FORAMINIFERAL ABUNDANCE TRENDS IN VIBRACORES OF RECENT MACRO TIDAL SALT MARSH SEDIMENTS ON SKIDAWAY ISLAND, GA

This study focuses on benthic and planktonic foraminiferal biofacies as part of an NSF-REU (ACRES) project examining human impact on the salt marsh. Vibracores of low (3.8 m) and high (2.2 m) marsh sediment from the relatively undeveloped Skidaway Island were collected and sampled at 5 cm intervals. Sediment for foraminiferal analysis was preserved in a buffered ethanol (pH=9) solution with Rose-Bengal stain. The low marsh sediment is composed of organic rich mud with brown clay ( 0 - 1.7 m) overlying gray sandy clay with thin lenses of shell bearing sands and rare burrows (1.7 - 3.8 m). The high marsh has two distinct lithofacies; bioturbated, organic rich, brown sandy clay (0 - 1.3 m) and dense blue clay (1.3 - 2.2 m).

Preliminary high marsh data indicate low foraminiferal abundance and diversity (Textulariina spp. dominate).  Low marsh foraminifera are present in higher abundance and diversity, relative to the high marsh, with both increasing sharply in the sands between 1.7 and 1.8 m, and 2.1 and 2.3 m.  The assemblage in the top 2.5 m of the low marsh core is dominated by Brizalina spp. and Trochammina spp., while the sand lenses between 1.7 and 2.1 m are dominated by Elphidium spp.

Foraminiferal abundances in our cores are lower than other studies of the top 10 cm for the GA salt marsh (e.g., Goldstein and Watkins, 1999) but downcore values for muddy intervals are similar to a SC marsh study (Hippensteel and Martin, 1999). The difference between the other GA marsh results and those of our study may be explained by poor preservation, dilution or low production. Dissolution may be related to microhabitat and lithology, and also have occurred in the time between coring and sampling. To assess post-coring dissolution, vibracore data will be compared to surface samples taken from the vicinity of the original cores, washed and examined for foraminifera immediately on site. Low foraminiferal abundances may be due to high sedimentation rates (>.05 m/yr) in the low marsh. Environmental factors affecting production (salinity, and dissolved oxygen) can also contribute to lower overall abundance or absence of foraminifera. Furthermore, the sand lenses may have affected preservation.  The mid-core sand lenses are likely the result of high marsh progradation, tidal channel migration, or storm deposits and may influence foraminiferal abundance.