Clay soils and the importance of Base Saturation in limestone action and water quality maintenance: an evaluation for freshwater aquaculture setup

Abstract

This study investigates the influence of two clay soils on water quality, the action of limestone, and determines which chemical attributes of the soil have the greatest influence on water. A mesocosm system was set up in aquariums, where a 5 cm layer of soil was placed, and subsequently, 21 liters of water were added. Five treatments were evaluated: water + limestone; soil A + water; soil A + water + limestone; soil B + water; soil B + water + limestone. Soils A and B contained 456.00 g kg-1 and 642.00 g kg-1 of clay, 18.37 and 7.23 cmolc dm-3 of cation exchange capacity, 89.39% and 65.45% base saturation, respectively. After 28 days, the water in contact with soil A, without limestone addition, presented pH (7.60±0.14), alkalinity (69.21±4.50 mg L-1), and hardness (55.55±9.61 mg L-1) at levels suitable for freshwater aquaculture. The same effect was not observed for the water in contact with only soil B. When limestone was added, there was no statistical difference (p>0.05) in the water quality parameters in contact with both soils. The interaction between soil and water became evident by the decrease in acidity and increase in base saturation of soil B, without limestone addition. Base saturation showed a positive correlation with all evaluated water quality parameters, with coefficients ranging between 0.63 (alkalinity) and 0.72 (pH). It is concluded that, among the soil chemical parameters, the assessment of base saturation provides more relevant information on how the water in the aquaculture ponds will maintain alkalinity, pH, and hardness. In clay soils, when this index is at 89%, liming is unnecessary because the soil-water interaction maintains pH, alkalinity, and hardness at levels suitable for freshwater aquaculture.