Organic Matter Dynamics in Seasonally-inundated Forested Wetlands of the Gulf Coastal Plain

Research Team: Kevin Watt and Dr. Stephen W. Golladay (Associate Scientist)

Litterfall (LF) production and nutrient content, and benthic organic standing stocks were measured in three limesink wetlands of Southwest Georgia 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) was Sampling the benthic organic material using a pump and a stove pipe sampler. Litterfall traps are also shown. collected bi-weekly during fall and winter and monthly during the remainder of the year. Litterfall turnover rates 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 (means ± s.e.) was 582 ± 14, 410 ± 43, and 429 ± 40 gm^-2 yr^-1, with peak litterfall occurring in December. Litterfall nitrogen and phosphorus inputs ranged from 4.3-5.2 gNm^-2yr^-1 and 0.22-0.27 gPm^-2yr^-1. Standing stocks of CBOM ranged from 351 to 1842 g AFDM m^-2 over the duration of the study. Forest structural data suggests 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. High productivity may be a function of wetland catchment area, i.e. wetlands with larger catchments had higher productivity. Indices of nutrient use efficiency suggested that our 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.

Additional Information:

Watt, K.M. and S.W. Golladay. 1999. Organic matter dynamics in seasonally-inundated forested wetlands of the Gulf Coastal Plain. Wetlands 19:139-148.

Funded by: The Joseph W. Jones Ecological Research Center