72
Lake and Pond Sediments
Aspila et al. [218] found that the concentration of sulphuric acid in the sample
solution had an appreciable effect on the response for 1 JJg I-I of phosphorus; hence,
the need to control acidity levels carefully during the analysis. Additionally, acidity
levels which are too low allow serious interferences in the method by silica. By careful
control of acid concentration and reaction temperature, interference by silica can be
minimized. Arsenic, germanium, and bismuth would interfere in the method but not
at the low levels normally encountered in sediment in water samples.
The coefficient of variation obtained for the determination of total phosphorus in
sediment at the 1 400 ppm level was 2.5 %. Some 98-lO0 % recovery of inorganic
phosphate was obtained in spiking experiments carried out on lake sediments.
Dobolyi and Bidlo [219] determined the phosphorus-containing minerals in Balatien lake sediment, and thus the forms in which the phosphorus responsible for the
accelerating eutrophication of the lake are present. Samples were subjected to chemical, electron microscope and X-ray analysis. Hydroxylapatite was identified, but no
proof of the presence of other phosphorus minerals was obtained.
DePinto [220] measured the rate at which available phosphorus is released from
various types of particulates suspended in lake water. The equipment consists of two
culture vessels separated by a thin membrane fIlter, thus facilitating the separation of
two particulate suspensions, while at the same time permitting their interaction by
diffusion of solutes through the membrane.
Shukla et al. [221] investigated interference by arsenic in the spectrophotometric
determination of inorganic phosphate in lake sediments.
3.2.3
Inorganic Sulphide
Iron sulphides are ubiquitous in marine and freshwater sediments. They are usually
present either as pyrite or as monosulphides, which can be liberated by hydrochloric
acid. These acid volatile sulphides (AVS) give rise to an intense black colour that is
characteristic of anoxic sediments. They play an important role in recent diagenetic
processes in sediments and the ratio of pyrite to AVS has been used as an historical
indicator to determine whether sediments were formed in marine or freshwater conditions. They can be present over a wide range of concentrations. Oxic muds do not have
any free sulphide whereas anoxic muds may contain as much as 10 mg g-I.
The traditional method of analysis is based on the method of Kolthoff and Sandell
[222] in which 1 mol 1-1 hydrochloric acid is added to a sediment sample and the
mixture is boiled. Hydrogen sulphide is trapped as zinc sulphide and the final analysis
is performed by iodide titration after re-acidification of the metal sulphide. GilboaGarber [223] improved the final analysis step by using a colorimetric procedure based
on methylene blue. However, the inherent disadvantage of the method, including the
lengthy distillation step and extensive handling of an oxygen-sensitive sample, remained.
Various workers [224-226] have modified these procedures to improve precision,
by employing zinc sulphide as a standard in contrast to the sodium sulphide solution
used in earlier methods. The addition of sodium hydroxide to the hydrogen sulphide
absorption solution improves recovery.
Lake and Pond Sediments
Aspila et al. [218] found that the concentration of sulphuric acid in the sample
solution had an appreciable effect on the response for 1 JJg I-I of phosphorus; hence,
the need to control acidity levels carefully during the analysis. Additionally, acidity
levels which are too low allow serious interferences in the method by silica. By careful
control of acid concentration and reaction temperature, interference by silica can be
minimized. Arsenic, germanium, and bismuth would interfere in the method but not
at the low levels normally encountered in sediment in water samples.
The coefficient of variation obtained for the determination of total phosphorus in
sediment at the 1 400 ppm level was 2.5 %. Some 98-lO0 % recovery of inorganic
phosphate was obtained in spiking experiments carried out on lake sediments.
Dobolyi and Bidlo [219] determined the phosphorus-containing minerals in Balatien lake sediment, and thus the forms in which the phosphorus responsible for the
accelerating eutrophication of the lake are present. Samples were subjected to chemical, electron microscope and X-ray analysis. Hydroxylapatite was identified, but no
proof of the presence of other phosphorus minerals was obtained.
DePinto [220] measured the rate at which available phosphorus is released from
various types of particulates suspended in lake water. The equipment consists of two
culture vessels separated by a thin membrane fIlter, thus facilitating the separation of
two particulate suspensions, while at the same time permitting their interaction by
diffusion of solutes through the membrane.
Shukla et al. [221] investigated interference by arsenic in the spectrophotometric
determination of inorganic phosphate in lake sediments.
3.2.3
Inorganic Sulphide
Iron sulphides are ubiquitous in marine and freshwater sediments. They are usually
present either as pyrite or as monosulphides, which can be liberated by hydrochloric
acid. These acid volatile sulphides (AVS) give rise to an intense black colour that is
characteristic of anoxic sediments. They play an important role in recent diagenetic
processes in sediments and the ratio of pyrite to AVS has been used as an historical
indicator to determine whether sediments were formed in marine or freshwater conditions. They can be present over a wide range of concentrations. Oxic muds do not have
any free sulphide whereas anoxic muds may contain as much as 10 mg g-I.
The traditional method of analysis is based on the method of Kolthoff and Sandell
[222] in which 1 mol 1-1 hydrochloric acid is added to a sediment sample and the
mixture is boiled. Hydrogen sulphide is trapped as zinc sulphide and the final analysis
is performed by iodide titration after re-acidification of the metal sulphide. GilboaGarber [223] improved the final analysis step by using a colorimetric procedure based
on methylene blue. However, the inherent disadvantage of the method, including the
lengthy distillation step and extensive handling of an oxygen-sensitive sample, remained.
Various workers [224-226] have modified these procedures to improve precision,
by employing zinc sulphide as a standard in contrast to the sodium sulphide solution
used in earlier methods. The addition of sodium hydroxide to the hydrogen sulphide
absorption solution improves recovery.