The role of the cyanobacteria life cycle on

Impact of cyanobacteria life cycle on
biogeochemistry of the Baltic Sea
Kari Eilola, Inga Hense, Elin Almroth-Rosell, Matthias Gröger, Jenny Hieronymus, Bengt Karlson,
Ye Liu, Sofia Saraiva, Irene Wåhlström, Johannes Johansson and H.E. Markus Meier
Content
• Background
• Cyanobacteria life cycle and model validation
• Modelled historical development of nitrogen fixation
• Sensitivity to reduced nutrient loads
• Summary
Nitrogen fixation and harmful algae
Toxic Nodularia spumigena (left) and
non toxic Aphanizomenon sp. (right).
Photo: A.T. Skjevik
The nitrogen input by cyanobacteria in the
Baltic Proper is estimated between
20 000 – 800 000 tonnes N year-1
Degerholm et al. 2008
N-fix project
Use Baltic Sea ecosystem models that adequately represent cyanobacteria
dynamics and N2-fixation rates to quantify nitrogen input in the past and in future.
RCO-SCOBI
3D Baltic Sea model
Ocean model
RCO (Rossby Centre Ocean model)
3 meter vertical resolution
3.7 km horizontal resolution
Simulated time period: 1850-2008
Bathymetry and
model domain
Cyanobacteria Life Cycle Model
in SCOBI
CLC model
• 3 compartments:
• N2-fixing stage (HET), resting
stage (AKI), recruiting stage (REC)
• Transfer between stages:
• function of actual growth rate of
REC, HET
• maturation time (currently fixed)
• Functional dependencies:
•
Light & Temp-dependent growth,
uptake and fixation rate, Salinity
dependence
• Behaviour:
• Stage-dependent upward and
downward velocity
• Representing Nodulaira spumigena
(modified after Hense & Beckmann, 2006, 2010)
RCO-SCOBI 3D Baltic Sea model
Biogeochemical model
SCOBI (Swedish Coastal and Ocean Biogeochemical Model)
• Inorganic and organic
N and P dynamics
Denitrification
• Sediment N and P
Nitrification
• Oxygen
O2
• Cyanobacteria (N/Pratio dependent growth)
Sediment department
• Diatoms and flagellates
& others
NO3
NH4
PO4
H2S
• Resuspension
From upper layer
Nitrogen fixation
N2
Denitrification
Nitrification
From upper layer
Assimilation
Assimilation
A1
A2
A3
Grazing
Mortality
Assimilation
NBT
Decomposition
PBT
Burial
Resuspension
of sediments
Excretion
Predation
Decomposition
Ammonium
adsorption
ZOO
DET
Faeces
Grazing
Resuspension
Sedimentation
Sedimentation
To lower layer
To lower layer
SED
Waves and currents
RCO-SCOBI 3D Baltic Sea model
Biogeochemical model
SCOBI (Swedish Coastal and Ocean Biogeochemical Model)
• Inorganic and organic
N and P dynamics
• Sediment N and P
• Oxygen
• Resuspension
• Diatoms and flagellates
& others
• CLC model
Resuspension
of sediments
SED
Waves and currents
Evaluation: Cyanobacteria seasonal cycle
Model
No CLC
Model
With CLC
1980-2008
1980-2008
µg Chl l-1
µg Chl l-1
East Gotland deep (monitoring station BY15)
Evaluation: Cyanobacteria spatial distribution
Summer mean 2002-2008
Satellite chl > 4 µg Chl l-1
CLC model chl > 4 µg Chl l-1
Satellite: Aqua, (Terra)
Sensor: MODIS
Data: Level 2 (1km)
Processed using:
pytroll (www.pytroll.org)
Mean value from days with cyanobacteria presence
(summer chl > 4 µg Chl l-1) detected from satellite
images 2002-2008.
Mean value of HET based on CLC model
results. Note: Effect of clouds and surface
accumulation is not accounted for.
Nitrogen loads to the Baltic Sea
• Reference: Reconstructed historical loads
• Sensitivity experiment: Repeat the seasonal cycle of nitrogen and
phosphorus loads from 1950.
Nitrogen fixation
Difference with and without CLC
Difference with and without CLC
Difference with and without CLC
Difference with and without CLC
Baltic Sea nitrogen budget
• Increasing nitrogen fixation
counteracts N-load reductions
(both with and without CLC)
Summary of first CLC model results
• Including life cycle aspects into SCOBI improves the seasonal cycle
and spatial distribution of cyanobacteria.
• Nitrogen fixation of SCOBI with CLC is higher than in the version
without the life cycle aspects.
• Increased internal sinks efficiently remove increased N-supply before
1970; after 1970 the sink capacity is reduced.
• Results of 50 years nutrient load reductions experiment reveal limited
impact on nitrogen fixation in the CLC model version.
• Increased nitrogen fixation during the past decades counteract N-load
reductions.
Thank you for your attention
Future outlook
• Continue development of life cycle description and biogeochemical
model.
• Evaluate temporal and spatial variability of model results to satellite
and ferry box data as well as to monitoring station data.
• Evaluate with biogeochemical data assimilation the impact of bias in
nutrient concentrations of RCO-SCOBI on CLC model results.
Baltic Sea nitrogen budget
• Nitrogen supply mainly balanced to
internal sinks
Baltic Sea nitrogen budget
• Import from Skagerrak change to
export after 1950s
• Small reduction in pools in the last
decades
Evaluation: Oxygen concentrations
Modelled historical development in the central Baltic Sea
With CLC
No CLC
Oxygen deficiency
Cyanobacteria spatial distribution
Satellite
products
2002-2008.
Estimated number of days with cyanobacteria
precence 2002-2008 (based on 7-day composite
satellite images).
Mean value from days with cyanobacteria presence
(summer chl > 4 µg Chl l-1) detected from satellite
images 2002-2008.
Satellite: Aqua, (Terra)
Sensor: MODIS
Data: Level 2 (1km)
Processed using:
pytroll (www.pytroll.org)