Diffuse entries from agriculture
Pollution caused by agriculture consists especially of groups of nitrogen and phosphor compounds as well as plant treatment chemicals and insecticides. The entry of morbidic agents can also be of significance. Pollutants enter into the waters especially via tributaries, groundwater and drainage water, erosion and wash out, direct entries and atmospheric entries (Graphic: Problems).
use of the catchment areas is usually reflected by high nitrate contents
in the waters. The large excess of nutrients caused by not fertilising
according to requirements presents a large problem. A large proportion
of the phosphorus entries from diffuse sources enter into the waters via
soil erosion. The problem of soil erosion is especially large for field
surfaces not protected by vegetation and where agricultural methods do
not take profiles and soil conditions into consideration.
Seven drinking water reservoirs in Thuringia have a catchment area proportion of max. 10% of the agricultural acreage (Illustration A). The mean nitrate content for these reservoirs is below 8 mg/l (limiting value according to 50 mg/l). On the other hand, more than 50% of the catchment area for the Weida - Zeulenroda and Lössau reservoirs is used agriculturally, the nitrate concentrations are therefore correspondingly high (mean value untreated water 1995: 49 mg NO3/l).
Agriculture conducive to water conservation can be achieved for the reduction in the entry of materials from agriculture through consultation with the farmers concerned by advising agriculture; by developing cooperation between agriculture and water management and via development programs. Legally binding conditions can also be drawn up by designating water conservation areas. These higher ranking measures help in facilitating or enforcing direct measures.
Agricultural use of acreages in drinking water conservation zones must be orientated towards the place where the water is drawn off and must be suboptimally organised. Erosion and wash out have to be reduced by avoiding openly exposed soil: surfaces near the water should therefore be protected by a layer of vegetation the whole year. Agricultural fertiliser should not be applied to steeply sloping fields in order to avoid wash out being caused by heavy rainfall. Heavily flooded areas should also be taken out of intensive use.
Entry of nutrients into reservoir inflows can be reduced by fertilising according to requirements. Agricultural fertilisers, such as liquid manure, slurry, or stable manure should only be spread on the fields during the period of vegetation when the applied nutrients can be taken up by the plants. Further reductions in the entry of pollutants can be achieved by installing embankment strips at the inflows into the reservoir.
Several of the above
mentioned measures are currently being put into use for the Weida-Zeulenroda
reservoir system in East Thuringia which has a catchment area where 61
% of the acreage is used agriculturally in order to alleviate the very
tense situation there. A programme that is currently being drawn up shall
be used to inform farmers working in the catchment area of the options
of farming in a way that is conducive to water conservation whose implementation
shall be supported. At the same time contracts of cooperation are to be
worked out for the farmers and signed in order to contractually specify
the details of measures for water protection. Part of the measures to be
observed by the farmers implies additional limitations to proper farming
so that implementation means further increased costs and loss of yield:
these shall have to be compensated. The Thuringia Reservoir Administration
accordingly paid compensation to agriculture of several hundred thousand
German marks for the first time in 1994 in order to balance out extra costs
and loss of yield in favour of water conservation so as to bring about
favourable acceptance of vitally essential measures taken in the catchment
area. Long term success can neverthless be expected here.