Control of microorganisms associated with estuarine suspended sediment

BACKGROUND:  Consisting of dynamic particles, sediment plays a significant role in the transport, fate, and control of microorganisms in estuaries.  With a propensity to attach to sediment, microorganisms can be transported throughout estuaries while tethered to sediment particulate traveling between the estuary bed and water column.  Association of microbes with sediment can promote microbial survival by providing nutrients, protecting from protozoan predators, and shielding from UV.  Pathogens sequestered within sediment beds can suspend with particulate into water and pose a health risk to recreational bathers, boaters, and fishermen.  Microbial attachment to sediment particulate of ship ballast waters can protect pathogens from disinfectants and present a challenge to microbial control.  METHODS:  In this study, a Chesapeake Bay tributary (Magothy River) was examined to understand the association of microorganisms with estuarine suspended sediment and the potential impact of microbial attachment to control by disinfection.  Samples of estuarine sediment and water were subjected to vortical flow to suspend sediment into water columns.  Microbial association with suspended sediment was quantified by comparing densities of microbe-sized particles (MSP) of suspended sediment before and after treatments (chemical and mechanical) that disperse sediment and release MSP.  Potential impact of suspended sediment on microbial control was determined by measuring reactivity of chlorine disinfectant with whole and dispersed suspended sediment.  RESULTS:  Suspended sediment consisted primarily of floc masses with relatively few unattached MSP.  The vast majority of MSP were attached to floc as indicated by great increases in levels of unattached MSP following dispersion treatments.  Disinfectant was less reactive with intact suspended sediment than with dispersed suspended sediment.   CONCLUSION:  Strategies for microbial control of estuarine waters should consider that suspended sediment floc can (1) harbor high numbers of microorganisms and (2) serve as a barrier to disinfection by reducing disinfectant reactivity with sediment-associated microorganisms.