Salt marshes provide a range of ecosystem services and yet are subjected to anthropogenic impacts that alter the biogeochemical processes underlying these services. In particular, human activities may modify salt marsh greenhouse gas (carbon dioxide, methane, nitrous oxide) emissions by changing plant and microbial communities, hydrological regime, and sediment chemistry. Quantifying the effects of human impacts on greenhouse gas emissions is important for complete carbon budgets, and for effective management of salt marshes and the ecosystem services they provide. In Chapters 1 and 2, I investigate the effects of hydrology and plant invasion on greenhouse gas emissions. First, I show how the restriction and restoration history of four salt marshes influence methane flux in unpredictable ways. Despite comparable salinity, methane emissions from one partially restored marsh were 25 times higher than unimpacted reference sites 13+ years after restoration, but emissions from other restored sites were equal or lower. Next, I show that greenhouse gas emissions associated with invasive Phragmites australis are not different from those associated with native Spartina alterniflora. These Chapters demonstrate the de-coupling of greenhouse gas emissions, and carbon sequestration more generally, from ecosystem degradation and restoration. In Chapters 3 and 4, I quantify greenhouse gas fluxes and microbial community structure under precipitation changes that may occur with global climate change. In a field experiment, doubled rainfall and drought had significant transient impacts on porewater salinity following storms, and on the community structure of plants (doubled rainfall) or microbes (drought), yet greenhouse gas fluxes and other biogeochemical processes were not affected. The absence of biogeochemical change indicates functional redundancy and resistance or resilience exist in the microbial community, suggesting marshes may continue providing services as precipitation changes. In a lab experiment, rewetting intact cores to simulate tidal inundation or rainstorms produced a nitrous oxide pulse 10-20x the baseline flux rates, without changing the microbial community. A model of rewetting event frequency suggests that pulsed emissions may be responsible for the majority of marsh nitrous oxide emission. Precipitation change may increase coastal nitrous oxide emission if it causes more or stronger storms, and thus more rewetting events.

Klamath Marsh is a wetland complex that lies in the rain shadow of the Cascade Range in the Williamson River sub-basin of the Klamath Basin. The marsh lies directly east of Crater Lake in an area inundated by pyroclastic-flow and -fall deposits from the Holocene eruptions of Mount Mazama. The physical characteristics of rocks of Pleistocene versus Pliocene age combined with NNW -striking fault systems divide the Williamson River basin into two distinct hydrogeologic regimes. The northwestern regime includes the east slope of the Cascades and consists of at least 150 m of interbedded sand, gravel, and stacks (15 to 45 m) of thin (3-5 m) and vesiculated basalt lava flows. Mean annual precipitation ranges from 150 cm near the crest of the Cascades to 50 cm near Klamath Marsh. Moderate to high yield (100 to 4000 gpm) water wells, springs and flowing wells suggest high permeability and ground water potential. The southeastern regime is underlain by Pliocene pyroclastic flows (∼ 40 m) and lava flows (>30 m). Mean annual precipitation ranges from 70 cm in the highlands to 50 cm in the lowlands. Low-yield (20-100 gpm) water wells and perched unconfined aquifers in Holocene pumice deposits suggest low permeability and low ground water potential in areas underlain by the pyroclastic flows. Volumetric analysis of inflows and outflows in Klamath Marsh for 2000 indicates approximately 86% of inflow is from groundwater and 14% from surface water, with nearly 200 x 10⁶ m³ of water removed by evapotranspiration

Water levels of Malheur Lake in southeastern Oregon fluctuate widely with seasonal and cyclic climatic changes. Seven years of severe flooding from 1978 to 1984 produced the highest water levels in recorded history and covered almost all marsh vegetation. Seven years of drought followed the flooding, and by 1992 the water level had dropped to the lowest point in nearly 60 years. A survey of vegetation colonizing the lakeshore as flood water receded was conducted from 1989 to 1992 to describe the reestablishment of marsh vegetation. Six transects were placed in three different ecological units of the lake. Frequency and cover data for each plant species were recorded. Recruitment from seed banks produced germination the first year of annual, mud flat species followed the second year by perennial emergent seedlings. The emergent seedlings generally did not survive the drought as water levels continued to recede. The seeds of introduced Eurasian species were distributed by wind, became lodged in the cracks of drying mud flats and then germinated following winter rains. The central ecological unit, fed by both the Blitzen and Silvies Rivers, did not show severe effects of drought and species of emergent vegetation grew without apparent signs of drought stress.

Light, medium and heavy crude oils were studied at three concentrations and with two different sediments in experimental microcosm settings to determine the ability of Spartina alterniflora and associated microbes to breakdown total extractable hydrocarbons (TEH) in the water. It was a baseline experiment designed to quantify the rates of biodegradation under relatively quiescent conditions from different crude oils at moderate doses ranging from 0-150 mg/kg soil. Upon the completion of the experiment there were several key findings: (1) The lethal dosage for Spartina alterniflora was not reached within the 90 day experiment at these dosages, and all plants survived; (2) More than 97% of the total extractable hydrocarbons (TEH) were shown to be degraded by plants and rhizosphere microorganisms within the 90- day experiment; (3) The dose of oil introduced as a slick (simulated spill) on day zero did not significantly affect the results for TEH degradation within the range of dosages from 50-150 mg/g -- these dosages could be degraded by the marsh cord grass system; (4) A sediment type which was acclimated to oil for several months and one which was non-acclimated did not show significantly different results for TEH degradation in the microcosms -- both sediment systems resulted in TEH degradation over the 90-day experiment; and (5) A mathematical model was developed which simulated experiment results quite closely including TEH diffusion from the crude oil slick into the water and subsequent biodegradation.

Herbivore abundances are determined by a set of interacting factors that vary among different habitat types. Specifically, herbivore abundances in monocultures and polycultures may be governed by the same set of factors but with varying influences in the different habitats. In addition, monophagous and polyphagous herbivores may respond differently to the same set of influencing factors. I examined several abiotic and biotic factors in manipulated monocultures and polycultures of Borrichia frutescens in a west central Florida salt marsh. The experimental plots differed in both plant diversity and aboveground habitat structure to see how each component of diversity contributed to variability in the abiotic and biotic factors and how those factors were related to differences in herbivore abundances. The monoculture treatment involved clipping all above ground non-host plant material to achieve a host plant monoculture. The polyculture treatments involved pinning all non-host plant material to achieve a polyculture with reduced above ground habitat structure. The second polyculture treatment was a control in which the naturally diverse plots were unmanipulated. Two monophagous and one polyphagous herbivores were chosen for this study because of their abundance and availability in the field. The two monophagous herbivores on the host plant Borrichia frutescens were Pissonotus quadripustulatus (Homoptera:Delphacidae) and Asphondylia borrichiae (Diptera: Cecidomyiidae) both of which have been well studied in the field where the current experiment took place. The polyphagous herbivore was Cyarda acutissima (Homoptera: Flatidae), a poorly known invasive from Cuba. Soil salinity and host plant leaf nitrogen content were the abiotic factors measured. Herbivore abundances, percent egg and gall parasitism by parasitoids, spider abundances on host plant stems and ground spider abundances were the biotic factors measured. Both salinity and host plant leaf nitrogen were significantly different among the different treatments with clipped plots having the highest salinity and leaf nitrogen content. Population densities of both of the monophagous herbivores were not significantly different between treatments. The polyphagous herbivore had significantly higher abundances in the pinned and control plots than in the clipped plots. Stem spider abundances were not significantly different among treatments. Ground spiders, however, were significantly more abundant in control and pinned plots than clipped plots. Parasitism of both monophagous herbivores was not significantly different between treatments but was generally higher in the control plots. The results suggest that for monophagous herbivores bottom-up and top-down factors act antagonistically in monocultures but for the polyphagous herbivore, the presence of multiple host plants is more influential in diverse plots even given the higher abundances of generalist predators.

Coastal marshes serve important ecologic and economic functions, such as providing habitat, absorbing floodwaters and storm surges, and sequestering carbon. Throughout the northern Gulf of Mexico, coastal marshes are disappearing due to wave attack, sea-level rise, sediment export, and subsidence. Marsh area increases when sediments accumulate at the marsh shoreline, accrete vertically, and when non-marsh areas are colonized by marsh vegetation. Marsh shoreline erosion results in net marsh loss when transgression rates at the marsh-water edge exceed upland-marsh migration. The balance between marsh destroying and marsh creating processes determines the long-term survivability of a marsh system. Thus, processes of shoreline change are important considerations when evaluating the overall health and vulnerability of coastal marshes. Shoreline erosion can be measured using remotely sensed data in a geographic information system. Using shoreline position delineated from aerial imagery, historic maps, and field surveys, shoreline change analysis estimates long- and short-term shoreline movements to identify erosion or accretion for coastal marshes at the Grand Bay National Estuarine Research Reserve (GBNERR) and Wildlife Refuge (GBNWR) on the border of Mississippi and Alabama, USA. However, these techniques do not directly provide information on sediment deposition on the marsh surface. To understand sediment deposition, four study sites provide in-situ measurements of sediment deposition using sediment plates and sediment tracers (silica beads) that were collected every three months. Analysis of the shoreline change data and in-situ sediment data for the GBNERR showed that in 2017, all of the shorelines at the study sites are eroding at rates between -0.50 m/yr and -3.39 m/yr, an average rate of -1.45 m/yr. Positive sediment deposition rates were measured from 5-20 meters inland of the marsh shoreline during each season (3-month period) (0.19 ± 0.05 cm [Fall], 0.26 ± 0.11 cm [Winter], 0.48 ± 0.12 cm [Spring], 0.63 ± 0.15 cm [Summer]), indicating sediment deposition increased with every season. Sediment tracer (silica-bead) counts confirmed that sediment was transported onto the marsh surface from eroding marsh shorelines. Higher energy sites had more beads deposited on the sediment plates than the low energy tidal creek site, due to the different wave and tidal conditions between the sites. Increased wave and tidal energy correlated to increased sediment transport further into the marsh. The relative importance of this marsh cannibalism for the long-term marsh survival depends on factors, such as wave attack, as they control the rate of persistent lateral marsh loss. This findings in this thesis suggests that material from eroding marsh edges contributes to the ability of the interior of marshes to maintain their elevation with respect to rising sea levels.

It is well recognized that rivers are the primary pathway that delivers sediment to the ocean. However, the fate of these sediments is poorly understood, and is complicated by relative sea level rise and meteorological forcings. One coastal system to examine these issues is the Atchafalaya River-Chenier Plain (ARCP) of southwest Louisiana, which relies on Mississippi River sediment supply and is vulnerable to coastal erosion and land loss. Despite regional coastal degradation, some land gain and marsh growth have been observed here. Land gain in south Louisiana is generally observed at the mouths of the rivers – the Bird’s Foot, and the Atchafalaya and Wax Lake deltas. However, satellite imagery and sedimentological analyses indicate that coastal lakes in southwest Louisiana have also filled in and converted into salt marshes in the last 40 years. To understand sediment delivery in these marshes, multiple short cores were collected in a central Chenier Plain tidal creek system, and analyzed for 210Pb, 137Cs, 7Be, δ13C, and grain size distribution. We propose that Chenier Plain reactivation processes are triggered by the increase in Atchafalaya River flow that began in the early 1900s. Fluvial sediments delivered through westward longshore transport and resuspended during energetic events become available to the sediment-starved Chenier coast, leading to deposition, infilling, mudflat progradation, and marsh growth. / acase@tulane.edu

Several species of North American migratory songbirds reportedly experience seasonal diet shifts involving a shift from an insect diet during the breeding season to one incorporating fruits during migration and non-breeding periods but the extent to which dietary plasticity occurs in migratory songbirds is poorly quantified. Thus, I used stable carbon (ä13C) and nitrogen (ä15N) isotope analyses to evaluate the timing and extent of frugivory throughout the annual life cycle of 16 species of migratory songbirds, representing wide ranges in body size and reported diets. Birds were sampled during spring and fall migration at the Delta Marsh Bird Observatory in 2003. To investigate dietary patterns, I sampled multiple tissues (muscle, liver, whole blood, claws, bone collagen, feathers) as these represent different periods of diet integration due to varying elemental turnover rates.<p>Assuming that relatively low ä15N values represent a fruit diet and relatively high ä15N values represent an insect diet, I expected tissues representing fall migration (liver, blood, and muscle from fall-captured birds) and winter (greater coverts and claws from spring-captured birds) to have lower ä15N values than tissues representing spring migration (liver, blood, and muscle from spring-captured birds) and summer (tail feathers and claws from fall-captured birds) when fruits are presumed to be less common in songbird diets. Based on blood and claw ä15N values, there was no isotopic segregation of species I classified a priori as insectivores or omnivores. For most species, tissue ä15N values showed either no seasonal change or a shift opposite to my prediction (e.g., ä15N values higher in fall birds compared to spring birds). Boreal fruit ä15N values were lower than those for insects; however, ä15N values of agricultural fruits overlapped both boreal fruit and insect values suggesting that food web baselines did not conform to a simple (single) linear trophic-enrichment model. In Yellow-rumped Warblers (Dendroica coronata), within-tissue seasonal comparisons for liver, muscle and blood indicated a fruit diet during fall and winter and an insect diet during spring and summer; claws and feathers of birds captured in spring (representing winter diet) had unexpectedly high ä15N values. Diet-tissue isotopic discrimination factors associated with both a fruit diet and insect diet were taken from the literature and used to correct stable isotope values of tissues to putative diet because, currently, little is known about the nature of factors influencing discrimination factors to be used in simple linear dietary mixing models. There were differences in tissue ä13C and ä15N values depending on which discrimination factor was used. Based on mixing model results for tissue ä15N values, a higher proportion of insects vs. fruits was detected in the diet of Yellow-rumped Warblers for all tissues except muscle and claws. <p>My interpretations are contingent on the fact that the available natural history information, on which guild classifications were based, was correct and that elemental turnover rates and discrimination factors used were accurate. However, much uncertainty remains about the appropriate diet-tissue isotopic discrimination factors corresponding to fruit and insect diets. Due to extensive natural variability of stable nitrogen isotope values in food sources, possible anthropogenic influences and a lack of knowledge of the metabolic processes that can potentially affect stable isotope values, I caution against using stable isotope analysis alone to track frugivory in temperate North American migratory songbirds. Future research should focus on captive studies aimed at determining and validating discrimination factors of various tissues, particularly claws and feathers, for birds feeding on varying proportions of fruits and insects. Additionally, more information on the dietary habits of these migratory songbirds is needed, as previous estimates of insectivory and frugivory in songbirds may not be accurate.

Common carp (Cyprinus carpio) have been hypothesized to contribute to declines in aquatic macrophytes, waterfowl, and water clarity in Delta Marsh, an 18,500 ha freshwater coastal wetland on Lake Manitoba, Canada. Ten ponds (1-13 ha) were chosen for a two-year experimental manipulation study. Following a year of baseline monitoring, manipulations were conducted in 2002. To facilitate access by carp into isolated ponds, channels were blasted from the main marsh into two ponds. Meanwhile, to restrict or exclude carp access into ponds, channels were either screened or diked to four ponds. Two connected and two isolated ponds functioned as controls. Although common carp were the original subject of the study, it became apparent that hydrological connection to the surrounding marsh had a paramount importance on the abundance and diversity of the fish, amphibian and water-column invertebrate communities. Connectivity, or lack of connectivity, played an important role in the distribution of the fish community, and subsequently the composition and abundance of water-column invertebrates and amphibians. Ponds with direct connection had diverse, mixed-species fish assemblages, with fewer invertebrates and amphibians. Ponds with restricted connections had fish communities composed of tolerant small-sized species and increased abundance of invertebrates and amphibians. Ponds that lacked connection could freeze and lose all fish, and had higher numbers of invertebrates and amphibians. An absence of adult common carp may have been responsible for increased amphibian numbers in the screened ponds, however more study is needed. Confounding impacts of fluctuating water levels made it impossible to implicate common carp for most changes observed within ponds in Delta Marsh. / May 2006

Several species of North American migratory songbirds reportedly experience seasonal diet shifts involving a shift from an insect diet during the breeding season to one incorporating fruits during migration and non-breeding periods but the extent to which dietary plasticity occurs in migratory songbirds is poorly quantified. Thus, I used stable carbon (ä13C) and nitrogen (ä15N) isotope analyses to evaluate the timing and extent of frugivory throughout the annual life cycle of 16 species of migratory songbirds, representing wide ranges in body size and reported diets. Birds were sampled during spring and fall migration at the Delta Marsh Bird Observatory in 2003. To investigate dietary patterns, I sampled multiple tissues (muscle, liver, whole blood, claws, bone collagen, feathers) as these represent different periods of diet integration due to varying elemental turnover rates.<p>Assuming that relatively low ä15N values represent a fruit diet and relatively high ä15N values represent an insect diet, I expected tissues representing fall migration (liver, blood, and muscle from fall-captured birds) and winter (greater coverts and claws from spring-captured birds) to have lower ä15N values than tissues representing spring migration (liver, blood, and muscle from spring-captured birds) and summer (tail feathers and claws from fall-captured birds) when fruits are presumed to be less common in songbird diets. Based on blood and claw ä15N values, there was no isotopic segregation of species I classified a priori as insectivores or omnivores. For most species, tissue ä15N values showed either no seasonal change or a shift opposite to my prediction (e.g., ä15N values higher in fall birds compared to spring birds). Boreal fruit ä15N values were lower than those for insects; however, ä15N values of agricultural fruits overlapped both boreal fruit and insect values suggesting that food web baselines did not conform to a simple (single) linear trophic-enrichment model. In Yellow-rumped Warblers (Dendroica coronata), within-tissue seasonal comparisons for liver, muscle and blood indicated a fruit diet during fall and winter and an insect diet during spring and summer; claws and feathers of birds captured in spring (representing winter diet) had unexpectedly high ä15N values. Diet-tissue isotopic discrimination factors associated with both a fruit diet and insect diet were taken from the literature and used to correct stable isotope values of tissues to putative diet because, currently, little is known about the nature of factors influencing discrimination factors to be used in simple linear dietary mixing models. There were differences in tissue ä13C and ä15N values depending on which discrimination factor was used. Based on mixing model results for tissue ä15N values, a higher proportion of insects vs. fruits was detected in the diet of Yellow-rumped Warblers for all tissues except muscle and claws. <p>My interpretations are contingent on the fact that the available natural history information, on which guild classifications were based, was correct and that elemental turnover rates and discrimination factors used were accurate. However, much uncertainty remains about the appropriate diet-tissue isotopic discrimination factors corresponding to fruit and insect diets. Due to extensive natural variability of stable nitrogen isotope values in food sources, possible anthropogenic influences and a lack of knowledge of the metabolic processes that can potentially affect stable isotope values, I caution against using stable isotope analysis alone to track frugivory in temperate North American migratory songbirds. Future research should focus on captive studies aimed at determining and validating discrimination factors of various tissues, particularly claws and feathers, for birds feeding on varying proportions of fruits and insects. Additionally, more information on the dietary habits of these migratory songbirds is needed, as previous estimates of insectivory and frugivory in songbirds may not be accurate.