title: Internal ecosystem feedbacks enhance nitrogen-fixing cyanobacteria blooms and complicate management in the Baltic Sea.
abstract: Eutrophication of the Baltic Sea has potentially increased the frequency and magnitude of cyanobacteria blooms. Eutrophication leads to increased sedimentation of organic material, increasing the extent of anoxic bottoms and subsequently increasing the internal phosphorus loading. In addition, the hypoxic water volume displays a negative relationship with the total dissolved inorganic nitrogen pool, suggesting greater overall nitrogen removal with increased hypoxia. Enhanced internal loading of phosphorus and the removal of dissolved inorganic nitrogen leads to lower nitrogen to phosphorus ratios, which are one of the main factors promoting nitrogenfixing cyanobacteria blooms. Because cyanobacteria blooms in the open waters of the Baltic Sea seem to be strongly regulated by internal processes, the effects of external nutrient reductions are scale-dependent. During longer time scales, reductions in external phosphorus load may reduce cyanobacteria blooms; however, on shorter time scales the internal phosphorus loading can counteract external phosphorus reductions. The coupled processes inducing internal loading, nitrogen removal, and the prevalence of nitrogen-fixing cyanobacteria can qualitatively be described as a potentially self-sustaining "vicious circle." To effectively reduce cyanobacteria blooms and overall signs of eutrophication, reductions in both nitrogen and phosphorus external loads appear essential.
authors.affiliation: Department of Biological Oceanography, Finnish Institute of Marine Research, Helsinki, Finland. emil.vahtera@firmr.fi
authors.forename: Emil
authors.initials: E
authors.lastname: Vahtera
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Conley
authors.forename: Bo G
authors.initials: BG
authors.lastname: Gustafsson
authors.forename: Harri
authors.initials: H
authors.lastname: Kuosa
authors.forename: Heikki
authors.initials: H
authors.lastname: Pitkänen
authors.forename: Oleg P
authors.initials: OP
authors.lastname: Savchuk
authors.forename: Timo
authors.initials: T
authors.lastname: Tamminen
authors.forename: Markku
authors.initials: M
authors.lastname: Viitasalo
authors.forename: Maren
authors.initials: M
authors.lastname: Voss
authors.forename: Norbert
authors.initials: N
authors.lastname: Wasmund
authors.forename: Fredrik
authors.initials: F
authors.lastname: Wulff
mesh_terms: D001454:Baltic States; D000458:Cyanobacteria / Q000254:growth & development*; D017753:Ecosystem; D004784:Environmental Monitoring; D005068:Eutrophication; D000860:Hypoxia / Q000473:pathology; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D009586:Nitrogen Fixation; D010101:Oxygen Consumption; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism*; D011157:Population Dynamics; D012308:Risk Management; D012623:Seawater / Q000382:microbiology*; D013997:Time Factors
chemical_list: D010758:Phosphorus; D009584:Nitrogen