Location of Turbidity Maxima Within a Microtidal Estuary and Some Limitations of Laser In Situ Particle Sizing

Abstract

A study of suspended sediment concentration properties has been undertaken in a predominately microtidal estuary using an in situ profiling instrument package comprising a LISST-100 particle sizer and SeaBird CTD. This novel instrumentation arrangement permitted the simultaneous sampling of temperature, conductivity, pressure, transmissiometry and particle volume concentration (as a function of particle size) during profiling operations. The estuary was found to have two types of turbidity maxima. The first was associated with bottom resuspension, its vertical extend being inhibited by water column stratification. The second was associated with inflow, which was found to have high concentrations of fine particles whose concentration increased with inflow rate. The particles were observed to flocculate rapidly when the salinity of the inflow water reached about 5 0/ . The location of the 5 0/ 00 00 isohaline was found to be a power law function of the inflow rate, indicating that microtidal estuaries can be readily dominated by inflow water properties. The results from the study also showed that stratification could significantly influence the LASER derived results, and therefore care must be taken when using devices like the LISST-100 in stratified environments.