Report No DWI0391
The Nitrate Issue
DWI0391
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:
- 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.
- 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 These factors could soon become out of date.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.
- 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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Factors which indicate, on both a local cost and resource-cost
basis, that an agricultural contribution may repay closer examination
are:
- moderate effective rainfall (ie greater than 250mm per year and less than 400mm per year);
- aquifers such as limestone and sandstone, and which are rapidly recharged in response to rainfall;
- 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 'Find Completed Research' heading on the DWI website.