Longevity and efficacy of lanthanum-based P remediation under changing dissolved oxygen availability in a small eutrophic lake.

Autor: Neweshy W; Département de Chimie, Université Laval, Canada and GRIL (Interuniversity Research Group in Limnology), Canada. raoul.couture@chm.ulaval.ca., Planas D; Département de Sciences Biologiques, Université de Québec à Montréal, Canada and GRIL (Interuniversity Research Group in Limnology), Canada., Sanderson N; Département de Géographie, Université du Québec à Montréal, Canada and Centre de Recherche en Géochimie et Géodynamique (GEOTOP), Canada., Couture RM; Département de Chimie, Université Laval, Canada and GRIL (Interuniversity Research Group in Limnology), Canada. raoul.couture@chm.ulaval.ca.
Jazyk: angličtina
Zdroj: Environmental science. Processes & impacts [Environ Sci Process Impacts] 2024 Aug 14; Vol. 26 (8), pp. 1336-1347. Date of Electronic Publication: 2024 Aug 14.
DOI: 10.1039/d3em00572k
Abstrakt: We set out to study the seasonal variations in porewater phosphorus and lanthanum concentrations in the dated sediment cores from a small eutrophic lake that has been treated with Phoslock, a lanthanum-modified bentonite (LMB) amendment. Three sites were sampled when the hypolimnion was either oxygenated or anoxic: (i) the lake's deepest point, (ii) a littoral site receiving inflows from the catchment, and (iii) a littoral site influenced by nearby septic tanks. Phosphate (PO 4 3- -P), lanthanum (La), iron (Fe), dissolved organic carbon (DOC) and sulfate (SO 4 2- ) were measured in porewater samples. An inverse diagenetic model was used to quantify fluxes of dissolved elements across the sediment-water interface as well as the net rate of their reactions along the porewater concentration gradients. Results show that porewater P and Fe underwent strong seasonal dynamics, while La did not. P fluxes, 20-fold higher at the deepest site than elsewhere in the basin, were influenced by anoxic conditions in the hypolimnion during summer and winter, suggesting that P mobility remained sensitive to redox fluctuations despite the addition of La. At the deepest site, fluxes of P across the sediment-water interface increased from 1 to 9 × 10 -9 μmol cm -2 s -1 between spring and summer, while the rate of P production to the porewater also increased a hundredfold. These increases were concurrent with Fe mobilization. Finally, sediment dating shows that the fraction of P sequestered by La is buried under freshly deposited sediment at a rate of 2-3 mm per year. These results indicate that external P fluxes and erosion control remain crucial to maintain the longevity of the LMB treatment.
Databáze: MEDLINE