period June through February. The 

 approximate area of zone 2 is 374 

 ha. 



Zone 3 is dominated by fresh- 

 water red mangroves of the "spider" 

 type (Craighead 1971) with consider- 

 able acreage of open ponds along the 

 northern edge of the zone. These 

 ponds are often surrounded by tall 

 Eleocharis or Paspalum . The clear 

 water of these ponds, abundant peri- 

 phyton and scant organic content of 

 bottom muds suggests that, even here, 

 dry down occurs often enough to per- 

 mit oxidation of organics. 



Marginal depth of water over the 

 pond rims (30 cm) where Eleocharis 

 and Paspalum flourish is about the 

 same as the average depth in zone 1 , 

 but the depth of water in the open 

 ponds probably averages 40 cm at nor- 

 mal rainy season maximum or about 10 

 cm lower that the confining banks 

 which support tall Eleocharis , Paspa - 

 lum, and red mangroves. The hydro- 

 period in this area probably averages 

 10 to 11 months. 



Within zone 3 but a little far- 

 ther south of these clear water, 

 shallow ponds, one first encounters 

 permanent water ponds surrounded by 

 dense stands of trees dominated by 

 red mangroves. The water is heavily 

 stained with humic acids and Chara 

 sp. becomes the dominant submerged 

 macro-plant. Ruppia maritima , or 

 widgeon-grass, is often found in 

 shallow margins of these ponds. Typi- 

 cally, a berm surrounds these ponds 

 and it appears that these ponds were 

 once surrounded by buttonwood ridges 

 on which cabbage palms grew as well. 

 Peaty soil may exceed 60 cm in depth 

 in these berms. The pond bottom sedi- 

 ments are not peat but fine sand 

 mixed with a high percentage of fine 

 organic flocculent material which 

 makes these muds extremely sticky. 



Where Chara flourishes there invari- 

 ably is a blue mud deposit indicating 

 natural anerobiosis and high produc- 

 tion of H S and methane. Zone 3 oc- 

 cupies 34f> ha . 



Seaward of the east-west running 

 levee one enters the main mangrove 

 forest association which can be best 

 described as zone 4, polyhaline man- 

 groves. Strictly speaking this zone 

 encompasses the entire mangrove com- 

 munity between Mcllvaine Bay and 

 Unknown Bay. Primary interest, how- 

 ever, is focused upon those portions 

 lying east of the existing airport 

 runway (Figure 1). The majority of 

 this community consists of a 119- 

 ha semi-impounded forest dominated 

 by black mangroves of small to medium 

 height lying behind the crest of a 

 low levee (dashed line between L and 

 Q of Figure 1) topped by large, dead 

 buttonwoods . From that levee the 

 land slopes gradually seaward to Un- 

 known Bay and its associated creeks. 



The impoundment behind the low 

 buttonwood levee had evidently expe- 

 rienced greater fresh water influence 

 prior to major drainage diversions 

 further north. The increased saline 

 influence has favored black and white 

 mangroves at the expense of button- 

 woods. In spite of the reduced fresh 

 water input this impounded area re- 

 mains inundated for up to 10 months 

 of the year, and its lowest spots are 

 probably always flooded to between 10 

 and 20 cm by a combination of resid- 

 ual fresh and tidal waters. 



ACKNOWLEDGEMENTS 



I greatly appreciate the as- 

 sistance and keen observations of 

 Durbin C. Tabb and Gary L. Beardsley 

 in preparing this report. 



217 



