Environmental Engineering Reference
In-Depth Information
two polyethylene screens to maintain integrity during shaking. The polyethylene
screens hold the FeO paper in a fixed orientation during shaking. This helps to
prevent contamination from soil particles lodging in the pores of the paper (Myers
et al.
1995
,
1997
) and prevents the paper from sticking to the walls of the shaking
vessel, which could reduce adsorption effectiveness of the paper. The FeO paper-
screen assembly is inserted into a bottle containing the runoff sample. Both
deionized water and a CaCl
2
solution (0.01 M) has been used as the shaking matrix
for the FeO paper and soil. Deionized water can disperse soil, causing it to lodge in
the pores of the filter paper (Sissingh
1983
), leading to errors in P analysis (Myers
et al.
1995
). The need for CaCl
2
probably depends upon the clay content of the
sediment, the P content of the clay, and the amount of sediment in the runoff. The
bottles are shaken on a reciprocating shaker to facilitate adsorption of P to the paper.
Phosphorous is extracted from the papers by the addition of H
2
SO
4
and further
shaking. An aliquot of the H
2
SO
4
solution is analyzed for P after neutralization of
acidity. For further details on this procedure, see Myers et al. (
1995
,
1997
).
7.7 Sulfur
7.7.1 Overview
Sulfur exists in both organic and inorganic forms. Inorganic forms can be classified
as gaseous (e.g., sulfur dioxide-SO
2
, and hydrogen sulfide-H
2
S), reduced (e.g.,
elemental S-S
, sulfide-S
2
), or oxidized (e.g., sulfate-SO
4
2
, and sulfite-SO
3
2
).
Common S containing minerals are gypsum (CaSO
4
) and pyrite (FeS
2
). In wetland
soils, S is found mainly in organic forms (Reddy and DeLaune
2008
). Under highly
reduced conditions (Eh
100 mV), obligate anaerobes use SO
4
2
as a terminal
electron acceptor to produce H
2
S. Sulfate reduction dominates anaerobic decom-
position in brackish marshes, inhibiting CH
4
production and regulating soil C
storage (Megonigal et al.
2003
). Soluble S
2
at levels found in estuarine marshes
can be detrimental or toxic to many organisms, and it has been shown to limit the
growth of common marsh grasses including
Spartina alterniflora
Loisel (Koch
et al.
1990
; Mendelssohn and McKee
1988
).
Detrimental environmental impacts occur when reduced S compounds (like
sulfides) are oxidized to form sulfuric acid (H
2
SO
4
). Acid mine drainage refers to
the outflow of acidic water from mines. The acidity, due to oxidation of metal
sulfides like FeS
2
, and subsequent dissolution of heavy metals can cause fish kills
and loss of vegetation. Acid sulfate soil is the common name given to soils and
sediments exhibiting these problems. Soils containing Fe sulfides (the most com-
mon being FeS
2
) are referred to as potential acid sulfate soils, but when they oxidize
and begin to generate acidity, they are referred to as active acid sulfate soils
(Fanning et al.
2010
).
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