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Water Quality Research in Farmington Bay, Great Salt Lake, Study notes of Water Resources Planning and Management

This document reports on the findings of an aquatic ecology practicum class at utah state university regarding the water quality in farmington bay, a part of the great salt lake. The class discovered excessive nutrient levels and anoxic conditions in the bay, which negatively impacted the biomass of brine shrimp and brine flies. The researchers also examined the potential role of oxygen levels and predation in controlling brine shrimp populations. The document concludes with implications for management issues in farmington bay.

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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
pf3

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6 Winter 2003 Vol. 9 No.2 FRIENDS 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/m 2 (21,000 lbs/mi 2 ) 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

I S FARMINGTON B AY H EALTHY?

C O N T I N U I N G S T U D I E S O F W AT E R Q U A L I T Y I N T H E G R E AT S A LT L A K E

by Amy M. Marcarelli and Wayne A. Wurtsbaugh

1

, 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

FRIENDS of Great Salt Lake Winter 2003^ Vol. 9 No.2^7

the salt wedge area, but if the sediments are stirred by strong winds, additional hydrogen sulfide may be released from other parts of the bay. Additionally, we don’t know if additional hydrogen sulfide is produced at night if the water column goes anoxic.

We hypothesized that low oxygen levels in Farmington Bay at night may be contributing to the low biomass of brine shrimp in Farmington Bay. Jennie Bassett conducted experiments to determine the sensitivity of juvenile brine shrimp (nauplii) to oxygen. She found that nauplii were very sensitive to anoxic conditions, with 50% of nauplii dying after 3 hours without oxygen. This indicates that anoxic events that last longer than could have a large effect on brine shrimp populations. However, very low concentrations of oxygen (0.6 mg/L) were not as lethal to nauplii (50% dead after 16- 20 hrs), indicating they could survive under these conditions.

As an alternative to oxygen, we examined the potential of predation by an insect (water boatmen, or corixids) to control brine shrimp populations. Erik Archer examined the distribution of corixids from the shore to the open water and found them to be evenly distributed with a mean density near 50 organisms/m^3. Mike Hadley conducted lab experiments and found that these corixids could eat 14- brine shrimp per day, depending on the size of the shrimp. With the density of corixids we found in the lake they have the potential to eat 20% of the adults and 60% of the juvenile brine shrimp in Farmington Bay each day. This is equal to or higher than the population growth rate of 20% per day that has been reported for another brine shrimp population (Zhang and King 1993), suggesting that corixids have the potential to significantly impact brine shrimp populations. However, water clarity in the experiments was high compared to conditions in Farmington Bay, where abundant phyto- plankton greatly reduce water clarity. Because corixids are a visual predator, actual predation rates will need to be deter- mined in field experiments.

Since little research has been conducted on brine flies in the Great Salt Lake, we examined the distribution of brine fly larvae in Farmington Bay and Ogden Bay. These larvae live primarily in algal mats (periphyton) growing on hard substrates (Collins 1980). Te-hui Ting found mean densities of brine fly larvae on benthic (or bottom) substrates near 50 organisms/m2 in Farmington Bay, but densities over 7000 organisms/m2 were present in Ogden Bay. However, these results were highly variable because it was difficult to sample the benthic substrates in both bays. We have two hypotheses to explain the much lower densities that may occur in Farmington Bay. First, the periphyton that the brine fly larvae feed on may not grow well in Farmington Bay because the extreme populations of phytoplankton may “shade-out” the

algae on the bottom. We found that benthic chlorophyll concentrations were 2.5 times higher in Ogden Bay than in Farmington Bay, and brine fly abundance was related to benthic chlorophyll levels. Secondly, we hypothesized that the different densities of brine fly larvae could be due to lower dissolved oxygen concentrations in Farmington Bay than in Ogden Bay. However, Jason Kling conducted oxygen sensitivity experiments that indicated that brine fly larvae are less sensitive to anoxic conditions than brine shrimp (50% of pupae dead in 6.8 hrs). This indicates that anoxia events in Farmington Bay may not be long last enough to result in significant brine fly death. Much more work needs to be done to understand the factors controlling brine flies in Farmington Bay and elsewhere because brine flies are an important food resource for bird populations, and because they are often perceived as a nuisance species.

Although these field examinations and experiments are simply a snapshot of chemical, biological and physical conditions in October, 2002, the results have implications for management issues in Farmington Bay. While microbes decomposed large amounts of organic matter, anoxia in the sediments did result in high organic matter content in 2 of 5 sites examined. In these same two sites, hydrogen sulfide production was high, indicating that anoxia was changing chemical conditions in the bay. Experiments indicated that anoxic events have the potential to limit brine shrimp survival. However, predation of brine shrimp by corixids may also limit populations, and the interaction of these two factors must be further examined. While juvenile brine flies are not as sensitive to oxygen as brine shrimp, the low benthic periphyton levels in Farmington Bay may limit brine flies populations. Lowered oxygen levels and decreased benthic algae are conditions caused by pollution in Farmington Bay, and they clearly have the potential to impact the Farming- ton Bay ecosystem.

Although the results of the student’s projects have greatly increased our understanding of pollution issues in Farmington Bay, we must be careful in interpreting information collected from just a short period during the fall. Fortunately, the Utah Division of Water Quality has recently developed a working group of scientists and managers from agencies, NGOs and universities that will soon bring the needed resources to understand water quality issues in the bay. 1 Department of Aquatic, Watershed and Earth Resources, Utah State University, Logan, UT 84322-

Please direct correspondence to amym@cc.usu.edu More about this work can be found on the class webpage, http://www.cnr.usu.edu/online/awer4510/. (continued on pg. 14)