Table of Contents

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

Data were collected on several single-day cruises on small privateers out of the Virginia Institute of Marine Science, Gloucester Point, VA

Stations on each date were visually selected to cover a wide range of chlorophyll-a concentrations, including sites with no clear presence of a bloom.  At each site, a YSI EXO2 datasonde was used to collect vertical profiles of water temperature, salinity, chlorophyll-a, and turbidity.  On the first cruise (8/19/21), readings were recorded sub-surface (0.1 m) and then in 1 m increments to the bottom.  On the second date (8/26/21), the YSI logged continuous vertical profiles.  On the three dates in 2022, we again targeted discrete depths including 0.1, 0.5, 1, and 1.5 m, and then in 1 m increments to the bottom, although actual depths varied.  Data from 8/26/21 were bin-averaged into the increments from 2022 for ease of comparison (averaging all profile values within 0.1 m of the target depths).  Vertical profiles of irradiance were measured with LI-COR surface (LI-190SA) and underwater (LI-192SA) quantum sensors; the LI-COR datalogger (LI-1400) was programmed to record the ratio of irradiance at depth to that at the surface.  Depth increments varied among cruises but generally included a measurement just beneath the surface, and then measurements in 0.1-0.25 m increments down to 1-2 m depth.  

Values were used to compute the vertical attenuation coefficient using Beer’s Law.  Sub-surface (~ 10 cm) water samples were collected in triplicate at each station and returned to the lab where they were filtered through 0.7 um glass fiber filters which were frozen prior to analysis following Arar and Collins (1997, EPA Method 445.0).  Samples were extracted in the dark for 24 h in 8 ml of a 45:45:10 dimethyl sulfoxide : acetone: distilled water solution with 1% diethylamine (Shoaf and Lium 1976, Limnol Oceanogr 21: 926−928), and read on a 10 AU Turner Designs fluorometer before and after acidification to compute uncorrected chlorophyll-a, active chlorophyll-a, and phaeophytin.

To facilitate comparisons with profiles collected at discrete depths, continuous vertical profile data from 8/26/21 were bin-averaged into the increments from 2022 by averaging all profile values within 0.1 m of the target depths.  Vertical attenuation coefficient was computed from irradiance data using Beer’s Law.  Concentrations of uncorrected chlorophyll-a, active chlorophyll-a, and phaeophytin were computed using the equations in Arar and Collins (1997, EPA Method 445.0); values represent the mean and standard error of triplicate values.  Extracted pigment data and attenuation coefficients are included in the dataset at the shallowest depth for each date and station.

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.