RECOVER MAP 3.1.4.4 Decomposition Dynamics, Community Composition, and Ridge-Top Senescence in the Ridge-Slough Mosaic

The proposed work will build on the findings of Clark and Reddy (2003, 2004), Lewis (2005), and Jorczak (2006), conducted under a CESI-funded project titled: Spatial Variability and Modeling of Soil Accretion in Shark River Slough. That study evaluated ridge and slough vegetative characteristics, soil accretion rates, and mechanisms of ridge-slough formation. Key findings include the observation that bedrock elevation does not co-vary with surface soil elevations. This suggests that mechanisms behind clearly evident differences in surface soil topography are not geomorphologic factors, but rather driven by biologically-mediated organic and inorganic matter deposition, in turn regulated by environmental forcing functions such as fire, hydrology and nutrient regime. Moreover, marked differences in standing biomass and annual production between ridge and slough communities suggest similar differences in organic matter input, with obvious implications for soil accretion rates. Investigation of plant tissue quality (nutrient content and recalcitrant fiber content â Lewis 2005) showed that species most commonly found in ridges (Cladium jamaicense) have three times more residual fiber (i.e., lignin) than species found in wet prairie or slough communities. In addition, C:N ratios indicate that greater potential for nitrogen limitation in ridge biomas than in slough biomass; N limitation is expected to result in reduced decomposition rates, and consequently greater accretion potential. The combination of greater tissue recalcitrance and increased biomass production in ridges suggest far greater soil accretion potential than sloughs. A reciprocal transplant decomposition study using litter bags corroborated these expectations. C. jamaicense tissue (representing ridge biomass) and Eleocharis spp. (representing slough biomass) were placed in both ridge and slough environments. Results suggest that tissue properties are the primary regulator of decomposition (Eleocharis spp. decomposed faster than C. jamaicense), and that environmental conditions are also significant (faster decomposition in ridgs than sloughs). Lastly, lowering water levels 15cm below the soil surface was sufficient to double soil respiration rates in cores obtained from both ridge and slough communities suggesting a significant influence of hydrologic variability on the rate of litter decomposition.

This research will allow investigation of mechanisms of ridge-slough maintenance and diagnostic monitoring thereof as described in the Greater Everglades Wetlands Module section 3.1.4.4, targeting two priority performance indicators, vegetation communities and peat soils. To meet restoration targets for the ridge-slough requires first understanding ecohydrologic processes that maintain the integrity of unimpacted ridge-slough areas, and second discerning early-warning rapid assessment diagnostics of changes in those processes that can guide adaptive management. Previous research has identified key processes regulating ridge slough topographic relief, suggesting that interactions between biological and environmental process and not underlying geomorphology are behind the striking landscape pattern of intact ridge-slough areas. Biogeomorphic processes are characterized by strong feedbacks between abiotic and biotic processes, and because biological drivers operate on a much shorter time scale than bedrock dissolution processes, research to identify, quantify, and potentially modify management activity is warranted to preserve the integrity of process regulating ridge slough development and maintenance. Results of this work are expected to include key information of management of ecosystem stables states, and perhaps as importantly, diagnostic metrics of process integrity that can be used as part of ongoing monitoring efforts.

Project Objectives
This research focuses on the drivers of ridge-slough landscape mosaic maintenance. The objectives of this study are 1) to describe ridge and slough stable states in relation to carbon accretion and respiration, and describe phase transitions between states in response to exogenous hydrologic forces, and 2) to determine the prevalence and incidence of ridge-top senescence, ascertain evidence for causal mechanisms, and where appropriate link our observations to existing hydrologic management and to conditions expected with restoration.. Together these two objectives, and the investigations they represent, will provide information useful for successful management of the ridge/slough landscape.