The first comprehensive year-round investigation of Mountain Lake, Virginia since 1970-71 was begun in March 1985 and continued through November 1987. Monthly studies suggested that this unique natural lake is undergoing change. Whereas inorganic nitrogen, orthophosphate, Secchi disc transparency, and primary productivity continue to suggest an oligotrophic condition, important limnological changes are indicated by the greater seasonal hypolimnetic oxygen depletion and extractable chlorophyll a which at times approach mesotrophic levels. In addition, the decrease in alkalinity, the increase in sulfate levels, and the increase in pH fluctuations compared to the past, suggest that Mountain Lake is susceptible to damage or change by acid rain and perhaps other perturbations that effect pH alkalinity, or hardness.
Changes were also noted in phytoplankton composition. One hundred sixty-three taxa were identified which included 56.4% Chlorophyta, 17.8% Chrysophyta, 13.5% Cyanophyta, 8% Pyrrophyta, 3.7% Cryptophyta, and 0.6% Euglenophyta. Sixty percent of these taxa were new reports for Mountain Lake. Dominant pyrrophytes included Gymnodinium sp. and Peridinium wisconsinense. Dominant chlorophytes included Scenedesmus bijuga, Quadrigula chodatii, and Oocystis pusilla. Important cryptophytes were Cryptomonas erosa var. reflexa, C. pusilla, and C. pyrenoidifera. The most abundant cyanophyte was Aphanocapsa elachista var. conferta. The only diatom (chrysophyte) that ever dominated was Cyclotella meneghiniana.
Studies of ammonia uptake by the phytoplankton, using the ammonia analog [¹⁴C]methylamine (MeA), revealed that during thermal stratification, phytoplankton succession was related to rapid ammonia uptake. Each successive phytoplankton community had significantly higher Vmax values for ammonia (methylamine) until midsummer when ammonia-nitrogen levels were at a seasonal low. At that point, the Vmax values dramatically declined and the community became dominated by blue-green algae. When allochthonous inputs of inorganic nitrogen renewed the levels of ammonia-nitrogen, Vmax values increased and the community changed, replacing the blue-green algae. Communities dominated by green algae (Chlorophyta) had higher MeA (and thus ammonia) uptake rates than those dominated by cryptophytes or blue-green algae (Cyanophyta).
The effect of various treatments and inhibitors on MeA uptake by the phytoplankton support the conclusion that ammonia uptake is a chemical, light-independent, energy-dependent process. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/109237 |
| Date | January 1988 |
| Creators | Parson, Marolyn J. |
| Contributors | Botany |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xxi, 283 leaves, application/pdf, application/pdf |
| Coverage | Virginia, United States, Giles County |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 18160908 |
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