ý.,,: V. ý ýý . - Nottingham eTheses - University of Nottingham

2.7.2 -
Inorganic chemical analysis
Analyses of ammonia, nitrate, nitrite and soluble reactive phosphorus (NH4-N,
N03-N, N02-N, P04-P) concentrations were performed on the lake water samples.
2.7.2.1 -Ammonia
(NH4-N)
This method was taken from Mackereth et al. (1988, after Chaney & Marbach.
1962). The principle is that the ammonia reacts with phenol and hypochlorite to form
indophenol blue (catalysed by nitroprusside). A calibration curve was established using
an ammonium chloride standard. Absorbance was measured at 635nm in a 4cm cell.
2.7.2.2- Nitrite (NO2-N)
This method is taken from Mackereth et al. (1988, after Bendschneider and
Robinson, 1952). In principle, nitrite yields nitrous acid in acid solution which diazotises
sulphanilamide; the diazonium salt that is formed binds to N-1-napthylethylenediamine
dihydrochloride and forms a red azo dye. A calibration curve was established using a
sodium nitrite standard solution. Absorbance was measured at 543nm in a 4cm cell.
2.7.2.3 -
Nitrate (NO3-N)
This method was taken from Mackereth et al. (1988). The principle is that nitrate
is reduced to nitrite using spongy cadmium and the nitrite is then determined as shown
above in the nitrite methodology. A calibration curve was established using a potassium
nitrate standard solution. Absorbance was measured at 543nm in a 4cm cell.
2.7.2.4 -
Soluble reactive phosphorus (P04-P)
This method was taken from Mackereth et al. (1988), (taken from Murphy &
Riley, 1962). The principle is that an acidified phosphate solution reacts with molybdate
to form molybdo-phosphoric
acid. This is then reduced to form a coloured molybdenum
blue complex, the absorption of which is determined spectrophotometrically.
The
concentration of ortho-phosphate was established by running the unknown samples
against a calibration curve formed from standards of known concentration. The
absorbance was measured at 880nm in a 4cm cell.
2.7.3 -
Dissolved organic carbon analysis
DOC was analysed using a Total Carbon Analyser (Shimadzu). The analysis is
based on the combustion/non-dispersive infrared gas analysis method (Najm &
Marcinko, 1995). Non-purgeable organic carbon was measured. A liquid sample was
40