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emoval varied between periods from –84% to 20% and –183% to 46%, respectively.
The area is therefore at times a source of nutrients, particularly during low flows. The
removal of FIOs is good (e.g. 83% for Escherichia coli bacteria; Vinten, pers. comm.).
A positive (but not significant) relationship was observed between % removal of SS,
total P and total N and hydraulic load which was attributed to the entry of larger
particles (with faster settling velocity and containing total P and N) into the pond
at higher flows. Marginally significant relationships between total P (P = 0.088) and
total N (P = 0.075) removal and SS removal suggest that designing a pond/wetland
to maximise SS removal should also result in good total P and N removal. In order to
elucidate P retention within farm ponds/wetlands, the fractionation of P needs to be
explored in more detail, although this was not possible at Langside because of the
field storage of water samples.
Figure 1: Inlet discharge and total P concentrations at the inlet and outlet to
Langside pond/wetland, days 138-180 of 2005. Horizontal bars on
total P values show the time period represented by each sample
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