Abstract
Macrophyte-dominated eutrophication (MDE) lakes have attracted wide attention due to the high phosphorus (P) loading in sediments that poses a wide spread risk for P release and pollution management. However, because of the superior productivity characteristics, the role of organic P mineralization in sediments in the internal P loading of MDE lake is still under debate. This study investigated the release dynamic of P in the sediments of Lake Caohai, a MDE lake in southwest of China, using a combination of the modified Huffer sequential extraction method, 31P nuclear magnetic resonance spectroscopy (NMR), and composite diffusive gradient in thin films (DGT) technology. Results showed that the apparent P diffusion flux at the sediment-water interface was remarkably high, with a mean value of 0.37 mg m−2 d−1. The phosphate ester organophosphorus components (i.e., Mono-P and Diester-P) continuously deposited and degraded in the sediments maintained the high productivity of the lake, and the mineralization process plays a critical role in the release of internal P. Although the content of inorganic P in sediment is relatively high (accounting for approximately 60% of total P), the reductive mechanism based on P-containing iron oxide/hydroxide has a low contribution to the internal P loading, as was indicated by the low release rate of P-combination iron-manganese (Fe-Mn)/iron-aluminum (Fe-Al) (BD-P and NaOH-P) and the insignificant positive correlations between DGT-labile P and DGT-labile Fe in the sediment cores. Additionally, organic P in sediments could transfer to P-combination Fe-Al/Fe-Mn. However, in severely expropriated environments, the enrichment of P-combination Fe-Al/Fe-Mn in surface sediments inhibited the mineralization of monophosphate to some degree. Taken together, this study emphasized the impact of sediment organic P loading on the release of internal P in lake, highlighting that organic P is also the valuable objects for avoiding eutrophication of MDE lakes.
Highlights
Phosphorus (P), as a limiting nutrient, is very important to lake ecosystems, but its excessive enrichment leads to eutrophication (Álvarez et al, 2017; Lin et al, 2021)
Concentrations of TP and SRP in the overlying water and pore water of surface sediments were higher in the east and lower in the west (Figure 2), which was consistent with the water quality report of Liu et al (2020)
This study reports the dynamic changes of P in the surface sediments of Macrophyte-dominated eutrophication (MDE) lakes with high Dissolved oxygen (DO) and organic-rich environment
Summary
Phosphorus (P), as a limiting nutrient, is very important to lake ecosystems, but its excessive enrichment leads to eutrophication (Álvarez et al, 2017; Lin et al, 2021). Sediments is an important source and sink of P in water, and plays a critical role in the deposition, transformation, and recycling of nutrients in the lake system (Chen et al, 2020; Pu et al, 2020). Studies have substantiated that the release of P in sediments significantly affected the concentration of P in the lake water as well as the migration and transformation of P at the sediment-water interface (SWI) (Recknagel et al, 1995; Wang et al, 2021). Understanding the biological availability and release dynamic of sediment P is of profound significance for the management and restoration of eutrophic lake ecosystems. A thorough understanding of the chemical dynamic of Po and Pi in sediments is vital for predicting the eutrophication process of lakes and the biogeochemical cycle of P
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