Modelizacion matemática de la hidroquímica de las aguas de un macizo dolomítico-yesífero. Aplicación a la génesis de los travertinos de las Lagunas de Ruidera

Abstract

Thermodinamíc equations of solution and precipitation carbonates-calcium sulfates let us stablish a mathematical model of calcareous tufa deposits simulation. The conceptual genetic model of calcareous tufa is related with solution of preexisting carbonates in high CO₂, presure ground-water. When ground-water reach surface, the fast degassing processes lead to calcite precipitation. Ground-water are considered placed in two different types of acuifer system: dolomitic aquifer (D) and dolomitic-gypsiferous acuifer (DY). Calcium activity in ground-water (a_S) may be expressed by the relation:

a_s=10^p1 ∙ (pCO₂)^p2 ∙ (T_s)^p3

where, pCO₂ is partiel pressure of CO₂ in equilibrium with ground-water, and T_s, is absolute temperature of ground-water. Values of p₁, p₂ and p₃, constant are, in the case ofa dolomitic aquicer:

p₁= 6,71624   p₂= 0,32933   p₃= 3,64469

However values of p₁, p₂ and p₃ constants in dolomitic-gypsiferous aquifer are:

p₁= 3,29381   p₂= O,03392   p₃= -0,40223

In the same way we may calculate the end calcium activity in surface watering (a_f) after degassing CO₂ in equilibrium with a rural atmosphere (pCO₂=10^-3,503atm). Urban and urban industrial areas may reach pC0₂= 10^-3atm. The rate of precipitation of calcareous tues (Tons per year) may writte:

[[(V_t ∙ a_B / (V_I - S_L (e_L - p_L))] – a_t] ∙ (V_I - S_L (e_L - p_L)) ∙ 10⁵

V_I=water infiltration in the basin (Hm³/year), s_L=marsh and/or lake surface (Km²), e_L=evaporation rate (m/year), P_L=precipitation rate (m/year). This equation let us also stablish, the influence on calcareous tufs sedimentation of basinal, climatological and environmental parameters. Their use may focus to conservation of many present day damaged travertine systems.