Solute transport and retention in some soils of West Bengal

Abstract

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 soils for each solute over the entire permeation period. This may be due to the presence of smectitic and iliitic clay minerals having high specific surface area. The value of 'r' in all the soils was greater for the passage of aqueous potassium salts as compared to aqueous MgCl2. This may have arisen from the presence in these soils of considerable amounts of illitic minerals having a high degree of specificity for 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 suggested the 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 for Kaiimpong soil than for Baruipur soil despite the fact that the former had lower clay and organic matter contents, possibly due to greater size of aggregates in the former. The present study also revealed that the increase in compaction level resulted in a greater degree of the aforesaid shifting of the inflexion point of the breakthrough curves.