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| Floodplain forests provide unique ecological structure and function, which are often degraded or lost when watershed hydrology is modified. Restoration of impacted ecosystems requires an understanding of surface water, groundwater, and vadose (unsaturated) zone hydrology in the floodplain, however most wetland restoration efforts focus on monitoring and modeling only surface water processes. Soil moisture and porewater salinity are of particular importance for seed germination and seedling survival in systems impacted by saltwater intrusion, but are difficult to monitor! And often overlooked. This study contributes to the understanding of floodplain hydrology in one of the last bald cypress (Taxodium distichum [L.] Rich.) floodplain swamps in southeast Florida (USA) by investigating groundwater, soil moisture, and porewater salinity dynamics in the floodplain of the Loxahatchee River, where reduced freshwater flow has led to saltwater intrusion and a transition to salt-tolerant, mangrove-dominated communities. Twenty-four dielectric probes measuring soil moisture and porewater salinity every 30 minutes were installed along two transects - one in an upstream, freshwater location; the other in a downstream tidal area. Additionally, a network of twelve groundwater wells was developed along five transects that encompass a gradient of floodplain conditions from upstream freshwater areas downstream to the estuary. Data collected over four years quantified the spatial variability and temporal dynamics of groundwater and vadose zone hydrology and showed that soil moisture can be closely predicted based on river stage and topographic elevation (coefficient of efficiency = 0.83). Porewater salinity rarely exceeded tolerance thresholds for bald cypress upstream, but did so in some downstream areas, fully explaining observed vegetation changes for the first time. Dynamic factor analysis (DFA), a multivariate times series analysis technique, proved useful for studying interactions among experimental times series and other hydrological variables in the watershed and helped us develop dynamic factor models (DFMs) of groundwater level, salinity, and soil moisture. The results offer a methodological and analytical framework for floodplain monitoring in locations where restoration success depends on groundwater and vadose zone hydrology and provide relationships for evaluating proposed management scenarios for the Loxahatchee River. |
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| Title: | Growth of bald cypress [Taxodium distichum (L.) Rich.] seedlings in the tidal floodplain of the Loxahatchee River. Biological Sciences 2(74):84-99. |
| Authors: | Liu, G.D., Li, Y.C., Muñoz-Carpena, R., Hedgepeth, M., Wan, Y.S., and R. Roberts |
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