Theses and Dissertations

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Defense Date

1996

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Ocean Science

Department

Oceanographic Center

First Advisor

Curtis Burney

Second Advisor

Bart Baca

Third Advisor

Richard E. Dodge

Abstract

While limestone quarry lakes have existed in South Florida for many years, only recently have they received serious scrutiny. A thorough understanding of the trophic dynamics of these lakes has yet to be achieved. Questions have arisen as to the value of these lakes for such purposes as water reclamation, conservation, and recreational use. The purpose of this study was twofold, 1) to investigate the trophic processes within these lakes with special regard to phosphorus limitation, and 2) to help provide a better understanding of the linmology of these lakes, specifically through the quantification and identification of the invertebrate life and water quality analysis.

The pH in the four lakes in this study averaged above 8.0 over a two year period from January 1994 to December 1995. The surface dissolved oxygen averaged 7.1 mg/L during the same period. Chlorophyll-a averaged 1.1 mg/m3 during a six month period from April through September 1995. Surface total phosphorus levels averaged 0.012 mg/L (0.39 ug-at L·1) over the same six month period, which is not indicative of highly productive systems. While phytop1ankton were abundant during the two year period, the populations were dominated by very small forms of chlorophytes and cyanobacteria. The average alkalinity was high (150.4 mg CaCO3/L, 3.0 meq L-1), which is not surprising considering the geochemistry of these lakes. However, alkalinity was poorly correlated with the trophic measures (chlorophyll a, total phosphorus, alkaline phosphatase activity and orthophosphate).

To investigate phosphorus limitation in these lakes, the specific activity of the enzyme alkaline phosphatase, secreted by the phytoplankton, was studied over the course of 6 months and during a 24 hour period. The assumption was that if these lakes were phosphorus limited, then alkaline phosphatase activity should vary inversely with orthophosphate. Furthermore, chlorophyll-a should be positively correlated with orthophosphate. In the six-month study the Jatter relationship was found to be significant (Spearman r= 0.69; p= 0.0002, n= 24). Alkaline phosphatase activity and orthophosphate showed a nearly significant, inverse relationship (Spearman r= -0.402, p= 0.051, n= 24). Regression analysis from the diel study also showed a significant inverse relationship between alkaline phosphatase activity and orthophosphate (r= 0-.548, p= 0.033, n= 12). Alkaline phosphatase activity appears to provide a simple means of assaying the degree of phosphate limitation and the trophic state of these lakes.

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