Internal phosphorus loading in a chain of eutrophic hardwater lakes in Saskatchewan, Canada

• Published in: The Science of the total environment 2024-05, Vol.924, p.171493-171493, Article 171493
• Main Authors: Wauchope-Thompson, Michelle S., Baulch, Helen M., Cade-Menun, Barbara J.
• Format: Article
• Language: English
• Subjects: aluminum; Biogeochemical processes; Calcium; cations; environment; eutrophication; fractionation; iron; lakes; magnesium; manganese; nuclear magnetic resonance spectroscopy; organic matter; P-NMR; phosphates; phosphorus; principal component analysis; Saskatchewan; Sediment cores; Sediment P flux; Sediment P fractions; sediments; summer
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.171493

Sediments can act as a source or sink of phosphorus (P) for the water column of lakes. In iron (Fe)-rich softwater lakes, redox processes are important contributors to sediment P flux. However, the contribution of redox processes to P flux in hardwater lakes, with high pH and high concentrations of redox-insensitive calcium (Ca) is unknown. Intact sediment cores, collected in different seasons (summer or fall) from a chain of eutrophic hardwater lakes in southeastern Saskatchewan, Canada, were used to quantify sediment P fluxes in laboratory incubations under hypoxic or oxic conditions at temperatures consistent with the season of sample collection. Geochemical analyses determined concentrations of sediment total (TP) and organic P (TPo), organic matter (OM), total Ca and magnesium, and total and extractable manganese, Fe and aluminum. Sediment P pools were determined using sequential fractionation and solution 31P nuclear magnetic resonance spectroscopy. Sediment P fluxes were significantly higher in sediment cores incubated under hypoxic conditions (−24.4 to 28.5 mg P m−2 d−1) than oxic conditions (−60.3 to 14.2 mg P m−2 d−1). There were significant seasonal and lake differences for TP, TPo and cation concentrations, with Ca the dominant cation in all but one lake. Phosphate bound in the redox-sensitive pool was the only sediment P fraction that significantly differed among the lakes (0.10 to 0.18 mg P g−1 d.w.; 9 to 16 % of TP), with an inverse relationship to sediment P flux. Principal component analysis suggests that high concentrations of internally-generated TPo forms and OM in surface sediments play a key role in internal P loading in these lakes. However, sediment Ca appears to have an overriding effect on sediment P, partially masking the impact of redox control on internal P loading in these hardwater prairie lakes. [Display omitted] •Sediment P flux and chemistry were studied in hardwater eutrophic lakes.•Organic P and redox play an important role in sediment P flux.•P fluxes were higher under hypoxic than oxic conditions.•Calcium had overarching effect on P flux in these hardwater lakes.