409
Primary Production in the Oceans
sidered is marine sediments (Simoneit, 1978). Although marine sediments act as a sink for
organic matter, in local situations they may act as an important source due to resuspension.
9.4.2 Dissolved and Particulate Organic Matter
In aquatic systems, it is traditional to divide organic matter into the two major categories of dissolved and particulate (DOM and particulate organic matter [POM]). POM
includes those species that will be retained by a 0.45-μm glass fiber filter. When seawater
is passed through a 0.45-μm filter, some colloids are retained as well as suspended matter.
Various workers have used filters with pore sizes ranging from 0.40 to 1.0 μm to achieve
this separation.
The DOC is determined on the filtered sample by first acidifying and bubbling with
nitrogen to remove the inorganic CO 2 . The sample is then treated with a strong oxidizing
agent (such as potassium peroxydisulfate, K 2 S 2 O 8 ), sealed, and heated to 130°C for 1 h. The
CO 2 produced is removed using a carrier gas such as He or N 2 . The released CO 2 is determined by an infrared analyzer or by GC. The addition of H 2 O 2 before the UV (ultraviolet)
irradiation of the sample can also be used to oxidize the organic carbon to CO 2 . In recent
years, the DOC has been determined using a high- temperature catalyst (Pt) to oxidize
the sample. The CO 2 produced is analyzed using an IR (infrared) detector. The dissolved
organic nitrogen (DON) and phosphate (DOP) can be determined on the oxidized sample
by measuring the total inorganic NO 3
– and PO 4
3– and subtracting the inorganic nutrient in
the sample prior to oxidation (e.g., DON = [NO 3 ] T – [NO 3 ]).
DOC is about 50% of the DOM, and POC is about 50% of the value of POM. The concentration of DOC in seawater is typically significantly greater than that of POC (see Table 9.8).
While the typical range of DOC concentrations in surface seawater is 75 to 170 μM, the
average concentration of POC in surface seawater is only 8 μM (range of 1 to 17 μM).
Typical profiles of dissolved and particulate carbon in the oceans are shown in Figure 9.35.
Seasonal variations in DOC and POC occur primarily in shallow waters and are similar
to the variations in primary productivity. At depths below a few hundred meters, the
average DOC is 40 μM; the average POC is 0.8 μM. The POC frequently goes through a
Table 9.8
Levels of Dissolved and Particulate Organic
Material in Natural Waters
Source
Dissolved (μM)
Particulate (μM)
Seawater
Surface
75–150
1–17
Deep
4–75
0.2–1.3
Coastal
60–210
4–83
Estuarine
8–833
8–833
Drinking water
17
Groundwater
58
Precipitation
92
Oligotrophic lake
183
80
River
420
170
Eutrophic lake
830–4170
170
Marsh
1250
170
Bog
2500
250
Primary Production in the Oceans
sidered is marine sediments (Simoneit, 1978). Although marine sediments act as a sink for
organic matter, in local situations they may act as an important source due to resuspension.
9.4.2 Dissolved and Particulate Organic Matter
In aquatic systems, it is traditional to divide organic matter into the two major categories of dissolved and particulate (DOM and particulate organic matter [POM]). POM
includes those species that will be retained by a 0.45-μm glass fiber filter. When seawater
is passed through a 0.45-μm filter, some colloids are retained as well as suspended matter.
Various workers have used filters with pore sizes ranging from 0.40 to 1.0 μm to achieve
this separation.
The DOC is determined on the filtered sample by first acidifying and bubbling with
nitrogen to remove the inorganic CO 2 . The sample is then treated with a strong oxidizing
agent (such as potassium peroxydisulfate, K 2 S 2 O 8 ), sealed, and heated to 130°C for 1 h. The
CO 2 produced is removed using a carrier gas such as He or N 2 . The released CO 2 is determined by an infrared analyzer or by GC. The addition of H 2 O 2 before the UV (ultraviolet)
irradiation of the sample can also be used to oxidize the organic carbon to CO 2 . In recent
years, the DOC has been determined using a high- temperature catalyst (Pt) to oxidize
the sample. The CO 2 produced is analyzed using an IR (infrared) detector. The dissolved
organic nitrogen (DON) and phosphate (DOP) can be determined on the oxidized sample
by measuring the total inorganic NO 3
– and PO 4
3– and subtracting the inorganic nutrient in
the sample prior to oxidation (e.g., DON = [NO 3 ] T – [NO 3 ]).
DOC is about 50% of the DOM, and POC is about 50% of the value of POM. The concentration of DOC in seawater is typically significantly greater than that of POC (see Table 9.8).
While the typical range of DOC concentrations in surface seawater is 75 to 170 μM, the
average concentration of POC in surface seawater is only 8 μM (range of 1 to 17 μM).
Typical profiles of dissolved and particulate carbon in the oceans are shown in Figure 9.35.
Seasonal variations in DOC and POC occur primarily in shallow waters and are similar
to the variations in primary productivity. At depths below a few hundred meters, the
average DOC is 40 μM; the average POC is 0.8 μM. The POC frequently goes through a
Table 9.8
Levels of Dissolved and Particulate Organic
Material in Natural Waters
Source
Dissolved (μM)
Particulate (μM)
Seawater
Surface
75–150
1–17
Deep
4–75
0.2–1.3
Coastal
60–210
4–83
Estuarine
8–833
8–833
Drinking water
17
Groundwater
58
Precipitation
92
Oligotrophic lake
183
80
River
420
170
Eutrophic lake
830–4170
170
Marsh
1250
170
Bog
2500
250