MEROMIXIS IN A COASTAL ZONE EXCAVATION 



Charles M. Courtney 



Applied Environmental Services 

 Marco Island, Florida 



INTRODUCTION 



Lake Marco Shores was created as 

 a dredge and dragline excavation in 

 1972 when The Deltona Corporation de- 

 veloped the Marco Shores Golf Course 

 and Airport (Figure 1). Much inter- 

 est has been expressed in this lake 

 because of its use as a prototype of 

 additional proposed excavations. 



Over the period 28 October 1976 

 to 21 June 1977, I conducted seven 

 preliminary profiles of temperature, 

 conductivity, salinity and dissolved 

 oxygen in the lake. Observations 

 indicated that Lake Marco Shores was 

 developing a meromictic type of 

 stability composed of three vertical 

 strata: the mixolimnion, the chemo- 

 cline, and the monimolimnion. 



MATERIALS AND METHODS 



Because each of the three layers 

 was easily definable by in situ mea- 

 surement, an intensive sampling pro- 

 gram was employed from January to 

 December 1978 to describe changes 

 within these layers over an annual 

 cycle. During that interval over 40 

 trips were made to each of two sta- 

 tions on the lake (Figure 2) to moni- 

 tor the vertical distribution of 

 the following routine parameters: 

 Secchi depth, temperature, conducti- 

 vity, salinity, and dissolved oxygen. 



On 20 January 1977 during an unpre- 

 cedented cold spell (air temperature 

 reached 2.2°C) a profile of tempera- 

 ture was made to a depth of 3.5 m in 

 0.3 m increments using a YSI Model 

 47 Scanning Telethermometer coupled 

 to a YSI Model 80A Single Channel 

 Laboratory Recorder. A series of 

 twelve monthly chemical profiles were 

 made. Nutrients were analyzed by 

 standard methods (Strickland and 

 Parsons 1972; USEPA 1974, 1975; 

 Rand et al. 1976) . 



The bathymetry of the lake (Fig- 

 ure 2) was accomplished during the 

 period 25-26 October 1976 using a 

 Raytheon Model DE-719B Survey Fatho- 

 meter. Continuous climatological 

 data were collected at two sites 

 (Marco Island and Rookery Bay) which 

 bracketed the lake at distances of 

 approximately 4.8 km. Additional 

 rainfall data were collected on 

 a weekly basis at two locations in 

 the watershed of Lake Marco Shores 

 and at two locations on the lake 

 shore (Figure 1), using Taylor wedge 

 type rain collectors mounted on 

 staffs which also served as ref- 

 erences to monitor weekly surface 

 water levels. On each trip to the 

 lake actual wave heights were mea- 

 sured against a fixed staff at the 

 eastern end of the lake for compari- 

 son with maximum theoretical values. 

 Five clusters of 4 well points each 

 were installed around the lake to de- 

 termine if ground water exhibited the 

 same vertical structure as the lake. 



219 



