Abstract
BackgroundAchieving nitrogen (N) and phosphorus (P) control in sediment remediation projects by adding natural materials is receiving increasing attention. In this study, different natural materials, including iron-rich clay minerals, calcite, kaoline, sugarcane bagasse and Phragmites detritus, were applied to test their effects on N and P in a mesocosm experiment.ResultsIron-rich clay minerals and Phragmites detritus had obvious advantages for P control; they resulted in almost undetectable levels of soluble reactive phosphorus (SRP) in the water column throughout the experiment. This finding can be explained by their strong P adsorption ability. The high level of available organic carbon in the sediment and water column after sugarcane bagasse addition provided enough electron donors for denitrification and dissimilatory nitrate reduction to ammonium (DNRA), which caused nitrate (NO3−-N) deficiency and ammonium (NH4+-N) accumulation in the water column. Additionally, this resulted in anaerobic conditions, further fuelling the release of P from iron-bound P induced by anoxia. Thus, the amount of sugarcane bagasse applied should be considered carefully in order to balance denitrification and DNRA as well as P releases. Calcite and Phragmites detritus are recommended as remediation materials for N removal based on their significant promotion of denitrification and limitation of DNRA, which resulted in low NO3−-N and NH4+-N levels. These results can be explained by the shifts in the functional microbial community composition and abundance after the addition of natural materials.ConclusionsIron-rich clay minerals and Phragmites detritus are promising sediment remediation materials for P immobilization due to their strong P adsorption ability. Taken together, the selection of sediment remediation materials should consider the N and P coupling relationship, to prevent NO3−-N removal from causing P leaching or NH4+-N accumulation.
Highlights
Achieving nitrogen (N) and phosphorus (P) control in sediment remediation projects by adding natural materials is receiving increasing attention
The high level of available organic carbon in sediment and water after sugarcane bagasse addition provided a great deal of electron donors for denitrification and dissimilatory nitrate reduction to ammonium (DNRA) and resulted in anaerobic conditions
The amount of sugarcane bagasse applied for sediment remediation should be controlled in order to balance denitrification and DNRA and to reduce P leaching
Summary
Achieving nitrogen (N) and phosphorus (P) control in sediment remediation projects by adding natural materials is receiving increasing attention. When external N and P loadings have been controlled effectively, the release of internal nutrients dedicates to eutrophication increasingly [41]. The movement of endogenous nutrients is mainly caused by the relative environmental conditions [26]. Several drivers of P release generally include pH, dissolved oxygen, redox potential, temperature, flow rate and biological activity [24, 27]. The crucial factors that can result in the exchange of N at the sediment–water interface, mainly involve the capacity of sediments to retain nutrients (e.g., sediment accumulation rates), the conditions of the overlying water (e.g., dissolved oxygen, pH, redox potential, temperature) and the biota (e.g., bioturbation, bioadvection or rates of microbial N transformation) [7, 30]
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