RESULTS 



Precipitation at the National 

 Weather Service station in Fort Myers 

 (1940-1970) indicated an annual aver- 

 age rainfall of 135 cm for the study 

 area (Reynolds et al. 1979). When 

 1978 records at the two sites brac- 

 keting Lake Marco Shores are compared 

 to these data, they indicate a below 

 average rainfall (115 cm). Further- 

 more, the more coastal site has a net 

 rainfall deficit when compared to the 

 mainland site. 



Theoretical maximum wave heights 

 (0.3 m and 0.46 m) for the longest 

 fetch distances (944 m and 881 m, re- 

 spectively) were never approached 

 during periods of maximum wind (60 

 km/h) at the lake. Observed wave 

 heights only ranged from zero 

 to 0.24 m for the forty observations. 

 Increased wind speed was not corre- 

 lated with increases in mixolimnionic 

 salinity. 



Water level hydrographs for each 

 of the staffs in the lake and in the 

 surrounding watershed are shown in 

 Figure 3 along with mean rainfall re- 

 cords for all (4) of the wedge rain 

 gages. Minimum water elevations oc- 

 curred during the month of April as 

 a result of the effects of the pre- 

 vious dry season while maximum water 

 levels occurred in the August- 

 September period at the end of the 

 rainy season. 



Well chemical data generally in- 

 dicated that the same type of hyper- 

 saline water which occurred below the 

 chemocline in the lake was typical of 

 ground water in the area surrounding 

 the lake. Salinities from the two 

 deepest well points were always 

 hypersaline. The surface aquifer on 

 on the other hand was usually brack- 

 ish. Ammonia-nitrogen was generally 

 highest in samples from the deeper 



well points. Total phosphate and 

 orthophosphates were always highest 

 in samples from the deeper aquifer. 

 Hydrogen sulfide and high color were 

 most frequently observed in samples 

 from Well No. 3 located nearest to 

 tidal waters. All wells showed 

 slightly acidic pHs (range 6.3-6.9). 



Analysis of water elevations in 

 wells revealed a general trend of de- 

 creasing ground water levels in the 

 surface aquifer over the October- 

 December period. This coincided with 

 a drop in surface water levels in the 

 impounded area. 



Secchi disk transparencies (Fig- 

 ure 4) ranged over a small interval 

 for the year (1.37 m to 2.44 m) , and 

 averaged 1.89 m (n=38; s.d.=0.31m) 

 although there was a general trend 

 toward decreased transparency during 

 the April-September rainy season. 

 Secchi depths never exceeded the 

 depth of the bottom of the chemo- 

 cline . 



Temperature profiles in the lake 

 for the periods January-June and 

 July-December are presented in Fig- 

 ure 5. Each monthly value represents 

 an average of from two to four 

 "weekly" measurements. Lake Marco 

 Shores was homiothermic below a depth 

 of 4.0 m for the entire year with 

 monimolimnionic waters only ranging 

 from 25.0° to 26.5°C. This tempera- 

 ture interval coincided with the 

 average maximum summer air tempera- 

 tures . 



Dissolved oxygen profiles (Fig- 

 ure 6) were remarkably uniform over 

 the study period and showed a nearly 

 saturated mixolimnion to a depth of 

 2.0 m. There was a rapid rate of 

 oxygen decrease across the chemocline 

 (2.0 m to 2.5 m) with no oxygen below 

 the 3.7-m depth. This stability was 

 evident throughout the coldest, wind- 

 iest, and rainiest months (January, 

 December, September, respectively). 



222 



