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Saltmarshes are highly valued habitats but the majority of the Eden Estuary's saltmarsh was buried under sea defences and ad hoc rubbish dumps during the last century. Without saltmarsh, the degraded shoreline may be even more vulnerable to rising sea levels and increased wave and tidal energy. This study investigated planting native saltmarsh species, common in the estuaries of Eastern Scotland, to restore saltmarsh development and sedimentation to the Eden Estuary's shoreline. The survival and growth of the sedge Bolboschoenus maritimus (Sea Club-rush) and the grasses Phragmites australis (Common Reed) and Puccinellia maritima (Common Saltmarsh Grass) were compared in planting trials. These were seeded or transplanted onto unvegetated upper mudflats in front of eroded P. maritima saltmarsh and a disused rubbish dump. The longer term sustainability of this practice was assessed by comparing sediment deposition and surface elevation in the transplant sites, natural saltmarsh and upper unvegetated mudflats. B. maritimus outperformed P. australis and P. maritima. Springtime, high density planting was successful, whereas seeds, planting in autumn and low density planting failed. Growth in the transplanted B. maritimus sites was relatively slow for the first three years but subsequently overtook growth of the seaward edge of natural B. maritimus marsh. Sediment was not deposited on natural P. maritima and was low on upper unvegetated mudflats and in young transplant sites. Most deposition occurred in four year old sites of B. maritimus. Sediment surface elevation in natural P. maritima remained constant throughout the year, but increased in all the other sites during the summer. The upper mudflat was the only site to erode during winter. A significant, positive association was found between tide height and sediment deposition, while winds from the south-east were associated with significantly more deposition than winds from the south-west. The direct planting of saltmarsh vegetation has restored a valuable and rapidly disappearing habitat to the degraded shoreline of the Eden Estuary. The low-cost and simplicity of this restoration practice give it great potential as a sustainable coastal management option that should be explored in other Scottish estuaries. This form of restoration could help to increase the resilience and reduce the vulnerability of degraded shorelines to climate change and rising sea levels.

Peatlands are a diverse type of wetland ecosystem, characterized by high levels of soil organic matter, that provide a wide array of ecosystem services including water storage and filtration, carbon sequestration, and unique habitats. Draining peatlands degrades their resilience to future disturbances, notably including high intensity, soil-consuming fires. Peat soil fires are unique in that they can smolder vertically through the soil column, with consequences ranging from large carbon emissions to altered hydrology and dramatic shifts in vegetation communities. In this work we had two complementary objectives to understand both the drivers and impacts of smoldering fires at the Great Dismal Swamp (VA and NC, USA). First, we developed and verified a new method to model peat burn depths with readily available water level and peat hydraulic property data. Our findings suggest that drainage weakens both short- and long-term controls on peat burn depths by reducing soil moisture and by decreasing peat water holding capacity. To address the impacts of smoldering fires, we quantified the abundance of the noxious Phragmites australis in a large fire scar and the extent to which altered hydrology influenced its occurrence. We did so by leveraging satellite imagery, random forest models, LiDAR data, and water table observations. Our results suggest that P. australis is aided by a hydrologic regime generated, in part, from the combined effects of drainage and deep smoldering fires. Our conclusions from these two studies contribute to the scientific understanding of smoldering peat fires and can inform management efforts.

Phragmites australis is an invasive wetland weed found throughout much of the United States. Documenting and mapping the growth and spread of this emergent macrophyte can be an important step in developing and implementing successful management strategies. Characterizing the phenology of a vegetation species with a sensor capable of hyperspectral resolution, positioned at close proximity to the canopy of interest, is often a first step necessary for understanding the basic species-specific reflectance patterns, and for quantifying the manner in which light interacts with the plants comprising particular communities. Spectral data over a P. australis canopy were collected during 22 field campaigns in 2011. Research was aimed at characterizing the spectral responses of a P. australis canopy throughout a growing season, and then relating the acquired reflectance data to individual stages in the life cycle, as well as changes in the vegetation fraction associated with the plant canopy. A deconvolution of primary constituents comprising the spectral signal upwelling from the canopy aided in understanding the temporal variations in reflectance. Analyses of both spectra and digital photographs of the canopy led to the development of a new transformation, termed the “Albedo Corrected Vegetation Index” (ACVI), aimed at increasing the accuracy in estimating vegetation fraction. Seed production and shoot density, both of which are closely linked with the invasive qualities of P. australis, were estimated using methods involving a simple digital camera as well as dual spectroradiometers. Additionally, considerations and procedures for collecting spectral data in the field were reviewed, and a procedure was developed, based upon concurrently acquired pyranometer data, to correct for incongruities that often occur due to the variable environmental conditions encountered during field campaigns. The findings of this research provide the necessary fundamental steps in the effort to monitor invasive species such as P. australis by means of remote sensing.

There are two biotypes of common reed, which includes the native common reed (Phragmites australis subsp. americanus) and non-native (invasive) common reed (Phragmites australis subsp. australis).The non-native biotype of common reed has invaded wetland habitats in many states of the US, including Nebraska. Three studies, disking followed by herbicide, mowing followed by herbicide, and herbicide followed by mechanical treatment were initiated in 2008 in Nebraska. The objective was to evaluate common reed control along the Platte River using an integrated management. Herbicide followed by mechanical treatment had excellent control (≥92%) with all treatments except glyphosate applied in the summer of 2008 alone or followed by a mechanical treatment 817 DAT. Field studies were conducted the Platte River with the objective to determine the effect of herbicide selection and timing of application on common reed. Three herbicides were applied at two rates and three growth stages of common reed. In general, common reed showed more tolerance to applications during vegetative stage, with control ratings increasing with later timings. Imazapyr provided the highest levels of control (≥92%) across all three timings, while imazamox provided the lowest level of control 60%). Measurements of gas exchange and leaf area index were collected in undisturbed stands of both native and non-native common reed stands. Stomatal conductance and leaf assimilation on average was higher in native common reed than in non-native common reed. LAI in invasive common reed was dramatically larger on average. There was 243 mm year-1 estimated difference in transpiration with non-native common reed having a higher estimation of transpiration. An economic analysis of common reed management options reflecting water savings and net return on investment was performed. Returns ranged from $1,326 to $4,235 per hectare over three years. Treatments of disking followed by herbicide tended to have the highest initial net return. All treatments provided a net gain return after 3 years of control of common reed.

Vegetation and climate both play integral roles in water availability, particularly for arid to semi-arid regions. Changes in these variables can lead to extreme shortages in water for regions that rely on water for crop irrigation (i.e., the Great Plains). The objective of this study is to evaluate the impacts of vegetation on water availability in the Republican River basin in central Nebraska. Decreases in streamflow have been observed in the river basin for many years and, as a result, an invasive riparian plant species (Phragmites australis) is being removed in an effort to reduce evapotranspiration and reclaim surface water. Meteorological variables and energy balance data have been collected at a field site during the 2009 and 2010 growing seasons. Vegetation was sprayed with herbicide in July 2009, killing all P. australis in the wetland. Significant decreases in evapotranspiration were observed during the 2010 growing season due to the limited amount of transpiring vegetation in the wetland. Greenhouse growth experiments were also conducted with both invasive and native varieties of P. australis to determine basic plant physiological parameters. Nitrogen fertilizer was applied to half of the plants in each subset. Gas exchange (e.g., photosynthesis, stomatal conductance, and transpiration rates), and the efficiency of the water and nitrogen use, were assessed under variable light, temperature and CO2 concentrations. As well as providing specific vegetation parameters for modeling purposes, this study was interested in evaluating the differences in physiology and growth characteristics between the two varieties of P. australis present in Nebraska. Lastly, the plant physiological parameters were incorporated into Agro-IBIS, a dynamic vegetation model, and this model was evaluated using observed energy balance data from the wetland field site from 2009. Experiments were also performed for 2010 to assess the ability of the model to capture the response to vegetation removal. Adviser: John Lenters

Climate and vegetation can dramatically alter the water cycle on local to regional scales. A change in the surface energy and water balance, especially in arid regions, can have significant impacts on local water availability and, therefore, water resource management. The purpose of this study is to understand the role of climate and vegetation in the energy and water balance of a riparian wetland in the central Great Plains. The site is located near the Republican River in southwestern Nebraska, where decreases in streamflow have been observed in recent decades. In an effort to reduce consumptive use from evapotranspiration (ET), and thereby reclaim surface water, invasive species such as Phragmites australis are being removed throughout the riparian corridor of the river basin. In this study, we have installed two energy/water balance monitoring stations, a Large Aperture Scintillometer (LAS), and various water and soil temperature probes in the P. australis and native (Typha latifolia) portions of the wetland to determine the energy and water balance during the 2009 growing season (April 11−October 3). Sensible heat flux is measured using the LAS, while ET is calculated as a residual of the energy balance (i.e., net radiation minus the sensible heat flux and heat storage in the canopy, water, and soil). Comparisons are also made with ET rates calculated from the simpler Priestley-Taylor method. Additional calculations of ET rates for both P. australis and T. latifolia (Cattail) were made using Landsat remote sensing imagery during five days from April 19 to September 26. Lastly, an open water evaporation model was developed to simulate the potential rate of evaporation from an open water body, in the absence of vegetation. The model assumes a shallow, well-mixed water layer that is similar in area and depth to the existing wetland, and the results are used to infer the potential amount of “water savings” that might be achieved by the removal of P. australis vegetation from the wetland. The results of the energy budget analysis show that the average ET rate for the wetland during the growing season is 4.4 mm day-1, with a maximum rate of 8.2 mm day-1 occurring around June 29. This measured daily ET is higher than some values found in previous studies (e.g., 6.9, 6.5, 6.3, 5.0, and 5.8 mm day-1) and is attributed to differences in plant structure/biology, environment, and regional climate. The vegetation phenology and net radiation are the two largest meteorological/vegetation drivers for the seasonal variability in ET. Remote sensing-based estimates of ET are similar than those of the in-situ energy balance during full vegetation, and they also reveal that the ET rates from P. australis are, on average, about 28% (1.18 mm day-1) greater than those for T. latifolia. We concluded that the Priestley-Taylor equation provides a good estimate of ET, particularly during the height of the growing season, when most of the net radiation is balanced by latent heat flux. Results of the water balance analysis reveal a reasonable correspondence between water level fluctuations and the energy budget-derived estimates of ET. Periods when the two curves do not agree imply influx (outflux) of groundwater early (late) in the growing season. Results suggest that the removal of P. australis from wetlands within the Republican River basin could potentially result in a growing season “water savings” of up to 28% if the native species of T. latifolia replaces the non-native P. australis. If a free water surface replaces P. australis, depending on wind sheltering, a “water loss” or a “water savings” could occur. We conclude that due to the general presence of wind sheltering throughout the riparian corridor of the Republican River basin, this would more likely lead to a small, but tangible amount of “water savings” if replaced by open water.

Emergent plant litter is a major source of energy and carbon in wetland food webs. Detritus and the associated microbes are eaten by invertebrates, thereby transferring the carbon and energy to higher trophic levels. Monocultures of an invasive common reed, Phragmites australis, can alter wetland food webs and decrease native plant diversity. Therefore, stands are often controlled by cutting and/or herbiciding. The processes of decomposition were studied using leaves of herbicided and non-herbicided Phragmites and non-herbicided native wool grass, Scirpus cyperinus, using litterbags in wetland mesocosms. Leaf mass loss, percent organic content, C:N ratios, fungal biomass, bacterial numbers and biomass, and invertebrate community composition (total numbers, abundance of functional feeding groups and dominant taxa, richness) were examined on ten dates over the course of 293 days. There were no differences in invertebrate communities or most chemical characteristics between herbicided and non-herbicided Phragmites leaf litter, and both litter types decayed at similar rates (0.0047 k-1 and 0.0051 k-1, respectively). However, herbicided Phragmites litter had higher fungal and bacterial biomass than non-herbicided Phragmites litter. In contrast, Scirpus litter decayed much more slowly (0.0029 k-1) and had higher organic content remaining than either Phragmites litter. At the end of the study, over 44% of the Scirpus litter remained but only 13 - 14% of Phragmites litter remained. Significant differences were found in microbial communities between Scirpus and Phragmites litter, where Phragmites litter generally had higher fungal and bacterial biomass. Invertebrate richness was also higher on Phragmites than Scirpus litter. Furthermore, there were non-significant trends that total invertebrates, detritivores and collector-gatherers were higher on Phragmites than Scirpus litter by the last sampling date (25 May 2007). Principle components analysis also showed high positive correlation between fungal biomass and invertebrate richness. Collectively, these results indicate that the use of herbicide to control Phragmites may not significantly alter decomposition processes or the associated invertebrate community compared to non-herbicided Phragmites stands. Furthermore, although dense stands of the invasive Phragmites can decrease overall wetland plant diversity, numbers and diversity of detritivorous invertebrates on the litter, invertebrates on Phragmites leaf litter may be as high as those occurring on native plants that have slow decay rates.

Polycyclic aromatic hydrocarbon (PAH) bioavailability does not correlate directly with total PAH sediment concentration because PAHs strongly sorb to organic matter. Many current toxicological models assume that PAHs present in the dissolved phase reflect actual PAH bioavailability to organisms. Plants can release significant amounts of plant organic matter (POM) to soils and sediments; however, the mechanisms by which POM may affect PAH bioavailability in sediments are unclear. The rhizosphere may increase PAH bioavailability by destabilizing soil organic matter (SOM) and enhancing PAH desorption, or the rhizosphere may alter SOM composition and provide new carbon matrices to sorb⁄sequester PAHs and reduce PAH desorption. Desorption studies were conducted to determine if vegetation decreased or increased the rate and mass amounts of desorbable PAHs. Replicate desorption studies were conducted using vegetated and non-vegetated bulk sediment and HF⁄HCl humin fractions; sediments were collected from a coastal refinery distillate waste pit (RP) and refinery-impacted sediments from a freshwater canal (IH). Desorption isotherms for four PAHs were determined by two methods, aqueous and TenaxTM bead extractions. PAHs were quantified by gas chromatography⁄mass spectrometry selected ion monitoring (GC⁄MS SIM). Results showed differences in PAH desorption based on the amount of time vegetation had been present in sediments. Vegetated sediments with 30+ years of vegetative growth (RP) desorbed more PAHs than non-vegetated sediments by TenaxTM extraction in both bulk and humin sediment fractions. Recently vegetated, IH freshwater sediments desorbed fewer PAHs than non-vegetated IH sediments by aqueous and TenaxTM extractions in bulk and humin sediment fractions. These findings suggest that initial exposure of sediment to vegetation slows PAH desorption and that extensive exposure to vegetation enhances PAH desorption from both labile and refractory SOM.

My thesis involves two distinct projects related to wetland plants. The first evaluates plant traits for their contribution to the success of invasive Phragmites australis in North America and their interaction with herbivores. The second investigates the relative effects of six plant species, with different growth forms, status (native v. nonnative) and tissue quality, on litter dynamics and invertebrate diversity in a New York freshwater wetland. Prevention is the most cost-effective and successful means of managing invasive plants. Predicting future invasions depends on identifying plant traits that facilitate invasive success. We investigated the influence of above-ground growth phenology and increased stem height on the success of invasive Phragmites australis in North America, using a phylogenetically-controlled comparison with a native, non-weedy P. australis subspecies. We also measured the effects of specialist stem-galling Lipara flies and a generalist aphid (Hyalopterus pruni), both nonnatives to North America, on these above-ground traits. Comparisons were made in 1) a common garden at Cornell University, Ithaca, NY, in 2003 and 2004, and 2) a field site at Montezuma National Wildlife Refuge, Seneca Falls, NY in 2003. In the garden, but not the field, nonnative P. australis leaves remained green for about a month longer (native v. nonnative: 2003 = 59.93 v. 85.5 days, P = 0.0002; 2004 = 52.29 v. 87.39 days, P = 0.02). For nonnative P. australis, leaves of the upper canopy consistently lived longer while leaf lifespan in the lower canopy was shorter or the same. Greater investment in high canopy leaves may increase carbon gain efficiency of nonnative P. australis. Nonnative P. australis grew taller in the field but this was mediated by disproportionate Lipara attack rather than plant status (native or nonnative). Lipara attack reduced stem height of all stems but only increased the lifespan of nonnative P. australis? low canopy leaves. Aphids had no significant effect on measured plant traits. Through increased carbon gain, leaf phenology may contribute to P. australis? competitive superiority over its native conspecific. Higher susceptibility of native P. australis to nonnative herbivores may also facilitate nonnative P. australis? competitive superiority. Senesced plant litter from emergent macrophytes fuels freshwater wetland productivity and nutrient cycling. Litter nitrogen content generally has a direct, positive effect on quantity and rate of resource availability to wetland biota. Since plants vary in their nitrogen content, shifts in plant community composition may alter important wetland functions. To study the consequences of changing plant dominance, we compared litter mass loss and invertebrate richness and abundance of six common macrophytes in a central New York freshwater wetland. Plants studied include Typha latifolia L. (broad leafed cattail, Typhacea), T. angustifolia L. (narrow leafed cattail), Phragmites australis (cav.) Trin ex. Steudel (common reed, Poaceae), P. australis subspecies americanus Saltonstall, P.M. Peterson & Soreng, Lythrum salicaria L. (purple loosestrife, Lythraceae), and Phalaris arundinacea L. (reed canarygrass, Poaceae). After nine months, mass loss of most plant species diverged significantly. Plant effect on invertebrate colonization was season and species-specific, with P. arundinacea almost consistently supporting higher invertebrate densities. Although %N differed among some plant species, it was not a good predictor of mass loss or invertebrate abundance and richness. Including plastic drinking straws as a treatment revealed that several invertebrates used litter for substrate rather than food. We conclude that shifts in plant dominance among the six wetland macrophytes investigated could potentially alter wetland function, by changing decomposition rates and the invertebrate community. Net quality of litter resources, which depends on the combined influence of morphology, chemical quality of specific plant organs, and feeding ecology of specific taxa, may be a better predictor of species effects on decomposition and diversity.