Dense blooms of diazotrophic filamentous cyanobacteria are formed every summer in the Baltic Sea. We estimated their contribution to nitrogen fixation by combining two decades of cyanobacterial biovolume monitoring data with recently measured genera-specific nitrogen fixation rates. In the Bothnian Sea, estimated nitrogen fixation rates were 80 kt N year⁻¹, which has doubled during recent decades and now exceeds external loading from rivers and atmospheric deposition of 69 kt year⁻¹. The estimated contribution to the Baltic Proper was 399 kt N year⁻¹, which agrees well with previous estimates using other approaches and is greater than the external input of 374 kt N year⁻¹. Our approach can potentially be applied to continuously estimate nitrogen loads via nitrogen fixation. Those estimates are crucial for ecosystem adaptive management since internal nitrogen loading may counteract the positive effects of decreased external nutrient loading.

每年夏天在波罗的海都会形成密集的固氮丝状蓝藻水华。我们通过将二十年的蓝藻生物量监测数据与最近测量的特定属的固氮率相结合，估计了它们对固氮的贡献。在波的尼亚海，估计的固氮速率为 80 kt N 年^-1，近几十年来翻了一番，现在超过了河流的外部负荷和大气沉降 69 kt 年^-1。对波罗的海地区的估计贡献为 399 kt N 年^-1，这与先前使用其他方法的估计非常吻合，并且大于 374 kt N 年^{-1的外部输入}. 我们的方法可以潜在地应用于通过固氮持续估计氮负荷。这些估计对于生态系统适应性管理至关重要，因为内部氮负荷可能会抵消外部养分负荷减少的积极影响。