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established pond/wetland for nutrient removal and FIO mitigation. In summer 2005,
water samples from the inlet and outlet of the pond were collected by ISCO 6712
samplers equipped with an Area Velocity Flow 750 module and WAVECOM Modem
Control, serviced by a FLOWLINK data retrieval package. Composite water sampling
(10 shots per bottle) was triggered by discharge at the inlet and by time (hourly)
at the outlet because the stream cross-section below the outlet structure was too
wide for flow-based sampling. Water samples were analysed for total N, total P and
ammoniacal N (NH 4
-N) using automated colorimetric methods and SS (mass of dried
solids retained on filter paper from a known volume of sample). Although bottles from
the water samples were collected on a weekly basis, comparison of fresh versus
aged samples showed < 5% decline in ammoniacal N content. Discharge at the inlet
was estimated by the area-velocity method from 5-minute measurements of water
level and velocity. Outlet water level data showed that there was little hydraulic delay
in the system (about 1 hour) and that the water residence time during storm events is
about 1 day. From the water sample analysis results, hourly interpolated water quality
data were calculated for the monitoring period using a double-parabolic interpolation
function (XlXtrFun, Advanced Systems Design and Development, 2003). These were
then combined with hourly discharge data from the inlet to provide a continuous
estimate of loads.
Comparison of Biodiversity Between Existing Farm Pond/Wetland
Systems
To provide a measure of the habitat value of farm ponds/wetlands, vegetation and
macroinvertebrates were surveyed in three systems in Scotland in July 2005: (i)
Langside farm, Ayrshire (described above); (ii) Black Loch wetland, Lunan Lochs,
Angus – an established wetland of ~ 1.5 ha area and ~ 20,000 m 3 volume (again
constructed prior to best practice guidelines) that receives run-off from fields
amended with poultry manure; (iii) a pond/wetland system designed in accordance
with best practice guidelines and constructed in 2004 at Old Castle mixed arable
farm, Berwickshire. Each system was arbitrarily divided into six compartments from
inlet to outlet and within each compartment plant species were identified and counted
in five randomly located 1-m x 1-m quadrats. Macroinvertebrates were sampled and
identified to species level in each system using the National Pond Survey method
(Biggs et al., 1998).
RESULTS
Performance of an Established Onstream Farm Pond/Wetland
Inlet and outlet total P and discharge for Langside pond are shown in Figure 1. Total
P concentrations at the inlet rise with inlet discharge, peaking during storm events,
while outlet total P concentrations often exceed inlet concentrations. When compared
with total P water quality standards for Scottish freshwater lochs (SEPA, 2002), the
outlet water quality would be classified as ‘hypertrophic’ (total P > 0.1 mg/L). To
assess the performance of the pond/wetland in pollutant removal, mean hydraulic
load, and total N, total P, NH 4
-N, and SS concentrations at the inlet and outlet were
used to calculate the overall mass removal efficiency (as % of inlet load) for five
periods where continuous inlet–outlet data exist (Table 1). Removal of SS by the
pond/wetland is good. The overall efficiency of removal of both N and P is poor, but
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