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Georgia Journal of Science

Article Title

INVESTIGATING THE DEEP CHLOROPHYLL MAXIMUM IN LAKE LOUISE, GEORGIA**

Abstract

Lake Louise is a large sink-hole lake in south-central Georgia, USA, approximately 13 hectares in area, 6.5 meters deep at its deepest point. Previous monitoring programs indicate that the lake stratifies each year, typically lasting from mid-March until mid-November, with the thermocline located at a depth of 2.0 to 2.5 meters. High tannin concentrations in the water also cause a sharp decrease in light levels with less than 0.1% of incident light reaching a depth of 2.5 m during the summer. However, a distinct deep chlorophyll maximum (DCM) develops at a depth of about 3.0 m, below the photic zone. Furthermore, the DCM contains higher chlorophyll b concentrations than are found in the surface waters. The purpose of this project is to determine the source of the chlorophyll b. Preliminary data indicate the most abundant photosynthetic organisms in this layer are species of filamentous cyanobacteria. The presence of chlorophyll b suggests that some of them may belong to genus Prochlorothrix. Conditions within the hypolimnion during thermal stratification appear to be compatible with this hypothesis, and, although cultures of Prochlorothrix have yet to be established from North America, genetic markers for the genus have been observed in samples from New Orleans, Louisiana. We intend to look for similar markers in Lake Louise. Filtered samples from different depths were collected May 30, 2018, and stored at -20o. DNA was extracted from the filters, and the 16s rRNA gene was amplified using PCR and standard bacterial primers. The collected PCR products will be cloned using the TOPO TA cloning system. Plasmids extracted from the resultant colonies will then be sequenced and the sequences compared with published cyanobacterial 16s sequences, including those of Prochlorothrix. This will allow us to assess biodiversity of the cyanobacterial microflora of Lake Louise and, potentially, confirm the presence of Prochlorothrix.

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