UNDERSTANDING ANCIENT WETLAND PALEOECOLOGY FROM THE TAPHONOMY OF MODERN MANGROVE PEATS

Characterization of modern mangrove peat provides insight into peat taphonomy with implications for understanding ancient wetland paleoecology and nutrient cycling in coastal wetlands. Peat particle size is an important indicator of depositional environments and provides a way to track the history of decomposition. Many researchers have analyzed particle size of modern mangrove peats to understand the peat to coal transition; we aim to understand the plant debris to peat transition because detritivory and other taphonomic processes are not new phenomena in coastal swamps. We collected mangrove peat cores (15 cm depth) from two sites at Barnes Sound, Key Largo, Florida: a basin site, which is generally flooded, has a thick leaf mat (19-37 stacked leaves) and a tidally influenced fringe site that has a sparse leaf mat (0-4 stacked leaves). From each core, we sieved peat samples from 0 cm, 5 cm, and 10 cm depths. We dried sieve-samples for 24 hours at 50°C, weighed them to determine peat particle size distribution, and conducted point counts of identified peat constituents. We followed the protocol of Cohen and Spackman (1977) and split peat particles into two size fractions: framework (≥ 106 µm) and matrix (< 106 µm). Because no large wood was found in cored peat, we assessed surficial wood for xylophagy. In the taphonomically active zone, peat particle size decreases with increased decomposition and organism-peat interactions, such as detritivory and bioturbation. Thus, peat particle size distribution can be used as a proxy for rates of decomposition in wetlands, enabling comparisons between ancient and modern wetlands. The accumulation of thick leaf mats in basin mangrove sites where nearly continuous flooding excludes burrowing crabs and limits access of pulmonate snails to the leaf litter, could be the modern mangrove depositional environment most comparable to that of ancient peat.