Phytoplankton cell densities were low (to 100 cells/ml) in collections from Station A (1 m and 8 m) and the 1 m and 4 m samples from Station D. Density at 8 m at Station D was 3600 cells/m and ranged from 4700 to 6600 cells/ml in collections from Station B. The dominant alga in collections from 1 m at stations A, B, and D was the filamentous blue-green Lyngbya. At Station A, L. contorta composed 87% of the cells counted in the 1 m collection and 92% at 8 m. At Station B, L. contorta (74% at 1 m, 70% at 4 m, 65% at 8 m) and Lyngbya sp. (16% at 1 m, 30% at 4 m, 27% at 8 m) were also strongly represented. Except for the filamentous blue-green Oscillatoria sp. (10% at 1 m and 8% at 8 m), the associated algae accounted for <1% of the cell counts in the Station B samples. At Station D, Lyngbya sp. composed 32% of the cells counted at 1 m and 83% at 8 m. Other blue-green well represented at Station D were Anabaena sp. 1 (20% at 1 m, 23% at 4 m), Anabaena, sp. (38% at 4m), Anabaena cf. torulosa (16% at 1 m), Oscillatoria (15% at 8 m), Chroococcus (23% at 4 m). The green alga Oocystis sp. composed 16% of the count at 1 m and 11% at 4 m.
The most abundant algae in the May, 1988, collections from Omak Lake were the filamentous blue-green Lyngbya and centric diatoms. In the September collections Lyngbya contorta, Anabaena sp. and Oscillatoria sp. were the abundant algae.
Anabaena is frequently abundant in eutrophic lakes in early to mid-summer (Hutchinson 1967; Taylor, et al. 1981) and Lyngbya and Oocystis are typical of eutrophic waters (Taylor, et al. 1981). Although some species of Oscillatoria are found in oligotrophic lakes, others are common in mesotrophic to eutrophic lakes, ponds and stagnant waters (Paerl 1988). Chroococcus is commonly a subdominant in mesotrophic and eutrophic lakes, ponds and rivers (Paerl 1988). Gloeocystis is most frequently found in ponds and shallow, fertile lakes (Hutchinson 1967).
The presence of moderate numbers of phytoplankton typical of mesotrophic to eutrophic waters in the May and September, 1988, collections from Omak Lake indicates that nutrient availability is moderate.
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| Sample Depth | Phytoplankton | Algal Cells per ml | Percentage |
|---|---|---|---|
1 M| Lyngbya cf. contorta | 40 | 43% |
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| small centric diatoms | 39 | 42% | |
| large centric diatoms | 5 | 5% | |
| Oocystis sp. | 4 | 4% | |
| Ankistrodesmus sp. | 2 | 2% | |
| Lagerheimia wratislavensis | 2 | 2% | |
| 4 Meter | small centric diatoms | 107 | 70% |
| large centric diatoms | 15 | 10% | |
| erismopedia tenuissima Lemm. | 8 | 5% | |
| Lyngbya cf. contorta | 6 | 4% | |
| Rhodomonas sp. | 5 | 3% | |
| Oocystis sp. | 3 | 2% | |
| Ankistrodesmus falcatus var. mirabilis | 3 | 2% | |
| 8 Meter | small centric diatoms | 165 | 97% |
| Oocystis cf. pusilla | 4 | 2% | |
| 14 Meter | small centric diatoms | 666 | 87% |
| large centric diatoms | 99 | 13% | |
| Scenedesmus sp. | 2 | 2% | |
Autumn 27, September 1988 |
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Station A |
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| Sample Depth | Phytoplankton | Algal Cells per ml | Percentage |
| 1 Meter | Lyngbya contorta | 75 | 87% |
| Chlamydomonas sp. | 3 | 3% | |
| Anabaena sp. | 2 | 2% | |
| Chroococcus varius | 2 | 2% | |
| Gloeocystis planktonica Lemm. | 2 | 2% | |
| 8 Meter | Lyngbya contorta | 100 | 92% |
| Oocystis cf. pusilla | 2 | 2% | |
| Chroococcus varius | 2 | 2% | |
Station B |
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| Sample Depth | Phytoplankton | Algal Cells per ml | Percentage |
| 1 Meters | Lyngbya contorta | 4500 | 74% |
| Lyngbya sp. | 940 | 16% | |
| Oscillatoria sp. | 600 | 10% | |
| 4 Meter | Lyngbya contorta | 3300 | 70% |
| Lyngbya sp. | 1400 | 30% | |
| unidentified blue-green alga | 15 | 1% | |
| 8 Meters | Lyngbya contorta | 4300 | 65% |
| Lyngbya sp. | 1800 | 27% | |
| Oscillatoria sp. | 550 | 8% | |
Station D |
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| Sample Depth | Phytoplankton | Algal Cells per ml | Percentage |
| 1 Meter | Lyngbya sp. | 17 | 32% |
| 11 | 20% | ||
| Oocystis cf. submarina | 9 | 16% | |
| Anabaena cf. torulosa | 8 | 16% | |
| Lagerheimia subsalsa | 1 | 3% | |
| Scenedesmus bijuga | 1 | 3% | |
| Gloeocystis planctonica | 1 | 3% | |
| unidentified spherical flagellates | 1 | 3% | |
| Ankistrodesmus falcatus | 1 | 2% | |
| small centric diatoms | 1 | 2% | |
| 4 Meter | Anabaena sp. | 30 | 38% |
| Anabaena sp. | 16 | 23% | |
| Chroococcus dispersus | 6 | 23% | |
| Oocystis sp. | 3 | 11% | |
| Chroomonas acuta | 1 | 4% | |
| small centric diatom | 1 | 3% | |
| 8 Meters | Lyngbya contorta | 3100 | 83% |
| Oscillatoria sp. | 550 | 15% | |
| Chroococcus dispersus | 8 | 2% | |