Solute Transport and Retention in Some Soils of West Bengal

Solute transport involving passage of aqueous electrolytes, namely KCl, K₂SO₄ and MgCl₂ in vertical columns of soils from four locations, namely Baruipur, Gayeshpur, Kalimpong and Matimahal at two different compaction levels has been studied. The experimental data were analysed to obtain the hydraulic conductivity, solute accumulation and breakthrough curves for the aqueous electrolytes in the given soils. The hydraulic conductivity of.the aqueous electrolytes through the soils decreased with the increase in compaction. Baruipur soil having high clay and organic matter contents gave distinctly lower values of hydraulic conductivity for K₂SO₄ than those for KCl. The values of solute accumulation parameter ‘r’ for Baruipur and Gayeshpur soils were greater than those for other soil for each solute over the entire permeation period. This may be due to the presence of smectiticand illitic clay minerals having high specific surface area. The value of ‘r’ in all the soils was greater for the passage ofaqueous potassium salts as compared to aqueous MgCl₂. This may have arisen fromthe presence in these soils ofconsiderable amounts ofillitic minerals havinga high degree ofspecificityfor retaining K⁺ ions. The sigmoid shape of the breakthrough curves (BTCs) for the electrolytes indicated hydrodynamic dispersion. The shifting of the BTCs to the left of the inflexion point suggestedthe preferential flow of solute in the large pores. The shift was minimum for the Matimahal soil having lowest clay and organic matter contents. On the other hand, the shifting was greater forKalimpong soil than for Baruipur soil despite the fact that the former had lower clay and organic matter content, possibly due to greater size of aggregates in the former. The present study alsorevealed that the increase in compaction level resulted in a greater degree of the aforesaid shifting of the inflexion point of the breakthrough curves.