Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : [26]-29).

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Coastal lagoon systems are complex and dynamic environments that respond rapidly to the changes of fluvial, marine, climatic and anthropogenic influences. The purpose of this research was to investigate the morphology and dynamics of the New River Lagoon before and after the implementation of engineering outlet management using a methodological framework to analyse active process environments. This information was then used to determine the functional effectiveness of engineering management at reducing the risk of flooding and erosion to the local community and imposing minimal impacts on the environmental integrity of the lagoon system. This investigation used a multidisciplinary approach to investigate the morphology and dynamics of the New River Lagoon in relation to active process environments. Outlet dynamics, lagoon channel structure and adjacent shoreline stability were assessed over a decadal timescale prior to engineering management by analysing temporal aerial photographs. Following engineering management, the hydrology of the lagoon was investigated, along with the relationship between morphological changes to the artificial lagoon outlet and changes in lagoon hydrology, local wave climate and local precipitation levels. Water depth, conductivity and temperature records were used to explain lagoon hydrology and Global Navigation Satellite Surveying (GNSS) and weekly oblique photographs were used to explain and document changes in outlet morphology. Wave and rainfall data were used to explain the balances between marine and fluvial environments and their affects on outlet dynamics. Significant changes in lagoon morphology and dynamics were observed at the New River Lagoon between pre- and post-management periods, with the former considered more stable in terms of outlet migration patterns and hydrodynamics. The lagoon outlet prior to engineering management showed morphological characteristics similar to hapua-type systems, migrating along the coastline and forming shore-parallel outlet channels in response to the dominance of a strong longshore drift of sediment. Current outlet dynamics are restricted by artificial outlet management and typically cycle intermittently between open/closed phases in response to variable levels of rainfall and marine sediment supply; characteristics similar to Intermittently Open/Closed Lagoons (ICOLs) found in areas of Australia and South Africa. Hydrologically, the lagoon is considered to be located on a continuum between hapua and estuaries during pre- and post-management periods due to intermittent tidal influences. However, artificial outlet management has significantly increased the frequency and duration of tidal exchange, which now classifies the New River lagoon closer to an estuarine environment. The artificial lagoon outlet and associated breakwater were effective at flushing high flows of water during the study period. However, the outlet was prone to blockage and migration; two morphological states capable of causing flooding. Currently, the greatest risks to flooding at the lagoon are flash floods, following dry periods where marine sediment has established a solid barrier across the outlet, during which water levels are already elevated. Increases in tidal influences, lower lagoon water levels and an increase in lagoon salinity are a direct result of engineering management intervention. An increase in freshwater flushing through the lagoon outlet and deepened of the outlet channel to below sea level, allows for pronounced tidal influences during outlet opening. Restriction of the lagoon outlet from forming a natural migration outlet channel in the direction of littoral drift has meant the outlet is most often oriented perpendicular to the sea, as appose to at an angle away from the direction of incoming waves and currents, further increasing tidal influences. In order to make sustainable management decisions, future management of the lagoon system must weight-up the effects of a high energy coastline to the integrity of the engineering structure, the impact of the structure on the lagoons environmental integrity and the outlets ability to become unstable and cause a flood risk. The findings of this research have improved the understanding of the New River Lagoon system, and its response to engineering management intervention, while adding to the understanding of river-mouth lagoon systems both nationally and internationally.

Worldwide, estuaries are under increasing pressure from numerous contaminants. There is a need to develop reliable bioassay methodologies to assess the effects of these stressors on estuary health. This thesis aimed to develop and validate toxicity tests in a New Zealand marine harpacticoid copepod species for use in monitoring and evaluating the effects of estuarine pollution. A survey and toxicological assessment of a range of native copepod species resulted in the selection of Quinquelaophonte sp. as the ideal bioassay species. This selection was based on a broad regional distribution, ease of culture and high reproductive rate in the laboratory, sexual dimorphism, and sensitivity to contaminants. To validate the bioassay, spiked sediments were used to expose Quinquelaophonte sp. to three reference compounds representing important categories of estuarine chemical stressors: zinc (a metal), atrazine (a pesticide), and phenanthrene (a polyaromatic hydrocarbon). A method for spiking sediments that Quinquelaophonte sp. inhabit was developed to ensure even contaminant distribution in sediments. Two sediment bioassays using lethal and sublethal endpoints were validated, one acute (96 h) and one chronic (14 d). These assays incorporated both lethal and sublethal endpoints, which included reproductive output and mobility. Acute-to-chronic ratios were calculated for use in environmental risk assessment and to provide insight into the mode of action of the reference contaminants. The chronic sediment bioassay was used to assess sediment quality in three estuaries across New Zealand: Napier, Christchurch and Invercargill. This validated the bioassay for use with naturally-contaminated field sediments with varying mixtures of pollutants and sediment types (coarse sandy to fine silty organic rich sediments). Quinquelaophonte sp. was also tested to assess whether it can be used to characterise multi–generation impacts. After four generations of exposure to zinc, there were changes in acute sensitivity, indicating this species possesses mechanisms for acclimating or adapting to toxic stressors. Sediment bioassays in Quinquelaophonte sp. were successfully developed and validated, offering significant promise as a tool for monitoring effects of pollution in New Zealand estuaries.

Rising atmospheric carbon dioxide (CO2) concentrations are increasing the rate at which anthropogenic CO2 is accumulating in the ocean, and thereby acidifying ocean water. However, accumulation of anthropogenic CO2 is not the only process affecting coastal oceans. Anthropogenic inputs of nutrients to coastal waters can result in massive algal blooms, a process known as eutrophication. Microbial consumption of this organic matter depletes bottom waters of oxygen and increases acidity through the release of CO2. This study assesses the synergistic effect of ocean acidification and eutrophication in the coastal ocean using data from six cruises to the northern Gulf of Mexico. In addition, this study investigates the effect of the 2011 Mississippi River flood on coastal pH and aragonite saturation states. Data from a model simulation using data collected from the northern Gulf of Mexico indicates that eutrophication is contributing to acidification of subsurface waters and plays a larger role than acidification from atmospheric CO2 uptake. Furthermore, results from the model simulation show that the decrease in pH since the industrial era is 0.04 units greater than expected from ocean acidification and eutrophication combined. The additional decrease was attributed to the reduced buffering capacity of the region and may be related to the uptake of atmospheric CO2 into O2-depleted and CO2-enriched waters, the addition of atmospheric CO2 into O2-rich and CO2-poor waters, the input of CO2 via respiration into waters in equilibrium with high atmospheric CO2, or a combination of all three processes.

Graduation date: 1987

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