The aim of this investigation in Offatts Bayou was to quantify natural shifts in
distributions and abundances of algal groups and to examine spatio-temporal patterns of
abiotic and biotic characteristics in the water column over a one year period. To
accomplish this, hydrological and meteorological parameters were collected and
phytoplankton biomass, community composition and chlorophyll a data were examined
for significant relationships. Seasonal variations in water temperature, salinity,
dissolved oxygen concentrations and pH levels, as well as wind effects, zooplankton
grazing, light availability and hydrodynamic restriction were considered as the key
controlling factors in phytoplankton dynamics in Offatts Bayou.
Surface water samples and water column hydrological data were collected at
eleven stations in the Offatts Bayou embayment on a regular basis (2 to 4 times per
month), along with phytoplankton tows on a monthly basis. Spatial patterns of
phytoplankton abundance generally reflected the degree of circulation in Offatts Bayou
with higher abundances observed in the restricted areas and lower abundances in the
well mixed regions. Temporally, diatom blooms became more prominent during winter, spring and autumn, which were characterized by cooler temperatures, less light
availability, increased dissolved oxygen concentrations and reduced salinities than
observed in summer. The most dominant diatoms were Guinardia delicatula, Ditylum
brightwelli, Rhizosolenia setigera, Dactyliosolen fragillissimus and numerous
Chaetoceros species. During summer, the waters of Offatts Bayou were warmer and
more saline, which lead to the haptophyte, Corymbellus aureus, becoming the dominant
taxa, with highest standing crops at the circulation restricted stations in Lake Madeline.
While the results of this study support the importance of temperature, dissolved
oxygen and pH as the critical controlling factors (p < 0.05) of phytoplankton biomass
and diversity, it is clear that phytoplankton dynamics in Offatts Bayou must be viewed
within the broader context of additional parameters such as salinity, stratification and
wind effects. The progressively degrading conditions within Offatts Bayou emphasize
the significance of studying and understanding the interrelationships of factors and
mechanisms that influence phytoplankton dynamics. Long term monitoring of Offatts
Bayou is essential for tracking, recording and assessing various human impacts to
phytoplankton distribution, abundance, and productivity as well as impacts to higher
trophic levels such as fish and humans.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1177 |
| Date | 15 May 2009 |
| Creators | Roehrborn, Linda Rae |
| Contributors | Quigg, Antonietta S |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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