relative to production in community 

 metabolic studies of the standing 

 water in these ponds and marshes. 

 Periodic severe oxygen depletion was 

 observed. 



Examination of plant community 

 structure (Figure 1), aerial photo- 

 graphy and water depths strongly sug- 

 gest that the area north of the east- 

 west levee, airport, and golf course 

 was a freshwater habitat that was in- 

 vaded by salt water species such as 

 the red mangrove which have the abil- 

 ity to live in "hard" freshwater. 



South of the artificial east- 

 west levee and east of the airport 

 runway lies a weak tidal mangrove 

 community occupying a shallow basin 

 approximately 119 hectares (ha) in 

 area. It is dominated by black man- 

 groves up to 6 m in height with a 

 considerable admixture of smaller 

 reds and whites. Large buttonwood 

 snags along the dashed line between L 

 and Q (Figure 1) attest to a formerly 

 fresher regime, and a comparison of 

 1952, 1963 and 1974 aerial photogra- 

 phy suggests a rapid continuing inva- 

 sion of mangroves there, as well as 

 to the north of the levee. Most of 

 the basin remains shallowly inundated 

 for much of the year, as a result of 

 direct rainfall combined with rela- 

 tively frequent though weak tidal 

 penetration. 



evident in the 119-ha basin. This 

 suggests that either (a) production 

 of these materials is very low, or 

 (b) tidal export is adequate to pre- 

 vent accumulation of particulates. 

 We suggest that the latter case pre- 

 vails, and that there is a gradual 

 net movement of particulates in a 

 southeasterly direction through the 

 basin or "impoundment" rim (shown as 

 dashed line in Figure 1) toward the 

 head of Unknown Bay. 



Figure 2 divides the 1,011- 

 ha area south of the Belle Meade 

 grade into four main zones based on 

 the present duration of flooding. 

 Zone 1 includes the living pinelands 

 and adjacent sand barrens. These 

 areas are infrequently flooded in 

 their upper elevations and to depths 

 of only about 13 cm at the lowest 

 barren sites during the period June 

 through September in years of normal 

 rainfall. Zone 1 lies at a somewhat 

 lower elevation than the lowest level 

 of zone 1 but higher than zone 2. 

 Zone 1 supports short spike rush, 

 Eleocharis , which grows in water es- 

 timated to average 28 cm in depth. 

 This area is called "light rush" to 

 conform with the terminology of Reark 

 (I960; 1961) and Van Meter (1965). 

 Flooding in zone 1 probably lasts 

 from June through December .at the 

 present time. Zones 1 and 1 cover 

 about 267 ha. 



Tides probably penetrate the 119- 

 ha basin on a seasonal basis by over- 

 flowing laterally from the large ti- 

 dal creek that flows north from the 

 head of Unknown Bay. Tidal waters 

 enter also on a more frequent basis 

 via a series of shallow creeks and 

 swales which penetrate the "lip" of 

 the basin in the southeast. These 

 also provide the main drainage from 

 the basin. 



A build-up of flocculent mate- 

 rial and leaf debris is not strongly 



Zone 2, variously covered by 

 Eleocharis , red mangroves, rushes and 

 salt joint grass, Paspalum distichum , 

 lies at a still lower elevation. 

 Measurement of water marks and peri- 

 phyton growth on plant stems indicate 

 an average maximum depth of flooding 

 of about 38 cm, so these areas must 

 lie about 10 cm lower than the zone 

 1 lands and about 25 cm lower than 

 the seaward margins of the pineland 

 barrens. Zone 2 is a region of "heavy 

 rush" which probably remains flooded, 

 at least with some water, during the 



215 



