Comprehensive analysis of nitrogen distributions and ammonia nitrogen release fluxes in the sediments of Baiyangdian Lake, China.

The condition of Baiyangdian Lake (BYDL) will improve as the Xiongan New Area evolves and fulfills its role of easing overcrowding and supporting economic growth. Water and sediment samples from BYDL were analyzed to provide information on nitrogen (N) contamination in BYDL. The mean ammonium N (NH4+-N), nitrate N, and total N concentrations in the water samples were 0.36, 0.12, and 2.22 mg/L, respectively, and the ranges were 0.003-8.38, 0.06-0.30, and 1.25-10.34 mg/L, respectively. The N concentrations in water gradually increased from the north to the south of BYDL. Sediment at 90% of the sampling sites was in or above the moderately contaminated class (1000-2000 mg/kg) defined in US Environmental Protection Agency total N pollution standards. Positive NH4+-N fluxes were found for 28 of the 34 sediment core samples, so the potential for NH4+-N being released from sediment was relatively high. The NH4+-N fluxes were 5.35-48.76 mg/m2/day, and the mean and maximum fluxes were 8.71 and 48.76 mg/m2/day, respectively. Benthic organisms will be affected more by NH4+-N and NH3·H2O in the surface sediment pore water (mean concentrations 4.93 and 0.13 mg/L, respectively) than by the other forms of N.