Posts Tagged 'methods'

Accurate determination of total alkalinity in estuarine waters for acidification studies

Highlights
• This work studies the best way to determine alkalinity in estuarine waters.

• The usefulness of some available stability constants of the CO2 system were tested.

• A mixing of two existing sets of stability constants gave the optimum results.

• Non-linear least square regression was the best approach to determine alkalinity.

Abstract
One of the effects of the atmospheric CO2 increase is the ocean acidification. Over the past 20 years, accurate measurements of the seawater carbonate system have become a high priority because this is the main system controlling seawater acidity. However, this phenomenon has not been widely studied in estuaries, even if they are among the most productive natural habitats in the world, lodging some of the highest biotic diversity and production. Due to that lack of information, this work aims to develop and discuss new strategies for the determination of total alkalinity (TA), one of the most measured parameters in the study of acidification, in estuarine waters in the wide range of salinities that can be found in these systems. For that purpose, a new set of stability constants for the carbonate system was established and compared with those most widely used up to date. For the determination of TA, different approaches were studied for the data treatment of the potentiometric titration data.

Continue reading ‘Accurate determination of total alkalinity in estuarine waters for acidification studies’

Detecting the calcium carbonate saturation state under the stress of ocean acidification using saturometry technique

CO2-induced ocean acidification lowers the degree of carbonate saturation state of the seawater, which affects calcification of marine organisms and influences the marine carbonate cycle, thus have negative impacts on the entire marine biogeochemical system. This study seeks to develop a rapid technique to detect carbonate saturation state of seawater based on conductivity changes. A series of batch and flow-through experiments were conducted using various CaCO3 materials. Results show that the conductivity ratios of seawater with and without carbonate addition increase generally with decreasing carbonate saturation states (Ω). The relationship between conductivity ratio and log10Ω apparently follows a linear trend when Ω < 1. It suggests that conductivity measurements can be used to indicate carbonate saturation state of seawater. It is expected to be deployed on CTD instrument to produce depth profiles of seawater carbonate saturation state and will be of great help to future studies on ocean acidification.

Continue reading ‘Detecting the calcium carbonate saturation state under the stress of ocean acidification using saturometry technique’

Smart pH sensor using untreated platinum sheet based on chronopotentiometry and long-term stability analysis

In this study, we design a smart pH sensor using untreated platinum sheet based on chronopotentiometry. This novel pH sensor is very suitable for applications in the deep sea, highly polluted water, and other harsh environments where maintenance is difficult. In order to verify the long-term monitoring stability of the pH sensor, 17-day monitoring experiments are conducted in river water. We draw some conclusions for properties of the pH sensor. Firstly, the pH values obtained from the positive current agreed well with the pH glass electrode, indicating that it is suitable for pH monitoring. Moreover, the deviation derived from hysteresis is small. Secondly, the pH values obtained from the negative current could not reflect actual pH of river water in long-term measurement. There may be two reasons for this: the changing conductivity in the river water and the unstable composition of the platinum sheet. Thirdly, the conductivity may has an obvious impact on the potential obtained from the negative current; the electrochemical reaction where Pt is oxidized to PtO may be influenced by the ionic strength of the solution. Therefore, the pH values obtained from the positive current is more suitable for long-term pH monitoring.

Continue reading ‘Smart pH sensor using untreated platinum sheet based on chronopotentiometry and long-term stability analysis’

A low-cost long-term model of coastal observatories of global change

The identification and quantification of global change, including climate change, requires long time series of key variables. In this work, the fundamentals and operation of low-cost long-term coastal observatories are described, and preliminary data are shown. The vision is to offer a scientific platform of physicochemical data for at least the next 100 years, what requires establishing sustainable strategies, training human resources, strong institutional support, and long-term funding sources. The network formally operates since 2013 and has generated more than 6 million data points, continuously growing, of which >1.5 million data points are permanently stored and available through a public access web platform. The strategies and methodologies are described and, in the Mazatlan observatory, data recovery and basic statistics of eight environmental variables are presented. During 2015, an extreme El Niño year, marine temperatures increased from the bay to the middle Urias coastal lagoon, were higher than atmospheric temperatures, and showed the impact of a thermal power plant. In surface waters of Mazatlan bay, hypoxic periods were also observed. It is expected that results will foster the development of other projects, and will be useful to the scientific community and decision makers, for a better management of coastal ecosystems worldwide.

Continue reading ‘A low-cost long-term model of coastal observatories of global change’

Automated spectrophotometric determination of carbonate ion concentration in seawater using a portable syringe pump based analyzer

Highlights
• First fully automated determination of carbonate ion concentration in seawater

• A flow batch analyzer with laboratory-made hardware and software

• 13-day real-time underway determination of carbonate ion in the South China Sea

• High resolution field seawater analysis with rare maintenance

Abstract
Observations of seawater carbonate ion concentrations are critical to assess the ecological effects of ocean acidification. Nevertheless, currently available methods are labor intensive or too complex for field applications. Here, we report the design and performance of the first fully automated portable carbonate ion analyzer. Measurements are based on reaction of carbonate and chloride ions with Pb(II) followed by quantitative UV spectrophotometric detection of the PbCO30 complex. The core hardware is a syringe pump equipped with a multi-position valve that is controlled by software written in LabVIEW. Measurement precision is 1.1% (n = 13) with a measurement frequency of 12 h−1. The analyzer was used to continuously monitor carbonate ion concentration variations in a 2500 L coral reef tank for five days (test 1), and used for shipboard underway and vertical profile analysis during a 13-day cruise (test 2). The analyzer attained a combined standard uncertainty of 3.0%, which meets the Global Ocean Acidification Observing Network’s “weather level” goal. Through use of a syringe pump mechanism for mixing seawater and reagent solution, the analyzer is robust, functionally flexible, and quite suitable for continuous environmental monitoring under harsh conditions.

Continue reading ‘Automated spectrophotometric determination of carbonate ion concentration in seawater using a portable syringe pump based analyzer’

Free Ocean CO2 Enrichment (FOCE) experiments: scientific and technical recommendations for future in situ ocean acidification projects

Highlights

• Recommendations for FOCE systems are proposed based on past experience.
• Field testing the system design is essential; a backup power supply is recommended.
• Replicate treatment enclosures; focus on a core set of common scientific hypotheses.
• Accurately monitor carbonate chemistry; allow sufficient time for CO2 equilibration.
• FOCE can inform conceptual and quantitative models of ecosystem responses to CO2

Abstract

Free Ocean CO2 Enrichment (FOCE) experiments are a relatively recent development in ocean acidification research, designed to address the need for in situ, long-term, community level experiments. FOCE studies have been conducted across different marine benthic habitats and regions, from Antarctica to the tropics. Based on this previous research we have formed some core operating principles that will aid those embarking on future FOCE experiments. FOCE studies have potential to provide important insight into the effects of ocean acidification that can add to or refine conclusions drawn from laboratory or single species studies because they are conducted in situ on intact assemblages. Scaling up from sub-organismal and individual effects to also include indirect impacts on the ecosystem and ecosystem services, make FOCE experiments essential in filling in current knowledge gaps in our understanding of ocean acidification. While FOCE systems are complex, relatively costly, and somewhat difficult to operate, the challenges they pose are tractable and they have proven to be a useful approach in ocean acidification research. The aim of this paper is to draw from the experiences of past FOCE experiments and provide practical advice for designing, building and operating a FOCE experiment. Some of the most important recommendations include: field testing the system design; having a backup power supply; using replicate treatment enclosures; monitoring and maintaining the chemistry appropriately; allowing sufficient time to achieve near CO2 equilibrium conditions; and having a scientific focus with a core set of hypotheses. Future FOCE experiments could focus on longer durations, multiple factors, and testing more intact benthic marine communities and ecosystems. We hope this paper will encourage further FOCE deployments and experiments, as well as provide some guidelines to improve future FOCE studies and advance ocean acidification research.

Continue reading ‘Free Ocean CO2 Enrichment (FOCE) experiments: scientific and technical recommendations for future in situ ocean acidification projects’

Ocean acidification in the Baltic Sea: involved processes, metrology of pH in brackish waters, and calcification under fluctuating conditions

The oceanic uptake of anthropogenic CO2 emissions counteracts global warming, but comes at the cost of Ocean Acidification, which is a threat to many marine organisms. In the Baltic Sea, the acidification process and its impact could so far not be quantified due to a lack of appropriate pH measurement techniques and the large pH variability. Looking back, in the first focus of this study acidification scenarios are derived from a detailed analysis of past alkalinity trends in the Baltic Sea water, which are put into context of the atmospheric CO2 forcing. In the second focus, the scientific basis for meaningful pH measurements in brackish waters is formed. Therefore, pH buffer solutions are characterized as primary standards and used to calibrate high-quality spectrophotometric pH measurements. In the last focus, pH fluctuations in benthic ecosystems are quantified. The importance of periods with high pH, during which organisms can maintain calcification rates even under acidified conditions, are highlighted.

Continue reading ‘Ocean acidification in the Baltic Sea: involved processes, metrology of pH in brackish waters, and calcification under fluctuating conditions’


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