Different characteristics of sediment nitrogen and phosphorus recycling during cyanobacterial growth and their succession

Purpose Sediment internal nutrient loading plays an important role in algal blooms. Thus, understanding the specific characteristics of nutrient (nitrogen (N) and phosphorus (P)) recycling from sediment is important for clarifying the processes and mechanisms of cyanobacterial growth and succession. Materials and methods Sediments and water samples were collected monthly from five sampling sites in Lake Chaohu for 1 year. N and P concentrations in surface and interstitial water were determined, and fractions of sediment organic matter, P, and iron were quantified. P adsorption characteristics were modeled with adsorption isotherms. Results and discussion Dolichospermum was the dominant bloom species in the western lake in April, followed by Microcystis from May to September in the whole lake. The impulsive regeneration and release mode from iron-bound P and ammonium (NH 4 + -N) regeneration from sediment in spring triggered the Dolichospermum bloom. In early summer, continuous P release potential as well as nitrate accumulation and NH 4 + -N deficiency due to NH 4 + -N prior assimilation by Dolichospermum jointly drove the transition from Dolichospermum to Microcystis due to the energy saving and competitive advantage of rapid uptake and storage of inorganic P as well as a wide range of N utilization forms for Microcystis . All these facts put the Dolichospermum towards common N and P stress. Furthermore, in summer, NH 4 + -N rapid regeneration from organic algal detritus remineralization due to the decline of Dolichospermum developed Microcystis blooms. Conclusions The specific mode and pathway of N and P recycling from sediment determined the dominant algal species based on the particular N and P utilization strategies of the algae. Pulsed and a vast amount of P release facilitated the Dolichospermum growth, while continuous and a small quantity of P release was in favor of Microcystis growth. Organic N hydrolysis from Dolichospermum detritus further supported the development of a Microcystis bloom.