20
N E
0
~
~
N E
0
~
~
3,000
2.000
1.000
0
10
8
6
4
2
0
400
Exercise 2
1m
20 m
700
Figure 2.2. Comparison of the spectral distributions of energy
using a scanning spectroradiometer, Gull Lake, KalamazooBarry counties, Michigan, November 16, 1975. at I m (upper) and
at 20m (lower). IIlW/ cm2 ~ O.0461IEinst/ m2/sec.
Analyses of spectral energy distribution are especially useful in fresh waters. Large
variations in concentrations of organic compounds occur among different lakes and
streams and seasonally within the same water. Absorption of light energy increases
drastically with increased concentrations of dissolved organic compounds, particularly
humic and fulvic acids (Hutchinson, 1957; Wetzel, 1983). The spectral energy
distribution also is altered markedly. Distilled water has a very high absorption in the
red and infrared wavelengths but absorbs very little of the energy of shorter
wavelengths (UV, blue). Even very low concentrations of dissolved organic compounds
greatly increase absorption of the shorter wavelengths of the spectrum. The distribution of spectral energy at depth can be analyzed by comparison of vertical profiles of
total irradiance to those in which narrow band filters are used to exclude specific
portions of the spectrum. Profiles and mean extinction coefficients of each of these
spectral distributions can be compared.
Turbidity
Turbidity in water is caused by suspended inorganic and organic matter, such as clay,
silt, carbonate particles, fine organic particulate matter, and plankton and other small
organisms. This suspended matter causes light to be scattered and absorbed rather
than transmitted. However, measurements of turbidity, although simple to perform, do
not always yield significant correlations with concentrations of suspended materials.
The size and refractive characteristics of particulate matter, while important optically,
bear little direct relationship to the specific gravity and concentrations of the
suspensoids. Nonetheless, turbidity measurements are very useful for evaluating the
microstratification of microorganisms in density layers of lakes [e.g., Whitney (1937),
Stewart et al. (1965), Baker and Brook (1971), Baker et al. (1985)]. Turbidity is a major
concern of water treatment operations where suspended particulate matter must be
removed prior to use for domestic or industrial purposes. Many aquatic organisms,
especially filter feeders, cannot tolerate appreciable concentrations of inorganic
particulate matter.
N E
0
~
~
N E
0
~
~
3,000
2.000
1.000
0
10
8
6
4
2
0
400
Exercise 2
1m
20 m
700
Figure 2.2. Comparison of the spectral distributions of energy
using a scanning spectroradiometer, Gull Lake, KalamazooBarry counties, Michigan, November 16, 1975. at I m (upper) and
at 20m (lower). IIlW/ cm2 ~ O.0461IEinst/ m2/sec.
Analyses of spectral energy distribution are especially useful in fresh waters. Large
variations in concentrations of organic compounds occur among different lakes and
streams and seasonally within the same water. Absorption of light energy increases
drastically with increased concentrations of dissolved organic compounds, particularly
humic and fulvic acids (Hutchinson, 1957; Wetzel, 1983). The spectral energy
distribution also is altered markedly. Distilled water has a very high absorption in the
red and infrared wavelengths but absorbs very little of the energy of shorter
wavelengths (UV, blue). Even very low concentrations of dissolved organic compounds
greatly increase absorption of the shorter wavelengths of the spectrum. The distribution of spectral energy at depth can be analyzed by comparison of vertical profiles of
total irradiance to those in which narrow band filters are used to exclude specific
portions of the spectrum. Profiles and mean extinction coefficients of each of these
spectral distributions can be compared.
Turbidity
Turbidity in water is caused by suspended inorganic and organic matter, such as clay,
silt, carbonate particles, fine organic particulate matter, and plankton and other small
organisms. This suspended matter causes light to be scattered and absorbed rather
than transmitted. However, measurements of turbidity, although simple to perform, do
not always yield significant correlations with concentrations of suspended materials.
The size and refractive characteristics of particulate matter, while important optically,
bear little direct relationship to the specific gravity and concentrations of the
suspensoids. Nonetheless, turbidity measurements are very useful for evaluating the
microstratification of microorganisms in density layers of lakes [e.g., Whitney (1937),
Stewart et al. (1965), Baker and Brook (1971), Baker et al. (1985)]. Turbidity is a major
concern of water treatment operations where suspended particulate matter must be
removed prior to use for domestic or industrial purposes. Many aquatic organisms,
especially filter feeders, cannot tolerate appreciable concentrations of inorganic
particulate matter.