Geoscience Reference
In-Depth Information
relative share of agricultural sources and settlements was similar to the 1960 level
again and the total emissions decreased again to less than 10,000 t. However, the
total emissions were still 50% higher compared to 1960. The Polish part of the
Oder basin is responsible for 84% of the P emissions. Eleven and five percent of
the P emissions can be attributed to the Czech and German parts of the Oder basin,
respectively.
Due to phosphorus retention in the river, only 39% of these emissions or 3,640 t/a
(for the period 1998-2002) enter the Oder Lagoon with the river. Twenty-two per-
cent or 2,070 t/a of the total emissions are bio-available for primary production in
the lagoon. In 1960, the total P load entering the Oder Lagoon was about 2,400 and
increased to 6,200 t around 1990. The load around 2000 was only 60% above the
level of 1960.
which describe the effect of single management measures or sets of measures in the
river basin on the nutrient loads into the Oder River. Figure
18.6 (bottom)
shows
the results of one scenario, which links all best-practice measures in the river basin
and shows to what extent the total phosphorus input into the Oder River can be
reduced. Ninety-five percent of the Oder river basin belongs to Poland and the Czech
Republic. Both countries are member states of the European Community but their
sewage water treatment quality does not yet comply with EC standards.
This optimal scenario is based on the following assumptions and measures: The
emissions from point sources in the entire river basin meet the requirements of the
Urban Waste Water Treatment Directive (91/271/EEC). The following thresholds
shall not be exceeded: Biological oxygen demand (BOD)
=
25 mg O
2
/l, chemical
oxygen demand (COD)
=
125 mg O
2
/l, SS
=
35 mg/l, total phosphorus (TP)
=
2 mg/l, total nitrogen (TN)
15 mg/l for municipalities with a population between
10,000 and 100,000 as well as 1 mg TP/l and 10 mg TN/l for municipalities with
more than 100,000 inhabitants. The use of phosphorus-free detergents is postulated
in Poland and the Czech Republic.
It is assumed that best management practices on arable land are implemented
to reduce the load from diffuse sources. Soil erosion is strongly reduced as well.
Conservation tillage is applied on all arable land in the Oder basin. The nutri-
ent load reduction in this scenario is realistic and the required measures could be
implemented during the next two decades.
Despite the fact that only around 5% of the present loads can be regarded as
natural background emissions, the potential for emission reductions is limited. For
this scenario, emissions of 4,900 t TP are calculated. This means that a reduction
of about 47% of the emissions in 2000 seems possible or an emission reduction of
about 18% compared to 1960.
What does this mean for the water quality in the Oder Lagoon? A comparison
of model results for the years 2000 and 2001 with the years 1960, 1961 and 1962,
where the annual load was only about 20% above the loads in the emission reduc-
tion scenario, can give an impression of how the ecosystem would react to load
reductions. However, the effect of changes in nitrogen loads and shifts in N/P ratios
cannot be taken into account. In general, the DIP concentrations in April and May
=
