Dissolved aluminum and silica release on the interaction of Okinawan subtropical red soil and seawater at different salinities: Experimental and field observations

Abstract

The experiment was conducted to investigate the dissolution of Al and silica when two red soils interact with seawater at different salinities. Different soil weights (3, 10 and 20 g) of bulk soil, coarse sand and silt + clay were mixed with 100 mL of natural seawater, 10, 100, and 1000 times diluted seawaters and shaken for 4 hours to obtain the extracts. Two field surveys were also carried out to observe the impact of red soil in four red soil-impacted estuaries in Okinawa Island during September (summer) and January (winter). Our results revealed that the red soils were acidic (pH ~5), dominated by SiO 2 and Al 2 O 3 contents. During the interaction of red soils with the solutions, dissolved Al and silica increased with an increasing soil/solution ratio while the pH decreased to the lowest value of 3.96 in seawater extracts. The highest Al concentration ranged from 5.03 to 40.3 mgL -1 in seawater extracts and differed with diluted extracts by 1 to 3 fold, 6 to 24 fold, and 12 to 45 fold for 10, 100 and 1000 times dilution, respectively. The highest silica concentrations of about 1 to ~11 mgL -1 were observed in seawater extracts and in 10 times dilution, and they varied with 100 and 1000 times diluted extracts by about 1 to ~3 fold only. Salinity is more sensitive to Al release than silica but the pH significantly correlated to both logarithmic concentrations of Al (P < 0.01) and silica (P < 0.001) suggesting the exchange process and H + promoted weathering of silicates, respectively. The field observation also revealed Al increase with salinity from <0.170 mgL -1 in the river waters to the highest value of 0.474 mgL -1 in seawater, suggesting an increasing Al solubility by exchange process. The trend of silica in the field differed from that of the laboratory with the highest concentration of 17.8 mgL -1 in the river and the lowest value of 0.128 mgL -1 in the seawater, which could be largely attributed to the diatom utilization in summer and dilution in seawater, particularly during winter.

Disponibilidade de macronutrientes e rendimento de milho em latossolo fertilizado com dejeto suíno

“…Esse efeito atua em sentido contrário às reações de efeito alcalinizante citadas e também pode ter contribuído para a ausência de efeito do DS na correção da acidez do solo no atual estudo. Entretanto, Shen & Shen (2001) (Chung & Zasoski, 1993;Norton, 2000) derivado da ureia, que foi a fonte de N utilizada nesse tratamento, mostrando consonância com resultados (Mkadam et al, 2006;Ernani, 2008).…”

Seawater causes rapid trace metal mobilisation in coastal lowland acid sulfate soils: Implications of sea level rise for water quality

“…Similarly, decreases in pH have been observed in porewaters of peat soils due to the addition of marine-derived sea salts causing H + exchange (Haraguchi et al, 2003). In particular, the addition of seawater derived cations can increase the concentrations of aqueous Fe 2+ , Al and Si (Portnoy and Giblin, 1997;Mkadam et al, 2006) and decrease pH (Wright et al, 1988). Under acidic conditions, metals such as Al and Fe are more soluble and become increasingly available for biogeochemical transformations (Dent, 1986).…”

Seawater inundation of coastal floodplain sediments: Short-term changes in surface water and sediment geochemistry

“…For example, Al can be readily hydrolysed to further contribute to solution acidity (Driscoll and Schecher, 1990). The acidic surface waters can also potentially enhance dissolution and weathering of silicate minerals, which then contributes to higher concentrations of Al in solution (Mkadam et al, 2006). Similarly, enhanced dissolution of aluminosilicate minerals, such as feldspar, with increasing salinity can also act to increase solution Al (Weston et al, 2006).…”