Towards a consistent description for dynamics of
plankton, suspended matter and nutrients
Ecosystem Modelling Group (KSE)*
in collaboration with Coastal Oceanographic Measurement Systems and Modelling for the Assessment of Coastal Systems
Wadden Sea SPM consists of 30%
organic particulate matter (POM)
Residual coastal transport affects
community production
In our approach we link classical descriptions of passive tracer SPM
dynamics to organic matter production and degradation. For
biogeochemical modelling we need to explicitely resolve the organic
content of total SPM, thereby accounting for the Wadden Sea act as a
large bioreactor with high turnover rates of organic matter. Typical
observed SPM concentrations comprise a mean fraction of 30% organic
matter.
Coastal nutrient gradients are observed in the German Bight for phosphate
and silicate. Residual estuarine circulation an important mechanism for net
transport of organic matter towards the coast. Photosynthetically available
light, controlles the magnitude of plankton productivity, which largely
depends on turbidity. Thus, horizontal variation in primary production thus
underlies processes that affect turbidity (like tides, horizontal density
gradients, surface waves, wind mixing and aggregation of SPM).
Fig. 1: Relative ignition loss of filtered
SPM samples of different campains
in the Wadden Sea plotted over the
respective SPM concentrations. The
logistic regression assumes that a
hypothetically smallest detectable
SPM concentration does not include
any lithogenic particulate matter but
is purely organic.
Fig.
2:
The
simulated
net
community production along a
transect from Buesum (right hand
side) in direction of Helgoland.
During vertical mixed conditions,
the bloom starts earlier in shallow
areas. Organic matter is transported
towards the coast which causes the
shallow waters to become net
heterotroph.
river
runoff
PLANKTON
SHELF SEA
us
d ie
s, a
es
ggr
Light
ega
te s
growth needs
a ffe
c te d
to
Residual
transport
by
SPM
o rg
to
,
s
d
e
rri ra d e
a
c
g
de
ic s
n
a
Resuspension
(event driven)
NUTRIENTS
Pore water
exchange
COAST
sea surface
Fig. 3: Overview
of relevant physical-biological processes
creating lateral heteregoenity in ecosystem variables
(Plankton, SPM, Nutrients)
Consider
sediment
diagenesis
Wadden Sea nutrient budgets
50 m depth
Spring bloom
triggered by vertical stratification
Fig. 4: Location of the tidal front at the latitude of
Helgoland over the spring months and the bloom
onset for four different years
Interannual variability of plankton
production in the central German
Bight
is observed
at the
Helgoland Roads station. The
location of the tidal front, which
determines the importance of
resuspension
and
vertical
transport of SPM, can be linked
to the onset of the spring bloom
near
Helgoland.
Therefore,
vertical stratification needs to be
reproduced by the circulation
model in order to resolve
temporal variations in plankton
productivity.
for
Our ecosystem model MAECS (see MAECS poster) is coupled to a
sediment diagenesis model, based on OMEXDIA. This allows us to close
the nutrient budgets at the sediment boundary. The degradation of
particulate matter in the sediments under suboxic and anoxic conditions is
resolved while including denitrification and bioavailability of phosphates.
Fig. 5: Phosphate concentrations in water column and sediment pore water for
July 2003 along a transect in the German Bight. The vertical scales of the
sediment are shown ~100x larger compared to the ocean.
Tian, et al. Factors controlling the onset of spring blooms in the German Bight 2002-2005: light wind abs stratification, (2011), Cont. Shelf Res. 31, p. 1140-1148
Schartau, M., Riethmueller, R., Floeser, G., Breitbach, G., Doerffer, R., Hofmeister, R., Petersen, W., Wirtz, K., and Colijn, F. (2012) Prospects and limitations of synthesizing data from a coastal observatory for the analyses of
physicaland biological processes in the German Bight and the Wadden Sea. in preparation for Journal of Sea Research
Hofmeister, Flöser, and Schartau (2012) Coastal nutrient gradients in the Wadden Sea maintained by estuarine circulation, in preparation
* - Helmholtz-Zentrum Geesthacht, Institute of Coastal Research, Ecosystem Modelling Group, Richard Hofmeister, Kai Wirtz, Markus Schartau