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Table 1:
Concentrations of pollutants in leachate from lysimeters, compared
with slurry input {mean and SD of samples taken from 3rd May [after
cumulative input of rainfall (403 mm) + slurry (224 mm)] to 30 August
[after further cumulative rainfall input of 344 mm]}
Mean
slurry
value*
Material below woodchips
Control Ochre Straw Topsoil
Leachate concentration mg/L
EC
(mS)
DOC 33,000
(TOC)
NH 4
-N
(mg/L)
NO 3
-N
(mg/L)
PO 4
-P
(mg/L)
Log E. coli
(cfu/100 ml)
14.0 2.0
(0.3)
22.46
(19.3)
1,800 0.60
(0.48)
0 31.0
(6.7)
225 0.02
(0.02)
7.5 2.3
(0.5)
2.9
(0.3)
12.6
(7.8)
0.32
(0.01)
36.2
(2.5)
0.03
(0.01)
2.3
(0.2)
2.5
(0.03)
125.6
(69.7)
0.72
(0.22)
37.6
(3.2)
0.57
(0.04)
3.0
(0.05)
1.9
(0.17)
17.4
(1.9)
0.32
(0.19)
31.2
(0.4)
0.07
(0.05)
2.4
(0.3)
*Mean input slurry dilution factor with rainfall = 2.8.
The EC relative to the average EC value of the rainfall + slurry inputs (EC/EC input
)
until slurry application ceased (after 166 mm of drainage, 403 mm rainfall and 224
mm of slurry, 12 January to 3 May 2004) increased to a maximum of 0.62 in the
control treatment. If we assume the EC is controlled primarily by transport of weakly
sorbed ions such as Cl-, this line is indicative of the behaviour of a conservative,
non-reactive, non-adsorbed tracer. The initial EC in leachate from both the ochre
and straw lysimeters was significantly higher than from the other treatments, but it
is not clear why at present. The DOC concentrations began to rise at the same time
as the EC, but values were much lower, relative to input, showing that microbial
degradation and/or sorption occurred. The NH 4
-N showed a similar pattern to DOC,
and the DOC/NH 4
-N ratios were similar to the input values, suggesting that oxidation
and sorption of organic C and NH 4
-N follow similar patterns. Nitrate concentrations
rose steadily in the drainage water with time, to a maximum of approximately 40 mg/
L and there was no delay relative to EC, suggesting that rapid nitrification of NH 4
-N
occurred. However, NH 4
-N concentrations relative to input values were much lower
than EC/EC input
. This suggests either that for a large part of the NH 4
-N added,
nitrification is slow, and/or that denitrification is occurring. Given the time course
of nitrate breakthrough, the latter explanation is more likely, but the two alternatives
cannot be properly distinguished without further work, for example by comparison
of the d15N content of input and output N (e.g. Krapac et al., 2002) and assessment
of ammonium adsorption, which will delay the pollutant transport. The E. coli
concentrations in the leachate rose before the EC showing that there was significant
exclusion of bacterial cells from smaller soil pores. Except for the straw treatment,
E. coli concentrations were very low relative to input values, showing that most of
the E. coli was inactivated during transport through the soil. The concentrations were
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