Abstract Introduction Study Area >Material & Methods Results Discussion Acknowledgements Literature Cited Figures Tables

As part of an ongoing project that is investigating the hydrogeology of the upper part of the surficial aquifer, the USGS drilled 50 continuously cored test wells, using either a wireline coring system or conventional rotary coring system that collected whole-core samples, in the Lake Belt area in north-central Miami-Dade County (Fig. 1). Geophysical borehole logs were run in 47 of the test wells filled with clear freshwater using a RaaX® Borehole Image Processing System (BIPS®) digital optical logging tool. RaaX® designs BIPS® for clear-water bore- hole environments to monitor, process, and record optical images of borehole walls in digital format for geological and geotechnical analysis. The tool is useful in identifying large-scale secondary porosity (porosity developed in a rock through silution or fracturing) exposed along the borehole wall (Cunningham et al. 2003).

Of the 50 test wells, 15 wells northeast of ENP were selected for use as monitoring wells in this study (Fig. 1). The wells were located either on the levees of canals, or in the immediate proximity of levees along the north-south L-31N and L-30 canals, the east-west L-29 and Bird Road canals (Fig. 1). The number of water samples collected at each of the 15 wells depended upon the results of the borehole optical images analysis. We collected from each well at depths corresponding to highly porous strata identified in digital optical logs (Fig. 2). A total of 41 samples were collected monthly, from June 2000 to May 2001. Canals depths, in relation to the well caps, were measured in March 2002. Ground water levels were measured from ground surface.

Qualitative samples for biological analysis were collected using a Wayne® 1/2HP portable pump connected to a Coleman® 1750 watt portable generator, and several 1.5 m long PVC pipes that were connected to the pump through a flexible plastic hose. The pumping rate was about 90 l/min., the wells diameter 7.5 cm. A total of 1,000 L of water per sample was filtered using a 63 Bm mesh, 20 cm diameter plankton net. Water depth was a negative number, measured in centimeters below ground level. Environmental variables, such as temperature, conductivity, and dissolved oxygen, were recorded monthy using a YSI 85® Multi-Parameter Water Quality Meter. In October 2000, the instrument was sent to the factory for repair and, therefore, variables were not recorded at any of the wells for that month.

We collected samples at all available HFCs in each well. The displacement action of the pump can allow the collection of organisms at a good distance from the pump (Malard et al. 1997). At our collection depths, the assumption was made that we were collecting organisms that were present in the cavities of the HFC corresponding to the pumping depth. The presence of impermeable layers above and below each HFC limits the possibility of displacing organisms from HFCs that are shallower or deeper than the sampling HFC. Therefore, the distribution of copepods was characterized relative to the HFC where they were collected. The wells are identified with a letter and a number that indicate, respectively, the transect and the position along the transect (Fig. 2), followed by a number indicating the sampling depth, when required.

All samples were fixed in the field with 5% buffered formalin, and copepods were sorted and counted in the lab using a Leica® MZ8 stereoscope. Specimens of each taxon were mounted on permanent slides with Faure's medium and studied with a Leica® DMLS phase contrast microscope at 10X, 20X, 40X, and 100X. All copepod identifications included sex and developmental stage following Bruno et al. (2000, 2002b), Dussart and Defaye (1995), Reed (1994), Reid (1991, 1992a,b, 1993b), Suarez Morales et al. (1996), Williamson and Reid (2001), and Yeatman (1959). Larval stages are reported as copepodites (for copepodites stages I-V) or nauplii (for naupliar stages I-IV). All adults and most postembryonic stages (copepodids) were identified to species. Some of the postembryonic stages (early stage copepodids and all the nauplii) were not identified. The nauplii were not used in statistical analyses, because they might have been overlooked during sorting, given their extremely small size.

Data on physical and chemical variables, total number of individuals of each species and total numbers of species, calculated for each month and each well sampling depth, were used to run multiple correlation analyses. We did not collect the same numbers of HFCs for each well. Therefore, the number of individuals collected at each well was standardized by dividing the total number of individuals collected at each well by the number of HFCs sampled at that well, and reported as number of individuals per sampled depth (n.ind./depth). Detrended Correspondence Analysis (DCA) (Hill and Gauch 1980) was used to group the wells on the basis of species composition composition and realtive abundance. DCA was run on the number of individuals collected each month, at each well, at each depth, and log (x+1) transformed.