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(including algae) whereas for N nitrification/denitrification can be a significant sink.
Conversely, farm ponds may also be sources of N and P, released from sediment
and winter die-back of vegetation and algae. Pond performance may therefore vary
between farm types, depending on the nature and timing of pollutants received, and
this may need to be reflected in design guidance. For instance, it is hypothesised
that ponds could be less effective in retaining nutrients (particularly P) from livestock
farm run-off compared with arable farms for a number of reasons, including:
• Much of the P will be associated with organic waste in particulate, colloidal
and soluble form, and hence be less quick to sediment than inorganic soil
aggregates.
• Inorganic P may be sorbed onto organic colloids and desorb to form soluble P
when run-off is diluted strongly by water.
• Organic rich sediment accumulated in ponds may be highly susceptible to the
formation of anaerobic conditions, leading to potential P release from any iron
oxides present.
• Organic sediment will also be more prone to resuspension than inorganic sediment
because of its lower density.
Guidance on farm steading ponds in Scotland is currently limited. SEPA’s interim
guidance states that: ‘All livestock farms will have existing drainage systems in
place to allow roof water and run-off from ‘clean’ roads and yards to discharge to
local watercourses… it is this existing drainage that steading ponds are intended to
address… Such an approach would also be consistent with what is currently defined
as ‘good agricultural practice’ in The PEPFAA (Prevention of Environmental Pollution
from Agricultural Activity) Code’. To provide demonstration sites and increase
understanding of the factors affecting pond performance, the Scottish Executive and
SEPA’s Diffuse Pollution and Habitat Enhancement Initiatives have funded the design
and construction of four farm ponds throughout Scotland. This will be augmented
by ongoing SEERAD-funded work at SAC and the Macaulay Institute evaluating best
management practices (BMPs) on farms, supported by a new PhD project at The
University of Edinburgh that aims to investigate the factors (including design) which
influence the long-term performance of farm ponds and the relationships between
pollutant removal efficiency, biodiversity enhancement and costs. This paper presents
results from a SEERAD-funded project on the performance of a mature farm pond/
wetland (constructed prior to current best practice guidance) and from a biodiversity
survey of three existing farm pond/wetland systems. A discussion on plans for future
work is also presented.
MATERIALS AND METHODS
Performance of an Established Onstream Farm Pond/Wetland
The pond studied was on Langside dairy farm (110 dairy cows plus followers) in the
Cessnock catchment, Ayrshire. The main watercourse draining the farm steading
and 221 ha of land passes through an abandoned 5000-m 3 reservoir and associated
wetland, with a total area of 0.63 ha. The system is ‘onstream’ and not designed
in accordance with current best practice guidelines [as outlined, for instance, by
Campbell et al. (2004)], but it provided the opportunity to assess the efficacy of an
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