Aquatic Biology of South Florida Limestone Excavation Lakes

Although mitigation is now required on excavation lakes resulting from limestone mining in South Florida, little baseline information exists on which to base mitigation recommendations. For this study, 8 representative limestone excavation lakes in Dade County, Florida, were sampled during 1981-82 to measure selected limnological parameters. There was little within-lake variation in water quality but substantial differences in means and ranges among lakes. Depths ranged from 3.2 to 15.2 m and surface areas, 8 to 44 ha. Maximum water temperature observed was 33° C and the minimum 19° C. Surface dissolved oxygen was 7.5-8.3 mglliter and 2.0- 7.5 mglliter at lake bottoms. Other ranges measured included alkalinity 72-170 mg/liter, conductivity 221 to 1,058 p,mhos, pH 7.2 to 8.2, and transparency 1.4 to 5.6 m. Mean values for total phosphorus (7.1 to 12.3 mg/m3 ) varied greatly by lake. No correlation was found among the mean depth, age, or surface area of each lake and the productivity indicators just cited. The age of each lake was not correlated with density or numbers of macroinvertebrate families. However, the mean depth was negatively correlated with the number of macroinvertebrate/m2 and the number of families. Mean number of macroinvertebrates ranged from 218 to 2,704/m2 with dipterans the most abundant. Largemouth bass (Micropterus salmoides) , redear sunfish (Lepomis microlophus), bluegill (L. macrochirus), and mosquitofish) (Gambusia affinis) were common to all lakes although largemouth bass were generally small, and only 12% of those captured exceeded 300 mm in length. The low productivity and poor biological diversity suggests the potential for fisheries enhancement by such methods as addition of littoral areas, fish shelters, and return of the organic overburden to the lakes following mining.

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