Organic matter dynamics in seasonally inundated, forested wetlands of the gulf coastal plain

Abstract

Production and nutrient content of litterfall (LF) and benthic organic standing stocks were measured in three limesink wetlands of southwest Georgia, USA for one year to investigate how structural characteristics of relatively undisturbed cypress-blackgum wetlands influence organic matter inputs and processing. These isolated, non-alluvial wetlands are shallow and seasonally inundated, filling during late winter storms and drying during early summer droughts. Because they receive most of their organic carbon from litterfall, the forest canopy may regulate energy flows and influence biological processing of benthic organic matter (BOM). Forest composition was determined using the point-quarter method. Litterfall and BOM (coarse fraction ≥ 1 mm, CBOM) were collected bi-weekly during fall and winter and monthly during the remainder of the year. Litterfall turnover rates were estimated as kCPOM=total LF/mean annual CBOM. The wetlands were dominated byNyssa biflora (Importance Value (IV)=43.1, 50.3, 57.1) andTaxodium ascendens (IV=28.2, 27.6, 34.1). Total litterfall ranged from 410 to 582 g m−2 yr1, with peak litterfall occurring in December. Litterfall nitrogen and phosphorus inputs ranged from 4.3 to 5.2 gNm−2 yr−1 and 0.22 to 0.27 gPm−2yr−1. Standing stocks of CBOM ranged from 351 to 1842 g ash free dry mass (AFDM) m2 over the duration of the study. Forest structural data suggest that these wetlands have among the greatest basal area/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 efficient 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.