Archive for estuary

The curious role of organic alkalinity in seawater carbonate chemistry

Posted by mmaheigan 
· Wednesday, August 5th, 2020 

The marine chemistry community has measured organic alkalinity in coastal and estuarine waters for over two decades. While the common perception is that any unaccounted alkalinity should enhance seawater buffer capacity, the effects of organic alkalinity on this buffering capacity, and hence the potential CO2 uptake by coastal and estuarine systems are still not well quantified.

In a thought experiment recently published in Aquatic Geochemistry, the author added organic alkalinity to model seawater (salinity=35, temperature=15˚C, pCO2=400 µatm) in the form of 1) organic acid (HOA) and 2) its conjugate base (OA–). Results suggest that the weaker organic acid/conjugate base pair (pKa ~8.2-8.3) yields the greatest buffering capacity under the simulation conditions. However, the HOA addition first displaces dissolved inorganic carbon (DIC) and causes CO2 degassing; the resultant seawater buffer capacity can be greater or less than the original seawater, depending on the pKa. In comparison, OA– addition leads to CO2 uptake and elevated seawater buffer capacity. As the organic anions are remineralized via biogeochemical processes, a “charge transfer” results in quantitative conversion to carbonate alkalinity (CA), which is overpowered by the concomitant CO2 production (∆DIC>∆CA). Overall, the complete process (organic alkalinity addition and remineralization) results in a net CO2 release from seawater, regardless of whether it is added in the form of HOA or OA–.

Figure caption: A schematic illustration of the role of organic alkalinity on seawater carbonate chemistry in an open system (constant CO2 partial pressure). Organic acid (HOA) addition leads to CO2 degassing and varying seawater buffer (greater or lower than the original seawater) as a function of Ka. Organic base (OA–) addition causes initial CO2 uptake and overall elevated seawater buffer. Regardless, upon complete remineralization, more CO2 is produced than the amount of net gain in carbonate alkalinity (OA– addition only). Therefore, the complete process (organic acid/base addition and its ultimate remineralization) should result in net CO2 degassing.

While the presence of organic alkalinity may increase seawater buffer capacity to some extent (depending on the pKa values of the organic acid), CO2 degassing from the seawater, because of both the initial organic acid addition and eventual remineralization of organic molecules, should be the net result. However, modern alkalinity analysis precludes the bases of stronger organic acids (pKa < 4.5). This fraction of “potential” alkalinity, especially from river waters, remains a relevant topic for future alkalinity cycle studies. The potential alkalinity can be converted to bicarbonate through biogeochemical reactions (or charge transfer at face value), although it is unclear how significant this potential alkalinity is in rivers that flow into the ocean.

 

A backstory
The author used an example of vinegar and limewater (calcium hydroxide solution), which is employed by many aquarists to dose alkalinity and calcium in hard coral saltwater tanks, to demonstrate the conversion of organic base (acetate ion) to bicarbonate and CO2 via complete remineralization. It is also known the added vinegar helps microbes to remove excess nitrate. This procedure had been in the author’s memory for the past nine years, ever since his previous research life when he participated in a study at a coral farm in a suburb of Columbus, Ohio. A strong vinegar odor would arise every now and then at the facility. However, a recent communication with the facility owner suggests that this memory was totally false and the owner simply used vinegar to get rid of lime (CaCO3) buildup in the water pumps. Nonetheless, the chemistry in this paper should still hold, with that false memory serving as the inspiration.

 

Author:
Xinping Hu (Texas A&M University-Corpus Christi)

Impacts of atmospheric nitrogen deposition and coastal nitrogen fluxes on oxygen concentrations in Chesapeake Bay

Posted by mmaheigan 
· Tuesday, April 30th, 2019 

How do atmospheric and oceanic nutrients impact oxygen concentrations in the Chesapeake Bay? Generally, researchers focus on how terrestrial nutrients impact hypoxia. The relative importance of river, atmosphere, and ocean inputs have not been quantified, largely because estimates of nitrogen fluxes from the atmosphere and ocean are limited.

A recent study in Journal of Geophysical Research: Oceans quantified the relative impacts of atmospheric and oceanic nitrogen inputs on dissolved oxygen (DO) in the Chesapeake Bay. The authors combined a 3-D biogeochemical model and estimates of atmospheric deposition from the Community Multiscale Air Quality model and interpolations of nitrogen concentrations along the continental shelf from the Ocean Acidification Data Stewardship Project. Atmospheric nitrogen deposition and coastal nitrogen fluxes most impact Chesapeake Bay DO concentrations during the summer when surface waters are depleted in nitrogen. Overall, atmospheric nitrogen deposition has about the same gram-for-gram impact on Chesapeake Bay DO as riverine loading. Although all three nutrient sources vary spatially and temporally, in the central bay, where summer hypoxia is most prevalent, coastal nitrogen fluxes and atmospheric nitrogen fluxes have roughly the same impact on bottom oxygen as a ~10% change in riverine nitrogen loading (Figure 1).

Figure caption: (Left) Four-year (2002–2005) average increase in DO in the summer by removing the atmospheric nitrogen deposition (AtmN), reducing the riverine loading (ΔRiverN) by ~10% (roughly equivalent to turning off the atmospheric deposition), and removing the nitrogen fluxes from the continental shelf (CoastalN). (Right) Relative impacts of the three nitrogen modification scenarios on summertime bottom DO.

These results indicate that two often-neglected sources of nitrogen—direct atmospheric deposition and fluxes of nitrogen from the continental shelf—substantially impact Chesapeake Bay DO, especially in the summer. Future study is needed to investigate the long-term trend of these relative impacts by continued coordination between modeling and observational work, such as applying higher-resolution atmospheric deposition products and integrating more in situ data along the model ocean boundary when they are available. These efforts will improve our understanding of the impacts of different nutrient sources on biogeochemical cycles in coastal water bodies.

 

Authors:
Fei Da (VIMS, College of William & Mary)
Marjorie A. M. Friedrichs (VIMS, College of William & Mary)
Pierre St-Laurent (VIMS, College of William & Mary)

Biological and physical controls on estuarine nitrous oxide emissions

Posted by mmaheigan 
· Tuesday, February 5th, 2019 

Nitrous oxide (N2O) is a potent greenhouse gas with rising atmospheric concentrations. Atmospheric emissions of N2O are predicted to increase with continued anthropogenic perturbation of the nitrogen cycle, yet the magnitude of these emissions is uncertain, particularly in coastal systems where N2O fluxes are poorly constrained. How do N2O emissions from a eutrophic estuary vary in space and time?

Figure 1: Depth profiles of nitrous oxide (N2O) (circles), salinity (dashed line), and dissolved oxygen (solid line) in the Chesapeake Bay at three stations. Solid circles indicate oversaturation of N2O with respect to equilibrium with the atmosphere, and open circles indicate undersaturation.

In a recent publication in Estuaries and Coasts, Laperriere et al. (2018) examined how physical and biological processes influence the distribution of N2O in Chesapeake Bay using dissolved gas measurements (N2O and N2/Ar) and stable isotope tracer incubations. During stratified summer conditions, the mesohaline region of the Chesapeake Bay was always a source of N2O to the atmosphere. The highest N2O concentrations occurred in the pycnocline at the interface between reducing bottom waters and oxygenated surface waters (Figure 1). Vertical mixing of surface waters across the pycnocline caused elevated rates of ammonia oxidation, a biological source of N2O, and resulted in the accumulation of nitrite (NO2–) below the pycnocline. During periods of weak mixing, ammonia oxidation rates and N2O concentrations were lower, and low dissolved oxygen concentrations below the pycnocline set the stage for N2O consumption via denitrification (Figure 1). The interplay between biological and physical processes controlling fluctuations in N2O concentration was examined using a mass balance approach. Mass balance estimates indicated that both biological processes and physical transport contribute to local changes in N2O concentration. The authors suggest that the fate of N2O during stratified summer conditions is governed by vertical mixing across the pycnocline, controlling whether N2O is released to the atmosphere or consumed at depth.

 

Authors:
Sarah M. Laperriere (University of California, Santa Barbara)
Nicholas J. Nidzieko (University of California, Santa Barbara)
Rebecca J. Fox (Washington College)
Alexander W. Fisher (University of California, Santa Barbara)
Alyson E. Santoro (University of California, Santa Barbara)

Filter by Keyword

abundance acidification africa air-sea interactions algae alkalinity allometry ammonium AMOC anoxic Antarctic anthro impacts anthropogenic carbon aquaculture aquatic continuum aragonite saturation arctic Argo argon arsenic artificial seawater Atlantic atmospheric CO2 atmospheric nitrogen deposition authigenic carbonates autonomous platforms bacteria bathypelagic BATS BCG Argo benthic bgc argo bio-go-ship bio-optical bioavailability biogeochemical cycles biogeochemical models biogeochemistry Biological Essential Ocean Variables biological pump biophysics bloom blue carbon bottom water boundary layer buffer capacity C14 CaCO3 calcification calcite carbon carbon-climate feedback carbon-sulfur coupling carbon budget carbon cycle carbon dioxide carbon export carbon sequestration carbon storage Caribbean CCA CCS changing marine ecosystems changing marine environments changing ocean chemistry chemical oceanographic data chemical speciation chemoautotroph chesapeake bay chl a chlorophyll circulation climate change climate variability CO2 coastal darkening coastal ocean cobalt Coccolithophores commercial community composition conservation cooling effect copepod coral reefs CTD currents cyclone daily cycles data data access data assimilation data management data product Data standards DCM dead zone decadal trends decomposers decomposition deep convection deep ocean deep sea coral deoxygenation depth diatoms DIC diel migration diffusion dimethylsulfide dinoflagellate discrete measurements DOC DOM domoic acid dust DVM ecology ecosystem management ecosystems eddy Education Ekman transport emissions ENSO enzyme equatorial regions ESM estuarine and coastal carbon fluxes estuary euphotic zone eutrophication evolution export export fluxes export production EXPORTS extreme events faecal pellets fecal pellets filter feeders filtration rates fire fish Fish carbon fisheries fishing floats fluid dynamics fluorescence food webs forage fish forams freshening freshwater frontal zone functional role future oceans geochemistry geoengineering geologic time GEOTRACES glaciers gliders global carbon budget global ocean global warming go-ship grazing greenhouse gas Greenland ground truthing groundwater Gulf of Maine Gulf of Mexico Gulf Stream gyre harmful algal bloom high latitude human food human impact human well-being hurricane hydrogen hydrothermal hypoxia ice age ice cores ice cover industrial onset inland waters in situ inverse circulation ions iron iron fertilization isotopes jellies katabatic winds kelvin waves krill kuroshio lab vs field land-ocean continuum larvaceans lateral transport LGM lidar ligands light light attenuation lipids machine learning mangroves marine carbon cycle marine heatwave marine particles marine snowfall marshes Mediterranean meltwater mesopelagic mesoscale metagenome metals methane methods microbes microlayer microorganisms microscale microzooplankton midwater mixed layer mixed layers mixing mixotrophy model modeling model validation mode water molecular diffusion MPT multi-decade n2o NAAMES NASA NCP nearshore net community production net primary productivity new ocean state new technology Niskin bottle nitrate nitrogen nitrogen cycle nitrogen fixation nitrous oxide north atlantic north pacific nuclear war nutricline nutrient budget nutrient cycling nutrient limitation nutrients OA ocean-atmosphere ocean acidification ocean acidification data ocean carbon uptake and storage ocean color ocean modeling ocean observatories ocean warming ODZ oligotrophic omics OMZ open ocean optics organic particles oscillation overturning circulation oxygen pacific paleoceanography parameter optimization particle flux partnerships pCO2 PDO peat pelagic PETM pH phenology phosphorus photosynthesis physical processes physiology phytoplankton PIC piezophilic piezotolerant plankton POC polar regions policy pollutants precipitation predation prediction pressure primary productivity Prochlorococcus prokaryotes proteins pteropods pycnocline radioisotopes remineralization remote sensing repeat hydrography residence time resource management respiration resuspension rivers rocky shore Rossby waves Ross Sea ROV salinity salt marsh satellite scale seafloor seagrass sea ice sea level rise seasonal patterns seasonal trends sea spray seawater collection seaweed secchi sediments sensors shelf ocean shelf system shells ship-based observations shorelines silicate silicon cycle sinking particles size SOCCOM soil carbon southern ocean south pacific spatial covariations speciation SST state estimation stoichiometry subduction submesoscale subpolar subtropical sulfate surf surface surface ocean Synechococcus technology teleconnections temperate temperature temporal covariations thermocline thermodynamics thermohaline thorium tidal time-series time of emergence titration top predators total alkalinity trace elements trace metals trait-based transfer efficiency transient features Tris trophic transfer tropical turbulence twilight zone upper ocean upper water column upwelling US CLIVAR validation velocity gradient ventilation vertical flux vertical migration vertical transport volcano warming water clarity water mass water quality waves western boundary currents wetlands winter mixing zooplankton

Copyright © 2023 - OCB Project Office, Woods Hole Oceanographic Institution, 266 Woods Hole Rd, MS #25, Woods Hole, MA 02543 USA Phone: 508-289-2838  •  Fax: 508-457-2193  •  Email: ocb_news@us-ocb.org

link to nsflink to noaalink to WHOI

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.