Investigating the Spring Bloom in San Francisco Bay: Links between Water Chemistry, Metal Cycling, Mercury Speciation, and Phytoplankton Community Composition

Investigating the spring bloom in San Francisco Bay: Links between water chemistry, metal cycling, mercury speciation, and phytoplankton community composition This dissertation addresses the relationship between two problems facing estuaries nationwide: nutrient enrichment and metal contamination. The focus is on the southern reach of San Francisco Bay, where high nutrient concentrations can control the magnitude of the predictably occurring spring phytoplankton bloom. The bloom in this study, in spring 2003, was one of the largest blooms on record, exceeding 150 μg L -1 of chlorophyll α. As the bloom grew, diatoms (e.g. Thalassiosira punctigera ) depleted dissolved nutrients from the water column, including the silicate required for their frustules. Along with nutrients, the bloom depleted dissolved Mn, Ni, Pb, and methyl mercury (MeHg). That depletion was statistically significant when the water chemistry data were reduced into three factors by principal component analysis, and the effect of those factors on trace metal concentrations was examined. Algal uptake of trace metals could entrain those metals within the estuary and affect their bioavailability to higher trophic levels through bloom dilution. Consistent with bloom dilution, we calculated that McHg concentrations in phytoplankton decreased when the bloom peaked. However, that decrease was a transient event, caused by depletion of McHg from the water column. Concentrations of McHg and other dissolved metals returned to pre-bloom values, and even exceeded those values, as phytoplankton decayed. The decomposition of phytoplankton presumably caused suboxic conditions in surficial sediments and led to release of trace metals from historically contaminated sediments. Because sediments contain large reservoirs of metals, the most important impact of the recently observed increase in algal biomass in the estuary could be release of metals from sediments during algal decomposition. As the diatoms decayed following nutrient depletion, small phytoplankton (e.g., Synechocystis sp. ) increased. Statistical analyses (multidimensional scaling) found significant spatial and temporal differences in phytoplankton communities. Those community patterns were linked to water temperature and dissolved ammonium concentrations, demonstrating the myriad effects of nutrient enrichment in this system. However, algal community composition was not related to dissolved metal concentrations. This research shows that nutrient enrichment affects the magnitude of the bloom and thereby alters metal cycling, but the relationship is unidirectional because metals do not shape algal community composition

Role of Phytoplankton in Mercury Cycling in the San Francisco Bay Estuary

To study the role of phytoplankton in mercury cycling, we measured methylmercury (MeHg) and total mercury (HgT) in surface waters during the spring 2003 phytoplankton bloom in San Francisco Bay. Conditions that described the peak of the bloom, the amount of sorbent, and decay of the bloom were summarized by principal component analysis (PCA). Multivariate analyses conducted with the PCA factors demonstrated that the bloom accounted for a significant (p = 0.03) decrease in dissolved (-1 and was unaffected when chlorophyll a concentrations nearly tripled, indicating that bloom dilution could occur as a result of a limited amount of MeHg. The calculated algal MeHg concentration was 3-10 pmol g-1 (dry weight). As the bloom decayed, dissolved MeHg concentrations significantly (p = 0.04) increased, likely due to MeHg remineralization from decaying phytoplankton and/or production in sediments. By creating suboxic conditions in surface sediments and stimulating microbial activity, decomposing phytoplankton could bolster MeHg production, a potential side effect of large blooms. Unlike dissolved MeHg, dissolved HgT concentrations were not measurably altered by the bloom or decay factors. That difference corroborated previous culture studies in which phytoplankton actively accumulated MeHg, but not HgT. As the bloom decayed, HgT Kd values significantly (p = 0.012) increased, possibly because particles (i.e., phytoplankton) with low HgT concentrations were lost from the water column. Based on the relationship between HgT particulate concentrations and percent phytoplankton, the calculated algal HgT concentration was ~0.5 nmol g-1 (dry weight)

Contrasting Biogeochemistry of Six Trace Metals during the Rise and Decay of a Spring Phytoplankton Bloom in San Francisco Bay

The spring 2003 phytoplankton bloom in South San Francisco Bay (South Bay) affected the cycling of Mn, Co, Zn, Ni, and Pb, but not Cu. We followed this diatom bloom for 2 months, capturing a peak in chlorophyll a (Chl a) of \u3e150 µg L-1 and then an increase in dissolved organic carbon of \u3e400 µmol L-1 as phytoplankton decomposed. To determine how the stages of the bloom affected metal concentrations, we used principal component analysis to reduce our 15 water chemistry variables into a bloom factor, a sorbent factor, and a decay factor. Increasing values of the bloom factor, which was a composite of dissolved oxygen, Chl a, and other variables, significantly accounted for reductions in dissolved Mn, Ni, and Pb. We attributed those declines to microbial oxidation, phytoplankton uptake, and sorption onto phytoplankton, respectively. In contrast, dissolved Cu concentrations were not explained by either the bloom or decay factors, consistent with previous studies showing its strong organic complexation and limited bioavailability in South Bay. The decay factor significantly accounted for increases in dissolved Mn, Co, Zn, and Pb. Decomposing bloom material presumably caused suboxic conditions in surface sediments, resulting in release of metals to overlying waters during reductive dissolution of Mn and Fe (hydr)oxides. These alterations in metal cycling during a nutrient-enriched bloom were evidence of eutrophication. Annually, phytoplankton productivity has the potential to affect metal retention in the estuary; in 2003, 75% of Ni discharged into lower South Bay by wastewater treatment plants was cycled through phytoplankton

Decline in Methylmercury in Museum-Preserved Bivalves from San Francisco Bay, California

There are ongoing efforts to manage mercury and nutrient pollution in San Francisco Bay (California, USA), but historical data on biological responses are limited. We used bivalves preserved in formalin or ethanol from museum collections to investigate long-term trends in methylmercury (MeHg) concentrations and carbon and nitrogen isotopic signatures. In the southern reach of the estuary, South Bay, MeHg in the Asian date mussel (Musculista senhousia) significantly declined over the study duration (1970 to 2012). Mean MeHg concentrations were highest (218 ng/g dry weight, dw) in 1975 and declined 3.8-fold (to 57 ng/g dw) by 2012. This decrease corresponded with closure of the New Almaden Mercury Mines and was consistent with previously observed declines in sediment core mercury concentrations. In contrast, across all sites, MeHg in the overbite clam (Potamocorbula amurensis) increased 1.3-fold from 64 ng/g dw before 2000 to 81 ng/g dw during the 2000s and was higher than in M. senhousia. Pearson correlation coefficients of the association between MeHg and δ13C or δ15N provided no evidence that food web alterations explained changing MeHg concentrations. However, isotopic composition shifted temporally. South Bay bivalve δ15N increased from 12‰ in the 1970s to 18‰ in 2012. This increase corresponded with increasing nitrogen loadings from wastewater treatment plants until the late 1980s and increasing phytoplankton biomass from the 1990s to 2012. Similarly, a 3‰ decline in δ13C from 2002 to 2012 may represent greater utilization of planktonic food sources. In a complimentary 90 day laboratory study to validate use of these preserved specimens, preservation had only minor effects (\u3c 0.5‰) on δ13C and δ15N. MeHg increased following preservation but then stabilized. These are the first documented long-term trends in biota MeHg and stable isotopes in this heavily impacted estuary and support the utility of preserved specimens to infer contaminant and biogeochemical trends

Connected Hearing Devices and Audiologists: The User-Centered Development of Digital Service Innovations

Today, medical technology manufacturers enter the service market through the development of digital service innovations. In the field of audiology, these developments increasingly shift the service capacities from audiologists to manufacturers and technical systems. However, the technology-driven developments of manufacturers lack acceptance of hearing device users and undermine the important role of audiologists within the service provision. By following a user-centered design approach in order to deal with the technological and social challenges of disruptive services, we aim to develop service innovations on an integrated service platform in the field of tele-audiology. To ensure the acceptance of technology-driven service innovations among hearing device users and audiologists, we systematically integrated these actors in a participatory innovation process. With qualitative and quantitative data we identified several requirements and preferences for different service innovations in the field of tele-audiology. According to the preferences of the different actors, we proposed a service platform approach based on a connected hearing device in three pillars of application: 1) one-to-one (1:1) service innovations based on a remote fitting concept directly improve the availability of services offered by audiologists without being physically present. Based on this, 2) one-to-many (1:N) service innovations allow the use of the connected hearing device as an indirect data source for training a machine learning algorithm that empowers users through the automation of service processes. A centralized server system collects the data and performs the training of this algorithm. As a future outlook, we show potentials to use the connected hearing device for 3) cross-industry (N:M) service innovations in contexts outside the healthcare domain and give practical implications for the market launch of successful service innovations in the field of tele-audiology

SARS-CoV-2 particles promote airway epithelial differentiation and ciliation

Introduction: The Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), which caused the coronavirus disease 2019 (COVID-19) pandemic, enters the human body via the epithelial cells of the airway tract. To trap and eject pathogens, the airway epithelium is composed of ciliated and secretory cells that produce mucus which is expelled through a process called mucociliary clearance.Methods: This study examines the early stages of contact between SARS-CoV-2 particles and the respiratory epithelium, utilizing 3D airway tri-culture models exposed to ultraviolet light-irradiated virus particles. These cultures are composed of human endothelial cells and human tracheal mesenchymal cells in a fibrin hydrogel matrix covered by mucociliated human tracheal epithelial cells.Results: We found that SARS-CoV-2 particles trigger a significant increase in ciliation on the epithelial surface instructed through a differentiation of club cells and basal stem cells. The contact with SARS-CoV-2 particles also provoked a loss of cell-cell tight junctions and impaired the barrier integrity. Further immunofluorescence analyses revealed an increase in FOXJ1 expression and PAK1/2 phosphorylation associated with particle-induced ciliation.Discussion: An understanding of epithelial responses to virus particles may be instrumental to prevent or treat respiratory infectious diseases such as COVID-19

Factors Affecting Methylmercury Accumulation in the Food Chain

The common scientific wisdom is that dissolved organic debris (from rotting dead plant material, for example) reduces the biological activity, and hence toxicity, of heavy metals such as mercury. Prior to the start of this project, however, a study showed that organic debris could also sometimes enhance build up of the toxic form of mercury in phytoplankton. This toxic form is called methylmercury (MeHg). It is produced in the aquatic environment by sulfur-reducing bacteria and biomagnifies through aquatic food chains

Factors Affecting Methylmercury Accumulation in the Food Chain

The common scientific wisdom is that dissolved organic debris (from rotting dead plant material, for example) reduces the biological activity, and hence toxicity, of heavy metals such as mercury. Prior to the start of this project, however, a study showed that organic debris could also sometimes enhance build up of the toxic form of mercury in phytoplankton. This toxic form is called methylmercury (MeHg). It is produced in the aquatic environment by sulfur-reducing bacteria and biomagnifies through aquatic food chains

Factors Affecting Methylmercury Accumulation in the Food Chain

The common scientific wisdom is that dissolved organic debris (from rotting dead plant material, for example) reduces the biological activity, and hence toxicity, of heavy metals such as mercury. Prior to the start of this project, however, a study showed that organic debris could also sometimes enhance build up of the toxic form of mercury in phytoplankton. This toxic form is called methylmercury (MeHg). It is produced in the aquatic environment by sulfur-reducing bacteria and biomagnifies through aquatic food chains