Sediment pH structures the potential of the lake's internal P pollution involved in different types of P reactivation

Internal P pollution in lakes is being increasingly recognized as a dominant cause of eutrophication. Lake geo-engineering is a commonly used method to accelerate P deposition and control pollution. This study aimed to bridge the gap between the theory and practice of such geo-engineering methods based on a comprehensive investigation of sediment P reactivation using 171 samples from 64 lakes in China. Given the importance of pH on sediment P lability, sediment pH was hypothesized to structure the potential of the lake's internal P pollution. The results showed that the reactivation of sediment P tended to be promoted by lower Al, Fe, and Ca and higher loss of ignition (LOI) at different sediment pH; it was also promoted with increasing pH at sediment pH < 7 and with decreasing pH at sediment pH > 7. Notably, the key properties, besides total P, affecting the release of soluble P from sediments under anoxic conditions were pH at sediment pH > 7 and Fe content at sediment pH < 7. The factors affecting the potential sediment P pool available for Microcystis aeruginosa were LOI and pH at sediment pH > 7 and LOI, pH, Fe, and Ca at sediment pH < 7. These results verified our hypothesis and suggested that the mechanisms affecting bioavailable P pollution were more complex compared to those of soluble P. The sediment pH effect was further verified owing to the varied coupling of sediment properties with P distributions at different pH. Therefore, the sediment pH effect on the potential of internal P pollution should be taken into full consideration to design appropriate geo-engineering methods for lake restoration.