WATER BUDGET AND PROJECTED WATER QUALITY IN PROPOSED MAN-MADE 

 LAKES NEAR ESTUARIES IN THE MARCO ISLAND AREA, FLORIDA 



Wayne C. Huber and Patrick L. Brezonik 



Department of Environmental Engineering Sciences 

 University of Florida, Gainesville, Florida 



INTRODUCTION 



The proposed Marco Island de- 

 velopment plan calls for the excava- 

 tion of a large group of intercon- 

 nected lakes in two areas known as 

 Units 24 and 30 near Marco Island, 

 Florida . The area has been described 

 in detail elsewhere in this series. 



The land uses and lake areas are 

 tabulated in Table 1 for Units 24 

 and 30. The latter is considerably 

 larger both in total area and lake 

 area. Existing Lake Marco Shores 

 (see paper by Courtney) also will be 

 incorporated into the lakes of Unit 

 30. 



The quality of the proposed 

 lakes is of considerable importance, 

 both to the riparian owners and to 

 the nearby estuarine areas that will 

 receive surface discharges. Although 

 the areas will be surrounded by berms 

 sufficient to contain the 100-year 

 storm volume, some net runoff will 

 leave via spreader ditches and enter 

 the mangrove and marsh areas. 

 Hence, an a priori assessment of 

 lake water quality was desired to 

 evaluate the potential for problems 

 within and downstream of the lakes. 

 This paper describes the techniques 

 used for the assessment. 



Although the potential exists 

 for a variety of pollutants to enter 

 the lakes, only a few are criti- 

 cal to the lake evaluation. In par- 

 ticular, the nutrients, total nitro- 

 gen (T-N) and total phosphorus (T-P) 

 are important to the long term po- 

 tential for eutrophication and are 

 examined in detail. Such common 

 parameters as dissolved oxygen will 

 not be a problem on the basis of data 

 from existing Lake Marco Shores and 

 experience with similar lakes else- 

 where. Moreover, the scope of the 

 parent investigation did not require 

 a comprehensive evaluation of all 

 water quality parameters. Hence, 

 T-N and T-P are emphasized in this 

 paper. 



A complication is the fact that 

 the deep lakes will be stratified due 

 to the influx of hypersaline ground 

 water below a depth of roughly 6.5 

 ft (2.0 m) . Based on samples from 

 existing Lake Marco Shores, water in 

 the lower layer (monimolimnion) will 

 likely be of poor quality, with high 

 concentrations of nutrients. The 

 fresh upper layer (mixolimnion) , on 

 the other hand, should be of much 

 better quality; the point of this 

 investigation is to determine how 

 much better. The lakes will be 

 meromictic, that is, permanently 



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