Wetland impacts in the Mid-Atlantic USA are frequently mitigated via wetland creation in former uplands. Regulatory approval requires a site-specific water budget that predicts the annual water level regime (hydroperiod). However, many studies of created wetlands indicate that post-construction hydroperiods frequently are not similar to impacted wetland systems. My primary objective was to evaluate a water budget model, Wetbud (Basic model), through comparison of model output to on-site water level data for two created forested wetlands in Northern Virginia. Initial sensitivity analyses indicated that watershed curve number and outlet height had the most leverage on model output. Addition of maximum depth of water level drawdown greatly improved model accuracy. I used Nash-Sutcliffe efficiency (NSE) and root mean squared error (RMSE) to evaluate goodness of fit of model output against site monitoring data. The Basic model reproduced the overall seasonal hydroperiod well once fully parameterized, despite NSE values ranging from -0.67 to 0.41 in calibration and from -4.82 to -0.26 during validation. For RMSE, calibration values ranged from 5.9 cm to 12.7 cm during calibration and from 8.2 cm to 18.5 cm during validation. My second objective was to select a group of "design target hydroperiods" for common Mid-Atlantic USA wetland types. From > 90 sites evaluated, I chose four mineral flats, three riverine wetlands, and one depressional wetland that met all selection criteria. Taken together, improved wetland water budget modeling procedures (like Wetbud) combined with the use of appropriate target hydroperiod information should improve the success of wetland creation efforts. / Master of Science / Wetlands in the USA are defined by the combined occurrence of wetland hydrology, hydric soils, and hydrophytic vegetation. Wetlands serve to retain floodwater, sediments and nutrients within their landscape. They may serve as a source of local groundwater recharge and are home to many endangered species of plants and animals. Wetland ecosystems are frequently impacted by human activities including road-building and development. These impacts can range from the destruction of a wetland to increased nutrient contributions from storm- or wastewater. One commonly utilized option to mitigate wetland impacts is via wetland creation in former upland areas. Regulatory approval requires a site-specific water budget that predicts the average monthly water levels (hydroperiod). A hydroperiod is simply a depiction of how the elevation of water changes over time. However, many studies of created wetlands indicate that post-construction hydroperiods frequently are not representative of the impacted wetland systems. Many software packages, called models, seek to predict the hydroperiod for different wetland systems. Improving and vetting these models help to improve our understanding of how these systems function. My primary objective was to evaluate a water budget model, Wetbud (Basic model), through comparison of model output to onsite water level data for two created forested wetlands in Northern Virginia. Initial analyses indicated that watershed curve number (CN) and outlet height had the most influence on model output. Addition of a maximum depth of water level drawdown below the ground surface greatly improved model accuracy. I used statistical analyses to compare model output to site monitoring data. The Basic model reproduced the overall seasonal hydroperiod well once inputs were set to optimum values (calibration). Statistical results for the calibration varied between excellent and acceptable for our selected measure of accuracy, the root mean squared error. My second objective was to select a grouping of “design target hydroperiods” for common Mid-Atlantic USA wetland types. From > 90 sites evaluated, I chose four mineral flats, three riverine wetlands, and one depressional wetland that met all selection criteria. Taken together, improved wetland water budget modeling procedures (like Wetbud) combined with the use of appropriate target hydroperiod information should improve the success of wetland creation efforts.

Salt marsh creation provides functions and values that are essential to maintain the welfare of people and the integrity of coastal area ecosystems. The literature review provides greater understanding of salt marsh functions and values technical information regarding wetland creation in coastal regions. Interviews and case study analyses identify issues and opportunities regarding salt marsh creation. Products of this study include a model approach, criteria for project evaluation, and principles and guidelines for salt marsh creation and coastal residential development. Model approach applies the technical information and processes of salt marsh creation provided by scientists and engineers to the landscape architecture design process. The model approach encourages involvement of the client and other professionals throughout the planning and design process. The proposed criteria provide a framework for landscape architects to evaluate the structure and function of created ecosystems and developments. Four salt marsh creation projects around the Chesapeake Bay were selected for review and evaluated according to these criteria. Each project provides evidence that salt marsh creation can benefit residential developments by providing long-term shoreline protection, water purification, wildlife habitat, and amenity of a naturalistic landscape. Design principles and guidelines will help ensure that the model approach is used by developers to attain salt marsh creation that fits the patterns and functions of surrounding ecological systems and increases residents' awareness of both functions and values of salt marsh and the larger. / Master of Landscape Architecture

The purpose of this study was to determine the effects of amendments (control, (1x) compost, (2x) compost, (TS) topsoil, and 1x+TS) and microtopography (level, pit and mound) on three parameters (plant species composition, above-ground characteristics of Taxodium distichum, and plant root characteristics) of vegetation growing at a created tidal freshwater swamp in Virginia. None of the soil treatments met the traditional vegetation criteria for federal wetland jurisdictional determination, which only considers dominant species. When the same criteria were used for all of the species, the control, 1x, and 2x treatments met jurisdictional criteria. Considering these findings, vegetative criteria should be re-evaluated for young created wetlands. Compost addition produced the highest proportion of obligate wetland species (30%) while topsoil additions created the lowest proportion of wetland obligates (11%) and the highest proportion of upland plants. The 1x treatment generated the greatest species evenness and lowest weighted average (2.57). Topsoil treatments had the lowest diversity and evenness. Therefore, compost amendment is recommended to increase hydrophytes without compromising evenness and diversity. Bald cypress in pits were taller, had larger trunk diameter and basal trunk swelling than trees growing at higher elevations. Roots growing in mounds were more numerous with greater length than roots at lower elevations. Root length and count were highest for the control soil treatment. Amended treatments may have had lower rooting values because nutrient supply was adequate. Overall, incorporating microtopography and compost during wetland creation had a positive effect on vegetative function in this system. / Master of Science

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