FCE LTER Journal Articles


Lithologic controls on hydrologic and geochemical processes in constructed Everglades tree islands


Tree islands have been hypothesized to induce calcite precipitation by concentrating ions in the groundwater through evapotranspiration processes. This research investigates how lithology regulates the hydrologic and geochemical conditions within two types of constructed Everglades tree islands: peat-based and limestone-core surrounded by peat. Three years of hydrochemical and hydrologic data (2013–2015) obtained from the constructed tree islands suggest that under current climatic and managed hydrologic conditions, calcite dissolution is prevalent within the top meter of soil in both types of tree islands. Mass-balance calculations along groundwater flow paths in one peat-based tree island that contained clay at depth, indicated that calcite precipitation is likely 1 m below the soil surface. The lithological characteristics of that peat-based island supported a persistently depressed groundwater table, while tree islands with elevated ratios of peat-to-sand content did not. Limestone-core tree islands also supported a depressed water table, particularly during the dry season. This study determined that the lithology of a set of man-made Everglades tree islands played a primary role in regulating the seasonal fluctuation of the water table and hydrogeochemical processes. Understanding the mechanisms of tree-island formation and maintenance is important for preserving the overall ecosystem function of the freshwater-Everglades.


Originally published in Chemical Geology.



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