Dissolved salts, soils

The resistivity of the soil in any particular location will be a function of moisture content, soil temperature and presence of dissolved salts. At a site where climatic conditions vary considerably throughout the year, earth electrodes should be buried at a depth where such changes will not affect the resistivity. Grounding rods are generally made of copper bonded onto a steel core. The copper provides a good connection to earth and offers a high corrosion resistance, while the steel core gives the mechanical... 

Soluble salts of the soil Water in the soil should most properly be considered as the solvent for salts of the soil the result being the soil solution. In temperate climates and moderate rainfall areas, the soil solution is relatively dilute, with total dissolved salts ranging from 80 to 1 500 p.p.m. Regions of extensive rainfall show lower concentrations of soluble salts as the result of leaching action. Conversely, soils in arid regions are usually quite high in salts as these salts are carried to the surface layers of the soil by water movement due to surface evaporation. 

The liquid in which the SAH swelling takes place in real soil (the soil solution) always contains a more-or-less wide set of dissolved salts. Their nature and amount depend on the soil composition, the degree of its salinity, the nature of water entering the soil (rainfall, irrigation, river, or groundwater), the fertilizers used. As a rule, alkali cations, Ca2 +, Mg2+, Fe3+, Al3+, and anions CP, CO, SO4, etc. are the main components of the soil solution there exist various models of soil solution and nutrient mixtures employed in research, including SAH testing. 

In low-rainfall regions, salts are not readily washed out of soils and may even build up on the soil surface. This happens when rain dissolves salts in the soil surface and leaches them a little way into the soil. Subsequent evaporation of water from the soil surface causes water and dissolved salts to move to and be deposited on the soil surface. No salts or only the most soluble salts are leached out of the soil, in low-rainfall regions, and the pH is typically basic. 

Salinity occurs in coastal areas affected by seawater, in areas receiving salty water by lateral flow from salt-bearing rocks upstream, and also in otherwise non-saline environments as a result of soil waterlogging, mainly due to high ground water. In waterlogged land, whatever dissolved salt is brought in with the... 

Rain water dissolves salts present in rocks and soil. The dissolved salts then enters the rivers and underground water. 

Notation o=e1ectrical conductivity, ic-real relative permittivity, subscripts mix, f and p denote soil-flu id mixture, fluid, and particle, respectively, /-ionic valence, c-ionic concentration, u=ionic mobility is, F =96485.3 C/mol is Faraday s constant, TDS= total dissolved salts in [mg. L], n=porosity, p=density, =surface conduction, S,=specific surface, a=degree of saturation, m=cementation factor, Gv=volumetric water content... 

Freezing soil is considered as porous medium of skeleton (s) of soil grains filled up with pore fluid (/) and ice (i). It is assumed that skeleton and ice are elastic solids and have equal displacements and velocities, pore fluid is an ideal solution of water (w) and dissolved salts (c) and governed by adsorption... 

Another often irreversible constraint to land use is salinity (Scherr 1999), the increase of total dissolved salts in soil and water. Most of the world s saline land, approximately 955 Mha, is affected by primary salinity, a result of natural soil evolution (Ghassemi et al. 1995). Secondary salinity, however, is caused by human activities. 

Solutes (refers to the portion of soil composed of water and mostly dissolved salts (plant nutrients)... 

If weathering reactions prevail (see Section 5.3), the ions present in water depend on both local soil and mineral composition. The concentration of total dissolved salts (and thus the ionic strength) will be moderate in surface waters, and the main ions will be Ca2+, HCO, and silicates, due to the presence of silica (as silicic acid) and calcite or limestone (i.e., crystalline CaCOj), one of the most common and abundant minerals in soil. 

A similar case is that of the Great Salt Lake, whose origin is Lake Bonneville (a remnant of a huge freshwater lake that lost its outlet to the sea), which receives inputs from several rivers and streams but with no outflow other than evaporation. It receives 2 million tons of dissolved salts each year, leached from soils and rocks, and its salinity fluctuates from 5% (similar to seawater) to 27% (near saturation) depending on the water inflow and rain input. 

Sulfuric acid is found in nature in the vicinity of volcanoes. It is also used in industry for manufacturing numerous consumer products. Therefore, the chemical may be released to the environment as a waste product or from unintentional, accidental releases. If released to soil, it will dissolve in soil moisture and migrate with either soil moisture or groundwater flow. If released to water, it will dissolve or create sulfate salts. Dissolved sulfuric acid will react with calcium and magnesium to produce sulfate salts. Sulfuric acid can contribute to the weathering of soil and rocks by reacting with calcium and carbonates contained in soil and rocks. 

Almost all biogeochemical processes in Forest ecosystems are connected with aqueous migration in surface and ground water runoff. Low content of dissolved salts and organic species are the most characteristic features of surface runoff waters of Boreal-climate forest ecosystems. This feature is particularly distinct in Taiga Forest ecosystems with permafrost soils where the zone of extensive water exchange in the river valleys is confined to supra-permafrost waters and to ice-thaw waters. The review of leaching processes is shown in Box 4. 

Because the chemistry of stream water reflects its source in the soil profile, detailed studies of runoff chemistry from small basins should be very useful in delineating the ways and rates at which various elements are released in weathering. In the Mattole basin, it is apparent that groundwater inflow to the stream at the end of the dry season has a relatively high pH ( 8), relatively high dissolved salts (Spec. Cond. 300), and rather low silica (7-8 mg/liter). Thus, the alkalis and alkaline earths are preferentially removed as compared with silica from rock minerals at or near the water table. In surface soils, however, during storm runoff, quite different conditions prevail. The pH of the water may at first be low (5=t), silica release is relatively rapid (8-12 mg/ liter), and alkalis and alkaline earths are removed rather slowly (Spec. Cond. 70-150). The result is that the rate of silica removal compared... 

More recently salinity has been measur ed in terms of tire electrical conductivity (EC) of a solution. In addition to overcoming some of the ambiguities of TDS measurements, the EC measurement is quicker and sufficiently accurate for most purposes. To determine the EC, the solution is placed between two electrodes of constant geometry, including constant distance of separation. When an electrical potential is imposed, the electrical current varies directly with the total concentration of dissolved salts. The current is inversely proportional to the solution s resistance and can be measured with a resistance bridge. Conductance is the reciprocal of resistance and has units of reciprocal ohms or siemens (formerly mhos). The EC of the saturation extract of the soil measures the salinity of the soil. 

As for chemical aspects, the total quantity of non-volatile dissolved substances and their composition are important. Content of chlorides, sulphates and boron, as well as the ratio of sodium to calcium and magnesium are important. If water with a high concentration of soluble substances and sodium with respect to calcium and magnesium is used for irrigation, salting of soils can occur. Salted soils are less fertile, or they can be completely... 

In the world around us we see many solids (soil, rocks, trees, concrete, and so on), and we are immersed in the gases of the atmosphere. But the liquid we most commonly see is water it is virtually everywhere, covering about 70% of the earth s surface. Approximately 97% of the earth s water is found in the oceans, which are actually mixtures of water and huge quantities of dissolved salts. 

Saline soils that are not high in sodium are usually well flocculated as long as the dissolved salts are present. Even alkali soils usually remain flocculated if they contain considerable soluble salts, but if these are removed the deflocculating effect of sodium manifests itself rather quickly and the rate of movement of water through the soil is soon greatly reduced. 

The electrical resistivity method of subbottom exploration/surveying is based on the relationship/correlation between the conductivity of soils and rocks and the ion concentration in their pore waters. The resistivity is, therefore, low in saturated clays, moderate in saturated sands/granular soils, and hi in dense rocks with a few voids, little moisture, and small amount of dissolved salts. 

Mitchell Procedure Mitchell (1977) presented an unpublished consulting report which addressed computing the water content, void ratio, unit weight, and degree of saturation for soils with high salt content. Mitchell defines a readily measured quantity (r) being the mass of the dissolved salt (M J per unit volume of solution which is an easily... 

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