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Spatial and temporal variability of harmful algal blooms in a eutrophic lake
An Honors Thesis (HONR 499)
By
Jeremy Walls
Thesis Advisor
Kevin H. Wyatt
Signed
Ball State University Muncie, Indiana April 2015
Expected Date of Graduation
May 2015
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Abstract
To evaluate the environmental controls on harmful algal blooms (HABs) in a
hypereutrophic lake, we conducted a spatial and temporal survey of Grand Lake st.
Marys located in western Ohio. Water samples were collected for physicochemical
analysis and related to measures of algal biomass and community composition weekly
from August to May at 8 sites within the lake. Phosphate (P04 ) levels were elevated
throughout the growing season, ranging from 0.022 ± 0.059 mg/L to 0.154 ± 0.059
mg/L, and were above the EPA's designated use limit of 0.025 mg/L for a majority of the
sampling period. Hypereutrophic conditions present in the lake throughout our sampling
period, as a result of agricultural runoff, saturated algal growth and limited our ability to
evaluate nutrient controls on the relationship between nutrients and HABs. Chlorophyll
a, dry mass, and algal cell density were related to nitrogen (N) concentrations and were
greatest early in the growing season when N levels were greatest. Algal taxonomic
composition was dominated by the cyanobacteria Planktothrix agardhii. This alga
produces a hepatotoxin, microcystin, which has been detected at levels >100ppb in
Grand Lake St. Marys. Microcystin concentrations were related to algal abundance,
indicating that environmental conditions that promote nuisance algal growth contribute
to toxin production. Based on these results, we suggest that excess nutrients have
allowed P. agardhii to dominate, decreasing species diversity and diminishing water
quality for recreational and human use. The results of this study show that excess N
inputs to the lake influence the abundance of spring HABs.