Use of A Igal A ssays in Studying Eu trophication Problems
209
growth and that the addition of that nutrient to the water substantially increased algal
growth. The addition of phosphorus and nitrogen together, and of 10 percent secondary
wastewater effluent stimulated algal growth even more while the tertiary wastewater
effluent had no effect. In Shagawa Lake water only the addition of nitrogen and
phosphorus together and secondary wastewater effluent stimulated algal growth. Table 3
shows the effect on algal growth of adding phosphorus back to tertiary wastewater which
had been obtained by treatment of secondary wastewater by alum flocculation. These
data clearly show that, when the secondary wastewater was treated to remove
phosphorus, it no longer stimulated algal growth. The results of in situ algal assays, using
indigenous algal species, agreed closely with those obtained in the laboratory. As a result
of the data obtained from the algal assays and limnological studies, it was recommended
that a full-scale plant be constructed at Shagawa Lake. Construction of such a plant to
treat all of the secondary wastewater from the City of Ely using advanced waste
treatment technology is underway.
Identification of Algal Growth-Limiting Nutrients
Another project is concerned with determining the trophic condition of various lakes
throughout the country and predicting the effects of increasing or decreasing nutrient
input into these lakes. Table 4 shows the results of algal assays in which various nutrient
additions were made to membrane filtered water from eight Oregon lakes of varying
water quality. The water samples were collected just after fall overturn when there was
good mixing in the lakes' water column. The test alga was Selenastrum capricornutum
and, in the table, algal growth (mg dry wt/1) after 21 days incubation is shown. Of the
eight lake waters assayed, Diamond Lake water supported the heaviest algal growth
(13.50 mg dry wt/1). In addition to results of algal assays, low hypolimnetic dissolved
oxygen and the occurrence of heavy blue-green algal blooms confirm that this lake is
eutrophic. Waldo Lake, on the other hand, is a pristine ultra-oligotrophic mountain lake.
It supported practically no growth of the algal test species and one of the nutrient
additions significantly increased algal growth. Of the remaining six lakes, four (Woahink,
Lake of the Woods, Ten Mile, and Tahkenitch) are definitely algal growth-limited by
phosphorus, and two (Odell and Triangle) by nitrogen. It should be noted, however, that
Triangle Lake water supported a relatively high algal growth (10.10 mg dry wt/1) without
any nutrient additions. This lake has a heavy algal growth during the summer and it
appears to be in an advanced stage of mesotrophy. When both nitrogen and phosphorus
were added to the water it supported 33.00 mg dry wt/1 of algal growth.
Assessment of Receiving Waters to Determine Their Nutrient Status and Sensitivity to
Change
Another potential use of the algal assay is related to establishing nutrient criteria for
receiving waters as a basis for water quality control. For example, the nutrient criterion
for an individual stream could be based upon the amount of algal growth, obtained in a
standardized assay, which should not be exceeded by the addition of wastewater
effluents. The algal assay could be used to monitor receiving streams in much the same
way as the biochemical oxygen demand (BOD) test is presently used to monitor oxygen
demand loadings on, and in streams.
Our laboratory has been working closely with the Federal Regulatory Program in the
Pacific Northwest Region (Region X) of the United States in this regard. In June, 1971,
during the period of high water flow, personnel from Region X collected water samples
209
growth and that the addition of that nutrient to the water substantially increased algal
growth. The addition of phosphorus and nitrogen together, and of 10 percent secondary
wastewater effluent stimulated algal growth even more while the tertiary wastewater
effluent had no effect. In Shagawa Lake water only the addition of nitrogen and
phosphorus together and secondary wastewater effluent stimulated algal growth. Table 3
shows the effect on algal growth of adding phosphorus back to tertiary wastewater which
had been obtained by treatment of secondary wastewater by alum flocculation. These
data clearly show that, when the secondary wastewater was treated to remove
phosphorus, it no longer stimulated algal growth. The results of in situ algal assays, using
indigenous algal species, agreed closely with those obtained in the laboratory. As a result
of the data obtained from the algal assays and limnological studies, it was recommended
that a full-scale plant be constructed at Shagawa Lake. Construction of such a plant to
treat all of the secondary wastewater from the City of Ely using advanced waste
treatment technology is underway.
Identification of Algal Growth-Limiting Nutrients
Another project is concerned with determining the trophic condition of various lakes
throughout the country and predicting the effects of increasing or decreasing nutrient
input into these lakes. Table 4 shows the results of algal assays in which various nutrient
additions were made to membrane filtered water from eight Oregon lakes of varying
water quality. The water samples were collected just after fall overturn when there was
good mixing in the lakes' water column. The test alga was Selenastrum capricornutum
and, in the table, algal growth (mg dry wt/1) after 21 days incubation is shown. Of the
eight lake waters assayed, Diamond Lake water supported the heaviest algal growth
(13.50 mg dry wt/1). In addition to results of algal assays, low hypolimnetic dissolved
oxygen and the occurrence of heavy blue-green algal blooms confirm that this lake is
eutrophic. Waldo Lake, on the other hand, is a pristine ultra-oligotrophic mountain lake.
It supported practically no growth of the algal test species and one of the nutrient
additions significantly increased algal growth. Of the remaining six lakes, four (Woahink,
Lake of the Woods, Ten Mile, and Tahkenitch) are definitely algal growth-limited by
phosphorus, and two (Odell and Triangle) by nitrogen. It should be noted, however, that
Triangle Lake water supported a relatively high algal growth (10.10 mg dry wt/1) without
any nutrient additions. This lake has a heavy algal growth during the summer and it
appears to be in an advanced stage of mesotrophy. When both nitrogen and phosphorus
were added to the water it supported 33.00 mg dry wt/1 of algal growth.
Assessment of Receiving Waters to Determine Their Nutrient Status and Sensitivity to
Change
Another potential use of the algal assay is related to establishing nutrient criteria for
receiving waters as a basis for water quality control. For example, the nutrient criterion
for an individual stream could be based upon the amount of algal growth, obtained in a
standardized assay, which should not be exceeded by the addition of wastewater
effluents. The algal assay could be used to monitor receiving streams in much the same
way as the biochemical oxygen demand (BOD) test is presently used to monitor oxygen
demand loadings on, and in streams.
Our laboratory has been working closely with the Federal Regulatory Program in the
Pacific Northwest Region (Region X) of the United States in this regard. In June, 1971,
during the period of high water flow, personnel from Region X collected water samples