D10: Impact of Contaminants - Hydromod

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Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas EUROLAKES D10: Impact of Contaminants FP5_Contract No.: EVK1-CT1999-00004 Version: 4.0 Date: 25/07/01 File: D10-vers.4.0.doc Page 62 of 136 With exception of Loch Lomond, that turns out to be a “reference area”, the 3 lakes are, in terms of pollution, characterised by domestic sewage and its breakdown products. Although there is also industrial’s effect on the environment, the areas are not dominated by typical industrial pollution sources. The section hereafter gives a concise description of relevant pollutants in the catchment areas of the lakes. For some pollutants little information is currently available and (in contrast to e.g. heavy metals), and as yet no test methods and effective screening methods known. Therefore, the picture is still incomplete. 10.1 CATCHMENT AREA OF LAKE CONSTANCE (BODENSEE) After Lake Geneva Lake Constance is the second largest lake on the northern edge of the Alps [BROMBACH and MICHELBACH 1998]. The lake basin was formed by the erosive forces of the Rhine glacier which excavated a 500 m deep valley during its last extension, about 30.000 years before the present. At the end of this glaciation, 15.000 years ago, the lake area was more than twice its present cover, including large parts of the Rhine Valley and both Lake Walen and Lake Zurich. Lake Constance and its 11 487 km² large catchment area belong to the flow system of River Rhine [BROMBACH and MICHELBACH 1998]. The lake is divided into two parts, the upper lake (including the Überlingersee) and the lower lake (including the Gnadensee and Zellersee). The Rhine bridge Constance can be taken as the parting line. The contact between both parts of Lake Constance is named Seerhein. The catchment area of the upper lake is 10919 km² large. The catchment area of the lower lake is only 568 km² large [GURTZ et al 1997]. The surface of the lake is ca. 540 km² large. The catchment area includes parts of the German "Bundesländer" Baden-Wuerttemberg and Bavaria, Austria, Liechtenstein, Switzerland and Italy. The volume of Lake Constance amounts to 48.5 billion m³ and the maximum depth is ca. 254 m. The mean discharge referring to the tide gauge Constance is ca. 372 m³/s approximating 1.000 mm discharge rate per annum or a mean dwell of 4.1 years in the lake [BROMBACH and MICHELBACH 1998]. In its natural state, Lake Constance was a typical oligotrophic pre-alpine lake with low concentrations of nutrients, low densities of phytoplankton, high water transparency and high hypolimnic oxygen concentrations. Until the early 1970's, the major part of this sewage entered the lake without any treatment, resulting in a strong increase of the Pload, additionally enhanced by increasing inputs from agricultural sources and from precipitation. At present, 75 % of the sewage phosphorus is chemically precipitated in treatment plants. Further reduction of the P-load is expected after completion of the sewage purification programme in large treatment plants. Depending on the remaining P-load, new lower equilibrium concentrations will be reached in the lake. Thus, this provides an example of a successful restoration programme beyond national borders.The Lake Constance and its environs is a densely populated area with a Europe-wide relevance. The ecosystem Lake Constance has an unique flora and fauna and therefore having a high ecological value. The drinking water for more than 4 million people living in the neighbouring countries is gained from the lake. The whole drinking water draw-off from Lake Constance amounts 0.14 km³/a being 1.2 % of the yearly intake of 11.6 km³/a [BROMBACH and MICHELBACH 1998]. Table 10-1 shows the portion of area of the countries in the catchment area of Lake Constance. Country Area Part of the Forest Agricul- Non- Resi-
Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas EUROLAKES D10: Impact of Contaminants [ha] total area [%] FP5_Contract No.: EVK1-CT1999-00004 Version: 4.0 Date: 25/07/01 File: D10-vers.4.0.doc [ha] tural area [ha] productive [ha] Page 63 of 136 dential estate [ha] Upper Lake Bavaria 58762 5.4 15351 38365 1447 3599 Baden-Wuerttemberg 211998 19.4 58103 130098 3333 20463 Vorarlberg (A) 233539 21.4 71716 127710 25478 8636 Switzerland 519886 47.6 131874 204255 166072 17685 Italy 5400 0.5 75 0 5325 0 Lake area 47600 4.3 0 0 47600 0 Upper Lake total Lower Lake 109318 5 100.0 283300 506317 251109 52459 Baden-Wuerttemberg 42012 77.0 13910 21424 851 5827 Switzerland 6228 11.4 2503 2881 59 785 Lake area 6300 11.6 0 0 6300 0 Lower Lake total 54539 100.0 16413 24305 7209 6612 Catchment area total 114772 4 299713 26.1 % 530622 46.2 % 258318 22.5 % 59071 5.1 % Table 10-1: portion of area of the countries in the catchment area of Lake Constance [PRASUHN, et al. 1996]. Data of Land Use with Relevance to the Water Supply About 2.2 million people live in the international Lake Constance region, and almost one million work here. Beside that, this area is also a favourite vacation and recreational area. In the following the percentage of industry agriculture and forestry at the catchment area is described. (The data are taken from Table 10-1). Industry: The economic structure is dominated by the manufacturing industry. The main focus is formed by the mechanical engineering, vehicle construction, electrical engineering, precision mechanics and optics [Bodenseekreis].. Agriculture: The contamination of soil and groundwater by the high use of pesticides and nitrates in the agriculture is an environmental problem. The climate in the area of Lake Constance enables intensive cultivation of fruit, wine, vegetables and hops. Therefore agriculture plays an important role concerning the contamination of soil, surface and ground water in this region. Open land and traditional orchards have given way increasingly to plantations of dwarf fruit trees that require high levels of agricultural chemicals. As a result of that, the pollution of the lake with pesticides, fertilisers and petroleum waste has grown. The agricultural area of 530622 ha is equivalent to 46.2 % of the total catchment area.
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D10: Impact of Contaminants - Hydromod

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