I. Macroalgal physiological response to submarine groundwater discharge
My work focuses on macroalgal physiological ecology at sites of Submarine Groundwater Discharge(SGD), springs that deliver fluxes of fresh, nutrient rich groundwater from the subterranean estuary to nearshore reef ecosystems. A prominent feature on Hawaiʻi’s coasts and worldwide on basaltic high islands and shorelines, SGD conditions are tidally driven and create highly dynamic conditions of salinity, temperature, pH, and nutrient availability. At SGD influenced sites macroalgae can be exposed to changes from 0 to 100% open ocean salinity over the tidal cycle, so how do these plants physiologically cope with this and other physical changes associated with SGD influence? This chapter measures integrated response in photosynthesis and tissue water potential(TWP) regulation by four species across a gradient of SGD influence at Wailupe beach, on the south shore of Oʻahu. Two closely related species pairs were examined for comparison, two of Hawaiʻi’s most prominent invasives which are prominent across this and other SGD influenced sites, Gracilaria salicornia and Acanthophora spicifera, and a sister genera to each, Hydropuntia perplexa(which we had hoped was the native limu Manuaea, Gracilaria coronopifolia, but molecularly turned out to be this recently discovered cryptic invasive), and the native Laurencia dendroidea.
II. Characterization of the benthic community on submarine groundwater discharge influenced reefs
This chapter focuses on characterizing the community structure and diversity across three SGD influenced sites in Maunalua Bay: Wailupe beach, Kawaikui beach, and Kahala beach. Previous studies have demonstrated differences in the source and volume of nutrients delivered by SGD at these sites, and this work aims to examine how these and other differences in SGD characteristics might influence the diversity, species assemblages, and macroalgal abundance on SGD influenced reefs.
III. The Chardakov method for determining tissue water potential for macroalgae: a methodology
My final dissertation chapter describes and fine tunes the methodology used to measure tissue water potential(TWP) for the integrated response work. The Chardakov method measures the solute concentration within plant tissues by bathing plant tissues in solutions of known solute concentrations and finding the solution which does not change due to absorption or release of water from the plant part. A simple, cost effective, and efficient method for measuring TWP for macroalgal cells in the field, this method has not been updated and published in recent literature. Here, I take this method into the lab to measure how this method varies across morphologies, and how variables like incubation time, tissue volume, and surface area impact measured TWP.
I. Groundwater Dependent Ecosystems(GDEs) as social ecological systems and their linked cultural, ecological, and economic values in Kona Hawaiʻi
Abstract (article in review): Groundwater dependent ecosystems (GDEs) are increasingly recognized as important conservation targets with linked ecological and social value. However, the social values of GDEs are under-studied, precluding their full inclusion in policy and management decisions. We provide a case study from Kona, Hawaiʻi, where multiple types of GDEs are abundant, to illustrate the diversity of social values of GDEs. To do so, we combine a literature review, archival analysis, and key-informant-interviews with resource managers and lineal descendants connected to three prominent GDEs in Kona. Interviews focused on current and historical uses and values of GDEs, current management challenges and strategies, and desired visions for the future. Interviewees expressed a range of social values associated with GDEs, which we categorize using a Hawaiʻi-based cultural ecosystem service framework focused on social connections, physical and mental health, spirituality, and knowledge. Importantly, the historical value of these systems directly informs current cultural values, and restoration efforts are largely carried out through biocultural approaches, which emphasize the mutually reinforcing restoration of ecology and culture. Interviewees seek to restore ecosystem functions, cultural practice and connection to place, and in some cases, local food production. Achieving this requires addressing threats such as invasive species, land-based sources of pollution, and groundwater pumping, and rests on a continued amplification and revival of Indigenous knowledge and practice. Results provide important lessons for land and water management and policy in Hawaiʻi as well as other islands and coastal areas where GDEs have important linked social and ecological value.
II. Linking algal physiological and community data to groundwater and economic models of future land use and wastewater treatment scenarios
As part of a team of hydrogeologists, economists, and marine biologists we have created a model and decision making support tool for future scenarios showing the effects of land use, groundwater pollution and climate change on groundwater dependent ecosystems. The first part of this project has been published in PLOS one(link) . The next part of this research is ongoing, and will integrate macroalgal growth data into the model to project impacts of these scenarios on nearshore ecosytems, including areas of potential algal blooms and/or areas of coral and fisheries losses.
American Samoa: Linking hydrology, microbes, and macroalgae to human land use and coastal ecosystem health
As part of a Water Resource Research Center and USGS study I was a member of a multi-disciplinary team of hydrogeologists, microbiologists, and phycologists for a series of field expeditions to American Samoa led by PI Dr. Rosie Alegado. I first participated as a trainee under the apprenticeship of Hydrogeologist Dr. Chris Shuler, field ecologist Dr. Dan Amato, and microbiologist Dr. Lydia Baker, and in later expeditions acted as lead field scientist with fellow students, Nalani Olguin, microbiologist, and Eric Welch, hydrogeologist. Here we simultaneously collected hydrogeologic data for measuring submarine groundwater discharge fluxes using radon, water samples for nutrient profiles, algal species surveys, benthic analyses, and macroalgal tissue sampling and deployments for δ15N analyses, used in nitrogen source tracking (fertilizer, sewage, or natural soil level), and microbial samples for DNA analyses used to identify human versus non-human microbial sources. Our initial study linking land use to coastal ecosystems (abstract below) has been published in Hydrology. The microbial and benthic community analyses and write up are currently in progress.
This work provided key training from leaders in my field for the cross-disciplinary hydrology, ecology, and microbiology methods on which I have built the rest of my research. Some of the most rewarding parts of this research were working with and meeting local researchers in American Samoa at the Coral Reef Advisory Group(CRAG), USGS, and Sea grant, and being able to involve local students and colleagues from American Samoa Community College in our field surveys. We were very thankful to have the help in the field from Fa’asalafa Kitona, a Samoan researcher at CRAG, who assisted us by addressing the village matai(village head) in the formal Samoan tongue and to assist us in entering the village community at our study site in a culturally appropriate way, which likely vastly improved the village’s reception of our work.
Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa
Abstract: Anthropogenic nutrient loading is well recognized as a stressor to coastal ecosystem health. However, resource managers are often focused on addressing point source or surface water discharge, whereas the impact of submarine groundwater discharge (SGD) as a nutrient vector is often unappreciated. This study examines connections between land use and nutrient loading through comparison of four watersheds and embayments spanning a gradient of human use impact on Tutuila, a high tropical oceanic island in American Samoa. In each study location, coastal radon-222 measurements, dissolved nutrient concentrations, and nitrogen isotope values (δ15N) in water and in situ macroalgal tissue were used to explore SGD and baseflow derived nutrient impacts, and to determine probable nutrient sources. In addition to sampling in situ macroalgae, pre-treated macroalgal specimens were deployed throughout each embayment to uptake ambient nutrients and provide a standardized assessment of differences between locations. Results show SGD-derived nutrient flux was more significant than baseflow nutrient flux in all watersheds, and δ15N values in water and algae suggested wastewater or manure are likely sources of elevated nutrient levels. While nutrient loading correlated well with expected anthropogenic impact, other factors such as differences in hydrogeology, distribution of development, and wastewater infrastructure also likely play a role in the visibility of impacts in each watershed.