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The effects of water depth and flow on marsh plant litter decomposition and soil chemistry were measured in the Loxahatchee Impoundment Landscape Assessment (LILA) facility (Boynton Beach, FL), where macrocosms mimic Everglades ridge-and-slough landscape features. Experiments were conducted in two macrocosms that differed in flow but had ridge, shallow slough, and deep slough habitats that differed in water depth. Decomposition of three common Everglades species, Crantz, Torr., and Aiton, were measured using litter bags incubated in the macrocosms under both wet and dry conditions. Litter decomposition was similar among flow treatments and habitats but differed by species and between wet and dry conditions. Decomposition rates from fastest to slowest were > > litter had more total P than the other two species, confirming the importance of P availability in controlling decomposition in the Everglades. Planted species had no effect on soil nutrient content during the ~4 yr of plant growth. Average water velocities of ~0.5 cm s attained in the flow treatment had no effect on decomposition or soil chemistry. The plant species used in this study are major contributors to Everglades' organic soils, so their decomposition rates can be used to parameterize models for how restoration manipulations will affect soil-building processes and to predict the temporal sequence of landscape responses to these manipulations. The results suggest that longer periods and flows greater than studied here may be necessary to see restoration effects on soil building processes.

Tree islands provide a relatively dry habitat for flora and fauna and are biogeochemical hotspots within the oligotrophic Everglades' marsh. Tree islands occupy a small percentage of Everglades' surface area, yet they provide critical ecosystem functions. Hydrologic manipulations throughout the 20th century resulted in a significant loss of tree islands. This study was conducted to determine previously unknown characteristics of soil development important to creating self‐sustaining tree islands. Physicochemical characteristics of surface soil (0–3 cm), considered newly accreted, were compared with deeper, older soil (3–10 cm). Soil at varying relative elevations (leading to differences in hydroperiods) and under different tree densities were evaluated in reconstructed tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA). Accretion rates, using feldspar markers, averaged 0.70 cm yr−1 and maximized at high elevations. Soil nutrients were positively correlated with organic matter. Surface soils exhibited greater total P (TP, 374 μg g−1 dry wt.), total N (TN, 14.4 mg g−1 dry wt.), total C (TC, 190 mg g−1 dry wt.), and organic matter (OM, 0.36 g g−1 dry wt.) compared to 3‐ to 10‐cm soils (TP, 216 μg g−1 dry wt.; TN, 10.2 mg g−1 dry wt.; TC, 132 mg g−1 dry wt.; OM, 0.25 g g−1 dry wt.). Concentrations of TP and available P, determined by sequential fractionation, were greatest on surface soils in the densest planting. Findings indicate that tree islands gradually increase soil nutrient concentrations under the influence of plant activity, supporting previous work suggesting a mechanism by which groundwater nutrients are imported via the transpiration stream, and ultimately build soil.

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