TITLE THEME Hamburg Hamburg Oldenburg Bremen Lüneburg Oldenburg Bremen Lüneburg Nordrhein- Westfalen Osnabrück Hannover Braunschweig Osnabrück Nitrate content in drinking water Hannover Braunschweig Göttingen Thüringen under 25 mg/l (n= 430) 25 – 37.5 mg/l (n= 35) 37.5 – 50 mg/l (n= 13) over 50 mg/l (none) Göttingen Thüringen Comparing both maps shows that the red zones (l.) so far established in Lower Saxony are not identical with the regions that have slightly higher nitrate levels in drinking water (r.). XtraBlatt: Dr Kowalewsky, together with Dr Steffens you have evaluated the existing databases for Lower Saxony. Why only for this federal state? Dr Hans-Heinrich Kowalewsky: Firstly, we knew through our earlier activity where exactly to look for the required data. However, the second reason is definitely the more important: better than any other federal state, Lower Saxony permits subdivision into readily definable regions based on farmland cropping, livestock production intensity and topography. Thus, the situation on the coastal region with its high proportion of pastureland is very different from the western regions with their intensive pig production. There is again a difference in eastern Lower Saxony where livestock production plays a lesser role in total. The northeast is characterised by sandy soil and flatlands whereas in the southeast, loess-rich soils merge into the central German mountains and uplands. XtraBlatt: Have you further segmented these four regions? Dr Kowalewsky: For the assessment of Lower Saxony we divided the state into 22 roughly similar sized areas which are not, however, identical with the administrative districts. Decisive in this respect was the availability of data concerning nitrogen fertilising, as well as information on the nitrate content of seepage, ground and drinking water. Here, for example, we referred to data from the Lower Saxony Nutrient Report and the “Lower Saxony Institute for Water Management, Coastal and Nature Protection” as well as to information on waterworks available in the Internet. XtraBlatt: Are groundwater and drinking water not the same things? Dr Kowalewsky: No. It is practical for correct observation and assessment of nitrate values to differentiate between seepage water from the upper 2 m of soil, surface-near groundwater under this level, and the drinking water from deeper levels. There are no measurement values for seepage water, only commonly accepted calculation methods based on nitrogen application and removal, as well as yearly precipitation. The results for ground water are assessed from sampling pilot wells, mostly between 5m and 30 m deep, this information also being referred to for determination of red zones. The nitrate levels in drinking water are determined, and then published, by waterworks. These are chiefly assessed in water taken from depths between 40 m and 120 m. XtraBlatt: What levels did you find in the 22 districts you investigated? Dr Kowalewsky: Let us, first of all, take the mean nitrogen accrual from organic manures such as slurry and fermentation residues. As expected, this was highest in the livestock production areas of western Lower Saxony at 160 – 190 kg N/ha, while in southeastern Lower Saxony achieving only around a third of these levels with an average of some 55 kg N/ha. However, nutrient input takes place not only 8
Mittlere Nitratgehalte im Trinkwasser in den Regionen er in den Regionen 3 13 1Angaben in mg/l 2 1 regionally, it is noticeable that in the coastal region and in the southern part of Lower Saxony pilot well samples show lower nitrate levels with higher levels in central Lower Saxony. But = relativ hohe Werte these (über results 15 mg/l) on their own are not conclusive. Angaben in mg/l 1 2 1 7 17 . G. Steffens 19 1 1 3 8 13 Results 3given in mg/l • = relatively high levels (over 15 mg/l) • = median levels (5–15 mg/l) • = relatively low levels (under 5 mg/l) 3 3 23 = relativ hohe Werte (über 15 mg/l) 4 = mittlere Werte (5 – 15 mg/l) 10 = relativ niedrige Werte (unter 5 mg/l) 20 per region, values from 5 to 11 waterworks total n = 196 upper limit = 50 mg/l Mean nitrate content of drinking water in the regions. 2 1 7 17 19 7. 1 1 3 Grenzwert = 50 mg/l = mittlere Werte (5 – 15 mg/l) XtraBlatt: Why not? = relativ niedrige Werte (unter 5 mg/l) Dr Kowalewsky: Some pilot wells are only a few metres deep and thus lie very close to the seepage water zone border. Other pilot wells are many times deeper. In that nitrate content in ground water reduces with increasing depth, no comparability exists. Apart from this, the wells can be situated in residential areas or in the vicinity of roads, ditches or former silage or dung storage locations. Pilot wells are also thought to have been created on a former cemetery and a small refuse dump. Additionally criticised is that many of these 7. wells are not built according to the regulatory guidelines of the time. All of which can shed doubt on quoted nitrate measurement values. je Region Werte von 5 bis 11 Wasserwerken gesamt n = 196 through organic material but also with mineral fertilisers and there is also the nutrient removal through harvest products to consider. From this, there results in the west of Lower Saxony, e.g. in the area Vechta/Cloppenburg, a calculated nitrogen oversupply of 60 – 80 kg/ha, whereas in the Northeim/Göttingen area, this lies at 0 – 5kg/ha. Taking into account precipitation, and after conversion of the nitrogen oversupply (kg/ha) into nitrate content (mg/l), the result for seepage water in Vechta/Cloppenburg area is an average nitrate content of around 100 mg/l. In the Northeim/Göttingen area we found, on the other hand, a content of only around 40 mg/l. As corresponding evaluations have shown, it is not possible to decide on the nitrate content of pilot wells based on nitrogen fertiliser application. Conversely, however, this also means that the nitrogen fertiliser applied cannot be estimated from pilot well nitrate recordings. Thus, our assessments indicate that it is not technically acceptable to base management regulations on nitrate levels recorded in pilot wells. XtraBlatt: Does this mean that drinking water nitrate levels are significantly different than those of surface-near groundwater? XtraBlatt: To what extent does this apply to groundwater or drinking water? Dr Kowalewsky: Naturally there is a connection. If there is no nitrate present in the seepage water, there can be none in the groundwater and drinking water. On the other hand, a high content in seepage water does not automatically mean that there is always a high nitrate content to be found in groundwater. The nitrate content is measured in the groundwater near the surface layers in the oft-quoted pilot well water samples. In Lower Saxony there are around 1,300 of these wells, 68% of which reveal nitrate levels less than 25 mg/l, i.e. less than half the permitted maximum level. In a further 11%, the levels vary between 25 and 50 mg nitrate/l, in other words still under the permitted maximum. However, there’s no denying that in 13% of the pilot wells the level lay between 50 and 100 mg/l, in 8% even above 100 mg/l. When regarded Dr Kowalewsky: This is correct. We were ourselves surprised that the nitrate levels in drinking water in high-density livestock production areas – with the associated higher application of organic manure – were especially low. For instance, published levels from the appropriate waterworks in the coastal area and central Lower Saxony areas with relatively high livestock densities often lay between 1 mg/l and 5 mg/l. In the southern part of the state these values often ranged between 20 and 30 mg/l. The southern areas of Lower Saxony are characterised by upland terrain such as the Teutoburger Wald, the Deister and the Solling areas with farming featuring very little animal production. We estimate that this data confirms that manuring through application of slurry and fermentation residues cannot thus be the reason for higher nitrate content in drinking water. Or, less formally stated: slurry is not the problem. 9
