We sampled water chemistry (Na, K, Ca, Mg, specific conductance) and fish species occurrence in freshwater wetlands in the lower Myakka River drainage area in southwestern Florida. Three fish species were absent from wetlands below 100 microS/cm. None were absent from natural wetlands, but six species were absent from constructed wetlands. The sailfin molly (Poecilia latipinna) was the only estuarine fish found and it was rare. About one-half of the wetlands at both sites had a dilute water chemistry, with specific conductance <100 microS/cm (range 20-1000 microS/cm). In both wet and dry seasons there was a strong positive correlation between [Na] and [Ca] or [Mg], but not with [K]. Ponds of widely differing solute concentrations obeyed a simple linear model relating specific conductance to summed cation concentrations; it thus appears that there is only one surface water "type" present. Differences in concentration among wetlands are probably due to differing degrees of isolation from surface water flow, since the most isolated wetlands and those with the smallest drainage areas were those with the lowest specific conductance, the shortest hydroperiod, and the greatest proportion of volume derived from rainwater.
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