In the upper slough, still 

 within the park, Kolipinski and 

 Higer (1969) studied the dissolved 

 oxygen dynamics of an alligator hole 

 within a willowhead, and the sur- 

 rounding sawgrass marsh. Under high 

 water conditions, diurnal oxygen 

 levels in the hole and marsh were 

 very similar, ranging from about 

 3.0 mg/l in early morning to as much 

 as 9.0 mg/l during early afternoon. 

 As water levels dropped below ground 

 level, respiration in the alligator 

 hole increased. At low water levels 

 diurnal fluctuations remained small, 

 and concentrations seldom reached 

 greater than 2.0 mg/l. Similar 



conditions were reported for the 

 Tamiami Canal waters. 



Pesticide concentrations in 

 surface waters from both the upper 

 Shark Slough and the lower estuary 

 are reported to be uniformly low 

 (Kolipinski and Higer 1969, McPher- 

 son 1971). Concentrations of DDT 

 within sediments, however, are as 

 much as 1000 times greater than in 

 surface waters in the upper slough. 



Recently Flora and Rosendahle 

 (1981) documented an ominous but 

 confusing change in the inorganic 

 chemistry of Shark Slough surface 

 waters. Prior to construction of 

 L-29 on the north boundary of the 

 park, specific conductance in the 

 slough averaged 272 uohms/cm. The 

 sodium to chloride ratio (Na:CI) 

 averaged 0.34 for the same period. 

 After construction (1962 to present) 

 specific conductance averages 652 

 uohms/cm and the Na:CI ratio aver- 

 ages 0.88. This increased minerali- 

 zation of surface waters is believed 

 to be the result of increased drain- 

 age by canals, thereby removing the 

 buffering action of marsh filtra- 

 tion. Rainfall in the area is much 

 less mineralized and therefore tends 

 to improve the water quality. This 

 change is ominous because of its 



magnitude yet confusing because its 

 effects on marsh productivity and 

 ultimately the food web are not 

 easily predicted. 



McPherson (1971) reports an 

 expected seaward increase in the 

 concentration of inorganic ions 

 toward the mouth of the Shark River 

 estuary. Silica (Si0 2 ), tannins, 



and lignins occur in higher concen- 

 trations at the freshwater end of 

 the estuary. Nutrients, trace met- 

 als, and pesticides vary widely, 

 exhibiting no regular seasonal or 

 spatial trends. 



Information on changes in the 

 long term, overall water quality of 

 the Shark River estuaries are re- 

 ported by Davis and Hilsenbeck 

 (1974). These authors document the 

 gradual inland migration of saline 

 waters in response to upstream 

 diversion and management activities. 

 Their findings are particularly 

 important in that they point out an 

 insidious change in the availability 

 of habitat for estuarine organisms, 

 whose survival and growth depend on 

 a certain timing and range of fluc- 

 tuating salinity conditions. 



5.4 WHITEWATER BAY 



Previous discussions of geology 

 and geomorphology have established 

 that Whitewater Bay is an eroded 

 depression lying just north of a 

 southeasterly extending ridge of 

 Miami Oolite. The relatively well 

 defined drainage pattern to the 

 northeast of the bay (the Watson, 

 North, and Roberts Rivers) suggests 

 that historical Shark Slough drain- 

 age at lower sea level conditions 

 traversed its present boundaries and 

 flowed directly into Whitewater Bay 

 (White 1970). The general north- 

 east/southwest orientation of the 

 many islands within the bay strongly 

 reinforces this conclusion (Spackman 



80 



