Asterionella formosa was the most abundant diatom taxon present in all May 10, 1987, Round Lake collections. Cyclotella comta was a subdominant. Also identified were Nitzschia holsatica (at 1 m) and Nitzschia acicularis. and Synedra delicatissima at 4 m.
Phytoplankton cell densities were low, approximately 110 cells/ml. in the September collections, the blue-greens alga Chroococcus sp. was dominant (57% at 0 m, 49% at 1 m, and 60% at 4 m). Anabaena flos-aquae composed 37%, 20% and 28% of the population at 0 m, 1 m, and 4 m, respectively, with a colonial green alga accounting for 23% at 1 m. Among the algae accounting for <5% were Ceratium hirundinella a dinoflagellatel), Ankistrodesmus falcatus (a green alga), Dinobryon cylindricum, Stephanodiscus (a centric diatom), and Coelosphaerium (a blue-green).
The red water collected from 10 m on May 13, 1988, was examined for sulfur bacteria. Chromatium okenii (Ehr.) Perty was identified. Two other taxa are probably Thiocystis rufa Winogradski and Beggiatoa sp. A small spherical to slightly elongate purple bacterium was not identified.
A grab sample from the surface of Round Lake, collected on September 29, 1988, contained Aphanizomenon flos-aquae. Net plankton collected on May 15, 1989, included Asterionella formosa, unidentified biflagellate greens, Fragilaria crotonensis, Synura and Mallomonas. On September 12, 1989, Aphanizomenon flos-aquae and Dinobryon cylindricum were present along with Cryptomonas sp., Asterionella formosa, and Ceratium hirundinella.
The May phytoplankton of Round Lake contained high proportions of Dinobryon and Crucigenia in addition to Coelosphaerium and two unidentified motile green algae. The September collections contained large populations of Chroococcus sp. and Anabaena flos-aquae. Total cell counts were low in both collections.
Dinobryon may dominate spring flora in phosphorus-rich ponds, although it is traditionally associated with unproductive, Phosphorus deficient lakes (Reynolds 1988). It has a low Phosphorus requirement (Rhode 1948), and apparently develops in productive lakes after the spring maximum when nutrients are exhausted (Hutchinson 1967). Reynolds (1984b) lists as Dinobryon as typical in mesotrophic lakes. Hutchinson (1967) reports that Crucigenia, along with several other species of small green algae, may be abundant in eutrophic waters, especially in small lakes.
Coelosphaerium and Crucigenia populations are known to increase in response to thermal stratification in lakes (Renolds 1984a). Anabaena flos-aquae, a blue-green capable of fixing atmospheric nitrogen, frequently forms massive water blooms and is considered an indicator of eutrophy (Hutchinson 1967). Chroococcus, a non-nitorgen fixing blue-green, is a common subdominant in the plankton of mesotrophic to hypertrophic waters (Paerl 1988). It is often associated with nuisance blooms but rarely forms blooms itself.
Beggiatoa, a colorless, filamentous bacterium tentatively identified from the May, 1988, collection of red water, occurs in water where there is sumultaneous production of H2S and adequate oxygen. This bacterium deposits elemental sulfur within the cells when it oxidizes H2S. Tchromatium and Thiocystis are photosynthetic purple bacteria which require light energy for the oxidation of reduced sulfur compounds such as H2S. They also deposit elemental sulfur within their cells (Buchanan and Gibbons 1974, Wetzel 1975).
Sulfur bacteria occur where decomposition of proteins releases H2S or where sulfur-reducing bacterial species are reducing sulfates to H2S. Conditions for optimal growth frequently occur in stratified lakes with steep physical and chemical gradients and result in the formation of "plates" or strata of bacterial populations. Layers of photosynthetic bacteria develop in stratified lakes which have anoxic hypolimnia, often at depths with light intensities lower than those required for phytoplankton growth (Wetzel 1975).
The trophic condition of Round Lake is not clearly indicated by the results of two phytoplankton colections because of the range of ecological preferences of the algae identified. The lake, however, is probably mesotrophic.
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Spring , 10 May 1987 |
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| Sample Depth | Phytoplankton | Algal Cells per ml | Percentage |
|---|---|---|---|
| Surface | Dinobryon sp. | 47 | 59% |
| Crucigenia rectangularis | 12 | 15% | |
| unicellular motile green alga sp. | 40 | 13% | |
| Pyramimonas sp. | 7 | 9% | |
| Cyclotella comta | 3 | 3% | |
| Peridinium willei | 2 | 1% | |
| 1 Meter | Dinobryon cylindricum | 43 | 55% |
| Dinobryon divergens | 12 | 15% | |
| unicellular motile green alga sp. | 224 | 18% | |
| Coelosphaerium sp. | 8 | 10% | |
| Gomphosphaeria sp | 6 | 8% | |
| Asterionella formosa | 6 | 7% | |
| Ankistrodesmus falcatus var. acicularis | 1 | 2% | |
| 4 Meter | Dinobryon cylindricum | 125 | 55% |
| unicellular motile green alga sp. | 375 | 33% | |
| Anabaena flos-aquae | 19 | 8% | |
| Asterionella formosa | 4 | 2% | |
| 8 Meter | Dinobryon sp. | 361 | 97% |
| Asterionella formosa | 10 | 3% | |
Autumn ,28 September 1987 |
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| Sample Depth | Phytoplankton | Algal Cells per ml | Percentage |
| Surface | Chroococcus sp. | 62 | 57% |
| Anabaena flos-aquae | 40 | 37% | |
| Dinobryon cylindricum | 3 | 2% | |
| 1 Meter | Chroococcus sp. | 55 | 49% |
| colonial green alga | 25 | 23% | |
| Anabaena flos-aquae | 23 | 20% | |
| Dinobryon cylindricum | 5 | 4% | |
| 4 Meter | Chroococcus sp. | 55 | 60% |
| Anabaena flos-aquae | 31 | 28% | |
| Stephanodiscus sp. | 5 | 4% | |
| Coelosphaerium sp. | 3 | 3% | |
| Dinobryon cylindricum | 2 | 2% | |
| Chlamydomonas dinobryonii | 2 | 2% | |