Peace and Myakka River Water Quality Summary 2002 - Southwest ...

this type should not be interpreted as evidence of degraded water quality. In manycases, however, exceedances of state standards can be linked to specific pollutantdischarges or other human activities that are causing negative water quality impacts.Information on the frequency and magnitude of exceedances can thus be helpful inidentifying sites where water quality may be declining or degraded. Once such sites areidentified, more detailed follow-up studies can be designed and implemented to identifythe cause(s) of the observed exceedances.Specific ConductanceSpecific conductance measures the ability of a water sample to carry an electric current,which depends on the presence of ions in the sample, their total concentration, andother physical and chemical characteristics. Freshly distilled water has a conductivity ofbetween 0.5 and 2 µmhos/cm. The Florida standard for specific conductance in freshsurface waters is 1,275 µmhos/cm, a level set to protect native fish and other aquaticorganisms.Exceedances of this standard were observed at four stations during water years 1998-2001:• Joshua Creek at Nocatee (during 1999, 2000 and 2001)• Shell Creek near Punta Gorda (during 2001)• Big Slough Canal near Myakka City (during 1999)• Big Slough Canal near North Port (during 1999).In Florida the presence of elevated specific conductance levels in fresh surface watersoften indicate that substantial discharges of groundwater — from the Intermediate orFloridan aquifers — are occurring at locations upstream of the sampling point.Agricultural and industrial operations are the most common sources of such discharges.Un-Ionized AmmoniaThe un-ionized form of ammonia is highly toxic to fish and other aquatic organisms. Inwater, ionized (NH 4 + ) and un-ionized (NH 3 ) ammonia exist together in equilibrium, withthe un-ionized form becoming more common at higher temperature and pH levels.The Florida water quality standard for un-ionized ammonia is 0.02 mg NH 3 /L. Levelsexceeding the standard were observed at two stations during water years 1998 – 2001:• Saddle Creek at Structure P-11 (in water years 2000 and 2001)• Horse Creek near Myakka Head (2000).Levels of un-ionized ammonia that were relatively high (>0.01 mg NH 3 /L) but did notexceed the water quality standard were also observed at several other stations,including:• Peace River at Zolfo Springs (2000, 2001)• Shell Creek near Punta Gorda (2001)• Myakka River at Myakka City (1999)12