Table of Contents

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

The columns used for this experiment had a length of 10 cm and a diameter of 1 cm. The sands used were carbonate sands with the grain size diameter ranges 1) 125 to 250 um and 2) 250-500 um. Prior to the experiments, the sands were cleaned through repeated washing in NaCl solution (salinity 35). For testing particle separation within these sands, seawater with a natural phytoplankton community dominated by green algae (5-10 um cell diameter) and cyanobacteria (1-5 nm cell diameter) were pumped through the sand. Computer-controlled syringe pumps pushed the seawater with the algae through the columns at a pore front velocity of 20 cm per hour. The eluent of the 2 columns were collected in a rotating sampler at 15 minute intervals. A total of 36 fractions was collected for each of the sand column for a flushing period of 9 h. The resulting samples were analyzed in a Cytoflex flow cytometer with gating adjusted to capture the green algae and cyanobacteria. Data collected include the area under the forward scatter peak, which provides information on cell size side scatter data, which are related to cell granularity. Calibration of the instrument used calibration beads with particle size ranging from 0.29 to 16.8 um. Explanations regarding flow cytometer analysis of phytoplankton samples as performed here are presented in Trask et al. (1982), best practices in Gallot et al. (2025), and details on the more recent instrumentation in Ugawa et. al 2024.

Cells penetrating through the sand columns were identified by analyzing forward (FSC) and sideward scatter (SSC) signals. The signals are used to gate and identify different cell populations. By combining information from the two scatter signals, particles can be distinguished based on their size and granularity. 

NSF Award Abstract:
This project will study the role of sandy sediments in the carbon cycle. Sandy sediments cover about one-third of the continental shelf but are not well studied. Like a sand filter, marine sands separate and trap dissolved and particulate materials as seawater moves through. These processes influence organic matter cycling in sediments. Because smaller particles travel more easily through the pore space than larger ones, they move deeper into the seabed. This causes a separation of particulate matter by size. Likewise, changes in oxygen and dissolved chemicals with depth alter the surface properties of the sediment grains. Molecules with different properties are separated based on these surface characteristics. The fates of organic carbon, dissolved nutrients and pollutants in the coastal ocean are linked to uptake by sediments, physical and microbial processes within sediments, and release. Thus, it is important to understand the processes that control the transport and accumulation of materials in the seabed. This project will study the separation of particulate and dissolved organic matter transported through marine sands. It will provide information critical for understanding the cycling of carbon and nutrients at the seafloor. Graduate and undergraduate students working on this project will receive training in marine sediment functions and state-of-the-art methods that can help solve pressing environmental issues.

The main objectives of this research are to: 1) demonstrate and quantify the chromatographic separation of organic matter in shelf sediments through the analysis of sediment cores from silicate and carbonate sand beds, 2) characterize and quantify the separation process of dissolved and particulate organic matter and identify key factors controlling this separation in the sands, and 3) quantify the influence of organic matter chromatographic separation on sedimentary oxygen consumption and dissolved inorganic carbon production in these sands. The researchers will test the hypothesis that chromatographic separation of particles and solutes takes place in both sand types but differs with respect to the substances affected and the effectiveness of the separation. Intra-grain permeability of biogenic sands can enhance separation in carbonate sands through exclusion chromatography effects. The separation process is expected to enhance decomposition activities through the concentration of degradable materials in specific sediment layers. The research objectives will be addressed with a combination of field and laboratory studies that include tracer experiments and the analysis of dissolved and particulate organic matter distribution in sand sediment cores sampled in the field. Oxygen consumption and dissolved inorganic carbon production will be measured to reveal the relevance of this process for the sedimentary degradation process. The demonstration of chromatographic separation of particles and solutes in marine sands will close a gap in our understanding of the chemical processes that govern the fate of organic matter, nutrients, and pollutants. This project will provide research training opportunities for graduate and undergraduate students. Results from this study will help improve models of the global cycles of elements that can be used for predicting global environmental change.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.