U.S. Forest Service
Date of Award
Master of Environmental Management (MEM)
Environmental Science and Management
The geographic range of mangrove forests is shifting quickly as they expand poleward in response to climate change while simultaneously being removed from their native extent to clear space for anthropogenic land-uses. Mangrove forests are also known to be sinks for anthropogenic contamination. Yet contamination research is under-researched in mangrove ecosystems, specifically the environmental fate, effect on biodiversity, and risk to human populations from contamination in the context of these changing conditions requires further research. The goal of this thesis is to address this data gap through analysis of contamination in the literature and through an investigational survey of mangrove ecosystems in Hawaii.
In chapter one, a review was completed for five classes of contamination in mangrove ecosystems, which was accomplished by summarizing other reviews and literature since those reviews. Four of these classes represent the most studied contaminants in mangrove literature, and include trace heavy metals, persistent organic pollutants, polycyclic aromatic hydrocarbons, and microplastics. The final category, pharmaceuticals and personal care products, is an emerging contaminant of concern that requires greater study in mangroves. This analysis identified several data-gaps that need to be addressed in the future. Pharmaceuticals and personal care products have received the least research despite biological activity at small concentrations. Research is concentrated in Asia and neglected in Africa and the Americas for all contaminant classes. Little discussion is given to whether the greater amount of research seen in Asia and Oceanic countries are due to the higher concentrations of mangroves in those regions of if there are other barriers preventing research. Some studies have noted that cost can be a prohibitive barrier to contaminant work, so efforts could be made to make contamination research more accessible. All contaminants were found to be widely present in mangrove ecosystems. Sources of contamination are correlated with proximity to waste water treatment plants, industry, and urbanized landscapes. Trace heavy metals and polycyclic aromatic hydrocarbons were found frequently at concentrations below the threshold to cause harm to plants, but may bioconcentrate in mangrove fauna. Persistent organic pollutants were found at levels that may cause harm to mangrove biota through long term exposure, and at some sites persistent organic pollutants were found at levels that might cause harm through short term exposure. Microplastics were found at variable levels, with some sites possibly being at concentrations that would cause harm to fauna, but more research is required in order to make that determination. In order to better assess the potential for environmental harm posed by contaminants, future research will need to consider multi-contaminant investigations. This is due to the potential for synergistic effects that different classes of contaminants can have when co-existing in the environment. Monitoring of contamination in mangroves should be increased, particularly given the ecologically or commercially important roles of mangroves, and in locations that have already be identified as hotspots for one or more of the contaminant classes. Finally, public outreach and involvement should be increased.
As mangroves are known to be an environmental sink for contamination where they are native, it is hypothesized that higher concentrations will be found in mangrove colonized coastal areas on Moloka'i, Hawaii where they are not native. In the second chapter this hypothesis was tested by comparing the microplastic and organic contaminant concentrations at coastal sites modified by non-native mangrove stands as well as unmodified coastline on Moloka'i, Hawaii in order to understand how mangrove invasion and land use interact to influence the distribution of contaminants along the coastline. Sediment, porewater, and mangrove plant tissues were investigated. MPs were found in sediment at an average abundance of 7.67 items/kg on the seaward side of mangrove transects, 10.11 items/kg on the landward side, and 8.49 items/kg along unmodified open coastlines. For porewater microplastics were found at an abundance of 10.89 items/L along the seaward side, 63.89 items/L along the landward side, and 9.84 items/L along the open coast transects. No relationship was found between mangrove presence and microplastic concentrations in porewater and sediment. However, a positive relationship was observed between sediment microplastic and percent impervious surface. The most commonly found polymers via microscope Fourier transform infrared spectroscopy (u-FTIR) were polyethylene terephthalate (PET) (31%), polyamide (24%), and polypropylene (13%). Pesticide analyses was completed for sediment, porewater, and mangrove tissues (leaf, root, propagule). Six contaminants were found, the most common of which was the insecticide bifenthrin, which was found in 35 of the 37 sediment samples at an average concentration of 11.3 ng/g, 11 of the 11 root samples at an average concentration of 243.3 ng/g, and one of the five propagule samples at a concentration of 8.60 ng/g. There were two detections of Imidacloprid in porewater that had an average concentration of 37.1 ng/L. p,p' - DDE was detected in roots in two samples at an average concentration of 11.57 ng/g. The other three contaminants detected were p,p'- DDT, trifluralin, and permethrin and all were found at concentrations < 1 ng/g. The high concentrations of bifenthrin found in all of the roots when compared to the much lower concentrations detected in sediment suggests that mangrove roots are strongly accumulating some pesticides. Microplastics were low on Moloka'i when compared to global trends. This may be due to the low population on Moloka'i, or the isolated position of the Hawaiian Islands or of the sheltered location of Moloka'i in the center of the island chain. Future work should be done to determine if Microplastics are similarly low in more populated areas and how localized currents may control the distribution of contaminants along the Hawaiian Islands. The slight association of microplastics to the population center on Moloka'i and the lack of relationship between mangrove presence and plastics suggests that on Moloka'i urbanization is a more important factor for controlling the distribution of coastal microplastics than non-native mangroves. However, the high concentrations of bifenthrin bound to roots when compared to sediment concentrations from all sites suggests that mangrove presence may be playing a role in concentrating some types of pesticides such as pyrethroid insecticides. Further investigations should focus on determining the fate and cycling of root bound pesticides, which will allow for better management decisions around mangroves on Moloka'i.
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Szafranski, Geoffrey, "An Examination of the Current Knowledge of Contaminants in Mangroves: Hawaii and Globally" (2023). Environmental Science and Management Professional Master's Project Reports. 81.