Decomposition: Particulate Organic Matter
287
2. Tether a known dry weight of the leaves of each type in packs with monofilament nylon line to
regular construction bricks. Label each brick appropriately. Make sufficient leaf "packs" of
each species to permit the removal of replicates for analysis at three-week intervals for 12 to 15
weeks.
3. Place the leaf packs within a relatively uniform area of the stream substrata with the leaves
facing upstream, to stimulate natural entrapment. Stake the shoreline area so that the samples
can be found later. If the current is strong or the stream is subject to spates that could move the
bricks, firmly anchor with rods penetrating through the holes of the bricks well into the
substratum.
4. Enclose some of the leaf packs completely with fine mesh (ca. 1.0-mm) nylon screening to
restrict access of large aquatic invertebrates. If large conifer needles are used, enclose the
samples in large mesh (e.g., 5-mm) and small mesh (ca. 1.0-mm) litter bags.
5. At biweekly intervals, remove a replicate of each leaf species (exposed and those in enclosures).
Carefully remove any aquatic invertebrates from the residual leaf material, and examine the
groups and amounts of invertebrates that have colonized the leaf material. Then place the
POM into tared trays made of aluminum foil and dry to constant weight at 105°C. Cool
under desiccation and immediately weigh.
6. If possible, remove subsamples of the dry material and grind in an appropriate mill (e.g., a
Wiley mill, 40-mesh) or to a fine powder with a clean mortar and pestle. Determine the organic
carbon, nitrogen, and phosphorus content by the methods outlined in Exercises 7, 9, and 27.
7. Determine the changes in dry weight and, if possible, organic C, N, and P through time for
the leaves of different species and exposed versus unexposed to the feeding activities oflarge
invertebrates.
8. Answer the following questions.
Questions
1. In analyses of phytoplankton mineralization, what types of controls might be incorporated
into the decomposition incubations? Since the filtrate was not acidified to remove 14COz,
rather relied on extensive sparging with nonlabeled COz for exchange and removal, would a
small amount of background contamination be expected? How severe do you think this
contamination would be? [See Cole and Likens (1979).J
2. Compare the estimated rates of mineralization to the estimated residence time (i.e.,
sedimentation rates) of phytoplankton in the water column. How might large thermal
discontinuities in the metalimnion alter the rate of sedimentation?
3. If much of the phytoplankton particulate detritus were to reach the sediments, how might the
rates of decomposition be altered in comparison to those in the water column? How might
the mineralization method be modified to measure rates in the sediments?
4. How might the benthic mineralization differ between hard and soft waters? [See Fallon and
Brock (1982) and Cole (1985).J
5. How might the rates of decomposition of algae differ among various species, temperatures,
pH, and other factors? [See Mills and Alexander (1974) and Gunnison and Alexander
(1975).J
6. How would the rates of mineralization of phytoplankton determined by the method outlined
be altered if the water sampled were completely anaerobic? What gaseous products might be
evolved? Soluble products?
7. It is easy to criticize methods that attack the difficult problem of measuring in situ rates of
decomposition. Suggest alternative methods. [See Saunders (1972) and Storch and Saunders
(1978).J
8. How might you calculate the theoretical turnover time for the POM of the macrophytes or
stream leaf packs?
9. What is the fate of organic matter (both DOM and POM) of macrophytes decomposing in
wetlands surrounding a lake basin? Of macrophytes in the littoral zone of the lake per se?
287
2. Tether a known dry weight of the leaves of each type in packs with monofilament nylon line to
regular construction bricks. Label each brick appropriately. Make sufficient leaf "packs" of
each species to permit the removal of replicates for analysis at three-week intervals for 12 to 15
weeks.
3. Place the leaf packs within a relatively uniform area of the stream substrata with the leaves
facing upstream, to stimulate natural entrapment. Stake the shoreline area so that the samples
can be found later. If the current is strong or the stream is subject to spates that could move the
bricks, firmly anchor with rods penetrating through the holes of the bricks well into the
substratum.
4. Enclose some of the leaf packs completely with fine mesh (ca. 1.0-mm) nylon screening to
restrict access of large aquatic invertebrates. If large conifer needles are used, enclose the
samples in large mesh (e.g., 5-mm) and small mesh (ca. 1.0-mm) litter bags.
5. At biweekly intervals, remove a replicate of each leaf species (exposed and those in enclosures).
Carefully remove any aquatic invertebrates from the residual leaf material, and examine the
groups and amounts of invertebrates that have colonized the leaf material. Then place the
POM into tared trays made of aluminum foil and dry to constant weight at 105°C. Cool
under desiccation and immediately weigh.
6. If possible, remove subsamples of the dry material and grind in an appropriate mill (e.g., a
Wiley mill, 40-mesh) or to a fine powder with a clean mortar and pestle. Determine the organic
carbon, nitrogen, and phosphorus content by the methods outlined in Exercises 7, 9, and 27.
7. Determine the changes in dry weight and, if possible, organic C, N, and P through time for
the leaves of different species and exposed versus unexposed to the feeding activities oflarge
invertebrates.
8. Answer the following questions.
Questions
1. In analyses of phytoplankton mineralization, what types of controls might be incorporated
into the decomposition incubations? Since the filtrate was not acidified to remove 14COz,
rather relied on extensive sparging with nonlabeled COz for exchange and removal, would a
small amount of background contamination be expected? How severe do you think this
contamination would be? [See Cole and Likens (1979).J
2. Compare the estimated rates of mineralization to the estimated residence time (i.e.,
sedimentation rates) of phytoplankton in the water column. How might large thermal
discontinuities in the metalimnion alter the rate of sedimentation?
3. If much of the phytoplankton particulate detritus were to reach the sediments, how might the
rates of decomposition be altered in comparison to those in the water column? How might
the mineralization method be modified to measure rates in the sediments?
4. How might the benthic mineralization differ between hard and soft waters? [See Fallon and
Brock (1982) and Cole (1985).J
5. How might the rates of decomposition of algae differ among various species, temperatures,
pH, and other factors? [See Mills and Alexander (1974) and Gunnison and Alexander
(1975).J
6. How would the rates of mineralization of phytoplankton determined by the method outlined
be altered if the water sampled were completely anaerobic? What gaseous products might be
evolved? Soluble products?
7. It is easy to criticize methods that attack the difficult problem of measuring in situ rates of
decomposition. Suggest alternative methods. [See Saunders (1972) and Storch and Saunders
(1978).J
8. How might you calculate the theoretical turnover time for the POM of the macrophytes or
stream leaf packs?
9. What is the fate of organic matter (both DOM and POM) of macrophytes decomposing in
wetlands surrounding a lake basin? Of macrophytes in the littoral zone of the lake per se?