Table of Contents

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

Sediment core data with accompanying environmental measurements from the middle region of the Chesapeake Bay, in seasonally anoxic bottom waters, collected in spring and summer of 2010-2011.

Core samples and sensor-based measurements were made during sixteen research cruises in 2010-2012: two 1-week cruises aboard the UNOLS vessel R/V Hugh R. Sharp, and fourteen 1-day cruises aboard the R/V Terrapin, which is a 25' Parker outboard motorboat with davit for deploying a CTD package.

Sediment cores were collected with an acrylic/PVC Soutar-design box corer to determine sediment-water fluxes.  
The sediment was sub-cored using two 7×30 cm (inner diameter × height) acrylic cylinders to a depth of ~15 cm.  
Sediment and water column blank cores were preincubated in a temperature-controlled walk-in chamber or
incubator at bottom water temperatures (±1 °C) for 6 h for oxic conditions and overnight for anoxic
conditions to allow any initial core disturbance artifacts to dissipate.  Each core was equipped with a
Teflon magnetic stir bar rotating at 20 rpm to mix overlying water without resuspension.  Overlying water was
collected four times during 4-6 hour incubations (oxic) or 24 h incubations (anoxic): gas and solute samples
were collected in triplicate 6 ml Exetainer vials and 20 ml syringes, respectively.  During each subsampling,
 <5 % water volume in each core was replaced with collected bottom water through a second port so that no
bubbles formed within the tubes.  Sediment-water fluxes were calculated using linear regressions of gas or
solute concentrations and the slopes of blank cores were used to account for water column processes.

Because sediment processing proceeded along with water column processing, see

SAMPLE ANALYSES

References:

Lane, L., Rhoades, S., Thomas, C., Van Heukelem, L. 2000. Standard Operating Procedures. Horn Point Laboratory Technical Report No. TA-264-00.

Brewer, P. G. and D. W. Spencer. 1971. Colorimetric Determination of Manganese in Anoxic Waters. Limnology And Oceanography 16:107-110.

Parsons, T. R., Y. Maita, and C. M. Lalli. 1984. A manual of chemical and biological methods for seawater analysis. Pergamon Press, Oxford.

Arar, E. J., Collins, G. B., 1997. In Vitro Determination of chlorophyll a and pheophytin a in marine and freshwater algae by fluorescence. Method 445.0. U.S. Environmental Protection Agency.

DMO notes:

Format or vocabulary adjustments to metadata primarily involved controlling the vocabulary and adding UNOLS names for the cruises. 
Date changed to date_local
Time -> time_local
Cruise -> cruise  [Inserted cruise_new  to give column for UNOLS name]
Lowercase Cast, Depth

Changed modifier from cruise name to cast and called new column cast_new (e.g. LDZ8_NO3 to LDZ8 and Channel_NO3).
Abbreviated Latitude, Longiture, Conductivity, Temperature, Salinity, Fluorescence
Decoded Oxygen1 -> O2_conc and Oxygen2 -> O2_rate

In keeping with BCO-DMO best practices, ISODateTime has been added as a formatted time column. At this time it is local time.

Every summer in many estuaries and coastal margins, eutrophication-elevated phytoplankton production drives rapid bacterial respiration creating hypoxic and anoxic bottom waters. These so-called “dead zones” exclude fish, kill benthic organisms, and eliminate habitat. Despite their popular name, anoxic/hypoxic zones are not really dead, but rather are populated with living and very active microbial communities. In fact, bacterial production in anoxic waters can exceed that in overlying oxic waters due, in part, to reduced grazing and increased cell size and abundance. Once oxygen is depleted, microbial respiration undergoes a succession of redox reactions with decreasing energy yield as terminal electron acceptors are depleted (e.g., O2, NO3-, Mn(IV), Fe(III), and SO42-). This combination of high production and reduced growth efficiency creates a condition in which respiration may be very high, making anoxic zones significant sinks for organic matter and key sites for nutrient cycling.

Previous research documented respiratory succession in Chesapeake Bay bottom waters based on redox chemistry measurements. Heterotrophic bacterial production was very high at some stages of this succession, suggesting elevated respiration. Also, the phylogenetic composition of bacterioplankton communities in anoxic waters was similar to oxic surface waters for nearly half the summer, only changing after the appearance of H2S. This suggests that typical aerobic estuarine bacteria are able to shift to anaerobic metabolisms and continue to dominate.

Most of what is known about microbial respiration and community composition in anoxic water comes from studies of permanently anoxic systems like the Black Sea and Cariaco Basin. By comparison, very little is known about what is a much more common and more dynamic marine environment – seasonally anoxic estuarine waters. This proposal describes a 3-year integrated study to advance the quantitative and mechanistic understanding of biogeochemical cycling in one of the largest seasonal estuarine anoxic zones in the USA. It hypothesize that:

• Dominant sub-pycnocline respiratory processes undergo a succession from aerobic respiration to nitrate respiration and metal reduction to sulfate reduction.
• Bacterial growth efficiency decreases with this respiratory succession, but bacterial production remains high, resulting in very high carbon respiration rates.
• Bacterial community composition changes little during respiratory succession until sulfate respiration dominates (i.e., the sulfide threshold), but gene expression closely tracks changes in redox conditions in order to support the most energetic respiratory processes.

These hypotheses will be addressed by quantifying carbon respiration rates using several techniques including delta CO2; quantifying bacterial production, biomass and growth efficiency; and characterizing succession in the composition and respiratory gene expression patterns of microbial communities in water column and sediments during each stage of respiratory succession. This project will integrate biogeochemical, biological, and genomic data to explain how biogeochemistry influences, and is influenced by, microbial respiration, production, diversity, and gene expression.

The proposed research will provide (1) reliable measurements of production and respiration in anoxic/hypoxic waters, (2) techniques applicable to other ecosystems, and (3) ecological insight for predicting future changes with ongoing restoration efforts in anoxia-impacted estuaries. These measurements will be useful for calibrating biogeochemical models and for estimating carbon budgets. This research will train two graduate students and one postdoctoral scientist in several state-of-the-art geochemical and molecular biology techniques. Applications will be submitted to the NSF Research Experiences for Teachers program to engage two teachers to work on this project and to participate in the seven-week Environmental Science Education Partnership (ESEP) Teacher Research Fellowship Program (www.esep.umces.edu) at UMCES Horn Point Laboratory. New discoveries will be incorporated into graduate-level courses entitled Aquatic Microbial Ecology, Biological Oceanography, and Environmental Geochemistry. Nucleic acid sequences will be deposited in online repositories including GenBank.