Nitrogen and phosphorus in water-sediment system of eutrophic lake amended with biochar-supported Effective Microorganisms: Temporal variation and remediation.

Eutrophication has received worldwide attention, and bioremediation is progressive research of lake control. In a five-month cultivation study, we aim to reduce various forms of nitrogen and phosphorus in the water-sediment system of eutrophic lakes amended with biochar/Effective Microorganisms (EMs) combined with different means. Self-organizing maps revealed that in the absence of exogenous contamination, the nitrogen and phosphorus levels in the water-sediment systems were greatly driven by the temporal variation in cultivation, followed by the depth of the water-sediment system and different amendments. The contents of nitrogen and phosphorus, especially NH-N and SRP, in overlying- and pore-water gradually decreased with cultivated time and increased with depth due to the biological purification and the nutrient deposition. During summer months, the activity of biota promoted the removal of nitrogen and phosphorus, while the decomposition of phytoplankton released the more amounts of DOM (mg/L of DOC) left in water. Based on the temporal and depth variation of nutrients, the amended-groups impacted the overall levels of nitrogen and phosphorus through altering microbial activity and adjusting nutrient redistribution in the water-sediment systems. As an ideal carrier, biochar promoted microbial colonization and biofilm growth, while its-supported EMs improved the microbial activity of amended sediments. Thus, the application of biochar-supported EMs (BE) achieved the most desired repairs in removing nitrogen, phosphorus and DOM in water-sediment system and increasing their immobilization in sediment. The combination of biochar-supported EMs with aeration (BE.A) decreased the overall levels of nitrogen and DOM, but promoted the release of phosphorus in water due to its strong suspended particles' affinity. Additionally, BE.A and BE showed desirable resistance to highly-polluting wastewater inputs. This study provided practical theories for biochar-immobilized microbes to alleviate eutrophication and cycle of nutrients and DOM during summer months.