Organic MaHer
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4. Determine the DOC and POC concentrations of the water samples as outlined earlier.
5. Plot the concentrations of DOC and POC comparatively and compare to similar analyses of
aquatic ecosystems studied by other workers.
6. Answer the questions following Option 3.
OPTION 2. VARIANCE IN DOC AND POC CONCENTRATIONS
1. Collect water samples with a Van Dorn or similar sampler from the central depression of a
lake or reservoir or from the same location in a stream as follows:
a. From the same depth location, three or four replicate samples out of the same Van Dorn
sampler.
b. Obtain four replicate Van Dorn samples from exactly the same depth and remove a 1-liter
sample from each for analyses.
c. Repeat at several depths. If stratified, take replicate samples within the epi-, meta-, and
hypolimnion.
2. Treat the collected samples as stated in Option 1.
3. Determine the concentrations of DOC and POC of the replicate water samples as outlined
earlier.
4. Determine the variance ofthe values obtained from the same water sample and from replicate
samplings of the same depth. Determine the standard deviation, standard error, and
coefficient of variance among the replicates.
5. Answer the questions following Option 3.
OPTION 3. LABORATORY ANALYSES
1. With samples provided by your instructor, determine the concentrations of DOC and POC
as outlined in Options 1 and 2.
2. Answer the following questions.
Questions
1. What is your opinion of using arbitrarily a O.5-.um pore size filter to separate
particulate and dissolved organic matter? What practical alternative methodology
can you suggest?
2. The particulate organic fraction includes all organic matter greater than 0.5 .urn up
to and including pieces of detritus as large as logs. From the standpoint of feeding
studies, such a composite category is not very meaningful. How might one
subdivide the particulate detritus further? What is meant by fine and coarse
particulate organic matter?
3. If one obtains the dry weight of particulate organic matter, how would the organic
carbon content be estimated by direct analyses?
4. What do concentrations of DOC or poe mean energetically within an aquatic
ecosystem? [See Rich and Wetzel (1978).]
5. A common observation in aquatic systems is that the vertical concentrations of
DOC change relatively little over an annual period. What do these observations
imply about the quality (i.e., the chemical composition) of the organic compounds?
6. How might the rates of utilization (turnover) of dissolved organic matter be
determined? Of particulate organic matter?
7. In the water samples you obtained, what do you believe is the primary origin of the
DOC measured? Of the POe?
8. What are the regions of the lake where decomposition of the DOC is likely to
occur? Of the POe? Why? How might these sites change seasonally?
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4. Determine the DOC and POC concentrations of the water samples as outlined earlier.
5. Plot the concentrations of DOC and POC comparatively and compare to similar analyses of
aquatic ecosystems studied by other workers.
6. Answer the questions following Option 3.
OPTION 2. VARIANCE IN DOC AND POC CONCENTRATIONS
1. Collect water samples with a Van Dorn or similar sampler from the central depression of a
lake or reservoir or from the same location in a stream as follows:
a. From the same depth location, three or four replicate samples out of the same Van Dorn
sampler.
b. Obtain four replicate Van Dorn samples from exactly the same depth and remove a 1-liter
sample from each for analyses.
c. Repeat at several depths. If stratified, take replicate samples within the epi-, meta-, and
hypolimnion.
2. Treat the collected samples as stated in Option 1.
3. Determine the concentrations of DOC and POC of the replicate water samples as outlined
earlier.
4. Determine the variance ofthe values obtained from the same water sample and from replicate
samplings of the same depth. Determine the standard deviation, standard error, and
coefficient of variance among the replicates.
5. Answer the questions following Option 3.
OPTION 3. LABORATORY ANALYSES
1. With samples provided by your instructor, determine the concentrations of DOC and POC
as outlined in Options 1 and 2.
2. Answer the following questions.
Questions
1. What is your opinion of using arbitrarily a O.5-.um pore size filter to separate
particulate and dissolved organic matter? What practical alternative methodology
can you suggest?
2. The particulate organic fraction includes all organic matter greater than 0.5 .urn up
to and including pieces of detritus as large as logs. From the standpoint of feeding
studies, such a composite category is not very meaningful. How might one
subdivide the particulate detritus further? What is meant by fine and coarse
particulate organic matter?
3. If one obtains the dry weight of particulate organic matter, how would the organic
carbon content be estimated by direct analyses?
4. What do concentrations of DOC or poe mean energetically within an aquatic
ecosystem? [See Rich and Wetzel (1978).]
5. A common observation in aquatic systems is that the vertical concentrations of
DOC change relatively little over an annual period. What do these observations
imply about the quality (i.e., the chemical composition) of the organic compounds?
6. How might the rates of utilization (turnover) of dissolved organic matter be
determined? Of particulate organic matter?
7. In the water samples you obtained, what do you believe is the primary origin of the
DOC measured? Of the POe?
8. What are the regions of the lake where decomposition of the DOC is likely to
occur? Of the POe? Why? How might these sites change seasonally?