Calcium carbonate is a liming product as good as calcium hydroxide in eutrophic CO2-rich waters

• Published in: Aquaculture Vol. 595; p. 741629
• Main Authors: Sá, Marcelo V.C., Ventura, Lara R., Boyd, Claude E.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.01.2025
• Subjects: Agricultural limestone; Carbon dioxide; Hydrated lime; Shrimp ponds; SC; LSI; DW; TH; SW; Agricultural limestone; Hydrated lime; CH; Carbon dioxide; Shrimp ponds; HDOM; TA
• ISSN: 0044-8486
• DOI: 10.1016/j.aquaculture.2024.741629

Currently, there is still much debate over the correct liming procedures to perform in shrimp ponds, concerning product, dosage, and timing, especially about the use of hydrated lime. The objective of this work was to determine the dissolution rates of Ca(OH)2 and CaCO3 in eutrophic CO2-rich waters with increasing Langelier saturation indexes (LSI), and discuss its importance to the rational liming of shrimp ponds. Three dilutions of seawater were prepared with increasing LSI values, namely −2.0, −1.0 and ≈ 0.0. The study was carried out in three consecutive phases of 5 weeks each. In the first, second and third phases, the flasks were filled with the LSI-2, LSI − 1 and LSI0 waters, respectively. In each phase, eight 2000-mL Erlenmeyer flasks received 1.0 g Ca(OH)2 p.a. and eight flasks received 1.0 g CaCO3 p.a. In four of the flasks that received Ca(OH)2 or CaCO3, one gram of a highly degradable organic matter (HDOM) was added. There were also four control flasks with no liming product but HDOM. The waters' temperature, pH, specific conductance, total alkalinity (TA), total hardness (TH), and the concentrations of Ca+2 and Mg+2 were monitored once a week. HDOM has moderated the increasing effect of Ca(OH)2 on the waters' pH. Regardless the water's LSI, and the liming product, the increase rate of TA was significantly greater in the HDOM-flasks. In all LSI-1 and LSI0 flasks, TH has decreased after the application of the liming products, despite the addition of HDOM. After one week, there was a marked Ca+2 drop in the Ca(OH)2 flasks with no HDOM. In all waters, the concentrations of Mg+2 have decreased significantly after the applications of Ca(OH)2 or CaCO3. Only the HDOM treatments have increased their initial LSI over time. The applications of Ca(OH)2 and CaCO3 in eutrophic CO2-rich waters have produced a total alkalinity higher than 100 mg L−1. Therefore, the anecdotal knowledge that hydrated lime is a superior liming product than agricultural limestone for shrimp ponds has not been supported by the present work. •The organic matter has moderated the increase of water's pH after Ca(OH)2 application.•The differences between CaCO3 and Ca(OH)2 for alkalinity were not significant when a highly degradable organic matter was added to the water.•The concentrations of Mg+2 have decreased after the applications of Ca(OH)2 in brackish waters.•The Langelier saturation index has increased more in the waters containing the highly degradable organic matter.