Winter 2003 Vol. 9 No.2
6FRIENDS of Great Salt Lake
For the past three years, an Aquatic Ecology Practicum
class at Utah State University has conducted research
examining pollution in Farmington Bay. In 2000, our class
discovered that Farmington Bay had excessive levels of
nutrients and phytoplankton (a condition known as
eutrophic) compared to the Great Salt
Lake proper (Marcarelli et al. 2001). In
2001, individual projects concluded
that sewage treatment plants discharged
sufficient nutrients to the bay to make
it highly eutrophic and that brine
shrimp biomass was 5 times lower in
Farmington Bay than in the Great Salt
Lake proper. In addition, sampling on a
windy night revealed that the entire
water column in Farmington Bay
lacked oxygen, resulting in a condition
known as anoxia (Wurtsbaugh et al.
2002). Additional sampling in 2002
indicated that brine flies were less
abundant in Farmington Bay than in
less eutrophic Ogden Bay. These
results prompted us to examine two
major research themes in October of
2002: oxygen effects on chemical,
physical, and biological characteristics
of Farmington Bay, and other factors
that may control the abundance of
organisms in Farmington Bay and the
Great Salt Lake.
Since we previously observed high
nutrient loads into Farmington Bay,
Olivia Lester conducted a laboratory
assay of algae from the Great Salt Lake
to determine whether nitrogen or
phosphorus limited phytoplankton growth. Her results
indicated that nitrogen was the primary limiting nutrient,
as has been reported previously for the Great Salt Lake
(Wurtsbaugh 1988). However, when the salinity was
reduced to 30 g/L phosphorus also stimulated algal growth.
Analyses of this experiment are still ongoing, but it suggests
that nutrient control of algal growth in the dynamic Farm-
ington Bay may be more complex than in freshwater lakes.
Microbes such as bacteria decompose organic matter such
as dead algae that settle to the bottom of the lake. During
decomposition, microbes can deplete oxygen in the water,
causing anoxia. Anoxia slows decomposition and causes
organic matter accumulation. Sampling in Farmington Bay
in 2000 and 2001 revealed that oxygen was usually absent
in the deeper waters of Farmington Bay where intruding
high-salinity water from the main lake
prevents water mixing. This “salt wedge”
protrudes several miles into the bay. Previous
sampling showed that the sediments
beneath the salt wedge were black and
appeared to be rich in organic matter. We
were unsure, however, of the sediment
characteristics in other parts of the bay
where the salt wedge was absent. Two students,
Brandon Albrecht and Mark Beckstrand,
were interested in whether the abundant
algae in the bay settled to the bottom, and
if so, whether microbial decomposition
prevented the accumulation of organic
matter. Using sediment traps to catch
falling plankton, Beckstrand found that
about 4 g/m2(21,000 lbs/mi2) of organic
matter sedimented to the bottom of Farm-
ington Bay each day. Albrecht found that
organic matter content in the sediments
under the salt wedge were 5-times higher
than in areas where oxygen was abundant.
These results suggest that organic matter
may accumulate primarily in the area
beneath the salt wedge and may result in
anoxia in this portion of the bay.
When anoxic conditions prevail in the
water column and sediments of lakes,
distinctly different chemical reactions
occur. In particular, sulfate, which is
abundant in the saline waters of the Great Salt Lake, is
converted to hydrogen sulfide. Hydrogen sulfide, also
known as “the rotten egg gas,” is one of the odors that
sometimes plague communities surrounding the Great Salt
Lake. Peter MacKinnon examined the sediments at five
sites in Farmington Bay and found that hydrogen sulfide
concentrations just above the sediments were only high in
the deep water (>1.5 m or 5 feet) where oxygen concentrations
were low. However, the noxious gas was present within the
sediments at all five sites. This early work suggests that
much of the odor produced in the bay could be localized in
ISFARMINGTON BAY HEALTHY?
CONTINUING STUDIES OF WATER QUALITY IN THE GREAT SALT LAKE
by Amy M. Marcarelli and Wayne A. Wurtsbaugh1, with Brandon Albrecht, Erik Archer, Jennie Bassett,
Mark Beckstrand, Michael Hadley, Jason Kling, Olivia Lester, Peter MacKinnon and Te-hui Ting.
photo by Amy Marcarelli
