Zangrando and Bryant 1978). The 

 seasonal changes in temperature 

 relative to salinity at Lake Marco 

 Shores did not permit a turnover of 

 the water column. The results of the 

 24-hour continuous profile of lake 

 water temperatures during the 19-21 

 January 1977 cold spell are depicted 

 in Figure 8. These data show that 

 even when night air temperatures 

 dropped to 2°C the only temperature 

 effects in the water column were a 

 3°C decrease in surface water temper- 

 ature and a slight compression of the 

 the rmoc line. 



During the times of minimal 

 temperature difference between the 

 mixolimnion and monimolimnion when 

 cooling might have caused mixing, the 

 salinity difference between the two 

 layers was greatest. Furthermore, 

 the thermocline that formed at the 

 interface between the two layers dur- 

 ing the remaining months was usually 

 quite pronounced imparting a great 

 degree of stability over an annual 

 cycle. Below this thermocline, I 

 found high suspended solids ( < 20 

 mg/1) and turbidity relative to the 

 surface layer. These data may indi- 

 cate an entrainment of suspended 

 materials in the dense lower layer. 

 Ritchie et al. (1978) have shown 

 that when such thermoclines were 

 present in four Mississippi reser- 

 voirs, a similar increase in suspend- 

 ed solids occurred in the top of the 

 lower layer due to water level regu- 

 lation in the reservoirs. X-ray 

 diffraction analysis of deep lake 

 sediments revealed that flocculation 

 of some magnesium occurred in the 

 lake. Riley and Chester (1971) note 

 that the flocculation of clay miner- 

 als, such as magnesium calcite, 

 occurs at fresh-salt water boundaries 

 because water is drawn out of clay 

 mineral settling units as the total 

 ionic concentration of the surround- 

 ing solution increases. Such a 

 boundary was present in the chemo- 

 cline of the lake. 



CONCLUSIONS 



The results of this investiga- 

 tion suggest that coastal transition 

 zone excavations in the area of the 

 proposed development can become 

 meromictic if they are sufficiently 

 deep so as to intersect the intrud- 

 ing saline ground water and if they 

 intersect seaward discharging surface 

 aquifers. Lake Marco Shores is mero- 

 mictic and extremely stable, permit- 

 ting the lowest layer to accumulate 

 nutrients. This same stability has 

 prevented the concomitant expected 

 stimulation of productivity and the 

 surface layer of the lake has, in 

 fact, become oligotrophic . Such 

 excavated lakes, if properly designed 

 and located in this unique area, may 

 represent an interesting alternative 

 for urban stormwater treatment in 

 coastal areas. 



LITERATURE CITED 



Anderson, G. C. Some limnological 

 features of a shallow saline 

 meromictic lake. Limnology and 

 Oceanography 3: 51-68; 1958. 



Rabl, A.; Nielson, C. E. Solar ponds 

 for space heating. Solar Energy 

 17112; 1975. 



Rand, M. C; Greenberg, A. E.; Taras, 

 M. J., editors. Standard methods 

 for the examination of water and 

 wastewater. Washington, DC: Am- 

 erican Public Health Assoc, 

 1976; 1193 p. 



Reynolds, Smith and Hills. Big 

 Cypress Basin excavation study. 

 Basin Program No. 2502. Rey- 

 nolds, Smith and Hills Environ- 

 mental Science and Engineering, 

 Inc. Report submitted to: Big 

 Cypress Basin Board, South 

 Florida Water Management Dis- 

 trict, January 1977. 1979; 1-1 

 to 6-23; 1979. 



229 



