Geoscience Reference
In-Depth Information
application of the Modular Ocean Model (MOM 3) code (Pacanowski and Griffies
Sea and freshwater discharge with rivers. A horizontal resolution of 3 nautical miles
was applied in the estuary. However, for time-slice experiments (e.g. 2000-2005),
the Oder estuary was resolved with 1 nautical mile. The vertical layer thickness in
our study area was 2 m.
The biogeochemical model consists of nine state variables. The nutrient state
variables are dissolved ammonium, nitrate and phosphate. Primary production
is provided by three functional phytoplankton groups: diatoms, flagellates and
cyanobacteria (blue-green algae). Diatoms represent larger cells which grow fast
in nutrient-rich conditions. Flagellates represent smaller cells with an advantage at
lower nutrient concentrations, especially during summer conditions. The cyanobac-
teria are able to fix and utilize atmospheric nitrogen, and therefore, the model
assumes phosphate to be the only limiting nutrient for cyanobacteria. Due to the
ability of nitrogen fixation, cyanobacteria are a nitrogen source for the system. A
dynamically developing bulk zooplankton variable provides grazing pressure on
phytoplankton. Dead particles are accumulated in a detritus state variable. The detri-
tus is mineralized into dissolved ammonium and phosphate during the sedimentation
process. A certain amount of the detritus reaches the bottom, where it is accumu-
lated in the sedimentary detritus. Detritus is buried in the sediment, mineralized or
resuspended in the water column, depending on the velocity of near-bottom cur-
rents. The development of oxygen in the model is coupled with the biogeochemical
processes via stoichiometric ratios. Oxygen concentration controls processes such
as denitrification and nitrification. The biogeochemical model is coupled with the
circulation model by means of advection diffusion equations for the state variables.
To analyse the phosphorus dynamics, a new model version with a more detailed
phosphorus and sediment module was applied. In this module, phosphate in the
sediment layer and iron oxides can form iron-phosphate compounds under oxic
conditions, which precipitate and accumulate in the sediment. Under anoxic condi-
tions, iron-phosphates are reduced and dissolved and phosphates are released into
the water body. Depending on the sediment thickness, a portion of the particulate
tions and validations. Weather data were taken from the ERA-40 re-analysis (grid
of 50 km and 6-hourly data) for the entire period between 1960 and 2001. For later
time period, data from ERA-interim were used.
The model MONERIS was applied to calculate the nutrient inputs and loads in
the entire Oder river basin. The model calculates the annual nutrient load into the
coastal waters, resulting from point and various diffuse sources. MONERIS is based
on a geographical information system (GIS), which includes various digital maps
and extensive statistical information. To be able to run the model, large amounts
of spatial information had to be compiled and transferred into the GIS, including
the river system, catchment and administrative borders, land use classifications, soil
maps, topographical information, groundwater tables, hydro-geological and hydro-
meteorological information as well as data on atmospheric deposition, river flow
