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This project monitored and described the impact of changes in stocking density on the
microbiological water quality of the Caldew Catchment in Cumbria, which was heavily
affected by foot and mouth disease (FMD). <P>
To characterize the catchment in agricultural terms, manure production and farm
management practices were monitored through the integration of Department of
Environment, Food and Rural Affairs (Defra) agricultural census data and livestock
movement statistics, by a field survey of representative farms and by the seasonal
modelling of manure management using the results of national and regional stratified
surveys of farm practices. <P>
Twenty-five farms, selected as typical of the catchment, were recruited for detailed
survey. The farms represented 23% of the total farmed area in the catchment and
accounted for 26% of the total cattle population and 14% of the total sheep population.
At the start of the project, they were surveyed using a questionnaire and farm map for
livestock and land-use practices both prior to and following the FMD outbreak. The
farm locations were distributed evenly across the subcatchments. Monthly log sheets,
which provided information on farming activities during the project, were completed by
each of the 25 farmers from December 2002 to December 2003. <P>
The timing of animal grazing is of special importance in assessing the risk of faecal
indicator delivery to watercourses, as fresh excreta voided directly onto fields is not
subject to die-off in storage. For the water-quality data analysis the study was divided
into ‘summer’ periods, when virtually all cattle are out in the fields, and ‘winter’
periods, when the majority of the cattle are indoors, defined as follows:
<UL> <LI> October 2001-April 2002: restocking winter;
<LI>May-September 2002: mostly stocked summer;
<LI>October 2002-April 2003: restocked post-FMD winter;
<LI>May-September 2003: restocked post-FMD summer. </UL>
Fifteen sites, selected for their particular catchment characteristics of topography,
potential land-use, stocking densities and management practices, were sampled for total
coliforms, faecal coliforms and enterococci between December 2001 and January 2004.
Discharge (m3 s-1) was estimated for each site based on data from Environment Agency
flow-monitoring stations, flow modelling and/or hydrometric survey.
Progress: The impact of foot and mouth disease on stock levels and manure management
The catchment is predominantly a productive grass-growing area with mainly dairy and
stock-rearing farms. Most are family farms of medium size, although there are a
substantial number of fairly large livestock holdings. 330 individual holdings were
located within the Caldew Catchment, of which half accounted for 90% of grazed
livestock. <P>
The catchment was heavily affected by FMD, with a total of 175 infected premises (IPs)
and dangerous contacts (DCs) where stock was culled, the majority between April and
May 2001. Approximately 80% of cattle and 90% of sheep in the catchment were
culled. The majority of stock was culled during April and May 2001. By mid-2002
stock numbers increased rapidly (i.e. to 75% of cattle and 52% of sheep numbers prior
to FMD), but this rate of increase has not been sustained and the most recent available
census statistics for June 2003 show only 79% and 59% of pre-FMD numbers,
respectively (Figure S1). Stock densities may never reach pre-FMD levels because of
Common Agricultural Policy (CAP) reforms and de-coupling of farm subsidies.
Monthly stock records from the surveyed farms and records of restocking during 2002
were used to identify stock numbers within the catchment from September 2001 to June
2003. It was assumed that no farm began restocking until September 2001. The
restocking of cattle, many of which were in calf, occurred between January and March
2002 at a time when animals were normally housed. Therefore, by the time the newly
introduced animals were out grazing and presented the greatest risk of faecal indicator
organism pollution of streams, the estimated excreta load was already at 70% of pre-
FMD levels. Sheep were restocked in two phases over the winters of 2001/02 and
2002/03, although some evidence suggests that some farms abandoned sheep rearing.
<P>
Generally, there was an increase in microbial concentrations downstream under both
base-flow and high-flow conditions. Geometric mean (GM) concentrations were lowest
in the headwater, fell and areas of the upper Caldew Catchment during all four study
periods. In contrast, the concentrations in the predominantly improved pasture
headwaters of the Roe Beck Catchment were greater. Overall, concentrations within the
Roe Beck and River Ive Catchment upstream of its confluence with the River Caldew
were greater than those within the upper and middle Caldew Catchment.
These differences in water quality may be explained by the variation in land use within
each subcatchment, with a greater proportion of improved pasture and lower proportion
of rough grazing in the Roe Beck and River Ive Catchment compared to the Caldew
Catchment. <P>
The subcatchment delivery of faecal indicators exhibits strong seasonality – summer
concentrations exceeded winter concentrations at all sites. This seasonality
is significant to the design of future studies of diffuse pollution remediation strategies.
High-flow periods exhibited the highest concentrations and dominated faecal indicator
fluxes from the catchments. This characteristic was further exacerbated after restocking. Low-flow concentrations did not exhibit any particular pattern, which
suggests the acquisition of low-flow survey data is of limited value in studies of faecal
indicator flux and of the evaluation of diffuse pollution-remediation strategies where
there are few point-source inputs.
<P>
Multiple regression was used to model the relationships between GM faecal indicator
organism concentrations and percentage land use, livestock numbers and animal waste
volumes within subcatchments. In the majority of cases, the best predictor of faecal
indicator organism concentrations was the proportion of improved pasture. Land-use
variables produced the most significant relationships when compared to the stocking
number and manure input variables. This reflects the potential sources of faecal
indicator organisms associated with this land-use type (i.e. grazing animals and
spreading of animal wastes). <P>
A generic model able to predict water quality using land-cover data and developed by
the Centre for Research into Environment and Health (CREH) was used to predict
summer faecal indicator organism concentrations at the sampling sites assuming a
condition of 100% pre-FMD stock levels. An analysis of the residuals (i.e. observed
minus predicted concentrations) indicated that concentrations in the Caldew Catchment
had not reached the modelled concentrations by the summer of 2003 (restocked post-
FMD summer). Furthermore, greater residuals were evident during the summer of 2002
(mostly restocked summer), which indicates that the increase in animal numbers
between the 2 years has resulted in concentrations moving towards the modelled levels.
Land-use data are more readily available than the remaining variables considered here
and the further development of the land-use-water quality models on this basis would be
possible. The similarity of the most significant predictor variables to previous CREH
modelling exercises suggests that this approach would be portable to other catchments.
Tentative relationships between stock density expressed in livestock units and GM
high-flow faecal indicator organism concentrations were developed. These
relationships may be used to relate stock density to estimated water quality, although
the confidence intervals of the relationships are currently quite large and the GM
concentrations upon which the relationships are based are poorly characterized.
However, further research into consolidating these relationships could produce a useful
management tool to inform estimates of the impact of agricultural practices on diffuse
pollution generation. <P>
Reforms to the CAP are likely to have a significant impact on the Caldew Catchment, in
terms of changes to stock numbers, which are likely to result in further changes to water
quality. An ideal opportunity therefore exists to characterize the impacts of CAP
reform on both stock numbers and water quality, and the relationships between the two,
through further study of this catchment. Such a study would also present an opportunity
to collect further data of the type necessary to improve the functions that describe the
relationships between stock density and water quality.
<P>