Abstract
Phosphorus (P) sorption in sediments plays a significant role in trophic status of a lake. This study investigated the characteristics of P sorption in sediments from three lakes with different trophic statuses (moderately eutrophic, lightly eutrophic and moderately trophic) through kinetic, batch equilibrium and thermodynamic experiments. Results show that pseudo-second-order kinetics best describe P sorption in sediments from the three lakes. Fitting by modified Langmuir and Freundlich isotherms indicates that the moderately trophic lake sediment has higher sorption capacity (maximum of 0.848 mg g−1 at 35°C) than the sediments of the other two lakes at different temperatures (5, 15, 25 and 35°C). Thermodynamic results indicate that the processes of P sorption of the three sediments are spontaneous, entropy-driven and endothermic reactions. The risk of P release in sediments was analysed according to the calculated results of isotherms combined with the change in P fraction. Sediments from the moderately eutrophic lake act as a source in summer. The lightly eutrophic and moderately trophic lakes act as sources in spring and winter, and a pool in summer and autumn, respectively. Furthermore, the amounts of reductant-soluble P, calcium-bound P and iron-bound P are significantly related to the sorption capacity of sediments from the three lakes (p < 0.05). The different sediments have different P release risk, and P fraction in sediment is one of the significant factors of P sorption.
Highlights
Eutrophication is one of the most serious environmental problems in lakes, especially for shallow lakes
The sediments from lakes with different trophic status have different sorption characteristics, with the sediment from a moderately trophic lake having a higher sorption capacity compared with the sediments from eutrophic lakes
soluble and loosely bound P (S/L-P) and Aluminium-bound P (Al –P) were the P fractions which had a significant relationship with sorption capacity in sediments from all three lakes
Summary
Eutrophication is one of the most serious environmental problems in lakes, especially for shallow lakes. The trophic status, one of the most significant indices of lake eutrophication, is commonly defined as the structural and functional quality of water bodies. This parameter is assessed using different indices, such as biological communities, combined with physical, chemical, morphological and hydrological characteristics in various aquatic ecosystems [5,6]. The composition, sorption and release of P in sediment can directly influence P concentration in lakes and may cause a shift in trophic status [7]
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