Dissolvable nitrogen variation at water-sediment interface during alga blooming process in Chaohu Lake.

In order to recognize the concentrations changes during the alga bloom and estimate the diffuse flux of inorganic nitrogen at the sediment –water interface, dissoluble nitrogen forms in the overlying water and surface sediment pore water from eight sites of Chaohu Lake were investigated and analysized from April to October in 2008. Concentrations of NH4+-N decreased as alga bloom intensity increasing, and concentrations of NO3--N decreased obviously only during the period of serious alga bloom, while concentrations of dissoluble total nitrogen (DTN) increased obviously after alga bloom. NO3--N and NH4+-N were the major dissoluble nitrogen forms in the overlying water before the big-size alga bloom during the period of April and May, however, the dissoluble organic nitrogen (DON) was the major nitrogen form after the alga bloom. NH4+-N was the major nitrogen form in the pore water, which concentrations increased with the temperature increase. Concentrations of DTN decreased firstly and then increased during the alga bloom process. According to the diffuse flux calculation, NH4+-N always released from pore water to overlying water, the diffuse flux in the western and eastern lake regions ranged from 13.06 to 32.94 mg/(m2·d) and 4.54 to 17.41 mg/(m2·d), respectively. Nutrient exchanges at the sediment-water interface are the most important nutrient supplement way for the sustainable algal bloom.