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Examination of Figure 2 (a) and (b) suggests that over 30% of new stream bank
length fencing is required before an effect can be seen. However, it is important to
note that:
i. there is considerable variability in this hypothesised ‘effect’ between the
remediated catchments; and
ii. this observation is based on only four relevant data points and must be considered
tentative.
Effectiveness of BMP Measures
The Brighouse Bay study was conducted in a small catchment where interventions,
such as stream bank fencing, could be implemented to cover a significant percentage
of the available stream bank length. The study therefore offers an exemplar of the
effects of remedial measures in this type of livestock farming area in South-west
Scotland.
The faecal indicator and nutrient results provide complementary evidence of
beneficial remediation effects. In particular, a measurable improvement in FIO flux
to the bathing waters is suggested when compared with the control catchment,
although compliance with EU bathing water standards after storm events is still
not guaranteed. Some validation of The Scottish Executive/SEPA’s bathing water
signage project was provided on the 19th August 2004, when a ‘poor’ bathing water
quality signal was confirmed by spot sea water samples that proved to have FIO
levels in excess of mandatory standards.
Early indications suggest that a beneficial effect can be seen in the Brighouse Bay
subcatchments (i.e. noticeable FIO reductions) when approximately 30% more of
the catchment stream bank lengths are fenced, which also results in a ‘protection’
from approximately 30% more of the catchment fields draining to a subcatchment
outlet.
The creation of farm ponds has yet to be shown as an effective BMP measure.
However, the beneficial effects of ponds and wetlands is demonstrated by one small
subcatchment (monitored at site 103) in the Brighouse Bay study. This exhibited
uniformly low pre- and post-remediation FIO concentrations at the catchment outlet.
The full beneficial effect of newly isolated wetlands and ponds is likely to be seen
only after plants in the water margins become established and the floor of the pond
partially seals, possibly taking 2 to 3 years to take full effect.
Owing to the project timescale and the necessity to initiate monitoring ahead of
carrying out the farm audits and determining the BMPs, rigorous evaluation of the
individual measures applied has not been possible. Seasonal factors and land
use changes in some fields (e.g. from autumn grazing to summer silage) are major
confounders in the pre- and post-remediation comparisons at the sub-catchment
level. To obtain full value from the project, monitoring in successive bathing seasons
over a suggested period of 5 years is advised to confirm the improvements seen
thus far.
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