Organic matter dynamics in seasonally inundated, forested wetlands of the Gulf Coastal Plain

Production and nutrient content of litterfall (LF) and benthic organic stan ding stocks were measured in three limesink wetlands of southwest Georgia, USA for one year to investigate how structural characteristics of relativel y undisturbed cypress-blackgum wetlands influence organic matter inputs and processing. These isolated, non-alluvial wetlands are shallow and seasonal ly inundated, filling during late winter storms and drying during early sum mer droughts. Because they receive most of their organic carbon from litter fall, the forest canopy may regulate energy flows and influence biological processing of benthic organic matter (BOM). Forest composition was determin ed using the point-quarter method. Litterfall and BOM (coarse fraction grea ter than or equal to 1 mm, CBOM) were collected bi-weekly during fall and w inter and monthly during the remainder of the year. Litterfall turnover rat es were estimated as k(CPOM) = total LF/mean annual CBOM. The wetlands were dominated by Nyssa biflora (Importance Value (IV) = 43.1, 50.3, 57.1) and Taxodium ascendens (IV=28.2, 27.6, 34.1). Total litterfall ranged from 410 to 582 g m(-2) yr(-1), with peak litterfall occurring in December. Litterfa ll nitrogen and phosphorus inputs ranged from 4.3 to 5.2 gNm(-2) yr(-1) and 0.22 to 0.27 gPm(-2)yr(-1). Standing stocks of CBOM ranged from 351 to 184 2 g ash free dry mass (AFDM) m(-2) over the duration of the study. Forest s tructural data suggest that these wetlands have among the greatest basal ar ea/stem ratios reported in the Southeastern U.S., with some of the highest rates of litter production reported for non-alluvial swamp forests. Indices of nutrient-use efficiency suggested that these wetlands were very efficie nt at recycling nutrients. Litterfall turnover rates fell within the range reported for forested wetlands, and turnover times exceeded one year (2.23- 2.38yr), suggesting organic matter accumulation within the wetlands.