Phytoplankton Biomass Variability in a Western Mississippi Sound Time-Series

Author(s): Dornback, M.; Lohrenz, S.

This study is observing the temporal and spatial fluctuations in phytoplankton biomass in the water column in relation to light availability, nutrients, and environmental factors such as salinity and temperature. The focus will be on what factors promote changes in phytoplankton biomass above and below the stratified layer and in a mixed water column. This is particularly important because harmful algal blooms and summertime hypoxia are both linked to water column stratification.

Monthly cruises (9/07-Present) are conducted to collect the samples. Optical instruments are used to measure in situ light absorption (ac-9), attenuation (ac-9), and backscatter (bb-9) in nine different wavelengths. Phytoplankton biomass is measured through the proxy of in situ chlorophyll a (chl a) fluorescence intensity using a FL-3. A CTD is used for measurements of salinity (converted from conductivity), temperature, and depth.

Water samples from the start, middle and end of the transect are collected at multiple depths and returned to the lab for analysis of nutrients (N, P, Si), chromophoric dissolved organic matter absorption, the pigmented and non-pigmented absorption fractions of suspended particulate matter and the bulk mass of the suspended particulate matter.

The western Mississippi Sound is a vital economic and ecological resource to the surrounding region. A large percentage of coastal residents between Bay St. Louis and Biloxi and rely on the Sound for revenue from tourism and fisheries. The water quality of fishery habitats and nurseries can greatly affect fauna health and the health of human consumers. It is important for coastal water quality to be properly assessed in order to understand the threats to the local ecosystem and to mitigate any anthropogenic causes.

Preliminary results show fluctuations in chlorophyll a abundance through the months and between sampling stations on a single month. Distinct phytoplankton blooms are detected above and below the pycnocline. More analysis of the water column properties will need to be conducted to understand the reason between the fluctuations.

In addition, major environmental disturbances such as hurricanes (Gustav 9/1/08-9/2/08, Ida 11/9/09-11/10/09) and the Bonnet Carre Spillway opening (4/11/08-5/12/08) have been detected in the monthly optical profiles. Further analysis of the data will have to be conducted to see if any anomalies are detected due to the Deepwater Horizon oil spill.

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Technical Sessions

Session I Sedimentation
Session II Weather/Climate
Session III Coastal Resources
Session IV Surface Water Management
Session V Wetlands
Session VI Education
Session VII Management/Planning
Session VIII Wetlands
Session IX Delta Groundwater
Session X Nutrients
Session XI Delta Water Resources
Session XII Ports

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