Loose fitting powered air purifying respirators (PAPRs) utilize a motorized fan to draw air throu... more Loose fitting powered air purifying respirators (PAPRs) utilize a motorized fan to draw air through the respirator's air purifying elements, delivering clean air to the wearer through a face piece that does not form an airtight seal with the wearer's face. Potential for wearer exposure to contaminants may exist if the breathing rate of the wearer exceeds the airflow rate supplied by the PAPR fan. In such an instance, ambient air could bypass the filters and enter the mask, potentially exposing the wearer to contamination. This investigation assessed the extent to which over breathing occurred in the Centurion MAX loose fitting PAPR. Sixteen subjects exercised at 80-85% max 2 O V & on a treadmill while wearing the PAPR inside a Portable Breathing Chamber (PBC). All subjects inhaled more air than was supplied by the PAPR blower, and 17% of the breathing volumes exceeded the 1.4 L dead volume of the PAPR face piece.
Phytoplankton in high-light, low-nutrient ocean environments are challenged with maintaining high... more Phytoplankton in high-light, low-nutrient ocean environments are challenged with maintaining high photosynthetic efficiency and simultaneously preventing photodamage that results from low levels of electron acceptors downstream of photosystem II (PSII). Here, we identify a process in open ocean picophytoplankton that preserves PSII activity by diverting electrons from the photosystem I (PSI) complex-mediated carbon assimilation to oxygen via a propyl gallate-sensitive
We quantified groundwater discharge and associated nutrient fluxes to Monterey Bay, California, d... more We quantified groundwater discharge and associated nutrient fluxes to Monterey Bay, California, during the wet and dry seasons using excess (224)Ra as a tracer. Bioassay incubation experiments were conducted to document the response of bloom-forming phytoplankton to submarine groundwater discharge (SGD) input. Our data indicate that the high nutrient content (nitrate and silica) in groundwater can stimulate the growth of bloom-forming phytoplankton. The elevated concentrations of nitrate in groundwater around Monterey Bay are consistent with agriculture, landfill, and rural housing, which are the primary land-uses in the area surrounding the study site. These findings indicate that SGD acts as a continual source of nutrients that can feed bloom-forming phytoplankton at our study site, constituting a nonpoint source of anthropogenic nutrients to Monterey Bay.
ABSTRACT Mitigating further anthropogenic changes to the global climate will require reducing gre... more ABSTRACT Mitigating further anthropogenic changes to the global climate will require reducing greenhouse-gas emissions (“abatement”), or else removing carbon dioxide from the atmosphere and/or diminishing solar input (“climate engineering”). Here, we develop and apply criteria to measure technical, economic, ecological, institutional, and ethical dimensions of, and public acceptance for, climate engineering strategies; provide a relative rating for each dimension; and offer a new interdisciplinary framework for comparing abatement and climate engineering options. While abatement remains the most desirable policy, certain climate engineering strategies, including forest and soil management for carbon sequestration, merit broad-scale application. Other proposed strategies, such as biochar production and geological carbon capture and storage, are rated somewhat lower, but deserve further research and development. Iron fertilization of the oceans and solar radiation management, although cost-effective, received the lowest ratings on most criteria. We conclude that although abatement should remain the central climate-change response, some low-risk, cost-effective climate engineering approaches should be applied as complements. The framework presented here aims to guide and prioritize further research and analysis,leading to improvements in climate engineering strategies.
In this study, we develop a mechanistic understanding of how temperature affects growth and photo... more In this study, we develop a mechanistic understanding of how temperature affects growth and photosynthesis in 10 geographically and physiologically diverse strains of Synechococcus spp. We found that Synechococcus spp. are able to regulate photochemistry over a range of temperatures by using state transitions and altering the abundance of photosynthetic proteins. These strategies minimize photosystem II (PSII) photodamage by keeping the photosynthetic electron transport chain (ETC), and hence PSII reaction centers, more oxidized. At temperatures that approach the optimal growth temperature of each strain when cellular demand for reduced nicotinamide adenine dinucleotide phosphate (NADPH) is greatest, the phycobilisome (PBS) antenna associates with PSII, increasing the flux of electrons into the ETC. By contrast, under low temperature, when slow growth lowers the demand for NADPH and linear ETC declines, the PBS associates with photosystem I. This favors oxidation of PSII and potenti...
This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in nor... more This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in northeastern Monterey Bay (the Red Tide Incubator region) of coastal California, with particular emphasis on how bacteria and phytoplankton that form harmful algal blooms mediate and respond to changes in P availability. In situ measurements of nutrient concentrations, phytoplankton community composition, and cell-specific alkaline phosphatase (AP) activity (determined via enzyme-labeled fluorescence assay) were measured during three cruises. Upwelling led to a 10-fold increase in dissolved inorganic (DIP) in surface waters, reaching ∼0.5 μmol L(-1). This DIP was drawn down rapidly as upwelling relaxed over a period of 1 week. Ratios of nitrate to DIP drawdown (∼5:1, calculated as the change in nitrate divided by the change in DIP) were lower than the Redfield ratio of 16:1, suggesting that luxury P uptake was occurring as phytoplankton bloomed. Dissolved organic (DOP) remained relatively c...
Coastal California is a dynamic upwelling region where nitrogen (N) and iron (Fe) can both limit ... more Coastal California is a dynamic upwelling region where nitrogen (N) and iron (Fe) can both limit productivity and influence biogeochemistry over different spatial and temporal scales. With global change, the flux of nitrate from upwelling is expected to increase over the next century, potentially driving additional oceanic regions toward Fe limitation. In this study we explored the effect of changes in Fe/N ratio on native phytoplankton from five currently Fe-replete sites near the major California upwelling centers at Bodega Bay and Monterey Bay using nutrient addition incubation experiments. Despite the high nitrate levels (13-30 μ M) in the upwelled water, phytoplankton at three of the five sites showed increased growth when 10 μ M nitrate was added. None of the sites showed enhanced growth following addition of 10 nM Fe. Nitrate additions favored slow sinking single-celled diatoms over faster sinking chain-forming diatoms, suggesting that future increases in nitrate flux could affect carbon and silicate export and alter grazer populations. In particular, solitary cells of Cylindrotheca were more abundant than the toxin-producing genus Pseudonitzschia following nitrate addition. These responses suggest the biogeochemistry of coastal California could change in response to future increases in nitrate, and multiple stressors like ocean acidification and hypoxia may further result in ecosystem shifts.
Abstract Atmospheric dust deposition is an important source of nutrients and trace metals to the ... more Abstract Atmospheric dust deposition is an important source of nutrients and trace metals to the ocean. It likely enhances ocean productivity and carbon sequestration, thus influencing atmospheric carbon dioxide concentrations and climate. We used well-characterized aerosol samples in incubation experiments to examine the effect of aerosol on phytoplankton growth and species distribution. Not all dust stimulates growth. The response of phytoplankton to aerosol additions depends on specific aerosol chemistry. Moreover, ...
Abstract In oligotrophic seas where inorganic nitrogen (N) and phosphorus (P) are below the limit... more Abstract In oligotrophic seas where inorganic nitrogen (N) and phosphorus (P) are below the limits of detection, organic forms of these nutrients may constitute greater than 90% of the total N and P in the euphotic zone. The combined enzymatic activity of phytoplankton and heterotrophic bacteria determines the rate of nutrient remineralization, thereby influencing phytoplankton growth rates and carbon sequestration in these regions. In this study we investigated the effects of fertilization with ammonium (NH4), nitrate (NO3), nitrite (NO2), ...
Abstract Rising partial pressures of CO2 in the atmosphere since the Industrial Revolution have c... more Abstract Rising partial pressures of CO2 in the atmosphere since the Industrial Revolution have caused a drop in ocean pH of 0.1 units. Ocean acidification is generally anticipated to result in a decrease in calcification by coccolithophores and other calcifying marine organisms. Coccolithophores are especially important in carbon cycling and ocean-atmosphere CO2 exchange since they not only fix organic carbon, but also calcify using inorganic carbon, resulting in the release of CO2 and the precipitation and transfer to the ...
Loose fitting powered air purifying respirators (PAPRs) utilize a motorized fan to draw air throu... more Loose fitting powered air purifying respirators (PAPRs) utilize a motorized fan to draw air through the respirator's air purifying elements, delivering clean air to the wearer through a face piece that does not form an airtight seal with the wearer's face. Potential for wearer exposure to contaminants may exist if the breathing rate of the wearer exceeds the airflow rate supplied by the PAPR fan. In such an instance, ambient air could bypass the filters and enter the mask, potentially exposing the wearer to contamination. This investigation assessed the extent to which over breathing occurred in the Centurion MAX loose fitting PAPR. Sixteen subjects exercised at 80-85% max 2 O V & on a treadmill while wearing the PAPR inside a Portable Breathing Chamber (PBC). All subjects inhaled more air than was supplied by the PAPR blower, and 17% of the breathing volumes exceeded the 1.4 L dead volume of the PAPR face piece.
Phytoplankton in high-light, low-nutrient ocean environments are challenged with maintaining high... more Phytoplankton in high-light, low-nutrient ocean environments are challenged with maintaining high photosynthetic efficiency and simultaneously preventing photodamage that results from low levels of electron acceptors downstream of photosystem II (PSII). Here, we identify a process in open ocean picophytoplankton that preserves PSII activity by diverting electrons from the photosystem I (PSI) complex-mediated carbon assimilation to oxygen via a propyl gallate-sensitive
We quantified groundwater discharge and associated nutrient fluxes to Monterey Bay, California, d... more We quantified groundwater discharge and associated nutrient fluxes to Monterey Bay, California, during the wet and dry seasons using excess (224)Ra as a tracer. Bioassay incubation experiments were conducted to document the response of bloom-forming phytoplankton to submarine groundwater discharge (SGD) input. Our data indicate that the high nutrient content (nitrate and silica) in groundwater can stimulate the growth of bloom-forming phytoplankton. The elevated concentrations of nitrate in groundwater around Monterey Bay are consistent with agriculture, landfill, and rural housing, which are the primary land-uses in the area surrounding the study site. These findings indicate that SGD acts as a continual source of nutrients that can feed bloom-forming phytoplankton at our study site, constituting a nonpoint source of anthropogenic nutrients to Monterey Bay.
ABSTRACT Mitigating further anthropogenic changes to the global climate will require reducing gre... more ABSTRACT Mitigating further anthropogenic changes to the global climate will require reducing greenhouse-gas emissions (“abatement”), or else removing carbon dioxide from the atmosphere and/or diminishing solar input (“climate engineering”). Here, we develop and apply criteria to measure technical, economic, ecological, institutional, and ethical dimensions of, and public acceptance for, climate engineering strategies; provide a relative rating for each dimension; and offer a new interdisciplinary framework for comparing abatement and climate engineering options. While abatement remains the most desirable policy, certain climate engineering strategies, including forest and soil management for carbon sequestration, merit broad-scale application. Other proposed strategies, such as biochar production and geological carbon capture and storage, are rated somewhat lower, but deserve further research and development. Iron fertilization of the oceans and solar radiation management, although cost-effective, received the lowest ratings on most criteria. We conclude that although abatement should remain the central climate-change response, some low-risk, cost-effective climate engineering approaches should be applied as complements. The framework presented here aims to guide and prioritize further research and analysis,leading to improvements in climate engineering strategies.
In this study, we develop a mechanistic understanding of how temperature affects growth and photo... more In this study, we develop a mechanistic understanding of how temperature affects growth and photosynthesis in 10 geographically and physiologically diverse strains of Synechococcus spp. We found that Synechococcus spp. are able to regulate photochemistry over a range of temperatures by using state transitions and altering the abundance of photosynthetic proteins. These strategies minimize photosystem II (PSII) photodamage by keeping the photosynthetic electron transport chain (ETC), and hence PSII reaction centers, more oxidized. At temperatures that approach the optimal growth temperature of each strain when cellular demand for reduced nicotinamide adenine dinucleotide phosphate (NADPH) is greatest, the phycobilisome (PBS) antenna associates with PSII, increasing the flux of electrons into the ETC. By contrast, under low temperature, when slow growth lowers the demand for NADPH and linear ETC declines, the PBS associates with photosystem I. This favors oxidation of PSII and potenti...
This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in nor... more This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in northeastern Monterey Bay (the Red Tide Incubator region) of coastal California, with particular emphasis on how bacteria and phytoplankton that form harmful algal blooms mediate and respond to changes in P availability. In situ measurements of nutrient concentrations, phytoplankton community composition, and cell-specific alkaline phosphatase (AP) activity (determined via enzyme-labeled fluorescence assay) were measured during three cruises. Upwelling led to a 10-fold increase in dissolved inorganic (DIP) in surface waters, reaching ∼0.5 μmol L(-1). This DIP was drawn down rapidly as upwelling relaxed over a period of 1 week. Ratios of nitrate to DIP drawdown (∼5:1, calculated as the change in nitrate divided by the change in DIP) were lower than the Redfield ratio of 16:1, suggesting that luxury P uptake was occurring as phytoplankton bloomed. Dissolved organic (DOP) remained relatively c...
Coastal California is a dynamic upwelling region where nitrogen (N) and iron (Fe) can both limit ... more Coastal California is a dynamic upwelling region where nitrogen (N) and iron (Fe) can both limit productivity and influence biogeochemistry over different spatial and temporal scales. With global change, the flux of nitrate from upwelling is expected to increase over the next century, potentially driving additional oceanic regions toward Fe limitation. In this study we explored the effect of changes in Fe/N ratio on native phytoplankton from five currently Fe-replete sites near the major California upwelling centers at Bodega Bay and Monterey Bay using nutrient addition incubation experiments. Despite the high nitrate levels (13-30 μ M) in the upwelled water, phytoplankton at three of the five sites showed increased growth when 10 μ M nitrate was added. None of the sites showed enhanced growth following addition of 10 nM Fe. Nitrate additions favored slow sinking single-celled diatoms over faster sinking chain-forming diatoms, suggesting that future increases in nitrate flux could affect carbon and silicate export and alter grazer populations. In particular, solitary cells of Cylindrotheca were more abundant than the toxin-producing genus Pseudonitzschia following nitrate addition. These responses suggest the biogeochemistry of coastal California could change in response to future increases in nitrate, and multiple stressors like ocean acidification and hypoxia may further result in ecosystem shifts.
Abstract Atmospheric dust deposition is an important source of nutrients and trace metals to the ... more Abstract Atmospheric dust deposition is an important source of nutrients and trace metals to the ocean. It likely enhances ocean productivity and carbon sequestration, thus influencing atmospheric carbon dioxide concentrations and climate. We used well-characterized aerosol samples in incubation experiments to examine the effect of aerosol on phytoplankton growth and species distribution. Not all dust stimulates growth. The response of phytoplankton to aerosol additions depends on specific aerosol chemistry. Moreover, ...
Abstract In oligotrophic seas where inorganic nitrogen (N) and phosphorus (P) are below the limit... more Abstract In oligotrophic seas where inorganic nitrogen (N) and phosphorus (P) are below the limits of detection, organic forms of these nutrients may constitute greater than 90% of the total N and P in the euphotic zone. The combined enzymatic activity of phytoplankton and heterotrophic bacteria determines the rate of nutrient remineralization, thereby influencing phytoplankton growth rates and carbon sequestration in these regions. In this study we investigated the effects of fertilization with ammonium (NH4), nitrate (NO3), nitrite (NO2), ...
Abstract Rising partial pressures of CO2 in the atmosphere since the Industrial Revolution have c... more Abstract Rising partial pressures of CO2 in the atmosphere since the Industrial Revolution have caused a drop in ocean pH of 0.1 units. Ocean acidification is generally anticipated to result in a decrease in calcification by coccolithophores and other calcifying marine organisms. Coccolithophores are especially important in carbon cycling and ocean-atmosphere CO2 exchange since they not only fix organic carbon, but also calcify using inorganic carbon, resulting in the release of CO2 and the precipitation and transfer to the ...
Uploads
Papers by Katherine Mackey