Julie C. Zinnert

Going with the flow or against the grain? The promise of vegetation for protecting beaches, dunes, and barrier islands from erosion

Coastlines have traditionally been engineered to maintain structural stability and to protect property from storm-related damage, but their ability to endure will be challenged over the next century. The use of vegetation to reduce erosion on ocean-facing mainland and barrier island shorelines – including the sand dunes and beaches on these islands – could be part of a more flexible strategy. Although there is growing enthusiasm for using vegetation for this purpose, empirical data supporting this approach are lacking. Here, we identify the potential roles of vegetation in coastal protection, including the capture of sediment, ecological succession, and the building of islands, dunes, and beaches; the development of wave-resistant soils by increasing effective grain size and sedimentary cohesion; the ability of aboveground architecture to attenuate waves and impede through-flow; the capability of roots to bind sediments subjected to wave action; and the alteration of coastline resiliency by plant structur...

Woody vegetative cover dynamics in response to recent climate change on an Atlantic coast barrier island: a remote sensing approach

Considering impacts of predicted increases in sea-level, storms, and alterations in precipitation patterns on geomorphological and associated ecological processes, woody vegetation dynamics may serve as sentinels to climate change on barrier islands. We examined island-scale conversion of land (i.e. sand to grassland to woody cover) while relating the importance of climate variables on rate of woody expansion. Light Detection and Ranging (LiDAR) was used to evaluate potential distribution of woody species based on distance to shoreline and elevation. Using Landsat TM imagery, we monitored changes in island size and vegetation classes (1984–2010). These comparisons revealed conversion of grassland to woody cover (285% increase) was closely linked to air temperature, precipitation and atmospheric [CO2]. LiDAR data indicated that woody species have not expanded completely into the potential range. Our results suggest that woody species are responsive to climate change, thus serving as sentinels on Virginia barrier islands.

Landscape position and habitat polygons in a dynamic coastal environment

In contrast to stable inland systems, coastal landscape positions are dynamic, changing as shorelines migrate and storms alter topography. We define landscape position by distance to ocean shoreline and elevation above sea level, two metrics that integrate a suite of environmental and biotic factors. As shoreline and elevation change, suitability of a geo-referenced position for a given plant species may also change. The objectives of our study were to use two methods for measuring landscape position (GPS and hyperspectral/light detection and ranging or LIDAR) to develop habitat polygons, compare habitat polygons for five species representing several adaptive strategies, and illustrate change in landscape position due to migrating shoreline for a Virginia, USA barrier island. Habitat polygons for each species were distinct, represented several growth forms or functional groups, and were indicative of tolerances to biotic and abiotic stresses. The habitat polygon for Cakile edentula (annual forb) was relat...

Effects of salinity on physiological responses and the photochemical reflectance index in two co-occurring coastal shrubs

Background and aimsThe photochemical reflectance index (PRI) is correlated to photosynthetic efficiency and has been successfully applied at multiple scales for remote estimation of physiological functioning. However, interpretation of the PRI signal can be confounded by many different variables including declines in photochemical pigments. Our study was aimed at investigating PRI in response to salinity stress, and evaluating physiological and pigment responses of two co-occurring shrubs, Baccharis halimifolia and Myrica cerifera in laboratory studies.MethodsPhotosynthesis, water relations, chlorophyll fluorescence, hyperspectral reflectance and leaf pigment contents were measured following salinity treatment.ResultsPhysiological measurements indicated that both species exhibit adaptations which protect PSII during periods of stress. Chlorophyll fluorescence parameters were affected in both species, but indicated that other photochemical reactions (e.g. photorespiration) were important for energy dissipation in absence of chlorophyll changes. After many days of reduced photosynthesis, photochemical changes were detectable using PRI indicating chronic stress.ConclusionsVariations in PRI were not related to changes in pigments but strongly related to tissue chlorides indicating salinity effects on the PRI signal. Thus, PRI is an indicator of salinity stress in these coastal species and may be as an early signal for increasing salt exposure associated with rising sea-level and climate change.

Spatial–Temporal Dynamics in Barrier Island Upland Vegetation: The Overlooked Coastal Landscape

AbstractBarrier islands provide the first line of defense against storms for millions of people living in coastal areas. Upland vegetation (that is, grassland, shrubland, and maritime forest) has received little attention, even though this land surface is most strongly affected by development pressures. We use remote-sensing analysis to assess state change on seven undeveloped Virginia barrier islands over 27xa0years (1984–2011) that are free from direct human influence. Our analysis highlights the spatial–temporally dynamic nature of barrier island upland land area and vegetation, with rapidly changing ecosystem states. Over the time period, upland vegetation was dramatically reduced by 29% whereas woody vegetation cover increased 40% across all islands. Although conversions between sand, grassland, and woody vegetation were variable within each island, three major patterns of vegetative land-cover change were apparent: overall loss of vegetative cover, frequent transitions between grass and woody cover, and gain in woody cover. These patterns are valuable for understanding natural evolution of barrier islands in response to sea-level rise. Evaluation of temporal dynamics in barrier upland is needed to characterize underlying processes including island resilience or chronic stress, and is a prerequisite to sustainable coastal management- and resilience-based planning, especially when implementing ecosystem-based solutions.n

Distinguishing natural from anthropogenic stress in plants: physiology, fluorescence and hyperspectral reflectance

Background and AimsExplosives released into the environment from munitions production, processing facilities, or buried unexploded ordnances can be absorbed by surrounding roots and induce toxic effects in leaves and stems. Research into the mechanisms with which explosives disrupt physiological processes could provide methods for discrimination of anthropogenic and natural stresses. Our objectives were to experimentally evaluate the effects of natural stress and explosives on plant physiology and to link differences among treatments to changes in hyperspectral reflectance for possible remote detection.MethodsPhotosynthesis, water relations, chlorophyll fluorescence, and hyperspectral reflectance were measured following four experimental treatments (drought, salinity, trinitrotoluene and hexahydro-1,3,5-trinitro-l,3,5-triazine) on two woody species. Principal Components Analyses of physiological and hyperspectral results were used to evaluate the differences among treatments.ResultsExplosives induced different physiological responses compared to natural stress responses. Stomatal regulation over photosynthesis occurred due to natural stress, influencing energy dissipation pathways of excess light. Photosynthetic declines in explosives were likely the result of metabolic dysfunction. Select hyperspectral indices could discriminate natural stressors from explosives using changes in the red and near-infrared spectral region.ConclusionsThese results show the possibility of using variations in energy dissipation and hyperspectral reflectance to detect plants exposed to explosives in a laboratory setting and are promising for field application using plants as phytosensors to detect explosives contamination in soil.

Physiological and transcriptional responses of Baccharis halimifolia to the explosive "composition B" (RDX/TNT) in amended soil

Unexploded explosives that include royal demolition explosive (RDX) and trinitrotoluene (TNT) cause environmental concerns for surrounding ecosystems. Baccharis halimifolia is a plant species in the sunflower family that grows naturally near munitions sites on contaminated soils, indicating that it might have tolerance to explosives. B. halimifolia plants were grown on 100, 300, and 750xa0mgxa0kg−1 of soil amended with composition B (Comp B) explosive, a mixture of royal demolition explosive and trinitrotoluene. These concentrations are environmentally relevant to such munitions sites. The purpose of the experiment was to mimic contaminated sites to assess the plant’s physiological response and uptake of explosives and to identify upregulated genes in response to explosives in order to better understand how this species copes with explosives. Stomatal conductance was not significantly reduced in any treatments. However, net photosynthesis, absorbed photons, and chlorophyll were significantly reduced in all treatments relative to the control plants. The dark-adapted parameter of photosynthesis was reduced only in the 750xa0mgxa0kg−1 Comp B treatment. Thus, we observed partial physiological tolerance to Comp B in B. halimifolia plants. We identified and cloned 11 B. halimifolia gene candidates that were orthologous to explosive-responsive genes previously identified in Arabidopsis and poplar. Nine of those genes showed more than 90xa0% similarity to Conyza canadensis (horseweed), which is the closest relative with significant available genomics resources. The expression patterns of these genes were studied using quantitative real-time PCR. Three genes were transcriptionally upregulated in Comp B treatments, and the Cytb6f gene was found to be highly active in all the tested concentrations of Comp B. These three newly identified candidate genes of this explosives-tolerant plant species can be potentially exploited for uses in phytoremediation by overexpressing these genes in transgenic plants and, similarly, by using promoters or variants of promoters from these genes fused to reporter genes in transgenic plants for making phytosensors to report the localized presence of explosives in contaminated soils.

Plants as Phytosensors: Physiological Responses of a Woody Plant in Response to RDX Exposure and Potential for Remote Detection

Using plants as phytosensors could allow for large-scale detection of explosives and other anthropogenic contamination. Quantifying physiological, photosynthetic, and hyperspectral responses of plants to hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) contamination provides the basis for understanding plant signals for remote detection. Plants of the woody shrub Baccharis halimifolia (a generalist species common on many military installations) were potted in soil concentrations of RDX ranging from 100 to 1500 mg kg−1. Physiological measurements of stomatal conductance and photosynthesis were significantly affected by RDX exposure at all treatment levels, with no overall effect on water potential. However, declines in photosynthesis and stomatal conductance were markedly different from those that occur under natural stress. Quantum use efficiency () and electron transport rate indicated that photosystem II (PSII) of RDX-treated plants was functional, with active photosynthetic reaction centers. Thus, declines in photosynthesis resulted from biochemical dysfunction in light-independent processes. Reflectance indices in the near-infrared region (, , and derivative indices) were most affected and may reflect the pathway on which RDX is contained within plants by being compartmentalized in the vacuole, cell wall, or lignin. These results demonstrate the potential for using plants as phytosensors to identify explosives exposure at remote distances.

Differential Response of Barrier Island Dune Grasses to Species Interactions and Burial

Barrier islands are at the forefront of storms and sea-level rise. High disturbance regimes and sediment mobility make these systems sensitive and dynamic. Island foredunes are protective structures against storm-induced overwash that are integrally tied to dune grasses via biogeomorphic feedbacks. Shifts in dune grass dominance could influence dune morphology and susceptibility to overwash, altering island stability. In a glasshouse study, two dune grasses, Ammophila breviligulata and Uniola paniculata, were planted together and subjected to a 20xa0cm burial to quantify morphological and physiological responses. Burial had positive effects on both plants as indicated by increased electron transport rate and total biomass. Ammophila breviligulata performance declined when planted with U. paniculata. Uniola paniculata was not affected when planted with A. breviligulata but did have higher water use efficiency and nitrogen use efficiency. Planted in mixture, differential reallocation of biomass occurred between species potentially altering resource acquisition further. As U. paniculata migrates into A. breviligulata dominated habitat and A. breviligulata performance diminishes, biotic interactions between these and other species may affect dune formation and community structure. Our study emphasizes the importance of studying biotic interactions alongside naturally occurring abiotic drivers.

Crossing Scales: The Complexity of Barrier-Island Processes for Predicting Future Change

Barrier islands are heavily influenced by external drivers such as sea-level rise, storm-related disturbances, and other complex factors that affect net sediment exchange. Numerous ecological processes (e.g., dispersal, competition, and facilitation) interact with these drivers and ultimately influence barrier-island state change and therefore stability. Our synthesis of physical and ecological processes controlling barrier-island function highlights the importance of incorporating ecological factors into predictive models of barrier-island state change. We present a conceptual framework that outlines how local-scale processes contribute to broadscale patterns of barrier-island function. We have also identified specific, scale-dependent drivers and cross-scale interactions that lead to different topographic states, which vary in species composition, and generate contrasts in function between and within individual islands. This multidimensional continuum of topographic states ultimately determines island resilience in response to climate change.