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HomeMy WebLinkAboutDWQ-2024-004578 1 Utah Lake Water Quality Study (ULWQS) Science Panel June 29, 1:00 PM to 5:00 PM Utah Lake State Park Office Meeting Summary ATTENDANCE: Science Panel Members: Mike Brett, Mitch Hogsett, Theron Miller, Michael Mills, Thad Scott, Tim Wool Steering Committee Members and Alternates: David Barlow, Scott Bird, Chris Cline, Eric Ellis, Rich Mickelsen, Cory Pierce Members of the Public: Jeff DenBleyker, Tina Laidlaw, Wood Miller, Dan Potts, David Richards, and Jonathan Wright Utah Division of Water Quality (DWQ) staff: Scott Daly, Jodi Gardberg, and Nicholas von Stackelberg Guest Presenters: Russ Franklin, Steve Nelson, and Tim Walsworth Facilitation Team: Heather Bergman and Samuel Wallace ACTION ITEMS Who Action Item Due Date Date Completed Tetra Tech and Janice Brahney Identify the species researchers screened for using eDNA in King (2019). June 28 Assess the Paleolimnology Study sediment cores to see how the dam's construction may have impacted lake levels and, in turn, impacted benthic and epiphytic diatom levels, particularly in open water. June 28 DECISIONS AND APPROVALS No formal decisions or approvals were made at this meeting. SCIENCE PANEL TOUR OF UTAH LAKE Science Panel members took a boat tour of Utah Lake, visiting Goshen Bay, Provo Bay, and the Provo River Delta. JUNE SUCKER RECOVERY IMPLEMENTATION PROGRAM OVERVIEW Russ Franklin, Central Utah Water Conservancy District, presented an overview of the June Sucker Recovery Implementation Program (JSRIP). The presentation, the subsequent Science Panel discussion, and public comments are summarized below. JSRIP Overview Presentation Below is a summary of the JSRIP overview presentation. 2 June Sucker Recovery Background Context • Utah Lake is large (96,000 acres) and shallow (max depth of fourteen feet). Historically, Utah Lake had 13 native fish species. There are now two native species remaining: June sucker and Utah sucker. • Based on historical accounts, many June suckers inhabited Utah Lake in 1890. The June sucker population served as a food supply to support First Nations and early settlers. • Around 1870, fisheries were collapsing across the United States. The US Fish and Wildlife Service (USFWS) decided to raise fish at the National Fish Hatchery and transport them across the United States using railroads, specialized train cars, and shipping containers. People purchased fish, including carp, to stock the collapsing fisheries. • The first shipment of 130 carp arrived in Utah in 1881. In 1882, 200 carp were shipped to Utah. By 1886, 11,960 carp were shipped to Utah. From 1888 to 1889, 17,400 carp were shipped to Utah. In a letter to the State Legislature, Amos Milton Musser, the Utah Fish Commissioner from 1883 to 1896, noted that he had overseen the stocking of 10,579,220 fish into the public waters of Utah. • The carp spread quickly once introduced. The carp stocked in the 1880s altered the native fish communities by outcompeting them. The carp population, along with the overutilization and diversion of water resources, was supplementally responsible for dwindling native fish populations. • The drought of the 1930s further impacted native fish populations in Utah Lake. In 1934 and 1935, Utah Lake was dry enough that someone could walk across the entire lakebed; the deepest spot in the lake was 12 inches. The drought negatively impacted macrophytes in the lake and altered the fish community. • In the 1980s, the June sucker was nearly extinct. In 1986, the USFWS designated the June sucker as an endangered species based on habitat alteration, nonnative introductions, and loss of recruitment. They designated 4.9 miles of the Provo River as critical habitat for the species. The USFWS gave June sucker a recovery priority, which applies to a species with a high threat of extinction, a low recovery potential, and the presence of conflict. • In the 1990s, former JSRIP Program Manager Chris Keleher oversaw the surveying of the June sucker population. They found fewer than 1,000 individuals in Utah Lake, of which they estimated the wild adult spawning population to be about 300. JSRIP Formation and Strategy • The JSRIP was formed in 2002 as a cooperative effort between the state, federal, and local agencies. The two goals of the JSRIP were: o Recover June sucker so that it no longer requires protection under the Endangered Species Act o Allow continued operation of existing water facilities and future development of water resources for human use in the Utah Lake Drainage Basin • The JSRIP identified six recovery elements: o Nonnative and sport fish management o Habitat development and maintenance o Water management and protection to benefit June sucker o Generic integrity and augmentation o Research, monitoring, and data management o Information and education • The nonnative and sport fish management strategy primarily involves removing carp from Utah Lake. To date, the JSRIP has removed nearly 30 million pounds of carp. The amount of carp removed from Utah Lake is equal to 119 blue whales, 53 dump trucks, or 2,121 African 3 elephants. The goal for carp removal was to reduce carp biomass by 75% based on 2006 levels, and the program got close to achieving that goal in 2017. • The water management and protection strategy involves acquiring water for instream flows through conservation projects. In 1995, the JSRIP managed 5,000 acre-feet of water; they currently manage almost 30,000 acre-feet. The JSRIP uses the instream flows to augment Provo River flows, which allows June suckers to swim upstream for spawning. • The genetic integrity and augmentation strategy primarily involves stocking the lake with June sucker. The JSRIP has stocked Utah Lake with over one million June suckers, and they will likely stock the lake with 80,000 this year. Augmenting the population is not a replacement for natural recruitment. • The JSRIP researched the June sucker life cycle and natural recruitment. In their studies, scientists found that the old river channels were not conducive to natural recruitment because there were few places for larvae to hide from predators. In 2008, the JSRIP implemented the Hobble Creek Delta Restoration Pilot Project to create June sucker nursery and brooding habitat. The project involved restoring 24 acres on Hobble Creek. Scientific evidence from the project suggests that most of the natural recruitment of June sucker in Utah Lake has come from Hobble Creek. The Provo River Delta Restoration Project is based on the success of the Hobble Creek Delta Restoration Project. Researchers will have to wait to assess the success of the Provo River Delta Restoration Project as it comes online. • The USFWS downlisted the June sucker from endangered to threatened in February 2021. This downlisting is very rare; the June sucker is only the fifth fish species to be downlisted. A complete delisting requires a five-factor analysis to assess that the major threats to the species are no longer present and that the population is self-sustaining. • One challenge that the JSRIP faced was how to tell whether a young June sucker came from natural recruitment in Utah Lake or from a fishery. The JSRIP studied the natal origins of the June sucker population by conducting a fin-ray analysis. Fin rays are composed of calcium carbonate, so the mineral deposit in each water body affects the fin ray structure. Researchers could use the mineral makeup of the fin rays to determine the natal origin (e.g., Utah Lake or outside fishery). • The JSRIP assessed the fin rays of 96 June suckers from known sources and origins. Of the 96, 28 June suckers came from Utah Lake. They also assessed the fin rays of 263 untagged June suckers from Hobble Creek, Spanish Fork, and Utah Lake. Of the 263 untagged June suckers, approximately 13% came from Utah Lake. The study indicated that wild recruitment has occurred over multiple years; researchers are now evaluating to see if they can determine whether natural recruitment is specifically coming from Hobble Creek or the Provo River. • The Provo River Delta Restoration Project will officially be completed and open to the public in 2024. The project involves 225 acres of restoration. The design of the delta will keep it wet in dry years, and in wet years, it will be completely inundated by the lake. The project will also provide community and non-motorized recreation opportunities. Public Clarifying Questions Members of the public asked clarifying questions about June sucker populations and the JSRIP. Their questions are indicated in italics below, with the corresponding responses in plain text. From an evolutionary standpoint, why did June suckers become zooplanktivores? Broadly speaking, the Utah sucker, one of the June suckers' competitors, was a benthic species. The June sucker may have evolved to eat the zooplankton in the open water as a selective advantage. This response is speculative, and the exact answer is not known. 4 Has there been natural recruitment out of the Provo River, or have the larvae spawned in the Provo River mostly been eaten? • The evidence suggests that the larvae from the old Provo River system were being washed down and eaten by other fish. • At times, there was insufficient water to push larvae out of the past Provo River channel. Approximately 300 cubic feet per second (cfs) was needed to flush larvae into Utah Lake, and many times, that flow was not achieved. Science Panel Discussion on the JSRIP The intersection of the JSRIP and the ULWQS lies within the carp removal effort. The JSRIP has maintained an ecosystem monitoring effort to assess the effectiveness of removing carp. Although the JSRIP has removed many adult carp from the lake, they have struggled to reach a level to maintain a suppressed population. The JSRIP has recently curtailed carp removal efforts as they reevaluate the goals and methods they use to recover June sucker populations. JSRIP ECOSYSTEM MONITORING RESULTS PRESENTATION Dr. Tim Walsworth, Utah State University, presented the results from the JSRIP ecosystem monitoring. The presentation, the subsequent Science Panel discussion, and public comments are summarized below. JSRIP Ecosystem Monitoring Presentation Below is a summary of the JSRIP ecosystem monitoring presentation. JSRIP Ecosystem Monitoring Overview • Dr. Tim Walsworth and Kevin Landom from the Utah State University (USU) Department of Watershed Sciences oversee the JSRIP ecosystem monitoring effort. • The JSRIP ecosystem monitoring is intended to answer the question, "How does the ecosystem June sucker rely on respond to restoration activities?" The monitoring program began with a workshop in 2006, and by 2007, a monitoring plan was in place. • The monitoring plan focuses on six topics: water quality, phytoplankton, zooplankton, macroinvertebrates, macrophytes, and fish community. DWQ monitors water quality and phytoplankton metrics, while USU focuses on zooplankton, macroinvertebrate, macrophyte, and fish community monitoring. The USU research intends to answer the question, "How have the different components of the Utah Lake ecosystem (zooplankton, macroinvertebrates, macrophytes, and fish community) responded to ongoing restoration efforts and concurrent environmental changes?" • The ecosystem monitoring focuses on two primary drivers of interest: common carp population and dynamic lake-level conditions. JSRIP Ecosystem Monitoring – Common Carp Results • Common carp represented over 90% of the fish biomass in the early 2000s. From 2009 to 2002, the JSRIP worked with commercial fishermen to mechanically remove carp to reduce competition with June sucker. The carp removal activities have been stopped for now. • The researchers developed a statistical catch-at-age model to estimate abundance/biomass, recruitment, and gear efficiency. The catch-at-age model suggests carp biomass declined from 2009 to 2017, with the JSRIP almost reaching its stated goal for carp biomass in 2017. Between 2017 and 2021, the carp biomass increased. It has remained relatively stable since 2021. 5 • Some challenges associated with removing carp include compensatory recruitment, selective gear, and lake-level effects on recruitment. o As one removes spawning biomass, individual juveniles survive at a higher rate – this phenomenon is known as compensatory recruitment. o The removal gear captures the adult carp but fails to catch the young or even mature ones; the result of the removal gear selectiveness is that there is always a spawning population in Utah Lake. o Lake levels affect recruitment and gear effectiveness. In high water, carp have a higher recruitment rate, and the gear is less inefficient at capturing carp because they move toward vegetation. During dry years, when the lake is lower, carp are more concentrated and easier to catch in open water. The lake level can fluctuate as much as two meters across years, affecting carp removal and recruitment rates. JSRIP Ecosystem Monitoring – Macrophyte Results • The ecosystem monitoring program divides the lake into nine strata. There is one stratum in Provo Bay and eight in the main body of the lake. The monitoring team samples the community within each stratum. They collect zooplankton, macrophyte transects, and water quality data monthly. They collect macroinvertebrate and lake-wide macrophyte data in the spring and fall and survey the fish community annually in August. • The monitoring team tracks data on emergent and submerged aquatic plants. These plants serve as important rearing habitat for juvenile June sucker and sport fishes. Water depth and light penetration are critical for establishing macrophytes. Common carp also uproot the vegetation during foraging, making it difficult for macrophytes to establish. • The research team uses multiple approaches to monitor macrophytes. They conduct a lake- wide presence/absence survey in the spring and fall. They also collect data monthly using ten 100-meter-long transects at four sites. A Master's student recently researched macrophytes using remote sensing across the lake. • The results of the macrophyte sampling indicate that when macrophytes are present, the community is primarily dominated by hardstem bulrush and phragmites. During the first two years of sampling (2014 and 2015), the monitoring team only found hardstem bulrush and phragmites. Macrophyte biodiversity increased starting in 2016, which coincides with the lowest carp biomass levels, and has continued to increase since, even with carp biomass levels also increasing. However, even with the increase in biodiversity, the coverage area of macrophytes has not expanded. These results suggest that although there is an increase in species richness, the overall extent of the macrophyte community is not spreading. • Additional analysis indicates that a higher lake level is positively related to hardstem bulrush, phragmites, and cattail and negatively related to alkali bulrush. Carp has an insignificant or negative relationship with all emergent taxa (hardstem bulrush, alkali bulrush, phragmites, cattail, and sago pondweed). • The remote sensing study assessed the entire lake using Landsat 8 imagery. The analysis uses the color of each pixel to determine the probability that each pixel contains emergent vegetation, submerged vegetation, or open water. The study does not identify the taxa of any identified macrophytes. The analysis sums the probabilities across all pixels to estimate the annual macrophyte coverage. The remote sensing study results indicate a positive relationship between lake levels and emergent macrophytes, meaning that emergent macrophytes increase in coverage as the lake elevation increases. There is a negative relationship between lake levels and submerged macrophytes, meaning submerged macrophyte coverage decreases as the lake elevation increases. As the lake gets deeper, less 6 light penetrates to reach submerged macrophytes. The study's results did not support a significant relationship between carp biomass and macrophyte coverage. • The overall results of the ecosystem monitoring indicate that macrophytes have a positive response to carp control at small scales. Carp control at small scales increases macrophyte species richness and increases the probability of occurrence for submerged taxa. The lake level strongly impacts both emergent and submerged vegetation coverage. These results have implications for the Utah Lake food web. JSRIP Ecosystem Monitoring – Macroinvertebrate Results • Macroinvertebrates include aquatic insects and other non-zooplankton invertebrates (e.g., annelids, oligochaetes, etc.). Macroinvertebrates are important prey species for fish in lakes and rivers. They are also sensitive to environmental change. • The monitoring team collected macroinvertebrate samples from nine strata around the lake in the spring and fall. They took the samples from within macrophyte and bare sediment habitats. • Chironomids and Oligochaeta dominated the macroinvertebrate samples. Additionally, more macroinvertebrates were found in macrophyte samples than in bare sediment samples. • A master's thesis found that macroinvertebrate biomass and species richness were greater in submerged and mixed macrophyte habitats than in emergent macrophyte habitats. The same thesis found that macroinvertebrate biomass increases at lower lake levels. • An analysis of the monitoring data indicates that Chironomids and Oligochaeta biomass are negatively related to both carp biomass and lake level. As carp biomass increases, Chironomids and Oligochaeta biomass decreases, and as lake level increases, Chironomids and Oligochaeta biomass decreases. The relationship between lake level and Chironomids and Oligochaeta may be due to either the concentration effect or temperature changes. • The primary conclusions from the macroinvertebrate data are that macroinvertebrates respond to changes in carp biomass and lake level and that macrophytes are important, productive habitats for macroinvertebrates. JSRIP Ecosystem Monitoring – Zooplankton Results • Zooplankton are important prey for fish. They are also important grazers of phytoplankton. The community composition and size structure of zooplankton respond quickly to changes in food web structure. • The monitoring team took monthly zooplankton samples from nine strata around Utah Lake. • The zooplankton sampling results indicate that Daphnia species and Calanoid copepods dominate the community based on biomass measurements. Diaphanosoma and Cyclopoids were also common. Large-bodied zooplankton taxa consistently have high numbers across multiple years, while small-bodied zooplankton populations declined between 2016 and 2019 and have since increased slightly over the past several years. • Overall, zooplankton biomass catch per unit effort (CPUE) increases with low carp biomass and low lake levels. • No zooplankton taxa were positively related to carp, and many had an inverse relationship with carp (i.e., as carp biomass increases, zooplankton taxa biomass decreases). • Lake-level impacts are less consistent across taxa. Diaphonosoma, Calanoid copepods, and Leptodora have a positive relationship with lake levels, while Bosmina, Ceridophania, cyclopoid copepods, and rotifers had a negative relationship with lake levels. 7 • Undergrad researchers assessed the relationship between zooplankton body size and carp biomass. They found that the body size of many zooplankton taxa is negatively related to carp biomass. In particular, Daphnia experienced a decrease in body size as carp biomass increased. Carp will selectively prey on the largest Daphnia, leaving smaller ones in Utah Lake. June suckers also selectively prey on larger Daphnia. • The primary conclusions from the zooplankton analysis are: o Large-bodied zooplankton density increases as carp biomass is reduced. o Size-selective predation also causes the body size of large-bodied zooplankton to increase as carp biomass is reduced. o These dynamics affect the food web. JSRIP Ecosystem Monitoring – Fish Community Results • The monitoring team sampled the fish community annually in August using large commercial seine hauls from standardized sites across nine lake strata. They measured the relative abundance of the fish community in CPUE. They also assessed the body condition of the fish as a metric of relative weight (i.e., higher weight means better body condition). Higher body condition is also a reflection of a higher growth rate. • The analysis focuses on eight fish: common carp, walleye, black bullhead, June sucker channel catfish, black crappie, bluegill, and white bass. • According to the CPUE data, carp have the highest biomass in kilograms/acre than any other fish. White bass and channel catfish are the most abundant taxa after carp and much more abundant than black bullhead, walleye, June sucker, bluegill, and black crappie. • The white bass biomass CPUE has generally increased through time. There was a decline in 2022, possibly related to the fish kill event in spring 2022. • Of all the monitored fish species, white bass is the only species with a negative relationship with carp biomass. The monitoring team is still attempting to determine why the other fish species have a positive or no relationship with carp biomass. • There is a negative correlation between carp and lake level (i.e., as lake level decreases, carp biomass increases). This correlation may be due to catch efficiency, which increases as lake levels decrease and concentrate the fish community. The benthic fish species (black bullhead and channel catfish) have a negative relationship with lake level. • The body condition of most taxa responds negatively to carp biomass. Only walleye showed a positive relationship with carp biomass. This result is likely due to a response in diet. Common carp, white bass, and June sucker have similar diets, which are primarily composed of chironomids, Daphnia, and cyclopoids. Additionally, channel catfish largely eat chironomids as part of their diet. The similarities in diet create competition. As carp biomass increases, food becomes a limiting factor for other fish species in the lake. • The body condition of benthic species is negatively related to lake level (i.e., as lake levels increase, the body condition of benthic species decreases). • The primary conclusions from the fish community surveys are: o Carp biomass reduction drives changes in the abundance and condition of other species. o White bass have demonstrated the greatest response to changing conditions. o There is evidence of competitive release for species with diet overlap, including June sucker. JSRIP Ecosystem Monitoring – Principal Components Analysis Results • The monitoring team conducted a Principal Components Analysis of all monitored ecosystem components to assess the effect of lake level and carp biomass across all 8 monitored components (carp biomass, lake level, submerged vegetation, emergent vegetation, macroinvertebrates, small zooplankton, large zooplankton, fish, water quality, and phytoplankton). • The Principal Components Analysis shows that lake level increases negatively impact small zooplankton but positively impact large zooplankton. It also shows that all vegetation (submerged and emergent) and macroinvertebrates respond negatively to carp. • The monitoring team created a Principal Components Plot, which allowed them to track the evolution of the ecosystem state over time. The plot indicates a decline in lake levels and carp between 2012 and 2016. There was then an increase in lake level and a slow increase in carp between 2017 and 2021. Between 2021 and 2022, the lake level decreased, but the carp population has stayed relatively the same. This plot only shows correlative effects and does not depict a mechanistic relationship. JSRIP Ecosystem Monitoring – Summary Results • The summary results from the JSRIP ecosystem monitoring are as follows: o There are substantial changes in carp biomass and lake level across the monitoring period. o Both drivers impact all trophic levels of the lake. o The lake level strongly impacts macrophyte habitat. o There are broad changes through time, including: ▪ The increase in large zooplankton densities and body size as carp decreases ▪ Increased body condition of fish species competing with carp ▪ Increased macrophyte species richness but not cover Science Panel Clarifying Questions Science Panel members asked clarifying questions about the ecosystem monitoring results. Their questions are indicated in italics below, with the corresponding responses in plain text. When the JSRIP began reducing carp populations in 2008, they hypothesized that carp removal would increase macrophyte cover for June sucker. Would the data suggest that this hypothesis is valid or not? The data suggests that decreasing carp populations will increase vegetation. However, this relationship is masked by large fluctuations in lake levels. Vegetation established in a wet area one year may be dry the next. The lake level ultimately limits any sustained benefits to vegetation over time. Does competition between carp and June sucker have a bigger influence on June sucker populations than macrophyte cover? The evidence cannot provide a definitive answer on whether competitive release is the most important factor limiting the abundance of June sucker. However, there is evidence that June suckers have a higher body condition when there are fewer carp in the lake. Public Clarifying Questions Members of the public asked clarifying questions about the ecosystem monitoring results. Their questions are indicated in italics below, with the corresponding responses in plain text. Why did the fish kill event in spring 2022 impact white bass in particular? The drastic changes in the lake levels resulted in temperature fluctuations. These temperature fluctuations impacted white bass, particularly as they are a sensitive species. 9 Which zooplankton species are growing larger as a result of lower carp levels? It is unclear how zooplankton species respond differently to changing carp and lake-level conditions. Public Comments There is competition occurring in Utah Lake within the zooplankton community. The density of midges in the lake is 10,000 to 15,000 midges/square meter, under the expected density of 60,000 midges/square meter. RESEARCH PRESENTATION ON DETERMINING THE ANTHROPOGENIC EFFECTS ON EUTROPHICATION OF UTAH LAKE SINCE EUROPEAN SETTLEMENT USING MULTIPLE GEOCHEMICAL APPROACHES Dr. Steve Nelson, Brigham Young University (BYU), presented the results from research conducted to determine the anthropogenic effects on the eutrophication of Utah Lake since European settlement. The presentation, the subsequent Science Panel discussion, and public comments are summarized below. Research Presentation Below is a summary of the research presentation on determining the anthropogenic effects on the eutrophication of Utah Lake since European settlement using multiple geochemical approaches. Research Overview • Several scientists were involved with the study, including Richard Williams, Stephen Nelson, Samuel Rushforth, Kevin Rey, Gregory Carling, Barry Bickmore, Adam Heathcote, Theron Miller, and Leland Meyers. The funding for the study came from the Wasatch Front Water Quality Council (WFWQC). • The study aims to examine the extent of the influence of European settlement on Utah Lake, with a special emphasis on eutrophication. This study is important because understanding the state of Utah Lake before European impacts can help define the limit of remediation. • The objectives of the study were to: o Obtain freeze cores (strongly preferred method because this method preserves the porosity and fabric of the upper part of the core) o Establish a chronology using lead-210, cesium-137, and pollen, and generate a table of human interventions that could have had a large-scale impact on the lake o Characterize the sediment using mineralogy, sediment chemistry (metals, nutrients, carbon-13:carbon-12 ratio, nitrogen-15:nitrogen-14 ratio, and carbon:nitrogen ratio (C:N)), pollen, and diatoms (results pending) o Establish performance parameters • The research team took freeze core samples at three sites. The first core sampling site was near a monitoring buoy in a deep water location. The second site was in Provo Bay, and the third was in Goshen Bay. The purpose of selecting these three sites was to sample a deep part of the lake (deep water), a shallow part of the lake (Provo Bay), and a site of intermediate depth (Goshen Bay). The Provo Bay site is periodically desiccated, has abundant emergent vegetation, and is impacted by discharges from the wastewater treatment plant and, historically, from the pig iron plant. • The growth in population around Utah Lake has been exponential since 1850. Some aspects of the growth have impacted the lake. The study will assess how much of the impact is from sheer population growth and how much is from industrial activity. • Below is a list of important events that have impacted the lake: 10 o 1849: The onset of European settlement of the Provo Area o 1870: Mining begins in the Tintic mountains o 1870-1880: Introduction of invasive Phragmites australis o The 1920s: Tetraethyllead( TEL) begins to be widely used as an antiknock agent in gasoline o 1920-1923: Construction and operation of the Tintic Standard Reduction Mill o 1924: Tintic Standard Reduction Mill closes o 1924: Construction completed for the Columbian Ironton (pig iron and coke) Plant o 1944: Construction finished on Geneva Steel o 1950-1955: Provo Wastewater Treatment Plant is completed and begins operation o 1958: Orem Wastewater Treatment Plant is completed and begins operations o 1962: Columbia Ironton (pig iron and coke) Plant closes o The 1970s: TEL stops being added to gasoline o 2002: Geneva Steel ceases operations Research Results • The research team conducted lead-210 dating to translate core depth into years. The lead- 210 dating method did not work well on the deep water cores but worked fairly well on the Provo Bay and Goshen Bay cores. The Goshen Bay cores were also aided by cesium-137 dating. The research team conducted an age-depth translation on the deep water cores and then modified the aging based on pollen results. • The pollen assessment results indicated a pollen assemblage change around 1850. Juniper pollen decreases, pollen from grasses (corn, wheat, barley, rye) increases, and amaranth pollen increases (potentially from sugar beets). The pollen results helped date the deep water core. The lower core was deposited well before 1850 despite uncertainty in the chronology. • The research team assessed mineralogy using X-ray diffraction data. They only included quartz, calcite, and dolomite in the analysis. The dolomite and quartz are detrital, and most calcite was believed to be endogenic. In open water, about 80% of the sediment (calcite) is produced in the water column; other studies suggest that upwards of 60% of the phosphorus is tied to calcite. In Provo Bay, a large fraction of the sediment has been blown or washed in, particularly detrital quartz, which appears as a higher percentage in the Provo Bay cores than the deep water cores. Iron oxides may be present but were not quantifiable by the X-ray diffraction methodology. Some clays are present in the sediment, but not enough to quantify. • The carbon isotope analysis results indicate that there has been a change in the photosynthetic community that is leaving organic matter in sediment. Carbon abundance increases from the bottom to the surface of the deep water and Goshen Bay cores and fluctuates in the Provo Bay core. The fluctuation in carbon abundance in the Provo Bay core is likely due to algal growth and emergent vegetation. • The nitrogen isotope analysis shows that nitrogen-15 increased between 1900 and 1950. The sources for nitrogen-15 most commonly include treated wastewater, feedlot runoff, etc. In Provo Bay, the net weight of nitrogen in the cores has remained relatively stable, but the nitrogen isotopes have become heavier, transitioning from nitrogen-14 to nitrogen-15. The evidence from the deep water cores shows a clear trend with nitrogen isotopes, which indicates that deep sediment mixing has not erased isotopic and chemical gradients. While the sediments do mix when the wind blows, the mixing has not pervasively or deeply mixed the sediment to the point that the geochemical patterns have disappeared. 11 • The C:N ratio analysis allows the researchers to understand the relative abundance of algae to vascular plants since vascular plants produce a greater C:N ratio than algae. The C:N ratio results in the deep water core extend 50 years before European settlement. The C:N ratio in the Provo Bay and Goshen Bay cores decreased throughout the 20th century, likely related to a decrease in vascular plants and an increase in algal abundance. • The research team measured the total phosphorus in the sediment using acid leaching, which liberated all the phosphorus in the sediment except the phosphorus bound in quartz, which represents a small percentage of the total phosphorus. The phosphorus increases with time in all three cores, with the phosphorus increase being particularly profound in Provo Bay. Total phosphorus increased slightly in the deep water core over time. The total phosphorus in the Goshen Bay core increases and then appears to reach a steady state, similar to the pattern in the Provo Bay core. The total phosphorus measured at the top of each core reflects the total phosphorus values identified in modern studies (Randall et al., 2019). The large increase in total phosphorus in the middle of the 20th century, followed by a steady state of total phosphorus in recent times, may represent a tradeoff between a growing population and improvements in effluent chemistry. The deep water data suggest that this core has not been deeply mixed. • The research team conducted nitric acid extractions to measure lead content. The lead content in all three cores (deep water, Goshen Bay, and Provo Bay) increased by a factor of three or five, starting at the beginning of the 20th century. In the Provo Bay core, there is a decrease in lead content from its peak in the 1950s to modern times. This trend may be due to a reduction in industrialization. Overall, the lead content in all three cores appears to have reached a steady state. The deep water data very strongly suggests that these cores have not been deeply mixed. • Copper and zinc behave similarly to lead. Other metals (vanadium, chromium, and nickel) also increase, but the data is noisier. • The research team used the vanadium:chromium and nickel:cobalt ratios to understand Utah Lake's oxic, dysoxic, and anoxic states. All three cores are in the oxic state. However, the study's results do not exclude the lake from becoming episodically anoxic during algal blooms or due to diurnal/nocturnal variations. • The results of the study indicate that anthropogenic activities have impacted Utah Lake. The paper suggests some proxies that are easily and inexpensively measured. Future research could involve putting out sediment traps and periodically retrieving sediment to measure nitrogen isotopes, carbon isotopes, total nitrogen, C:N ratio, total phosphorus, and lead. • The conclusions from the study include: o Exponential population growth, especially after 1950, has impacted the Utah Lake ecosystem. o Overall, the lake has become more eutrophic since European settlement, with added pressures in the mid-20th century. Effects were more pronounced in Provo Bay. o Some parameters suggest stabilization in recent decades (phosphorus, lead, nitrogen-15). o Calcite production has remained high and steady. Utah Lake has probably always been turbid. o Diatom analysis of selected horizons may better illustrate the increase in trophic levels since 1850. o The ecosystem state can be easily and inexpensively monitored with material collected in sediment traps. 12 Ongoing Work and Proposed Future Studies • Proposed future work includes directly measuring phosphorus in porewater to estimate internal loading. Researchers can use freeze cores to measure phosphorus in porewater to a one-centimeter resolution, which is difficult to obtain using peepers. Dr. Steve Nelson has used this method to measure phosphorus in porewater to estimate internal loading in Farmington Bay, the southeastern arm of the Great Salt Lake. • The research team has ongoing work. They deployed four (potentially five) active air samplers. The samplers filter total suspended solids at Lincoln Point, Saratoga Springs, Timpanogas Special Service District (TSSD), and Provo High. They planned on installing one at the state park but could not due to liability reasons. They also want to install a fifth sampler on Bird Island. The plan is to collect dust from the samplers every two weeks. They will then use X-ray fluorescence to analyze the phosphorus content of the dust and X-ray diffraction to measure the dust's mineralogy. They will also draw water through the filters and reanalyze the dust. These methods will allow researchers to distinguish how much phosphorus is deposited as dust from the atmosphere and how phosphorus is deposited from other sources, like birds. The purpose of the study is not to quantify how much phosphorus is deposited onto the Utah Lake surface; it is to quantify how much dust from the atmosphere becomes bioavailable. Science Panel Clarifying Questions Science Panel members asked clarifying questions about the results of the study. Their questions are indicated in italics below, with the corresponding responses in plain text. Regarding the five air samplers collecting dust particles, why is it not the purpose of the study to quantify the amount of phosphorus deposited on the lake? The study's results should allow researchers to quantify the amount of phosphorus deposited on Utah Lake by measuring the mass recovered in the air sampler filter. The study's primary goal is to identify how much phosphorus deposited onto Utah Lake from the atmosphere becomes bioavailable. Is it possible to install the sampler intended for the state park in the middle of the lake? Bird Island appears to be the only feasible location to install an air sampler on Utah Lake. The sampler originally intended to be placed in the state park is now located on the press box of Provo High. Other locations they considered for the study but were not feasible included the Provo River Delta (currently experiencing a high level of construction) and the airport. It is difficult to strategically locate samplers to quantify the whole lake's deposition. What is the data's resolution for comparing algae and macrophyte abundance using C:N ratios? Do the materials from macrophytes last longer? • The cellulosic material is refractory. The research team took cores in the open water, not where there was emergent vegetation. The results may have differed if they had taken cores near phragmites. • The diatom research will provide more evidence on nutrient loading, pH, and metabolism levels. The research team may be able to produce insights into the abundance of epiphytic diatoms, which in turn will provide information on the abundance of emergent vegetation. 13 What is the sedimentation rate for Provo Bay? Dr. Nelson would have to recalculate the sedimentation rate. When the research team collected the cores in Provo Bay, they did not experience refusal until 45 centimeters. The sedimentation rate between Provo Bay and Goshen Bay was similar; the deep water core had a slower sedimentation rate. Those estimated numbers will be in the published paper. Public Clarifying Questions Members of the public asked clarifying questions about the results of the study. Their questions are indicated in italics below, with the corresponding responses in plain text. Did the C:N ratio analysis results suggest that algae dominated in Utah Lake compared to macrophytes? Algae dominated the organic matter composition, more so than macrophytes, in all parts of the core. However, the domination of algae becomes more pronounced closer to the core surface, particularly for Goshen and Provo Bays. Is it possible to assess the C:N ratio to understand the abundance of zooplankton over time? Yes, but someone must provide the C:N ratio for zooplankton. Were there mollusk shells in the core? There were very few mollusk shells found in the cores. LIMNOCORRAL STUDY OVERVIEW Rich Mickelsen, TSSD, and Dr. David Richards, OreoHelix Ecological, presented an overview of the Limnocorral Study. The presentation, the subsequent Science Panel discussion, and public comments are summarized below. Limnocorral Study Presentation Below is a summary of the Limnocorral Study presentation. Limnocorral Study Overview • The TSSD provides wastewater treatment to over 300,000 households, discharging over 20 million gallons to Utah Lake. The TSSD is using limnocorrals to research how different factors will impact in-lake conditions. • The purpose of the Limnocorral Study is to conduct experiments to understand better how different management methods can improve the lake's water quality. The Limnocorral Study is intended to serve as a pilot project to test how changes to different variables in Utah Lake will affect water quality. Eventually, the idea is to use the study results to identify different management approaches at scale to improve water quality conditions in Utah Lake. • The research investigators of the study include: o Dr. David Richards, OreoHelix Ecological o Dr. Gus Williams, BYU o Brett Marshall, River Continuum Concepts o Rushforth Phycology o Blake Wellard and Company • The management team leads include Rich Mickelsen and Jeff Den Bleyker (Jacobs Engineering). BYU students, TSSD staff, and WFWQC technicians collected data and helped install the limnocorrals. 14 • The limnocorrals are similar to pulse disturbances to the ecosystem; they are designed to have a short-term but large impact on the ecosystem. They are expected to elicit a strong response (i.e., effect versus no effect). Limnocorral experiments often lack statistical rigor due to a lack of replication. However, results can provide evidence of either being consistent with and supporting known phenomena or not supporting them. • Technical challenges associated with limnocorrals include installing them and keeping them functioning properly. Wind gusts produce large waves that threaten to destabilize the limnocorrals. Over time, the research team found different methods for securing the limnocorrals, and they can now better withstand wind events and waves. • The research team uses the limnocorrals to assess the impact of wave reduction, carp bioturbation reduction, planktivorous and benthic fishes, aquatic plants, bivalves, and nutrients on several response variables. Those response variables include chemistry (e.g., nutrients and more), light attenuation, phytoplankton assemblages (including cyanobacteria and limited periphyton assemblages), zooplankton assemblages, benthic invertebrate assemblages, and limited native aquatic vegetation. Dr. Gus Williams is writing the paper on how the limnocorral treatments impacted the water chemistry. • The general hypothesis was that the limnocorrals, all of which blocked wave action (and most of which eliminated large carp effects), would reduce turbidity and decrease light attenuation. The researchers also hypothesized that the reduced turbidity would result in greater phytoplankton biovolume inside the corrals than in the lake and that the phytoplankton diversity and relative abundance would differ inside the corrals than in the lake. Limnocorral Study Design and Results • Each corral received a different treatment. Corrals 1-5 were considered shallow water corrals (depth less than one meter), and corrals 6-10 were considered deep water corrals (depth between one meter and two meters). Below are the treatment approaches for the ten corrals: o Corral 1: Included macrophytes and bivalves o Corral 2: Included macrophytes only o Corral 3: Included macrophytes, bivalves, and carp o Corral 4: Control o Corral 5: Control o Corral 6: Included zooplanktivores and lake mixing o Corral 7: Included nutrient addition o Corral 8: Included large carp and zooplanktivores o Corral 9: Included zooplanktivores at low density o Corral 10: Control • In Utah Lake, juvenile carp are estimated to consume more than 47 trillion zooplankton every growing season. In Corral 6, carp eggs were inadvertently laid on the inside of the corrals before deployment. Subsequently, early life stage and juvenile carp remained in the corral throughout the experiment. • Throughout the experiment, the research team identified 82 taxa genera/species of phytoplankton in 38 samples. They estimate 101 to 116 different taxa exist in Utah Lake, but the effective number of dominant taxa is between 9 and 28. The assemblages varied seasonally and inside versus outside the limnocorrals. The assemblages also varied by treatment. There was significantly less total phytoplankton biovolume in the corrals than in the lake, likely due to blocked wave action, carp exclusion, and zooplankton that ate the phytoplankton within the corrals. 15 • The analysis assesses zooplankton at the species level. The research team also analyzed differences in zooplankton population based on time, treatment, and inside versus outside the corrals. Overall, there were more zooplankton in the corrals than in the lake, which was expected given that corrals blocked wave action, increased light penetration, and excluded fish (which occurred in most of the corrals). A linear regression between zooplankton abundance and total phytoplankton biovolume shows a negative relationship; as zooplankton populations decrease, total phytoplankton biovolume increases. • The research team assessed the relationship between zooplankton and total phytoplankton across each corral. Corral 7, the corral in which the research team added nutrients, had the highest zooplankton abundance and the lowest total phytoplankton biovolume. The research team added nutrients to Corral 7 on August 3. The chlorophyll-a level in the corral spiked two to three days later. The research team measured the ecological response on August 16. They found that the zooplankton had devoured the phytoplankton. They also found that light penetration reached the bottom of the corral and beyond. The filamentous green algae proliferated, and periphyton growth inside the corral was highly abundant. The periphyton also outcompeted phytoplankton after heavy grazing. The filamentous green algae provided habitat for thousands of zooplankton and other invertebrates. • The benthic invertebrate population increased from May to October at a faster rate in the corrals compared to their rate of increase in Utah Lake. Most of the benthic invertebrates were chironomids. • Many filamentous green algae were present in the periphyton, not just Cladophora. The other green algae include Oedogonium, Mougeotia, Stigeoclonium, Microspora, and Spirogyra. There were also diatoms found in the filamentous green algae. • The unfiltered reactive phosphorus, filtered reactive phosphorus, and total phosphorus levels spiked in the lake in September, and by October, the phosphorus levels settled back to average levels. • The research team measured predicted turbidity, predicted Secchi depth, and light attenuation coefficients to measure light attenuation. Corral 6 had the lowest visibility, most likely because it was not sealed as well as other corrals, and some of the lake water flowed through it. The corrals that excluded fish had the highest light penetration. • The research team plotted the relationship between zooplankton abundance and turbidity. They found that higher zooplankton abundance is correlated to greater Secchi depth. This pattern may be due to zooplankton eating the phytoplankton, which improves water clarity. • The research team planted macrophytes in some of the corrals. The macrophytes present were primarily hardstem bulrush and cattails. The macrophytes survived when carp were excluded. Light penetration to the bottom of the lake affected how the team planted the macrophytes. Macrophyte seeds would not receive enough light at the bottom of the lake, so the research team had to plant tall macrophytes to receive light. The macrophytes continue to grow through the seasons, but the research team recently removed the fences, so it remains to be seen whether they will survive the reintroduction of carp. Limnocorral Study Conclusions • The conclusions from the study were that reducing wave and carp turbation resulted in the following: o An increase in light availability o A thriving zooplankton community that consumes phytoplankton, including cyanobacteria 16 o The stabilization of substrate (including skirts), which allowed filamentous green algae to attach, compete with phytoplankton for nutrients, and provide structural habitat for many species and the unique food web within • A healthy dynamic in Utah Lake would begin with the growth of macrophytes to stabilize the sediment. From the macrophytes, periphyton grows, and the nutrients cycle between the water column and periphyton. The phytoplankton primary production is eaten by zooplankton and bivalve filter feed. (The research team attempted to establish bivalves in the limnocorral, but they did not survive due to the muddy conditions.) • Based on these findings and what is known and practiced worldwide, restorative measures can improve Utah Lake's food web, including its health, integrity, and resilience to future perturbation. TSSD Integrated Solutions for Utah Lake Overview • The purpose of the ULWQS is to generate numeric nutrient criteria. The wastewater treatment plants want to know whether reducing nutrients will result in use attainment, as upgrades to wastewater treatment plants are expensive. • The TSSD hired Jeff Den Bleyker from Jacobs Engineering to oversee the Limnocorral Study and act as an independent third party. The TSSD is also conducting a different study on atmospheric deposition to better understand the atmospheric contributions to Utah Lake. • The goal of the Limnocorral Study and other studies conducted by TSSD is to look at Utah Lake as a whole system and develop integrated solutions that holistically consider watershed inputs, in-lake nutrient cycling, and ecosystem structures. Integrated solutions will help avoid using chemical amendments, such as aluminum chlorohydrate (ACH), to manage harmful algal blooms in Utah Lake. • The studies are not intended to compete with the ULWQS but to provide complementary information. The results of the Limnocorral Study align with many of the research questions proposed by the ULWQS Science Panel. • The next step for the TSSD is to consider how to establish native plants at scale on the shoreline. One potential option would be to use the area in front of the TSSD as a pilot study to figure out different methods to establish and recover vegetation in the littoral zone. • Atmospheric deposition changes annually, so it is an important factor to consider when determining how to reach use attainability in Utah Lake. • It is important to understand how different changes in nutrient levels may affect Utah Lake. For example, reducing nitrogen may make it more difficult for non-toxic green algae to compete against cyanobacteria, creating an environment that facilitates more cyanobacteria growth. • The Wasatch Front Water Quality Council (WFWQC) created a brochure identifying six strategies for addressing water quality in Utah Lake. The six identified strategies to restore Utah Lake as a functioning ecosystem are: o Sediment stabilization o Increased light depth o Carp reduction o Restoration of native aquatic plants and mollusks o Balanced fishery o Nutrient reduction 17 Science Panel Clarifying Questions Science Panel members asked clarifying questions about the results from the Limnocorral Study and the integrated solutions for Utah Lake. Their questions are indicated in italics below, with the corresponding responses in plain text. If there is a need to use chemical amendments, is there a reason TSSD would use ACH? The recommendation came from Jacobs Engineering, whose team has spent their careers recovering multiple lakes. The Jacobs Engineering team first used ACH in wetlands and then piloted it in other reservoirs. So far, the ACH treatments have reduced algal growth in other reservoirs and lakes. UTAH LAKE MASS BALANCE OVERVIEW Dr. Mike Brett, University of Washington, presented an overview of his effort to develop a mass balance model for Utah Lake. The presentation, the subsequent Science Panel discussion, and public comments are summarized below. Utah Lake Mass Balance Overview Presentation • The general mass balance model assumes that changes in the lake are equal to input minus output minus removal. This assumption can be applied to phosphorus to create the expression that the change in phosphorus in the lake is equal to the mass flux into the lake minus mass flux out of the lake minus any mass changes in the system (i.e., the phosphorus sequestered into the sediment). • If one assumes the lake is a steady-state system, then the change in phosphorus within the lake is assumed to be zero. This assumption allows one to rearrange the expression to assume that the input of phosphorus equals the output of phosphorus plus the amount removed from the system. • The phosphorus removed from Utah Lake is primarily lost to the sediments. There is a constant exchange of phosphorus between the water column and sediments. The mass balance model represents the net effect of this dynamic. The results of the mass balance model indicate that Utah Lake is sequestering 95% of the phosphorus. • Dr. Brett used data on phosphorus inputs from tributaries, stormwater drains, precipitation, wastewater treatment plants and atmospheric deposition to calculate the amount of phosphorus coming into the lake. All the inputs are quantified as concentrations, except atmospheric deposition, which is quantified as a load since it is not directly associated with water. The mass balance calculations apply an attenuation rate of 16.5% to wastewater discharges upstream from Utah Lake since some phosphorus and nitrogen are lost as it travels from the discharge point to the lake. • The mass balance model allows one to predict how the lake's phosphorus concentration will change based on the input concentrations for major point sources. There is a point of diminishing returns for removing phosphorus from wastewater effluent. The amount of capital required, operations and maintenance costs, energy use, and greenhouse gas emissions rapidly increase at lower wastewater treatment plant effluent concentrations. There is a balance between nutrient removal, greenhouse gas emissions, water quality benefits, and costs. • At wastewater treatment plant effluent total phosphorus concentrations less than one milligram/liter, wastewater discharges constitute less than 50% of phosphorus inputs to Utah Lake. At wastewater treatment plant effluent total phosphorus concentrations less than 0.5 milligrams/liter, the phosphorus inputs to Utah Lake become increasingly dominated by particulate phosphorus (as wastewater treatment phosphorus inputs come in 18 the form of dissolved phosphorus). Lakes are generally better at sequestering particulate phosphorus into the sediments than dissolved phosphorus, so a higher fraction of particulate phosphorus loading should result in less phytoplankton biomass production and greater phosphorus removal in Utah Lake relative to total phosphorus. • The mass balance model can predict how long Utah Lake would take to transition to a new steady state. The time it would take Utah Lake to transition to a new steady state is largely governed by the first-order loss rate since much of the phosphorus entering Utah Lake is removed from the water column and captured in the sediments. The mass balance equation indicates that if one accounts for the removal of phosphorus and the flushing rate of phosphorus from the lake, Utah Lake will transition to a new steady state in one to three years. Since Utah Lake is so effective at removing phosphorus from the water column and capturing it into the sediments, the transition to a new steady state will occur rapidly. • Another factor to account for in the future is an increase in population. Population growth will increase the flow coming from the wastewater treatment plants. The mass balance model can estimate in-lake phosphorus concentrations under different scenarios (e.g., flow increases/effluent concentration stays the same, flow increases/effluent concentration goes to 0.25 milligram/liter, etc.). The mass balance model indicates that biological-phosphorus removal or Membrane BioReactor (with water reuse) would result in a 50% total decrease in phosphorus concentration in Utah Lake, even when the flow is doubled, compared to current conditions. • The mass balance model can also simulate future climatic/hydrologic conditions like droughts. Dr. Brett calculated the 25th, 50th, and 75th percentile for precipitation over the past 100 years using the US Geological Survey (USGS)100-year flow index. Those percentiles can be used to define dry years (a 25th percentile precipitation year) and wet years (a 75th percentile precipitation year). These percentiles can be used to create future scenarios to run through the mass balance model (e.g., dry year with constant loading values, dry year with a decrease in loading values, etc.). The model indicated that Utah Lake is not very sensitive to hydrologic changes. Under drier conditions, the input concentrations increase, but residence time also increases, making it more likely that phosphorus will settle into the sediment. • The mass balance model estimates phosphorus dynamics by observing how much phosphorus is coming into Utah Lake and how much is leaving. The mass balance model does not directly measure the amount of phosphorus removed from the system. • The calculation to estimate the sediment phosphorus accumulation in Utah Lake is Sediment phosphorus accumulation = net sedimentation * (sediment dry mass/sediment wet volume) * (sediment phosphorus mass/sediment dry mass) * lake surface area. The result of this calculation can be compared to the loss rate identified in the mass balance model, which assumes that the input of nutrients in Utah Lake from the watershed, wastewater treatment plants, and atmospheric deposition equals the nutrient output and the amount of nutrients lost to the sediments. • When the calculated sediment phosphorus accumulation value is compared to the loss rate in the mass balance model, the sediment phosphorus accumulation rate is 75% higher than the mass balance model estimate. Within the sediment phosphorus accumulation calculation, there is high confidence in the dry weight conversion and sediment phosphorus content values; however, there is less confidence in the net sedimentation value in Utah Lake. The net sedimentation dataset has a small sample size and is highly variable. The uncertainty in the net sedimentation value results in less confidence in the sediment phosphorus accumulation value. 19 • There is a possibility to set up an interactive Utah Lake mass balance model to simulate future conditions under different scenarios (e.g., drought reduces inflow). Science Panel Comments • The sedimentation phosphorus accumulation calculation measures gross sedimentation, while the mass balance measures the net flux. They may not be comparable. • Mass balance scenarios are based on specific assumptions. An interactive Utah Lake mass balance model would allow people to modify the model with their assumptions to see if there is a convergence in ideas. • Utah Lake can be a source of phosphorus. The mass balance model does not necessarily account for that dynamic. If Utah Lake acts as a source of phosphorus, that could elongate the time it takes to reach a new steady state. • In Upper Klamath Lake, the sediments act as a source of phosphorus in the summer. The amount of phosphorus going into Upper Klamath Lake is three times less than that of Utah Lake. Yet, the phosphorous concentration of Klamath Lake is three times higher than the concentration in Utah Lake. Utah Lake is different from Upper Klamath Lake in that the calcite in Utah Lake allows it to hold phosphorus uniquely and effectively in the system. The phosphorus loss to the sediments in Utah Lake is being put into forms that are not likely to be re-released. Public Comments • The USGS flow data from the past 100 years is a good indicator of what has occurred in the past. It is less reliable when determining what will happen in the future. • The core location at which net sedimentation is measured in Utah Lake will impact the data. The density and porosity of the sediment change over time and location. • One potential research approach would be to look at the density in freeze cores as a function of depth/time to understand how it changes. • The phosphorus concentration in the water column is much lower than in the porewater. Mass Balance Next Steps The Science Panel will form a mass balance subgroup to help inform the development and functionality of an interactive mass balance tool, allowing users to test assumptions and future scenarios. The Science Panel subgroup will need to consider whether to create the tool for Provo Bay or expand the tool to nitrogen. The tool will also be useful for the Steering Committee's implementation planning effort, which will also explore non-point reduction and in-lake management strategies to address nutrient loading into Utah Lake. A mass balance tool will help assess management strategies and future conditions. UTAH LAKE NUTRIENT CYCLING OVERVIEW Dr. Theron Miller, Wasatch Front Water Quality Council, presented an overview of his hypothesis for nutrient cycling in Utah Lake. The presentation, the subsequent Science Panel discussion, and public comments are summarized below. Utah Lake Nutrient Cycling Overview Presentation • Jacob Taggart's 2021 Masters Thesis, titled Inorganic Phosphorus Chemistry Of Utah Lake's Effluent Mixing Zones, examined how treated effluent from the Orem Wastewater Treatment Plant effluent mixes with lake water. He took different combinations of effluent, primarily composed of orthophosphate, mixed it with lake water, and measured orthophosphate concentrations over time. The concentrations did not change over time, both in the 20 immediate aftermath of mixing and 30 days after the initial mixing. The samples were stored in the dark with a consistent pH between 8.3 and 8.5. The study concludes that the lake calcite is not sorbing orthophosphate. • Taggart (2021) used the PHREEQC model to assess the results. According to the PHREEQC models, the results of the Taggart (2021) experiment most closely aligned with a system that does not have apatite precipitation. • The next step in the study was to supplement the Utah Lake water with calcite and mix it with the wastewater treatment plant effluent. The Utah Lake water supplemented with calcite was effective at co-precipitating the orthophosphate in the effluent. • In the 2019 paper Sediment Potentially Controls In-Lake Phosphorus Cycling and Harmful Cyanobacteria in Shallow, Eutrophic Utah Lake, Randall et al. conducted sequential extractions on Utah Lake sediment. They found that 41-61% of the phosphorus in the sediment was associated with the BD fraction (iron and manganese bound). • The porewater in Utah Lake contains large amounts of orthophosphate, upwards of 10 milligrams/liter, depending on where someone is on the lake. The orthophosphate in the porewater is readily diffusible. The phosphorus in the porewater can be exchanged into the water column if phosphorus concentrations in the water column decrease. • According to the US Geological Survey's sediment traps, the Great Salt Lake experiences 4 to 4.5 millimeters of sediment deposition each year. This observation prompts the question of how much dust is falling on Utah Lake and how much phosphorus in the dust is biologically available. Is the phosphorus iron-bound or calcite-bound? • One hypothesis is that the phosphorus in the dust is primarily calcite-bound. If this hypothesis is true, then much of the calcite-bound phosphorus may be coming from the atmosphere and not from the co-precipitation of orthophosphate and calcite in the lake, which may explain why mixing effluent with lake water in Taggart's (2021) experiment did not result in the co-precipitation of calcite-bound phosphorus. If much of the calcite comes from the atmosphere, then the phosphorus inputs into the lake must bind with something. If not calcite, the phosphorus entering Utah Lake may be binding with iron/manganese. Science Panel Comments The Taggert (2021) experiments were designed to exclude primary production. Primary production drives calcite production by lowering the pH. The experiment's pH was 8.5, which is high enough to precipitate calcite. Evaporation can also impact phosphorus concentrations and calcite-binding. In the future, it may be valuable to repeat the experiments in a way that accounts for biotic and evaporation impacts. NEXT STEPS The Science Panel will convene on June 29 at 8 am to continue discussions.