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Dynamic stability and particle transformations: tracing pathways of production in Estuarine Turbidity Maxima (NSF-OCE 0453905)
PIs: E. D. Houde, B. C. Crump, E. W. North,
M. R. Roman, L. P. Sanford
Senior Investigators: S.-Y. Chao, R. R. Hood, D. Kimmel


Estuarine turbidity maxima (ETMs) are turbid water regions located at the heads of coastal plain estuaries near the freshwater/saltwater interface (Fig. 1). They trap sediment, detritus, zooplankton and fish early-life stages, enhance secondary production, and serve as critical nursery areas for economically important fishes. The Chesapeake Bay ETM (Fig. 2) has been characterized as a region of dynamic stability where restoring forces, both physical and biological, modulate the ETM ecosystem and periodically enhance trophic transfer. It is proposed that mechanisms promoting dynamic stability in ETMs are strongly associated with particle transformations and water column stratification that lead to predictable particle delivery, entrapment, nutritional enrichment, and trophic transfer from microbes to zooplankton to fish.

The overall goal of the BITMAXII (http://www.bitmaxii.org/) project is to evaluate and explain why ETMs are dynamically stable and predictable regions that support enhanced secondary production.  Our specific hypotheses are:

  • Particle aggregation promotes formation and retention of nutritious particles in the ETM.
  • Particle-attached bacteria enrich the nutritional value of food for copepods, transforming the microbial loop into a microbial shunt (Fig. 3).
  • Abundant food and stable stratification enhance the feeding conditions and production of copepods and fish larvae.
  • Life-history strategies of key ETM species are adapted to take advantage of event-scale changes (pulses) in ETM circulation patterns.

These hypotheses will be addressed with an integrated research program of comprehensive and coordinated field, laboratory, and numerical modeling experiments in the ETM region of upper Chesapeake Bay.
The Crump lab group is involved in several different aspects of this project.  We will work closely with R. R. Hood to evaluate the biology and biogeochemistry of ETM particles and their source materials by characterizing the biogeochemical composition of particles, bioavailability of associated organic matter, and distribution of bacteria and protozoa, phytoplankton biomass, production, respiration, and species composition in depth profiles and along both axial and cross-axial transects through the estuarine gradient associated with the ETM.  Working with E. W. North, this information will be incorporated into an ecosystem model, which will simulate bulk ecosystem properties such as total primary production and total heterotrophic respiration. 
We will work closely with L. P. Sanford to fractionate particles and study how bacterial growth and biofilm formation influences the “stickiness” of particles and causes them to aggregate into larger, rapidly-sinking flocs.  We will also work closely with M. R. Roman and D. Kimmel to explore the links between organic input to ETMs, microbial processes and copepod ingestion and growth by conducting laboratory incubations of radiolabeled (14C and 3H) ETM particles withthe copepod E. affinis.  These radioactive tracers will allow us to follow the flow of bacterial biomass and phytoplankton carbon through bacteria-protozoa-copepods-fecal pellets.