is usually 10-50 times greater than this.
Water Table: The level below the land surface at which the subsurface material is fully saturated with water. The depth of the water table reflects the minimum level to which wells must be drilled for water extraction.
For more meteorlogical definitions click here and hereHydrological Cycle Facts
Over 70% of the earth's surface is covered by water. However, not all of it is useable by human beings. Some sources of freshwater have long "replacement" times.
SOURCES OF FRESHWATER
| ALL WATER ON EARTH | |||
|---|---|---|---|
| Oceans | 97.5% | Freshwater | 2.5% |
| Glaciers and permanent snow | 79.0% | ||
| Fresh ground water | 29.9% | ||
| Freshwater lakes and river storage (only renewable portion of the system) | 0.3% | ||
| Other sources including soil moisture, swamps and permafrost | 0.9% | ||
QUESTION: How much of the earth's water supply is accessible for human consumption?
RENEWAL TIME OF SOME FRESHWATER SOURCES
| Water in the Hydrosphere | Period of Renewal |
|---|---|
| Ocean | 2500 years |
| Ground water | 1400 years |
| Polar ice | 9700 years |
| Mountain glaciers | 1600 years |
| Ground water in permafrost zone | 10000 years |
| Lakes | 17 years |
| Bogs | 5 years |
| Soil moisture | 1 years |
| Channel network | 16 days |
| Atmospheric moisture | 8 days |
QUESTION: How long does it take to completely replace the water in the hydrosphere?
Source: All data United Nations Educational, Scientific and Cultural Organization
Fresh Water Ice Phenology
Frazil ice forms small pancakes on the Chena River,
Fairbanks, Alaska in autumn 2006.
Border ice forms along the banks of the Chatanika River, Fairbanks, Alaska in autumn 2006.
The phenology of an ice cover is the freeze-up date, break-up date and ice cover duration.
Freeze-up (FU) defines the period between initial ice formation and the establishment of a complete ice cover. The FU data is the day that the pond is completely ice covered.
After the lake cools to 4°C (maximum density of water), the water surface cools to the freezing point and ice begins to form.
The first ice to form (initial ice skim) often appears first as border ice in shallow, protected areas. However, the entire lake surface can reach the freezing point simultaneously and a continuous ice cover will appear in a matter of a hours.
Break-up (BU) defines the period between the onset of snow melt and the complete disappearance of the ice. The BU date is the day when the lake is completely ice free.
When average daily air temperatures rise above the freezing point, ice begins to decay by:
- •dimensional thinning (top, bottom and sides) and
- •deterioration of the ice crystal grains at their boundaries.
Thinning of the ice layer is caused by heat transfer and by melting at the top or bottom surface (or both) or by contact with inflowing warm water.
Taken together freeze-up and break-up denote the endpoints of the ice cover duration.
A large ice jam forms at Crookston, MN (April 18, 1997) during the spring break-up. This kind of occurrence can lead to flooding further upstream.
Source: US Army Corps of Engineers.
Historical Changes in Northern Hemisphere Freshwater Phenology
There is ample evidence that freshwater ice freeze-up, break-up and ice duration (referred to as phenology) are primarily a function of weather and climate, particularly air temperature. The Magnuson et al. (2000) Northern Hemisphere data (right) show a trend towards later freeze-up, earlier break-up and shorter ice duration (decrease of 20 days since 1845). This equals a temperature change of 1.2°C per 100 years.
The Nenana Ice Classic data documents the first movement of ice on the Tanana River. As of spring 2004, break-up was occurring 5.2 days earlier relative to the vernal equinox than in 1917. The advance of break-up is strongly related to rising spring mean air temperatures.
More information: Nenana Ice Classic data.
Note: break up dates trend downwards (earlier), freeze up dates trend upwards (later) and duration values trend downwards (shorter).
Source: Magnuson et al. (2000) and NSIDC.
Project Details
Nenana River Project
Monitoring the freeze-thaw cycle of the Nenana River
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