Managing Eutrophication in a Tropical Brackish Water Lagoon: Testing Lanthanum-Modified Clay and Coagulant for Internal Load Reduction and Cyanobacteria Bloom Removal

Leonardo de Magalhaes (Corresponding author), Natalia Pessoa Noyma, Luciana Lima Furtado, Erick Drummond, Vivian Balthazar Goncalves Leite, Maira Mucci, Frank van Oosterhout, Vera Lucia de Moraes Huszar, Miquel Luerling, Marcelo Manzi Marinho

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Abstract

The release of phosphorus (P) stored in the sediment may cause long-term delay in the recovery of lakes, ponds, and lagoons from eutrophication. In this paper, we tested on a laboratory scale the efficacy of the flocculant polyaluminium chloride (PAC) and a strong P-binding agent (lanthanum-modified bentonite, LMB) on their ability to flocculate a cyanobacterial bloom and hamper P release from a hypertrophic, brackish lagoon sediment. In addition, critical P loading was estimated through PCLake. We showed that cyanobacteria could be effectively settled using a PAC dose of 2 mg Al L−1 combined with 400-mg L−1 LMB; PAC 8 mg Al L−1 alone could also remove cyanobacteria, although its performance was improved adding low concentrations of LMB. The efficacy of LMB to bind P released from the sediment was tested based on potentially available sediment P. A dose of 400 g LMB m−2 significantly reduced the P release from sediment to over-standing water (either deionized water or water from the lagoon with and without cyanobacteria). In sediment cores, LMB + PAC reduced sediment P flux from 9.9 (± 3.3) to − 4.6 (± 0.3) mg P m−2 day−1 for the experimental period of 3 months. The internal P load was 14 times higher than the estimated P critical load (0.7 mg P m−2 day−1), thus even if all the external P sources would be ceased, the water quality will not improve promptly. Hence, the combined LMB + PAC treatment seems a promising in-lake intervention to diminish internal P load bellow the critical load. Such intervention is able to speed up recovery in the brackish lagoon once external loading has been tackled and at a cost of less than 5% of the estimated dredging costs.
Original languageEnglish
Pages (from-to)390-402
JournalEstuaries and Coasts
Volume42
Issue number2
DOIs
Publication statusPublished - Mar 2019

Keywords

  • international
  • Lake restoration
  • Phosphorus control
  • PAC
  • Phoslock
  • Sediment release
  • Geo-engineering

Cite this

de Magalhaes, L., Noyma, N. P., Furtado, L. L., Drummond, E., Goncalves Leite, V. B., Mucci, M., van Oosterhout, F., de Moraes Huszar, V. L., Luerling, M., & Marinho, M. M. (2019). Managing Eutrophication in a Tropical Brackish Water Lagoon: Testing Lanthanum-Modified Clay and Coagulant for Internal Load Reduction and Cyanobacteria Bloom Removal. Estuaries and Coasts, 42(2), 390-402. https://doi.org/10.1007/s12237-018-0474-8