Recipient Organization
STATE UNIV OF NEW YORK
(N/A)
SYRACUSE,NY 13210
Performing Department
Chemistry
Non Technical Summary
Nearly half of terrestrial organic carbon export worldwide is lost through evasion from inland waters [Cole et al., 2007], and lakes and reservoirs contribute 10-15% of the total anthropogenic carbon dioxide and methane emissions to the atmosphere [Cole et al., 1994, St.Loids et al., 2000]. The exchange of C02 between freshwater bodies and the atmosphere can also be an appreciable component of ecosystem carbon budgets. Several processes are expected to affect carbon dioxide fluxes from lakes and the surrounding landscape, including phototrophic and heterotrophic processes in the water colunm, vertical mixing by wind and buoyancy, and physical and chemical processes that determine the efficiency of exchange (the piston velocity, k) at the air-water interface. However, quantifying the dependence of gas exchange on these factors remains a challenge, and almost invariably limnologists have used wind-only based piston velocities to study gas fluxes, though factors such as turbulence and buoyancy in the aquatic mixed layer, waves, and surfactants are believed to be important [ McKenna and McGillis, 2004; Banerjee and Macintyre, 2007]. Accurate representation of processes affecting gas exchange is required to understand the role of inland waters in ecosystem, regional, and global carbon cycles and associated impact of climate change. This necessitates an interdisciplinary approach that incorporates measurements of both physical and biogeochemical processes on the atmospheric and aquatic sides of the air-water interface.Awarded Start Date: 1/1/14Sponsor:Co-Project Director: Scott MillerCollaborating/Partnering Organizations: SUNY Albany
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Nearly half of terrestrial organic carbon export worldwide is lost through evasion from inland waters [Cole et al., 2007], and lakes and reservoirs contribute 10-15% of the total anthropogenic carbon dioxide and methane emissions to the atmosphere [Cole et al., 1994; St.Loids et al., 2000]. The exchange of CO2 between freshwater bodies and the atmosphere can also be an appreciable component of ecosystem carbon budgets. Several processes are expected to affect carbon dioxide fluxes from lakes and the surrounding landscape, including phototrophic and heterotrophic processes in the water colunm, vertical mixing by wind and buoyancy, and physical and chemical processes that determine the efficiency of exchange (the piston velocity, k) at the air-water interface. However, quantifying the dependence of gas exchange on these factors remains a challenge, and almost invariably limnologists have used wind-only based piston velocities to study gas fluxes, though factors such as turbulence and buoyancy in the aquatic mixed layer, waves, and surfactants are believed to be important [ McKenna and McGillis, 2004; Banerjee and Macintyre, 2007]. Accurate representation of processes affecting gas exchange is required to understand the role of inland waters in ecosystem, regional, and global carbon cycles and associated impact of climate change. This necessitates an interdisciplinary approach that incorporates measurements of both physical and biogeochemicalprocesses on the atmospheric and aquatic sides of the air-water interface. We propose a new, interdisciplinaiy collaboration between Dr. Scott Miller at the State University of New York (SUNY) at Albany and Dr. David Kieber at SUNY College of Environmental Science and Forest1y (ESF) to quantify the efflux of carbon dioxide from a wellstudied lake ecosystem at ESF's Cranbeny Lake Biological Station (http://www.esf.edu/clbs,t), the third largest lake in the Adirondack Mountain region. Our collaboration combines expertise in atmospheric physics and meteorology (Miller) and aquatic biogeochemistry (Kieber). Both Pis have established records in their respective fields, including research programs that span from equatorial to polar regions. The proposed intensive field campaign at Cranberry Lake will take place in the summer 2014. During this month-long study, we will make continuous measurements of meteorological conditions, surface waves, lake-atmosphere momentum, heat, water vapor and CO2 flux, and temporal and spatial variability in CO2 concentrations in the water column (Dr. Miller's lab, UAlbany). These measurements will be complemented by water column measurements of surface tension, solar spectral irradiance, chromophoric dissolved organic matter (CDOM) absorbance chlorophyll a ( chl a), pH, and dissolved and particulate organic carbon (DOC and POC, respectively) made by Dr. Kieber's ESF lab group. Carbon dioxide gas exchange coefficients (the key parameter needed for accurate gas flux determinations) determined by Dr. Miller's lab will be correlated to the water colunm parameters measured by Dr. Kieber's lab to evaluate potential relationships and processes warranting further study. In particular, we expectthat surface tension measurements made for the surface microlayer will be quite revealing, as the microlayer has been implicated to affect gas exchange [Frew, 2004] but never parameterized in either a marine or freshwater setting. It is expected that the microlayer organic content will show considerable diurnal and spatial variability and we hypothesize that this will have an important impact on the CO2 gas exchange coefficient.The proposed field study includes significant institutional support in the use of the Cranbeny Lake Biological station, existing platforms (e.g., boats, lab space) and instrumentation, and unpaid faculty effort. This study will enable us to collect preliminary data, and to understand how to effectively combine the expertise of our labs to produce results not possible with either lab independently. Our results will be used to leverage future proposals, expand to larger lakes (e.g., Great Lakes) and longer time spans to capture seasonal variability,and may include oceanic environments. The Pls will engage undergraduate and graduate students in both field and data analysis components of the proposed research effort.
Project Methods
B.1. Air water flux using eddy covarianceDr. Miller's lab has used eddy covariance to measure momentum, sensible and latent heat, and CO2 fluxes over terrestrial ecosystems [Miller et al., 2004], open ocean [Miller et al., 2010], rivers and lakes. They have a 24-foot pontoon boat instrumented for lake-atmosphere fluxes (Fig 1) that will be used for the proposed measurements. The pontoon boat will be set up on Cranberry Lake in a moored configuration, with scientific instrumentation powered by a battery bank (600 amp hours) that is periodically charged by a small generator. The pontoon boat has a custom canopy to shield sensitive electronics from weather, and the measurements can be made continuously. An example air-water fluxes measured above Lake Pleasant, NY (~600 ha, maximum depth ~24 m) using the pontoon boat are shown in Figure 2. Briefly, the wind vector will be measured using a fast-response (20 Hz) ultrasonicanemometer/thermometer and used to calculate wind stress (momentum flux) and sensible heat flux. The height of the flux sensors will be between 1-2 m above the water surface. Atmospheric CO2/H2O concentrations will be measured using a fast-response non-dispersive infrared gas analyzers (IRGA, LiCor LI7200, Licor Inc.). Corrections will be made to the measured CO2 density for in situ temperature and water vapor fluctuations [Webb et al., 1980] and for flux loss due to the damping of CO2 fluctuations in the tubing [Lenschow and Raupach, 1991]. Platform motion effects on the wind vector will be corrected using methods we have developed for ships at sea [Miller et al., 2008].The source area or "flux footprint" represents the upwind surface area that contributes to the tilrbulent flux. Heat loss at night from a lake will result in unstable atmospheric stratification and a smaller footprint than daytime conditions [Stull, 1988]. We will ensure that the flux footprint corresponds predominantly to water (and not terrestrial) surface by mounting flux sensors close to the water surface (1-3 m), orienting the flux package to optimize upwind fetch, and rejecting data when the source area may include non-water surface as will be determined by examination of field data and by use of a footprint model. We may deploy 2 levels of flux instruments to assess any flux divergence or effects of the surrounding land surface during low-wind, nighttime periods. Under such conditions, a nocturnal land breeze circulation may develop, transporting respired CO2 from the landscape to the lake, where it is vented vertically over the wam1er, unstable lake surface [Sun et al., 1998].B.2. Water side CO2 concentrationContinuous measurements of CO2 concentration will be made at the water surface using a shower-head type equilibrator. Lake surface water will be pumped through nozzles and into a closed vessel, and air will be drawn from the vessel headspace to an IRGA (LI820, LiCor Inc.) that will measure pCO2. The measurement will be made at the location of the pontoon boat, such that the air-water pCO2 difference can be calculated. This will allow for calculation of the CO2 exchange coefficient during each flux interval. The vertical profile of pCO2 in the water column will also be measured continuously using a second showerhead equilibrator. For this system, the water intake will be cycled through different depths to obtain pCO2 profiles. An example of profiles collected on Lake Pleasant, NY is shown in Figure 3. We will measure horizontal and vertical variability in pCO2 and temperature within the study lake. Periodic surveys of horizontal and vertical distribution of CO2 and water temperature will assist in identifying source regions for the observed variability of CO2 and water temperature in the continuous measurements. A portable equilibrator system designed in Dr. Miller's lab will be used to measure the variability in the surface water pCO2 within the lake. This roving pCO2 system will be deployed from a small boat.B.3. In-lake carbon chemistryIn addition to the above measurements for water pCO2, water samples will be collected from a small boat, and will include the surface microlayer and multiple depths below the surface to resolve water column chemical properties. Samples will be collected and analyzed for CDOM absorbance, DOC, POC, chl a, and pH using standard techniques (e.g., DOC and POC by high temperature combustion; chl a by acetone extraction and fluorescence detection). Particular focus will be placed on sampling the surface microlayer several times throughout the day and evening because we expect that microlayer variability will be one of the main drivers controlling C02 gas fluxes. To sample the microlayer, we will use a glass plate, which will sample the lake surface microlayer at a thickness of approximately a 100 μm [Cunliffe et al., 2013]; this sampling method will provide enough sample to measure several parameters including surface tension, DOC, POC, chl a and CDOM absorbance spectra. The surface tension will be measured using a dual capillary bubble tensiometer (Schramm and Green, 1992; SensaDyne model QC6000). Surface tension measurements will be an indicator of the presence organic surfactantsand will allow us to assess the influence of organic matter on interfacial properties of the lake. In addition to the glass plate we will also collect surface "thinner" microlayer samples employing both a polycarbonate and Teflon filter to collect a small volume of sample over a surface thickness of 5-50 μm [Cunliffe et al., 2013]. We will use these techniques to sample over a smaller thickness to determine if this has a substantial influence over measured surface tensions relative to the glass plate approach. Since solar radiation will affect several parameters that we will measure, we will also quantify in water irradiances three times a day at several wavelengths using calibrated Biospherical GUV51 l radiometer. This instrument has five filters, each with a nominal l O nm bandwidth in the UV, with center band wavelengths of 304, 320, 340, 380 and 395 nm; the sixth filter is used to determine the integrated PAR ( 400-700 nm). Spectral irradiance measurements from 290 to 600 nm will be made eve1y 15 min at the water surface with a calibrated Optronics spectroradiometer. Absorbance spectra of CDOM will be detennined using an Agilent Technologies diode array spectrophotometer with a 5 cm quartz flow cell [Helms et al., 2008]. All laboratory analyses will be done in the lab space provided by the Biological Station.