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

are transported from fresh to more saline waters. In estuaries, flocculation of humicacid colloids reportedly occurs preferentially at salinities between 0 and 5 ppt.Median color values for Florida rivers and estuaries, as reported by Friedemann andHand (1989) based on a survey of several thousand records retrieved from the U.S.EPA STORET database, are 70.0 and 20.0 pcu, respectively. Values observed in thetidal reaches of the Peace and Myakka river systems during water years 1994-2000were substantially higher than these statewide medians.Dissolved OxygenAnnual median dissolved oxygen concentrations varied over a relatively narrow range,between about 5.7 and 7.7 mg/L. Concentrations in the “stressful” (< 4 mg/L) rangewere recorded at least once during most years at every site. Concentrations in the“hypoxic” (< 2 mg/L) range, which are potentially fatal to organisms that cannot move toareas of higher oxygen availability, were observed at the following stations:• CH-02B (water years 1995, 1999, 2000)• CH-004 (all years)• CH-05B (1994, 1995, 1998, 1999)• CH-005 (all years)Chlorophyll-aChlorophyll-a concentrations, which provide estimates of phytoplankton biomass in thewater column, are helpful indicators of a waterbody’s trophic state. Annual medianconcentrations ranged between1.0 µg/L and 13 µg/L at the tidal Myakka River stationsand between 2.3 and 10.6 µg/L in the tidal Peace River. The statewide medianchlorophyll-a concentration for Florida estuaries, as reported by an FDEP surveyconducted in the mid-1980’s, is 8.5 µg/L.Algal blooms (indicated by chlorophyll-a concentrations > 20 µg/L) occurred at everyPeace and Myakka River station at some time during the monitoring period.Pronounced blooms, with chlorophyll concentrations > 50 µg/L, were observed at threesites.Annual mean chlorophyll-a concentrations observed at several stations during wateryears 1994-2000 exceeded 11 µg/L, a value that has been adopted by the State ofFlorida as indicating potentially impaired water quality conditions in the State’s estuarinewaters. Stations and years where the annual mean exceeded the 11 µg/L ‘impairment’level included:• Myakka River site CH-002 (water years 1995, 1999)• Myakka River site CH-02B (1995, 1998, 1999)• Peace River site CH-029 (1995, 1996)• Peace River site CH-004 (1994, 1995, 1996, 1999)• Peace River site CH-05B (1999)• Peace River site CH-005 (1994).xi