To recover or not to recover – the ”Laurentius-equation”

Søren Laurentius NielsenRoskilde University

Original dataset based on:

• 162 transects /stations• 23 areas• Data from years 1980 –

1991• Data from the then

Danish counties

Spearman- Rank Correlation Coefficients – all significant

Established these relationships:

• Nutrients (N, P) → Phytoplankton biomass• Phytoplankton biomass + suspended matter →

Secchi depth• Secchi depth → Eelgrass depth limit• TN → Eelgrass depth limit

N and P vs. Phytoplankton biomass2

2

2

ln( ) 1.072ln( ) 4.959 0.391

ln( ) 0.759ln( ) 1.197 0.277

ln( ) 0.806ln( ) 0.344ln( ) 4.666 0.414

phyto

phyto

phyto

B TN R

B TP R

B TN TP R

2ln( ) 0.367 ln( ) 0.444ln( ) 2.686 0.808sd phytoZ Susp B R

20.787 0.339 0.606c sdZ Z R

2ln( ) 0.755ln( ) 6.039 0.547cZ TN R

• The equations reflect a comparison between locations

• Not a development over time• Later uses imply a place for time substitution• Variation caused by differences among

locations in other factors

Sediment characteristics suspected

2

0.703 / 12.2

0.703 0.082( / 12.2) / 12.2 0.81c sd

c sd

Z Z C N

Z Z C N C N R

Krause-Jensen et al., Vand & Jord, 2007Krause-Jensen et al., MEPS, 2011

(it might get quite complicated…)

Krause-Jensen et al., MEPS, 2011

Causal links:

N - loading

N - concentration

Phyto-plankton

Light Depth limit

Algal mats

Organic matter

Changes insediment

Anoxia

Resus-pension

Markager S., Carstensen J, Krause-Jensen D, Windolf J, Timmermann K. 2010. Technical report from NERI no. 787. http://www.dmu.dk/Pub/FR787.pdf

Based on empirical analyses of data from Skive Fjord, Horsens Fjord and Odense Fjord

Kemp et al. 2009

Hysteresis and regime shifts

Duarte et al., Estuaries andCoasts, 2009

Conceptual modelMarkager S., Carstensen J, Krause-Jensen D, Windolf J, Timmermann K. 2010. Technical report from NERI no. 787. http://www.dmu.dk/Pub/FR787.pdf

Reasons for the hysteresisCausal links:

N - loading

N - concentration

Phyto-plankton

Light Depth limit

Algal mats

Organic matter

Changes insediment

Anoxia

Resus-pension

3d dynamic model

Sediment physics

Sediment lability

Benthic fauna

Vegetation

Wave & current energy

Input Output

Hydrodynamic simulation

TD, sediment transport simulation

Ecological simulation

Erosion/deposition

Bio-sedimentation