Increased urea is one of the common nitrogen forms polluting coastal waters and affecting nutrient dynamics. To investigate the effects of urea on sediment phosphorus (P) release, we carried out a 2-month mesocosm experiment with six targeted loadings of urea (0-0.6 mg N L-1 d-1). Results showed that: i) urea was rapidly transformed into ammonium and then nitrate (NO3-). ii) When nitrogen occurred as urea or ammonium, minor P release was observed. iii) After urea were mostly converted to NO3-, P release became clearer. iv) NO3- had a dual effect by promoting P release through decreasing sediment pH and increasing alkaline phosphatase activity or by inhibiting P release through improving sediment oxidation. v) The overall effects of urea on P release depended on the ultimate NO3- concentrations, being prominent when NO3- ≥ 11 mg N L-1. Our findings are of relevance when determining nitrogen reduction targets needed for combating eutrophication.
Keywords: Coastal eutrophication; Oxidation of sediment; Phosphorus release; Phosphorus-solubilizing bacteria; Sediment pH; Urea pollution and transformation.
Copyright © 2021. Published by Elsevier Ltd.