Linking River, Floodplain, and Vadose Zone Hydrology to Improve Restoration of a Coastal River Affected by Saltwater Intrusion

Abstract

Floodplain forests provide unique ecological structure and function, which are often degraded or lost when watershed hydrology is modified. Restoration of damaged ecosystems requires an understanding of surface water, groundwater, and vadose (unsaturated) zone hydrology in the floodplain. Soil moisture and porewater salinity are of particular importance for seed germination and seedling survival in systems affected 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. We investigated 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 min were installed along two transects-one in an upstream, freshwater location and one in a downstream tidal area. Complemented by surface water, groundwater, and meteorological data, these unique 4-yr datasets quantified the spatial variability and temporal dynamics of vadose zone hydrology. Results showed that soil moisture can be closely predicted based on river stage and topographic elevation (overall Nash-Sutcliffe coefficient of efficiency = 0.83). Porewater salinity rarely exceeded tolerance thresholds (0.3125 S m(-1)) for bald cypress upstream but did so in some downstream areas. This provided an explanation for observed vegetation changes that both surface water and groundwater salinity failed to explain. The results offer a methodological and analytical framework for floodplain monitoring in locations where restoration success depends on vadose zone hydrology and provide relationships for evaluating proposed restoration and management scenarios for the Loxahatchee River.

Dynamic factor analysis of surface water management impacts on soil and bedrock water contents in Southern Florida Lowlands

“…13) could be improved by 613 using location specific water table elevation since canal stage is simply a good approximation of the mean 614 water table elevation. Another simple sigmoidal regression model to predict soil and bedrock water 615 contents from canal stage proposed by Kaplan et al (2010a) was tried but later abandoned due to lower 616 Ceff (i.e., averaging 0.2). This approach is based on the physical concept of drain to equilibrium.…”

Untangling complex shallow groundwater dynamics in the floodplain wetlands of a southeastern U.S. coastal river

“…Transect notation is followed by distance from river mouth (river kilometer, RK). referred to as the "last free-flowing river in southeast Florida" [SFWMD, 2006] SFWMD, 2006SFWMD, , 2006SFWMD, , 2009VanArman et al, 2005;Mortl, 2006;Muñoz-Carpena et al, 2008, Kaplan et al, 2010.…”

“…[3] In these complex systems, long-term monitoring can characterize the ranges and temporal variation of hydrological and water quality variables [e.g., Muñoz-Carpena et al, 2008] and support the development of initial relationships between measured variables [e.g., Kaplan et al, 2010]. However, investigating relationships between multivariate time series to improve understanding of system dynamics using visual inspection and comparative statistics is difficult, subjective, and may not appropriately characterize the system [Ritter et al, 2007].…”

Calibration of a combined dielectric probe for soil moisture and porewater salinity measurement in organic and mineral coastal wetland soils

“…For example, the specific life-cycle requirements of many floodplain plant species (Burns and Honkala, 1990;Conner, 1988;Conner and Toliver, 1987;Conner et al, 1986;Middleton, 1999Middleton, , 2000Middleton, , 2002 dictate that restoration and management plans not only reestablish historical surface water dynamics (e.g., hydroperiod and salinity), but also maintain σ w below critical levels for freshwater vegetation (Corwin and Lesch, 2005;Kaplan et al, 2010) and periodically achieve an appropriate θ regime to facilitate germination of desired species in the floodplain (Middleton, 2000). One such ecosystem where vadose zone conditions are critical for the maintenance of ecosystem health is the Loxahatchee River (Fig.…”

“…Transect notation is followed by distance from river mouth (river kilometer, RK). Modified from Kaplan et al (2010). based dielectric probe for three soil series encountered in a coastal floodplain, ranging from sandy mineral to highly organic.…”