Hydrology, Community Structure, and Productivity Patterns of a Dystrophic Carolina Bay Wetland

A shallow, 5.4-ha dystrophic Carolina bay wetland was studied between 1974 and 1978 to test the premise that biomass and production are constrained by the stagnant hydrology and dilute, acidic chemistry of bay wetlands. Our objectives were to evaluate: (1) surface and subsurface hydrology, (2) sources of production, (3) community change along a depth gradient, and (4) seasonal community patterns. The hydrology study compared surface water levels to groundwater levels in four adjacent wells. A cylinder enclosure and total harvest procedure and 24-h dissolved oxygen curves were used for 2 yr in a 1-ha sampling area to measure spatial and temporal biomass patterns and organic production of community components. Surface hydrology was dependent on seasonal and annual precipitation patterns. Lateral, episodic groundwater exchanges accounted for the dilute surface chemistry and apparent differences in surface gains and losses. Substrate exposure and fire oxidation in dry years promoted low detritus standing crops and a dark, clay-loam mineral soil. A depth gradient, marked by a peripheral grass/sedge zone and central water-lily zone, produced strong spatial patterns for most community components. Aquatic macrophytes had low shoot biomass and a high root to shoot ratio. Algae were light limited and even less productive. Purple photosynthetic bacteria approached algal productivity levels and may have important chemistry and trophic support functions. As predicted from the stagnant, dystrophic conditions, autotroph biomass and production were low. However, the warm climate and periodic fire rejuvenation may stimulate higher production than that generally found in northern bog wetlands. Secondary production was also low. Animal biomass was dominated by insects (especially odonates) and salamanders. High turnover of prey (largely midge larvae and microcrustaceans) was implied by the predator-dominated community structure. This study of a wetland ecosystem lacking several common dystrophic bog features (peat deposit, high dissolved organic matter, acidophilic mosses) enlarges our perspective of the dystrophic condition.