Sources, Dynamics and Management of Phosphorus in a Southern Baltic Estuary - The Baltic Sea Basin - page 377

and water quality. Details about sources and data quality are given in Behrendt and
Dannowski ( 2005 ) . Point discharges from wastewater treatment plants and indus-
tries enter the river system directly, but diffuse emissions into surface waters have
very different pathways and are modelled separately. Altogether six diffuse path-
ways are considered in MONERIS: point sources, atmospheric deposition, erosion,
surface run-off, groundwater, tile drainage and paved urban areas. Along the way
from the emission source into the river, many transformation, retention and loss
processes have to be taken into account.
The use of a GIS allows a regional differentiated quantification of nutrient emis-
sions into river systems. In contrast to the study of Behrendt and Dannowski ( 2005 ) ,
the recent results on the long-term changes of the nutrient loads in the Oder have
been carried out with a higher spatial resolution of the river basin. Altogether,
484 different river sub-catchments were calculated separately. Later, the data were
aggregated for larger units and the entire river system. Because of data availabil-
ity and funding reasons, detailed model calibrations and validations took place for
the period 1993 until 1997 and 1998-2002 (Behrendt et al. 2008 ) . For these peri-
ods, detailed and spatially high-resolved data on different phosphorus sources are
available and formed the basis for the formulation of the scenario. Details about the
model, processes and validations are given in Behrendt and Dannowski ( 2005 ) . In
this study, the output of MONERIS was used as input for ERGOM. We transformed
the annual river load data from MONERIS into monthly data, by applying a typi-
cal annual dynamic of the nitrogen loads. This means that results with a temporal
resolution of a month are in general reliable but do not reflect real conditions.
18.3 Long-Term Pollution History
To a huge extent, the Oder discharge controls the nutrient dynamics in the Oder
Lagoon. Dissolved inorganic phosphorus (DIP) concentrations in the Oder River
were stable between the 1960s and the early 1970s. They increased afterwards from
around 4 to nearly 8 mmol/m 3 between the mid-1980s and the early 1990s and
decreased afterwards again (Fig. 18.2 ) . The concentrations reflect this general pat-
tern, but the water discharge is very variable between the years and so are the loads.
The concentrations during the late 1980s were not the highest but due to wet years,
the loads reached the maximum during that time. In wet years, the P load discharged
by the Oder can be up to twice as high as in dry years. The average total phosphorus
concentrations in the lagoon showed a decline between the late 1980s (11 mmol/m 3 )
and the late 1990s (6 mmol/m 3 ). This load pattern is very well reflected in phospho-
rus concentrations in the lagoon. The reduction in nutrient contents observed in the
early 1990s was largely an effect of the warm, dry years and cannot be attributed to
anthropogenic nutrient load reductions (Schernewski and Wielgat 2001 ) .
The DIP concentrations in the lagoon show a strong variability between the
years. In some years, the model ERGON is very well able to simulate the con-
centrations. During the 1990s, this was, for example, true for the years 1994, 1995,