Cation export, rates

The concentrations of the major ions are commonly expressed in mgL they are also reported in meq or peq L , which permits a check of the ionic balance of an analysis the sum of cations (S in eq L ) should equal the sum of anions (2 in eqL ). Dissolved silica is generally not ionized at pH values commonly found in rivers its concentration is usually expressed in mgL or in pmolL . Ionic contents can also be expressed as percent of S " or S (%Q), which simphfies the determination of ionic types. Ionic ratios (C,/C ) in eq eq are also often tabulated (Na /Cl, Ca " /Mg2+, Cl /SO, etc.). As a significant fraction of sodium can be derived from atmospheric sea salt and from sedimentary halite, a chloride-corrected sodium concentration is commonly reported (Na = Na -Cl (in rneqL )). The export rate... 

TABLE 7.9 Rates of cation export per square meter of catchment for some watersheds underlain by silicate rocks, based on mass-balance calculations... 

Weathering Rate Weathering Rate Cation Export ... 

Stage 1 corresponds to a steady state where base cation concentrations in runoff are relatively constant, averaged over periods longer than an annual cycle. BS of soils is also relatively constant. The rate of export of base cations is equal to the rate of chemical weathering of minerals... 

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