Spatiotemporal patterns of N 2 fixation in coastal waters derived from rate measurements and remote sensing

[摘要] Coastal lagoons are important sites for nitrogen (N) removal via sediment burial and denitrification. Blooms of heterocystous cyanobacteria may diminish N retention as dinitrogen (N 2 ) fixation offsets atmospheric losses via denitrification. We measured N 2 fixation in the Curonian Lagoon, Europe's largest coastal lagoon, to better understand the factors controlling N 2 fixation in the context of seasonal changes in phytoplankton community composition and external N inputs. Temporal patterns in N 2 fixation were primarily determined by the abundance of heterocystous cyanobacteria, mainly Aphanizomenon flos-aquae , which became abundant after the decline in riverine nitrate inputs associated with snowmelt. Heterocystous cyanobacteria dominated the summer phytoplankton community resulting in strong correlations between chlorophyll  a (Chl  a ) and N 2 fixation. We used regression models relating N 2 fixation to Chl  a , along with remote-sensing-based estimates of Chl  a to derive lagoon-scale estimates of N 2 fixation. N 2 fixation by pelagic cyanobacteria was found to be a significant component of the lagoon's N budget based on comparisons to previously derived fluxes associated with riverine inputs, sediment–water exchange, and losses via denitrification. To our knowledge, this is the first study to derive ecosystem-scale estimates of N 2 fixation by combining remote sensing of Chl  a with empirical models relating N 2 fixation rates to Chl  a .

[学科分类] 大气科学