Report No DWI0391

The Nitrate Issue


Dec 1988


Summary and Conclusions

45. This study comprises assessments in 10 catchment areas of agricultural and water options enabling the water supplies in those areas to comply with the nitrate parameter in the E C Drinking Water Directive. The assessments were all Desk Studies, being based on available information rather than on-the-spot examination. The areas chosen provide a wide range of differing hydrogeological, farm type and other conditions. The options were costed on a 1988 local price basis, ie a comparison of the farm income loss resulting from possible agricultural restrictions with the cost of possible water options. The agricultural options were also costed on a national resource basis by taking account of the public support element of farmers' income. Two agricultural options were examined in each case. so-called catchment-wide protection zones and more severe, localised protection zones within the catchment in question.

46. The Desk Studies have been based on the best information available at the time. However, it is important to stress a number of major limitations of the studies. For example:

    1. The studies compared water options with agricultural options although in the latter ease it was sometimes necessary to include provision for a temporary water option in order to achieve the desired nitrate level in the interim. Permanent combined wa ter/agriculture options were not examined. However, the Hatton Catchment Nitrate Study published earlier this year indicated that permanent combined options might offer clear financial advantages in many areas.
    2. In order to carry out the costings, assumptions had to be made about factors such as the level of United Kingdom and world agricultural prices, and types of Community support regimes, for the next 50 years. These factors could soon become out of date. For example, an increase in world agricultural prices would, other things being equal, reduce the attractiveness of agricultural options on a resource cost basis and a reduction in world prices would have the reverse effect.
    3. The Water Research Centre computer model, on which the Desk Studies have been based, has in the past had to be modified to take account of new information on leaching losses, for example the unexpected reduction in nitrate concentrations in parts of the Lincolnshire limestone aquifer. Further changes may become necessary in the light of new information.

47. Subject to these limitations, the conclusions of the Desk Studies are as follows:

    1. Groundwater in all 3 chalk areas examined would respond only extremely slowly to changes in agricultural practice. Even if the entire catchment areas were put down to non-fertilised grass now, the intended reduction in groundwater nitrate concentration to 45 mg/1 would not be achieved by the year 2040. No evaluation of the effect of control measures on agriculture was therefore made. It does not necessarily follow that changes in agricultural practice should be ruled out in all chalk areas but each case would need individual examination.
    2. In contrast, in one limestone area examined, the target reduction could be achieved by minimal farming changes, assuming no intensification of the existing relatively extensive pattern of farming there.
    3. In another limestone catchment area, the water option was cheaper than the agricultural options examined both on local and national resource bases. The availability of an alternative water source was a major factor here. When the much larger catchment area, of which that area was a part, was examined however, the agricultural option appeared cheaper on a resource cost calculation, albeit not on a local cost basis.
    4. In 3 of the 4 sandstone areas examined, the water options were much cheaper in every case than the agricultural options on a local cost basis but, on a national resource analysis, the agricultural options were cheaper in every case.
    5. In four areas where an agricultural option was assessed to be the least cost option on a national resource basis, this option would not itself achieve the imposed target of a nitrate concentration less than 50mg/l by 1998. Consequently some interim water measures would also be necessary, although of a much more limited nature than if there were no agricultural measures.
    6. Catchment-wide protection zones would in most cases be more difficult to monitor than more severe measures over localised areas within the catchment. In all the areas examined, however, the localised protection controls would produce a much greater loss of farm income than those applying to the whole catchment. In national resource terms localised controls often showed greater savings than catchment wide protection.
    7. Factors which indicate, on both a local cost and resource-cost basis, that an agricultural contribution may repay closer examination are:
      1. moderate effective rainfall (ie greater than 250mm per year and less than 400mm per year);
      2. aquifers such as limestone and sandstone, and which are rapidly recharged in response to rainfall;
      3. no nearby source of blending water.

On a local cost basis a further factor is the existence in the catchment area of predominantly mixed farming.

48. Most importantly, these studies have confirmed that each area has special characteristics which would need to be taken into account before any decision can be reached on the most desirable and practical option or set of options. The studies have also highlighted the contrasting conclusions which can be drawn, depending on whether the local cost or national resource cost approaches, are used.

49. Although these studies have produced some interesting conclusions, these must be regarded as tentative. If they were used for detailed decision making, there would have to be consideration of combined options, of the implications of the contrasting economic approaches, and of the results that might follow from detailed on-the-spot investigations rather than desk studies.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.