Abstracts Biological Sciences

It's a Small World After All: Insights, Interferences, and Implications of In Situ Chlorophyll Fluorescence Monitoring in Estuaries

by James Silas Tanner

Concentrations of the photosynthetic pigment chlorophyll a are used as a proxy for phytoplankton biomass by estuarine scientists to study eutrophication, food web dynamics, and harmful algal blooms. Coastal managers use chlorophyll as an indicator of nutrient pollution and for assessments to meet Clean Water Act standards. Chlorophyll a, as measured in the laboratory by extraction from monthly discrete water samples, is a core component of the National Estuarine Research Reserve (NERR) System-Wide Monitoring Program (SWMP). Field-deployable sensors based on the excitation and emission spectra of in situ chlorophyll have not been incorporated into SWMP to date because past studies showed inconsistencies across reserves. Several studies have shown in situ chlorophyll fluorescence to be temperature sensitive as well as subject to spectral interference from fluorescent dissolved organic matter (fDOM) and turbidity. The project objectives included the assessment of sensor reliability across a range of environmental conditions, identifying interferences that may affect sensor output, and developing estuary-wide or conditional relationships between chlorophyll monitoring using the datasonde and extractive chlorophyll measurements. To achieve these objectives, validation of the sensor output through paired sampling with extractive analysis was conducted. Additional testing focused on identifying sensor interferences was also conducted including temperature, turbidity and fDOM. Results indicate in situ chlorophyll fluorescence correlates to extracted chlorophyll, but this relationship is influenced by the environmental interferences mentioned. Utilizing hierarchical regression modeling to incorporate data from interfering parameters improved the relation between sensor and extracted concentrations. Incorporating this sensor into NERR SWMP long-term water quality monitoring program as a surrogate for chlorophyll concentration will give coastal managers around the country increased insight into what drives the base of estuarine food webs. Combined with satellite telemetry, these sensors provide near-real-time insight into phytoplankton dynamics, with the potential to provide early detection and rapid response to harmful algae blooms.