Date of Award
Doctor of Philosophy (PhD)
Civil and Environmental Engineering
David G. Chandler
connectivity, ecohydrology, evapotranspiration, restoration, thermal regime, wetland
More than half of wetland area in the U.S. have been converted to other land use types for agricultural use and development. Limited understanding of ecological services provided to society by wetlands is another reason for the massive wetland loss in the past. Section 404 of the Clean Water Act and the 1989 federal mandate of “no net wetland loss” supported increased efforts for wetland restoration and creation to compensate for two centuries of ecosystem degradation. Hydrology is a critical driver for wetland formation and sustainability, yet few studies have investigated the ecosystem benefits of restored or constructed wetlands relative to natural wetlands. Considering that unexpected ecohydrologic behaviors such as drought have been reported as a main cause of unsuccessful restoration over the U.S., understanding and quantifying water movement within the local seeing is imperative to future wetland restoration.
From an environmental engineering perspective, wetlands are regarded as complex environments controlled by regional geomorphology, atmosphere, geologic setting, and human activity. The U.S. Army Corps of Engineers was tasked with developing a hydrogeomorphic assessment approach for wetlands in the various regions throughout the U.S. to facilitate wetland restoration. This effort was redirected in the aftermath of Hurricane Katrina, but the need for assessment tools persists for several remaining regions including the southern coastlines.
The first part of the dissertation reports an investigation of impacts of geomorphic settings on hydrologic functions within the St. Lawrence River plain. Regional geomorphology links wetlands and surrounding areas by multiple pathways of water transfer such as groundwater exchange and surface water connections. However, recent U.S. Supreme Court rulings, including Solid Waste Agency of Northern Cook County versus U.S. Army Corps-SWANCC (2001) and Rapanos versus U.S. (2006) overturned federal protection of wetlands by the Clean Water Act unless the wetlands are shown to be geographically connected with jurisdictional waters. These rulings jeopardize mitigation wetlands without federal protection because typical restoration practices often minimize surface water connection as a result of dredge-and-fill methods. Hydrologic behaviors and services of the geographically isolated wetlands (GIWs) were hypothesized to be identical to those of geographically connected wetlands in this study. Experimental evidence suggest that hydrologic connectivity is maintained between GIWs and downstream waters via subsurface flow exchange. Greater correlations for GIWs than the other connectivity types were found between variables including standard deviation of groundwater, geographic attributes (e.g., site elevation) and hydrologic attributes (e.g., duration of subsurface flow reversal). Mean groundwater table depended most strongly on wetland fraction within a drainage area.
Water temperature, particularly in summer, strongly influences the environmental suitability for wetland species such as a Blanding’s turtle (Emydoidea blandingii) for nesting in northern New York. Although temperature dependency of wetland fauna has been investigated to determine the range of suitable environmental conditions, the hydrogeomorphic controls on seasonal thermal regimes of wetlands were not addressed in prior studies. In this study, temperature regimes at multiple sites under uniform climate and geologic settings were investigated to understand the controls on wetland temperature in several of hydrogeomorphic settings. Local geomorphology and alterations by wetland restoration affected wetland thermal regimes via various seasonal subsurface flow exchange patterns. Thermal sensitivity is defined as a response in surface water temperature to change in air temperature. Based on wetland temperature measurements, linear regression was used to estimate thermal sensitivity for each site. Summer temperature values were shown as primary determinants by site comparison. In addition, the thermal sensitivity values were compared to site variables to seek for local controls. Results suggest that geographical and hydrologic variables including site elevation, duration of subsurface flow reversal, and standard deviation of wetland stage and groundwater table are significantly correlated with thermal sensitivity. Geomorphic settings are useful resources to characterize site hydrology and thermal functions of wetlands. Wetland restoration practitioners need to carefully choose class-appropriate hydrogeomorphic settings to promote establishment and conservation of temperature-sensitive species.
Finally, the impact of the land surface energy budget was measured to assess the patch level controls on evapotranspiration by various wetland species. Infrared thermometry was used within a standard meteorological measurement system to determine energy partitioning between sensible and latent heat fluxes in wetlands. A portable thermal infrared (TIR) camera was used to capture radiometric surface temperature of leaves, i.e., evapotranspiring surfaces, and then to estimate sensible and thus latent heat flux associated with a portable weather station. Two TIR-based methods including TIR temperature-based surface energy balance (SEB) and Bowen ratio () were compared to the well-known Priestley-Taylor (P-T) method for four species-level patches. For wetland plants including hardstem bulrush (Scirpus Spp.), reed canary grass (Phalaris arundinacea), cattail (Typha Spp.) and meadow willow (Salix petiolaris), results are similar for the TIR-based and P-T methods with mean absolute difference of 17.1-53.0 W m-2 and root mean squared difference of 23.4-62.4 W m-2 across sites. Greater differences were found from parameterization of aerodynamic resistance for flexible and tall vegetation structure and especially for greater wind speed. Finally, estimated crop coefficients will be useful for regional wetland restoration planning by providing major losses in local water budget.
Hwang, Kyotaek, "Ecohydrology of Natural and Restored Wetlands in a Glacial Plain" (2018). Dissertations - ALL. 990.