PARENT SESSION
Oral Session # 15: Wetland Ecology I: The Everglades and Southern Wetlands.
Presiding: J Chick
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.

Dry benthic periphyton recovery and phosphorus buffering upon wetting in the Everglades: A microcosm survey.

Thomas, Serge^*,1, Gaiser, Evelyn¹, Gantar, Miroslav¹, Jones, Ronald¹, Scinto, Leonard¹, ¹ SERC/FIU, Miami, FL, USA

ABSTRACT- Calcareous periphyton mats attached to limerock in the southern Everglades (Florida, USA) were collected in June 2001 after 6 months of desiccation and before the annual wet season inundation. Primary production, phosphorus kinetics and microbial community composition were followed for 20 days after flooding three microcosms (51x37x14 cm³) with 20 L of artificial marsh water (AMW) in a greenhouse. The dry mat was dominated volumetrically and numerically by cyanobacteria (90-99%) and this dominance remained unchanged after wetting, confirming that cyanobacteria can both withstand 6 months of desiccation and recover faster than the other taxa upon rewetting. Cyanobacteria recovery was rapid enough to exhibit a positive net primary production just hours after wetting. The limited development of the other taxa (green algae and diatoms) showed the poor capabilities of these taxa to withstand 6-months of drying and to recover fast upon rewetting. The persistence of low abundances of such taxa during the dry season can be attributed to the moderate dry conditions of the Floridian dry season and the moisture-retaining capability of the mat. Light-corrected primary production was positively correlated with water total phosphorus concentration (TP, r²=0.6, P<0.001), which peaked 3 days after wetting (16 ug L^-1) but leveled fairly rapidly after 5 days (6.6 ug L^-1). This showed that TP limited the photosynthetic activity. Moreover, the comparison between a simulated TP desorption to the water from the C-111 mat (= abiotic TP release) and the real TP concentration in the water column exhibited that i) the mat microbial community recovers fast enough to absorb TP initially released to the water column, thus preventing high concentrations in water TP and ii) the mat does not absorb water TP below concentrations of 6.6 ug L^-1.

Key words: recovery, periphyton, rewetting, phosphorus