Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Project Information
• Funding

High resolution sampling surveys in the York River estuary (YRE): performed in 2018 during Feb, March, June, August, and October and in 2019 during Feb, April, July, and October at dawn, dusk, and the following dawn along a zig-zag cruise track, covering approximately equal areas of shoal and channel, a total distance of 30 km, using a DataFlow system modified from Madden and Day (1992). All sampling is performed during spring tides, the period following de-stratification in the YRE when the system is well-mixed (Haas 1977). This high resolution sampling plan enables us to capture day-time primary production (dawn to dusk) and night-time respiration (dusk to dawn) while sampling water masses exposed to the same tidal stage. The DataFlow system captures continuous measurements of water quality parameters and allows grab sampling (at five channel and five shoal stations) for DIC and other parameters shown in different spread sheets and used for multiple regression analyses. The pCO₂-DataFlow system is instrumented with a pCO₂ analyzer, a multi-parameter datasonde (YSI 6600V2), Wet Labs CDOM sensor, Garmin global positioning system (GPS MAP 546S), and data acquisition system. The system continuously samples surface water (approximately every 30 m at an average speed of 20 knots) from a stern-mounted water intake located 0.5 m below the water surface with a pump, which delivers water in parallel to (1) a shower-head equilibrator and (2) a flow-through cell attached to the YSI which is configured to measure water temperature, salinity, chl-a fluorescence, DO, pH, and turbidity. pCO₂ in the equilibration chamber is determined by recirculating a carrier gas at a flow of approximately 1.5 L min⁻¹ through the equilibrator chamber and a nondispersive infrared absorbance detection analyzer (LI-COR, LI-840). The mole fraction of CO₂ (xCO₂) is corrected for headspace pressure and temperature to determine surface-water pCO₂ with an attainable accuracy of ±4 µatm over the functional range of 100 to 5,000 ppmv (Crosswell et al. 2012). All measurements are taken at 2-second intervals, and the lag time between DataFlow and LI-COR data is measured and corrected for each sampling run. At the beginning, during, and end of each survey, ambient atmospheric air and two CO₂ gas standards (Praxair Inc.) are measured for calibration and verification of the absorbance detection analyzer.

Calculation of Air-Water CO2 and O2 Fluxes: Data in these spreadsheets are used to calculate CO2, O2 fluxes and metabolic parameters as described below. Air-water CO2 and O2 exchanges are driven by the differences between the gas concentrations in the surface water and the atmosphere (ΔpCO2, ΔpO2) scaled by the gas solubility, and the rate of exchange is set by the gas-transfer velocity (k, cm h-1). Input data include: K0, the solubility coefficient (K0(CO2): Weiss 1974; K0(O2): Benson and Krause 1984); k600 the gas exchange coefficient; ΔpCO2 and ΔpO2 and ScSST is the Schmidt number at ambient sea-surface temperature and salinity (Wanninkhof 1992). The gas solubility and Schmidt numbers for CO2 and O2 are determined based on temperature and salinity. The transfer velocity k is parameterized as a function of wind speed normalized to 10 m above the water surface (u10). We calculate air-water CO2 fluxes using the Jiang et al. (2008) parameterization, which provides a conservative estimate of k and has been widely used in reviews of estuarine CO2 fluxes (Crosswell et al 2014).

Spatial and Diel Interpolation of Dawn-Dusk Data for Calculation of Daily CO2 and O2 Fluxes: Data from each dawn–dusk survey is spatially averaged by calculating distance-weighted means of ΔpCO2 and delta pO2 (difference water and atmospheric concentrations), water temperature, salinity and other parameters within a series of five boxes of the YRE. Data are used to calculate CO2 and O2 fluxes, and metabolic parameters as described below.

Open Water measurements of metabolism (based on diel variations of DO): NEM gross primary production (GPP), and respiration (R) are determined from changes in DO concentrations in Dataflow samples collected at dawn, dusk, and the following dawn using the open water method (Kemp and Boynton 1980). ∆DO (dawn to dusk; dusk to dawn), corrected for air/sea exchanges of O2 are used to calculate NEM, GPP, and R. To scale metabolic measurements to regional estimates, the surface areas and water volumes of the YRE were determined for each spatial element using ArcGIS 10 and bathymetric data. Daily average hourly O2 fluxes (mmol DO m-2 d-1) for each box are multiplied by their respective spatial element areas and scaled to annual O2 fluxes. Daily fluxes for each spatial element are summed to provide seasonal and annual totals (moles O2 per m2 per y).

BCO-DMO Processing:
- formatted date/time to YYYY-MM-DDThh:mm;
- moved the box numbers from a row to a column.

NSF Award Abstract:
Estuaries, coastal water bodies where rivers mix with ocean water, are hotspots for the processing of carbon and nutrients moving from land to the coastal ocean. Within estuaries land-based nutrient inputs can cause intense blooms of single-celled algae called phytoplankton, which can have significant impacts on the ecosystem. As blooms move down-estuary some of the phytoplankton material is buried on the bottom, and some is decomposed, resulting in low oxygen conditions (hypoxia), harmful to marine life, and production of carbon dioxide (CO2), the major greenhouse gas, which can exchange with the atmosphere. The remaining phytoplankton material can be exported to the ocean. The type and amount of carbon exported from the estuary depend both on its biological activity and physical factors such as fresh water discharge, temperature, and light availability. If phytoplankton production is greater than decomposition, the estuary will take up atmospheric CO2 and export phytoplankton carbon to the coastal ocean. On the other hand, if decomposition is greater than production the estuary will be a source of CO2 to the atmosphere and dissolved CO2 to the coastal ocean. The investigators expect that intense phytoplankton blooms will greatly amplify carbon exchanges with the atmosphere, coastal ocean, and bottom sediments. As intense phytoplankton blooms increase in the future due to increased nutrient inputs and temperature, low oxygen events may become more frequent with potential negative impacts on fisheries and increased export of carbon to the coastal ocean and atmosphere. This study will fill critical gaps identified by the Coastal Carbon Synthesis Program in knowledge of how microtidal estuaries transform and export C to the atmosphere, benthos, and coastal ocean. In addition, there will be a strong teaching and training component to this project, with support for graduate and undergraduate students. The graduate student will be partnered with secondary teachers to gain teaching experience and enrich the middle school educational programs. Summer undergraduate interns will be recruited for a summer program from Hampton University, a historically Black college. There will be public outreach through participation in existing programs at VIMS.

Estuaries serve as critical hotspots for the processing of carbon (C) as it transits from land to the coastal ocean. Recent attempts to synthesize what is known about sources and fates of C in estuaries have noted large data gaps; thus, the role of estuaries, especially those that are microtidal, as important sources of carbon dioxide (CO2) to the atmosphere and total organic carbon (TOC) and dissolved inorganic carbon (DIC) to the coastal ocean, or as a C sink in bottom sediments, remains uncertain. Intensive phytoplankton blooms are becoming increasingly frequent in many estuaries and are likely to have important and yet unknown impacts on the C cycle. The trophic status of an estuary will determine in large part the species of C exported to the atmosphere, bottom sediments, and coastal ocean. The overarching objective of this project is to identify the impacts of intense phytoplankton blooms on C speciation, net C fluxes and exchanges in the Lower York River Estuary (LYRE), a representative mesotrophic, microtidal mid-Atlantic estuary. Metabolic processes are hypothesized to be spatially and temporally dynamic, driving the speciation, abundance, and fates of C in the LYRE. High spatiotemporal resolution sampling in the LYRE will capture rates of C cycling under both baseline conditions throughout most of the year, and during periods when the estuary is perturbed by widespread and intense, but patchy, late summer phytoplankton blooms. The short-term effects of physical drivers (wind, temperature, salinity, fresh water discharge, nutrient and organic carbon loads) and biological drivers (metabolic rates, bacterial and phytoplankton abundances and composition) on C transformations, speciation, and exchanges will be assessed. Expected longer term variations in the C cycle due to anthropogenic and natural disturbances will be predicted through use of modeling. In addition, laboratory manipulations will examine the impacts of specific organisms dominating intensive phytoplankton blooms on benthic metabolism, processing of organic C by the microbial community, and C fluxes to the water column.