T169 Perspectives in Floodplain System Science (Posters)

Tuesday, 6 November 2012
9:00 AM - 6:00 PM
Hall B

BELOWGROUND CARBON STOCKS IN AN OLD-GROWTH FLOODPLAIN FOREST: CONGAREE NATIONAL PARK, SOUTH CAROLINA

Paper number: T169-5
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Floodplains are depositional landscapes which may be a sink for carbon (C) at a watershed-scale, yet great variability has been noted in both soil and root C pools in many alluvial wetlands. Variability in floodplain C stocks is due to many factors including microsite differences in sedimentation rates, vegetation composition, nutrient availability, and annual hydroperiod. Most soil C accounting studies quantify to a depth of 1 m because the majority of organic C and live roots (>50%) are found within the top 40 cm of upland soils. Floodplain soils, however, form via episodic alluviation and progressive burial of previously stable soil surfaces can contribute to complex belowground C pools. In this study we investigated the spatial variability of soil C in an old-growth bottomland forest at Congaree National Park, South Carolina. The Congaree floodplain is one of the only remaining tracts of old-growth bottomland forest in the southeastern United States. As a result of historical bottomland losses, very little research regarding belowground C distribution has been completed in old-growth floodplain forests.

For this research we quantified soil organic C pools to a depth of 2 m across the park. We sampled four soil mapping units which encompass a drainage gradient from the well drained soils of the natural river levee to the very poorly drained organic soils found in groundwater seep wetlands of the floodplain. In addition, we quantified total root standing crop C pools in the upper 11 cm of select Congaree soils. Our soil C analyses found that hydric (wetland) soils within the floodplain stored significantly more soil C in the upper 1 m and had a greater percentage of C in the 1-2 m depths than non-wetland soils. Soils in landscapes receiving historically high sedimentation rates also had greater C pools due to burial of organic-rich floodplain surfaces. Root C stocks were significantly greater on the drier floodplain landscapes and ranged from 0.47 Mg C ha-1 on the natural river levee to 0.26 Mg C ha-1 in mineral wetland soils. On average, total root C made up 1.2% of total belowground C. These data suggest that root C stocks are minor when compared to soils and that deep soil C storage (below the upper 1 m) is an important function of floodplain ecosystems.