Atmospheric carbon dioxide (CO2) levels and global eutrophication are anthropogenic stressors impacting the environment of specific interest in wetland systems. Wetlands occupy a critical interface between terrestrial and aquatic environments. Fertilizer use for agriculture and treated wastewater disposal has increased nutrient loading to wetlands. Conflicting results on impacts of nitrogen loading to coastal wetland soils have been reported, though most studies have investigated short-term impacts of nutrient loading, not long-term integrated impacts. I investigated an 11-year period of nutrient loading on soils in an oligohaline coastal wetland. Nitrogen treatments of 0, 50, 200, and 1200 kg ha-1 yr-1 were paired with phosphorus treatments of 0, 131 kg ha-1 yr-1. I measured soil physiochemical characteristics, microbial biomass N (MBN), potentially mineralizable N rates (PMN), and denitrification rates. Total P increased with P additions. There were no significant differences in measures of soil microbial biomass or activity with N or P loading. Results suggest that after bioavailable nutrients are incorporated into the soil matrix, there are no lasting effects on measured microbial activities of these coastal marsh soils. I also investigated the impacts of increased CO2 levels on biogeochemical cycling and associated microbial activity. I conducted a 2-year experiment with CO2 treatment applications of 710 and 410 ppm applied to vegetated and non-vegetated wetland soils. I measured soil physiochemical properties, extracellular enzyme activity, MBN, PMN, and extractable NH4+. Phosphatase activity decreased (p = 0.09) with increased CO2 in the non-vegetated soils. PMN and extractable NH4+ varied significantly with the interaction between vegetation presence and CO2 (p=0.07, p=0.0001). Total P and organic matter content were significantly higher in the vegetated soils (p = 0.05, p=0.06). Higher bioavailable nutrient concentrations in non-vegetated soils under elevated CO2 indicate there is a mechanism to increase microbial activity under elevated CO2 conditions, with implications for carbon sequestration.

The northwest Gulf of Mexico (Gulf) shelf-edge banks both provide unique hard bottom habitat and support the northernmost coral reefs on the North American continental shelf in a region that is generally characterized by low relief, soft sediments. The habitat value of many of these banks has led to their designation as Habitat Areas of Particular Concern (HAPC) and the Flower Garden Banks National Marine Sanctuary (FGBNMS). However, little is known about the fisheries resources and dynamics of the banks outside the FGBNMS. This study had three main objectives: 1) define reef fish assemblages at northwestern Gulf shelf-edge banks and determine if assemblages were related to the varied benthic habitats present at these features, 2) define large-scale fish distributions at these same banks and determine the influence of habitat and environmental factors on distribution, and 3) examine the trophic ecology of red snapper (Lutjanus campechanus), a common and highly prized reef-associated fish, at these features. Assemblage definition and relation to habitat was based upon baited underwater video surveys conducted across a range of depths and habitats. Four distinct reef fish assemblages were resolved at the shelf-edge banks, the distribution of which corresponded to benthic habitat zonation. The specific habitat characteristics of mud substrate and live cover most strongly related to species distribution. Spatial distribution of fish biomass and density at the scale of individual banks was assessed using a mobile hydroacoustic approach. The highest fish biomass and density were observed directly adjacent to hard substrate, but showed high variability with regard to site, season, and habitat zone. Red snapper trophic ecology was assessed using stable isotope analyses to examine both relative trophic position and extent among bank sites. Results indicated a consistent carbon source, but differences in basal nitrogen between mid-shelf and shelf-edge locations. Differences in isotopic, and presumable trophic, variability between banks was attributed to different red snapper size distributions, with larger individuals displaying higher isotopic variability. Results of this study indicate the less studied northwest Gulf shelf-edge banks harbor predictable, habitat-related fish species assemblages that show variable large-scale distributions.

This study compares the reproductive potential of red snapper (Lutjanus campechanus) at artificial and natural habitats. Natural habitats are areas of vertical relief created from biogenic/geologic processes that are thought to be the historical centers of abundance for red snapper in the northern Gulf of Mexico. Red snapper were collected from 2011 to 2013 at three natural habitat sites and two artificial habitat oil and gas platform sites. The mean gonadosomatic indices (GSI), maturity at size and age, spawning indicators, batch fecundity, spawning frequency, and annual fecundity for red snapper at each habitat were analyzed to examine reproductive potential among sites and habitats. Results indicate red snapper on natural habitats exhibited higher mean GSI than those on artificial habitats during peak spawning season. Female red snapper on natural habitats showed 98% maturity, compared to 52% maturity of females on artificial habitats. These data support previous observation of demographic differences in red snapper reproduction between natural and artificial habitats. The differences observed may be due to red snapper at natural habitats being in better nutritional condition than red snapper on artificial habitats, thus allowing red snapper on natural habitats to invest more energy in reproduction and less energy towards rapid growth early in life.

This study is focused on a paleoenvironmental history of a backbarrier coastal lagoon situated on the seaward margin of the Lafourche delta lobe in coastal Louisiana. A 2.2 meter long sediment core (Core BC 53) was collected from a mangrove-covered land strip on the northern margin of Bay Champagne, and was studied using pollen analysis, Loss-on-ignition (LOI), X-ray Fluorescence (XRF) analysis, and Cesium-137 and radiocarbon dating techniques to establish sediment stratigraphy and core chronology. Bay Champagne, a backbarrier lagoon formed during the evolution of Bayou Lafourche, has shown to be highly sensitive to geomorphological and vegetation changes induced by sea-level rise as noted by palynological, paleotempestological, and sedimentological records. In addition to capturing the rise and fall of the Lafourche delta lobe, Core BC 53 also preserved hurricane-induced sedimentary record. Pollen data revealed that Bay Champagne is mainly characterized by coastal marsh taxa. Freshwater marsh was dominant during the active period of the Lafourche delta about 1600 years ago. This was followed by a shift to salt marsh during its deterioration phase around 300 years ago. Avicennia germinans (black mangrove) emerged within the stratigraphy around 1880 A.D., which shows a direct correlation to relative sea-level rise. LOI and XRF data uncovered the presence of four hurricanes. Storm layers were not overwashed from the beach barrier due to its far distance from the coring site; however, these sedimentary signatures originated from the center of Bay Champagne and fluvial regions north of the lagoon. The distinct increase in charcoal concentration and decrease in arboreal pollen following Layer B implies the occurrence of wildfires induced by the hurricane. This is comparable to the results in Liu et al. (2008), which recorded three hurricane-induced fire linkages in coastal Alabama. Geological changes caused by Hurricane Isaac (September 2012) are found in the upper 3 cm of the core. This storm produced extensive fluvial flooding to the area as shown by LOI and XRF. These findings from Hurricane Isaac may provide a modern analog for interpreting the impacts of prehistoric hurricanes in sediment stratigraphic studies from this coastal region.

Phosphorus (P) is an essential nutrient for life and excess P in aquatic systems can trigger algal blooms. Nutrient-rich Mississippi River water is diverted into the Lake Pontchartrain estuary (LPE) periodically through the Bonnet Carré Spillway (BCS) to avoid downstream flooding to the city of New Orleans, Louisiana and can significantly increase the internal P load in the sediment. A sequential P fractionation procedure was performed on sediments collected before the opening and after the closing of the 2011 BCS operation to understand the role of these large river diversions on P dynamics. Before the 2011 BCS opening, 10,368 Mt of P were found in the 0-10 cm sediment interval of the LPE. After the closure of the spillway, 13,293 Mt of P were measured in the 0-10 cm sediment interval. Total P significantly increased by 28% and a mass loading of 2,925 Mt of P was a consequence of the 42 days BCS opening. Sediment grain size analyzes revealed that majority of the finer sand and silt fractions were deposited near the BCS entrance, while the lighter clay fraction were transported tens of km towards the center of the LPE. Calculating the time for all newly added P from the 2011 BCS operation to flux out of the water column is important to understanding the impact on water quality of the LPE. Using a previously determined linear flux rate of ~517 Mt yr-1, it was estimated that ~6 years are needed to flux out the newly added sediment TP. While assuming a nonlinear model of flux rate, it is suggested that it would take a longer period of time to flux out all the newly P loaded from the sediments in the LPE. If the operations of these BCS opening are closely spaced in time (< 6 years), there will be an increase of P in the sediments which could lead to changes in the trophic status of the LPE. This increase of TP in sediments can lead to an increase in the frequency and persistence of harmful algal blooms for many years after the spillway opening.

The remnants of the wetland reclamation era of the early 1900s are visible in the leveed, drained, and failed impoundments across the United States, and especially in coastal regions. The common themes of their history are flooding, restoration, and sometimes - community resilience. The physical changes occurring during and after impoundment, and after failure includes subsidence, erosion, and flooding are well-documented. Here I construct an environmental history that integrates data on these physical changes with archival records, historical documents, site visits and personal interviews. The primary region of focus is Delta Farms - a failed agricultural impoundment in Lafourche Parish, Louisiana that was first farmed in 1909 and failed in 1971. It consisted of 4 agricultural units: one that was never drained, one that was drained but not farmed, and two that were farmed for different periods. Some of the physical data includes soil and water depth measurements in the flooded portions of the property. These physical measurements were combined to assemble an environmental history of the property that integrated the experience of individuals and community. The growth and declines in population, recreational activities, agricultural practices, occasional levee failures, and mineral recovery on the property can be related to sociopolitical decisions that shifted during its 61 year history. The accuracy and completeness of this re-creation of the Delta Farms environmental history was greatly enhanced by including residents as a source of observation. They gave insight into the rate of natural marsh recovery, the timelines of developmental activity, and of community resilience. The study was a great example of how to understand a community, the social dynamics driving environmental changes, and community reactions.

Thesis (Ph. D.)--University of Washington. / Bibliography: l. [132]-138.

Thesis (M.S. in Meteorology and Oceanography)--Naval Postgraduate School, March 1988. / Thesis Advisor(s): Smith, D.C. "March 1988." Includes bibliographical references (p. 37-38). Also available online.

Thesis (M.A.)--University of Wisconsin, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 186-202).

Tesis - Universidad Autonoma de Baja California. / Bibliography: leaves 80-82.