Spring-neap Variation in Fecal Pellet Properties within Surficial Sediment of

the York River Estuary

Emily WeiVIMS REUProspectus PresentationMentor: Carl Friedrichs

and Lindsey KraatzJune 29, 2011

Why study fecal Why study fecal pellets?pellets?

Fecal pellets and flocs Biological influences• Presence of fecal pellets and flocs changes

seabed surface

Studying erosional processes in the York River estuary

•navigation, engineering, ecology, contaminant spread

Clay Bank: deep physical mixing of seabed

•Spring/neap tidal currents•Stronger currents at spring•stratification

York River estuaryDickhudt (2009)

Fecal pellets and flocs coexist in the Clay Bank region

• Pellets are compact, consolidated sediments processed by benthic organisms

• Range in size from ~40 um to several mm

• Pellets are denser than flocs• As turbulence increases, more/heavier

resilient pellets resuspended• Pellets can “armor” seabed, decrease

erodibility• Flocs are loosely aggregated sediment

• van der Waals • mixing of seawater, particle-clay interactions

• Glued by extracellular polymeric substances (EPS)• Secreted by diatoms and other microorganisms

• Flocs are not as dense as pellets• Flocs have more water content

• With onset of turbulence, flocs suspended, broken apartCartwright et. al, (2010); Drake et. al, (2002)

Kraeuter and Haven (1970)

Fecal Pellets

Erodibility of cohesive sediment based on:• Water content, grain size, recent disturbance, biological activity

Lower water column: Suspended sediment concentrations based on: • tidal currents, availability of easily suspended sediment

Changes in sediment transport driven by changes in freshwater influx, stratification, and strong spring vs. weak neap tides

• Freshwater influx• More sediment transport/ bed

disturbance at Clay Bank• Similar to spring tide

conditions• Less consolidation and higher

erodibility• Low river flow• Less sediment transport/ bed

disturbance at Clay bank• Similar to neap tide conditions• More consolidation and lower

erodibility

Dickhudt et. al, 2009

Erosion processesErosion processes

River flow

There will be a higher fecal pellet concentration at neap tide rather than at spring tide• Expected: More fecal pellets will be resuspended at

spring tide The percentage of smaller-sized pellets (45 um)

will be higher at neap tide• Expected: Smaller pellets are resuspended first, so

smaller pellets will be in resuspension during stronger spring tidal currents

Mud at neap tide will have a higher water content• Expected: There will be more flocs at neap tide than at

spring tide. Flocs have more water content. Mud at neap tide will have lower erodibility

• Expected: There will be less bed disturbance and more time for consolidation at neap tide, so consolidation will increase

Hypotheses/ Expected Hypotheses/ Expected ResultsResults

MethodsMethods Sampling cruises coincide

with spring/neap Gomex box corer

• X-ray analysis• Core logger• Gust microcosm• Sliced at 1 cm intervals

• Water content, sieving Pellet presence/

concentration• Sieve

• aggregated particles• disaggregated particles

• 3 Methodologies compared

Cartwright

Kraatz

Kraatz

Cartwright

Sources CitedSources Cited• Cartwright, G.M., C.T. Friedrichs and L.P. Sanford, 2010. In situ characterization of estuarine

suspended sediment in the presence of muddy flocs and pellets. (submitted for Publication)

• Dickhudt, P.J., C.T. Friedrichs, L.C. Schaffner and L.P. Sanford, 2009. Spatial and temporal variation in cohesive sediment erodibility in the York River estuary, eastern USA: A biologically influenced equilibrium modified by seasonal deposition. Marine Geology, 267, 128-140.

• Friedrichs, C.T., 2009. York River physical oceanography and sediment transport. In: K.A. Moore and W.G. Reay (eds.), A Site Profile of the Chesapeake Bay National Estuarine Research Reserve, Virginia. Journal of Coastal Research, SI 57, 17-22.

• Haas, L.W., 1977. The effect of the spring-neap tidal cycle on the vertical salinity structure of the James, York, and Rappahannock Rivers, Virginia, U.S.A. Estuarine and Coastal Marine Science, 5, 485-496.

• Kraeuter, J. and D.S. Haven, 1970. Fecal Pellets of Common Invertebrates of Lower York River and Lower Chesapeake Bay, Virginia. Chesapeake Science, 11, 159-173.

• Rhoads, D.C. and D.K. Young, 1970. The Influence of Deposit-feeding Organisms on Sediment Stability and Community Trophic Structure. Journal of Marine Research 28, 150-177.

• Rodriguez-Calderon, C., 2010. Spatial and temporal patterns in erosional and depositional processes: physical and biological controls in the York River, Chesapeake Bay, Virginia. M.S. thesis, Virginia Institute of Marine Science/School of Marine Science, The College of William and Mary, Virginia.