Trees: a powerful geomorphic agent governing the landscape evolution of a subtropical wetland
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Transpiration-driven ion accumulation in soil has been invoked as a biological and physical feedback mechanism in wetlands that governs topographic differences by regulating soil accretion—with greater transpiration, ion accumulation and soil accretion occurring on tree islands as compared to the surrounding marsh. The strength of this mechanism is hypothesized to be controlled by the ratio of evapotranspiration (ET) to precipitation (P), where under greater ET to P conditions soil accretion may move from organic to mineral in nature. We tested the existence of this mechanism on tree islands in a subtropical wetland, determined if it supports mineral soil formation, and assessed its control on the development of nutrient resource contrasts (tree islands–marsh). To test our hypotheses, biannual measurements of groundwater, surface water and aboveground biomass were made from 2007 to 2012. Water samples were analyzed for water isotopes, concentrations of major ions, and total and dissolved nutrients on constructed tree islands. We found that tree transpiration led to the advective movement of water and associated ions toward the center of the tree islands, supporting CaCO3 precipitation. CaCO3 accretion on the tree islands was estimated at roughly 1 mm per decade, and represented 5 % of the total soil accretion since the islands’ planting. We also observed depletion in groundwater nutrient concentrations as tree biomass accumulated, indicative of tight nutrient cycling. This work provides direct evidence that trees can act as powerful geomorphic agents in wetland systems, forming mineral soils that support landscape heterogeneity on time scales of centuries to millennia.
KeywordsWeathering Soil formation Tree islands Plant-groundwater–surface water interactions Everglades
The South Florida Water Management District provided support for this research, with additional support from the Everglades Foundation, the Southeast Environmental Research Center and the Dissertation Year Fellowship at Florida International University. National Science Foundation’s Grant No. DBI-0620409 and the NASA WaterSCAPES Project supported a portion of Dr. Price’s time. We thank the following individuals for their help in the field: Ryan Desliu, Jeremy Stalker, Xavier Zapata, Estefania Sandoval and David Lagomasino. We also thank Drs. Sharon Billings and Gwendolyn Macpherson for comments on the manuscript. This is SERC Contribution No. 789.
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