Certain species of cyanobacteria (blue-green algae) contain cyanotoxins, which are harmful compounds that pose a growing threat to public health and recreational water safety. These toxins can accumulate in water and shoreline sediments at public beaches, potentially exposing the public, pets, and staff to health risks. Still, the detection and monitoring of cyanotoxins continues to be a challenge, especially because harmful algal events are not always visible, and the toxin levels can fluctuate rapidly. Laboratory tests like HPLC and ELISA are known for high accuracy but require trained personnel and are expensive. This poster explores tools that beach managers and environmental health professionals can use to assess cyanotoxin risk, including laboratory, field-based, and molecular, enabling timely and informed decisions about beach closures, signage, and public safety. 

Authors: Sarah Deguzman - University of Toledo;Garrett Moots - University of Toledo;Dr. Von Sigler - University of Toledo; Cas Smith - University of Toledo

Michigan beaches are monitored through EPA programs to ensure public health protection. Labs across the state participate in this program annually, employing a variety of testing methods. Labs use different testing methods due to differences in detection sensitivity, standardization, and to promote innovation in testing techniques. These methods are often employed simultaneously; however, specific studies comparing the sensitivity of these methods are few. Over the 2024 and 2025 beach seasons, this study tested the sensitivity of Quantitative Polymerase Chain Reaction (qPCR), Propidium Monoazide Quantitative Polymerase Chain Reaction (PMA-qPCR), Imaging Flow Cytometry (IFCM), and the EPA standard Colilert-18 Culture Method to perform a comparative analysis of the sensitivity of detection on freshwater lakes in Muskegon County.

Author: Christopher L. Kotkowicz, Katelyn R. Anderson, Jacob A. Kotkowicz, Kevin B. Strychar

Microbial Source Tracking (MST) was performed in an effort to determine the origin of fecal contamination in samples collected from Bay County (Michigan) beaches and inlets. Our MST analysis relies on the methods of digital drop Polymerase Chain Reaction (ddPCR), with duplexed targets for Gull/Human, Ruminant/Bovine, and Canine/ND2(Canada Goose). Here, a survey of multiple sample sites collected in the summers of 2024 and 2025 are included. The sites included were sampled at various areas in Bay County including beaches, streams, drains, and rivers. Particular attention in analysis was paid to days on which beaches were closed for human full-body contact, which was primarily Bay City State Park during this time frame. By cross-referencing the Colilert and MST assays, main contender(s) for sources of fecal contamination can be inferred and communicated with our local health department and government partners.

Authors: Alaina Seman*, Saginaw Valley State University undergraduate student, ahseman@svsu.edu; Logan Seyuin*, Saginaw Valley State University undergraduate student, ljseyuin@SVSU.edu; Lewisky Zacharia*, Saginaw Valley State University undergraduate student, lpzachar@SVSU.edu; Tami L. Sivy, Ph.D., Saginaw Valley State University undergraduate student, Professor of Chemistry, tsivy@svsu.edu

Harmful algal blooms (HABs) are increasing in prevalence and intensity worldwide, notably in Lake Erie. On the southern shore of Lake Erie, there are over 300 miles of shoreline that are impacted by annual algal blooms. The foreshore sands, where waves bring algal inputs and humans frequently interact, are of particular concern. To understand the presence of microcystin (MC) at public beaches on Lake Erie, foreshore sand and water samples were collected and analyzed for MC using Enzyme-Linked-Immunosorbent-Assay (ELISA) from Maumee Bay State Park Beach (MBSP) (Oregon, OH), Lakeview Beach (Lorain, OH), and Huntington Beach (Bay Village, OH) during the 2022 recreational swim season (June-September). Generally, MC concentrations in both sand and water were higher in the western beach (MBSP) and decreased on a gradient eastward. Additionally, MC concentrations in the sand tended to exceed the MC concentrations in the water, suggesting not only deposition, but also accumulation. Specifically, seasonal mean MC concentrations in sand at MBSP were 3.0 µg/L, whereas sand MC concentrations were 0.8 and 0.35 µg/L at Lakeview Beach and Huntington Beach, respectively. In the water, mean seasonal MC concentrations were 3.0, 0.64, 0.48 µg/L at MBSP, Lakeview Beach, and Huntington Beach respectively. Overall, as HABs increase in prevalence and intensity, beach managers will need to be more proactive in monitoring and management to protect recreational beachgoers.

Authors: Cas Smith- University of Toledo; Garrett Moots - University of Toledo;Sarah Deguzman - University of Toledo;Dr. Von Sigler - University of Toledo

In the last decade, several molecular tests for microbial contamination have been developed to assess levels of risk for human contact in recreational waters and to identify potential sources of contamination. Historical methods, such as Colilert, require overnight incubation, extending response times for beach closures and potentially increasing human exposure to microbial contaminants. As a result, the rapid quantitative PCR (qPCR)-based EPA Method C was developed and has been used in conjunction with standard 18-24 hour Colilert tests by our lab and others in MiNET to evaluate water quality at recreational beaches and rivers. In addition, digital drop PCR (ddPCR) technology has been employed to help inform whether sources of contamination are human, avian, or other mammals, known collectively as Molecular Source Tracking (MST). Our recent objectives have extended to study the efficacy of using ddPCR for E. coli quantification as a possible replacement for Method C in determining beach closings. Samples collected in 2024 and 2025 from Bay County, Michigan allowed for comparison of the three methods in measuring E. coli levels. Our preliminary results indicate a low degree of correlation between ddPCR and qPCR and ddPCR and Colilert, with better agreement between qPCR and Colilert. Further assay optimization of ddPCR E. coli assays is needed, as well as a threshold set for acceptable human exposure. If shown to be effective, a ddPCR-based method for measurement of E. coli as a fecal indicator organism would have the rapid results that qPCR provides while potentially eliminating inhibition.

Authors: Alaina Seman*, Saginaw Valley State University undergraduate student, ahseman@svsu.edu; Logan Seyuin*, Saginaw Valley State University undergraduate student, ljseyuin@SVSU.edu;Lewisky Zacharia*, Saginaw Valley State University undergraduate student, lpzachar@SVSU.edu; Tami L. Sivy, Ph.D., Saginaw Valley State University undergraduate student, Professor of Chemistry, tsivy@svsu.edu

Contamination of public recreational water and sand can be a human health concern, creating a management challenge for public health officials. Past research has shown that Escherichia coli can persist in sediment, which can be washed into recreational water. Currently, beach monitoring practices only utilize E. coli concentrations in water samples to determine beach safety and do not take into account potential exposure to sediment/sand concentrations. In this study, we have utilized commonly recreated beaches on Lake Michigan to investigate the relationship between E. coli concentrations in water and sand samples, which can aid public health officials in making more informed decisions about beach closures. This was achieved using culture-based measurements during four unique sampling events at two site locations to compare sand and water E. coli concentrations to one another and at different water depths. Additionally, we’ve tracked the sources of contamination using microbial source tracking methods(ddPCR). Results from this project have shown Colilert concentrations from tributary inputs exceeded the 300 cfu standard and can enter Lake Michigan beaches, leading to increased E. Coli concentrations in swimming areas. This research provides more information about the dynamic ways in which contamination can enter recreational areas and cause beach closures.

Water quality monitoring helps inform local health departments of contamination issues related to recreational water. The State of Michigan uses E.coli as a water quality indicator where 300 MPN/100mL is used as a threshold value for beach notifications. While this water quality test helps inform about exceedances in Lakes or Rivers, further investigation with microbial source tracking molecular tool helps provide information on the sources of contamination impacting water bodies. Michigan’s beach water testing network (MiNET) monitors water quality indicators and sources of fecal contamination using advanced molecular tools during the swim season and provides information on spatial and temporal trends for beaches in Michigan. The E.coli data is displayed on a public dashboard (https://mienviro.michigan.gov/explorer/Beach/map/results) and accessible to local health departments (LHDs). This project focuses on facilitating a data pipeline to harmonize, collate and aggregate microbial source tracking (MST) data from the program to create a statewide database which can be made available to LHDs. to facilitate decision making.

The project was initiated by creating a data template to compile quantitative MST target concentrations available during the monitoring period. The template includes site, sample specific metadata in addition to space for inputting E.coli and MST data with guidelines outlined in a data dictionary. We used this template to collate data from 52 samples (E. coli concentrations- 2.19x102-1.3x105MPN/100mL) collected from 11 sites in Michigan between July 2023-September 2024. Samples were tested for the Human HF183 and B. thetaiotaomicron (B.theta), Bovine CowM2 markers. 29% (15/52) of the samples tested were positive for at least one source tracking marker. Positivity rates were 17% (9/52) for HF183, 15% (8/52) for B.theta and 0% (0/30) for CowM2. The average concentrations of the HF183 marker was 4.19x103 gene copies/100mL and B.theta marker was 2.68x103 gene copies/100mL. The data. The data suggests that contamination from human sources was most abundant within this data set based on the markers tested and HF183 was the most frequent human marker detected.

The data template facilitated data characterization and analysis for this dataset and is a promising tool to create a comprehensive database for MST data at county, state or national levels. This knowledgebase can help inform testing within monitoring regions and allow prioritization of markers which may historically impact water quality, thereby providing focused and cost-efficient targeted insights and mitigation framework. The data can also be communicated to the public to support programs for water quality awareness and stewardship.

Authors: Gessica Portice1; Rebecca Riggi1; Alexis M. Porter2; Molly Rippke3; Nishita D’Souza1; 1Michigan State University; 2Annis Water Resources Institute; 3Michigan Department of Environment, Great Lakes and Energy

Microplastics are defined as particles of plastic ranging from 1 µm to 5 mm and nanoplastics as particles of plastic smaller than 1 µm. Micro and nanoplastics have been linked to negative health effects such as cancer, general inflammation and reproductive harm for both humans and animals. It is vital for research to be done on the formation of microplastics due to the fragmenting of larger pieces of plastics, as they permeate everything and are present all over the earth as well as being present in humans and animals. This research has focused on understanding the fragmentation of oxidized real world plastics obtained from the southern Lake Michigan shoreline in Indiana using techniques previously used on lab plastic, sourced as pure polymers; these were determined to release small microplastics and nanoplastics in water in the presence of other liquid compounds. Real world plastic has major differences from the pure polymers since chemicals are added that can soften plastic, absorb UV light, and impart color. Real world plastic is also often mixed with other plastic types in polymers. Furthermore, real world plastics in the environment are subject to conditions that can oxidize the surface, a process where plastic combines with oxygen. Pieces of plastic were solubilized in 15 mL of water, using 20 µL of the chemical, n-dodecane, that was used to facilitate the fragmentation of lab plastics based on earlier experiments using lab plastics. The different conditions included- 15 mL H2O and 20 µL of n-dodecane, with one set exposed to UV radiation; 13.5 mL of H2O,1.5 mL of 30% H2O2 and 20 µL n-dodecane, with one set exposed to UV. Each set of experiments involved pieces of polypropylene and polyethylene, separately, and each underwent solubilization a total of 5 times for 24 hours per solubilization. The UV light-exposed samples were irradiated for 5 hours. Infrared spectroscopy was used to determine the carbonyl index, the measure of oxidation, of the plastic surfaces after each solubilization. Thus far, the varying conditions show different changes in the surface. Further research needs to be done to obtain more data in order to better understand the oxidation and fragmentation process of real world plastics.

Authors: Dr. Christina Davis (Valparaiso University) , Vincent Grisolano (Valparaiso University), Jaden Gibson (Valparaiso University), Dr. Julie Peller (Valparaiso University)

Time and financial constraints during the COVID-19 pandemic disrupted many environmental monitoring efforts, including in Wayne County, Michigan. Prior to the pandemic (2010-2019), Sherwood Pond (SH; Sumpter Twp.), Van Buren Beach (VBB) on Belleville Lake, and Sumac Pointe on Newburgh Lake (NL) were monitored and occasionally closed or posted with advisories due to high Escherichia coli, up to 45, 26, and >75 days, respectively. Following the end of the federal COVID-19 public health emergency, public health was able to redirect capacity to resume monitoring in 2025. Wayne State University personnel conducted weekly surveys at SH, VBB, and NL from June to September 2025, analyzing three water samples per site for E. coli with Colilert-18/Quantitray 2000, along with sanitary surveys, physico-chemical measurements, and evaluation of ddPCR E. coli and source-tracking methods. At SH and VBB, single-day geometric means were below 300 CFU/100 mL throughout the sampling period. Thirty-day geometric means were <30 CFU/100 mL for VBB and <100 CFU/100 mL for SH. In contrast, NL sometimes exceeded 1,000 CFU/100 mL in June and July, coinciding with rainfall and many geese observed during sanitary surveys. NL’s 30-day geomeans exceeded 200 CFU/100mL for much of the season, leading to a 10-day closure when levels exceeded 1,000 /CFU/100 mL and a subsequent “no immersion” advisory issued by HHVS. The overall trends in E. coli levels at NL have prompted further discussion about shifting NL to “partial-body contact” access only.

Exploratory sampling of aquatic macroinvertebrates during monitoring activities revealed high abundances at NL of copepods, ostracods, and Acari (water mites). Among the water mites, Arrenurus and Lebertia species were common, with Lebertia specimens reaching up to 2 mm in diameter, among the largest water mites ever observed by our team. Collected Lebertia laid eggs in freshwater multiwell plates, displayed brooding behavior, and hatched larvae after approximately two weeks. Water mites are not known to transmit human diseases and may benefit public health by preying on mosquito larvae, as demonstrated by Next Generation Sequencing (Vasquez et al., 2021; McNay et al., in preparation). However, they may also compete nutritionally with fish for worms, larvae, and other aquatic invertebrates (Vasquez et al., 2021, 2022).

Future studies will further evaluate ddPCR sensitivity for E. coli, identify bacterial sources and diversity, and investigate the diets and ecological roles of water mites in Wayne County’s inland water access points and lakes.

Acknowledgements: HHVS participants include Lukas Ayers, Avani Sheth, Theresa Brestovansky, Brennan Burk, Katerina Stylianou. Funded by EGLE (State of Michigan) and Wayne State University.

Authors: Ali Jomaa1; Sneha Ghosh1; Zykevise Gamble1,2; Dylan McNay1,3; Wayne County Department of Health, Human, and Veterans Services (HHVS)4; and Jeffrey L. Ram1; Department of Physiology, Wayne State University, Detroit, MI; 2Kennedy Krieger Institute, Baltimore, MD; 3Environmental Science Program, Wayne State University, Detroit, MI; 4Members of HHVS will be acknowledged

The safety of the public relies on timely and accurate recreational water quality monitoring. Colilert (C) is a culture-based assay used to test water quality in Michigan by specifically testing for the presence of coliforms and Escherichia coli (E. coli). A threshold value for E.coli of 300 MPN/100mL is used in Michigan to close/notify a beach to protect public health . Although this assay provides reliable quantification, it requires qualified lab personnel and 24 hours to incubate, making it inefficient for real time results. This time delay allows beaches to remain open until beach managers receive test results the next day, subjecting the public to possible health risks.

The Bactiquick (BQ) test is a potential alternative to Colilert, as it is designed for rapid detection (within 15 mins) of a broad range of gram-negative bacteria through Endotoxin Risk Units (ERU).

In this study, we evaluated the performance of Bactiquick in comparison to Colilert with emphasis on its ability to detect endotoxin levels in recreational waters. A preliminary study using 8 sampling events at 5 different sites (3 inland lakes and 2 great lakes beaches) for a total of 39 samples was conducted. The results for each method were grouped into two categories based on how they would be interpreted for beach action. The first is a “risk” category was assigned when the results would trigger a beach notification or closure; for BQ this was when sample results were ≥44 ERU, and for Colilert when sample results ≥300 MPN/100mL. The second was a “no risk” category assigned when when the results would not cause a beach notification or closure; for BQ this was when results were <44 ERU, and for Colilert when results were <300 MPN/100mL. Overall, there was a 62% (24/39) agreement for the BQ and Colilert results. For results which were categorized in the “no risk” group, there was 100% (21/21) agreement with BQ and Colilert results. For results which were categorized in the “ risk” group, 16.6% (3/18) BQ “risk” results showed agreement with Colilert results (i.e. Bactiquick would have triggered a beach notification when Colilert would) but 83% (15/18) of Bactiquick “ risk” results did not show agreement with Colilert results (i.e. Bactiquick would have triggered a beach notification when Colilert would have resulted in keeping the beach open).

BQ was able to demonstrate consistent predictive values for Colilert with low-risk samples indicating that it can predict when beaches can be kept open. Our findings suggest more samples will need to be evaluated to determine the suitability of its application for samples associated with higher risk of contamination.

Author: Olivia Cardinell1,;Brian Scull2; Nishita D’Souza1; Rebecca Riggi1;Tayler Murphy1; Spencer Kuehn1; Emilia Emerson1; Erin Dreelin1;Stuart Jones2; Joan B. Rose1; Shannon Briggs3; 1Michigan State University; 2Annis Water Resources Institute, Grand Valley State University; 3Michigan Department of Environment, Great Lakes and Energy

Microbial source tracking (MST)is a tool that can be used to identify sources of fecal contamination in waterbodies that exceed bacterial water quality standards. Water quality managers can use MST information to target resources towards reducing contamination from these specific fecal sources. For human fecal source tracking, water managers may need to choose between multiple available source tracking markers when performing or requesting water analysis. We conducted a pairwise comparison of the HF183 and Bacteroides thetaiotaomicron (Btheta) human markers in 352 freshwater samples analyzed by droplet digital PCR to evaluate the differences in marker detection in environmental samples. In the full dataset, marker concentrations of HF183 were significantly higher than Btheta concentrations (P<0.001, a=0.05). Use of the HF183 marker produced more positive detections in the dataset than Btheta, picking up human source signal from an additional 31% of samples. Physiochemical data, precipitation data, and sample processing methods between human marker positive and human marker negative datasets were assessed to see if these factors were associated with differences in HF183 and Btheta marker detection.

Authors: Rebecca Riggi (MSU), Anika Ashraf (MSU), Nishita D’Souza (MSU), Wenjing Ren (MSU), Andri Rachmadi (MSU), Alshae Logan (MSU), Matthew Flood (MSU), Molly Rippke(EGLE), Joan B. Rose(MSU)

Microbial Source Tracking (MST) is a method used to identify the origin of fecal contamination in environmental water samples. In New York State (NYS), MST is used as a tool to determine appropriate mitigation measures and avert future health hazards. MST uses biological markers from gut microbes specific to different groups of animals such as humans, avians, ruminants, pigs, etc. The Laboratory of Environmental Biology (LEB) uses EPA Method 1696.1 which involves isolating human-associated Bacteroidales from water samples via membrane filtration, extracting total DNA, and concentration and purification of the lysates. In addition, the LEB utilizes assays to detect several non-human DNA markers which help determine if contamination is caused by local agriculture or wildlife. Plasmid-derived DNA standards for human-associated Bacteroidales were utilized to construct calibration curves needed to assess the accuracy and reproducibility of the qPCR assay's performance as well as estimate the concentration of target sequences in environmental water samples. Due to the LEB’s need for standard curves for multiple target sequences (human and non-human), a synthetic double-stranded DNA standard, known as a gBlock™ (Integrated DNA Technologies), was created and utilized in place of plasmid derived standard reference materials. The gBlock™ was customized to include human and six non-human targets. The 1696.1 Data Analysis Tool spreadsheet provided by the EPA is used to evaluate cycle threshold (CT) values for the human and non-human assays. In addition, the LEB also designed an intricate reporting matrix based on CTs generated in the qPCR assays regardless of if they are above or below the lower limit of quantitation determined in the 1696.1 Data Analysis Tool. This allows sample submitters and health department officials to consider low levels of contamination rather than just reportable DNA copies per volume filtered.

Author: F. Ahmed | S. Chmura | T. Hattenrath; New York State Department of Health, Wadsworth Center, Albany, NY

The Great Lakes present significant challenges for beach and lake bed management. Some of these challenges include erosion, sediment disruption, and the impact of nearshore structures. Accurate and repeatable bathymetric surveys are crucial for understanding and mitigating these issues. Traditional survey methods can be costly and logistically complicated for frequent monitoring. This study introduces the application of the Bathylogger Bathymetric portable, high-resolution single-beam echosounder systems for conducting bathymetric lake surveys. This presentation will showcase two projects from Door County, WI where the Bathylogger BL200 echosounder was deployed on a small vessel and used to generate a detailed digital elevation model of the lakebed. The data collected provides critical information on lake bottom alterations, rates of accretion, and erosion. It also provides a baseline for future monitoring. These projects demonstrate that the accessibility and convenience of Bathylogger systems are a cost-effective solution for local municipalities, research institutions, and environmental groups.

Authors: Willem Liebbrand, Greg Kleinheinz, Jackie Behrens - University of Wisconsin Oshkosh, Environmental Research and Innovation Center

Microcystins are toxins produced by cyanobacteria that can negatively impact wildlife and human health. They are commonly found during freshwater algal blooms that occur when there is high nutrient input of phosphorus and nitrogen, lots of available sunlight, and warm temperatures. Due to climate change and human impact, microcystin concentrations in lakes are only expected to increase. Quantifying microcystin levels is very time-consuming and costly, and other methods, such as phycocyanin probes, are being explored to quickly and effectively quantify microcystins. With warm weather and lots of sunlight, summers provide the best environment for cyanobacteria and microcystins. Several recreational beaches throughout Wisconsin were monitored during the 2021-2025 summers to observe patterns of microcystin concentrations throughout Winnebago County, Manitowoc County, Door County, and Kewaunee County. The samples went through a freeze-thaw cycle before being analyzed for microcystins using an ELISA assay. Winnebago County, which has inland lakes, was found to have elevated levels of microcystins compared to samples collected on the Great Lakes in Door County and Manitowoc County. June and July have the highest concentration of microcystins throughout all counties.

Authors: Emily Cole (Student Researcher), Brittany Dupree (Laboratory Manager), Jackie Behrens (Associate Director), Cole Lodholz (Student Researcher)

Microbial source tracking (MST) includes a suite of techniques used to identify which specific species are contributing to the suspected fecal contamination in surface and ground water. This allows managers to effectively characterize and combat the contamination. DNA based MST techniques use polymerase chain reaction (PCR) to amplify genetic targets in enteric bacteria species that are specific to a particular host species. To rely on these assays, it is critical to assess their specificity and sensitivity in the geographical context being monitored. The specificity indicates how well the assay is detecting the target species as opposed to other species, while the sensitivity indicates how reliably it is detecting its target. Fecal samples were collected over the summer of 2024 from multiple individuals from a target list of 19 wildlife, agricultural, and domestic species commonly found in northern lower Michigan. Sampling kits were provided to partner organizations such as wildlife rehabilitators and farmers for fecal collection from these target species. DNA extracted from these samples was tested by droplet digital PCR for a suite of commonly used MST targets including human, bovine, porcine, canine, gull, and goose markers. A literature review of sensitivity and specificity data for each target was then conducted, including which species contributed fecal samples for each study. Our study found that human HF183, porcine Pig2Bac, and gull Gull4 markers had sensitivities of 100%, while the sensitivity of the domestic canine marker BacCan was only 67% and the goose marker CGOF1 was only 17%. Specificity was highest for Pig2Bac at 100%, Gull4 and CGOF1 at 95%, while HF183 and BacCan were at 69% and 56%, respectively. The literature shows that many species included in previous sensitivity and specificity studies were not pertinent to North America or the Great Lakes Region, while our study included fecal samples from previously untested species. This sensitivity and host specificity data will help area managers effectively track and treat fecal contamination in Michigan waters.

Authors: Maggie Petersen, Senior Research, Great Lakes Environmental Center, Inc.

Effective coastal management in the Great Lakes benefits from basin-scale context on alongshore sediment pathways. We compile a shoreline-resolved Potential Longshore Transport Atlas for Lake Michigan using multi-decadal wave hindcasts (1979–2023). Offshore conditions are transformed to nearshore breaking parameters with standard linear theory, and potential transport is estimated at ~5-km intervals using a widely applied energy-flux framework. The atlas highlights coherent alongshore regimes, spatial heterogeneity in transport magnitude and direction, and cell-to-cell imbalances (ΔQ) that indicate potential convergence and divergence zones. These products provide consistent, first-order guidance for sediment budgeting, nourishment planning, and assessing connectivity near littoral barriers. Ongoing work seeks to quantify relationships between alongshore transport patterns and climatic variability, and to compare atlas-based “potential” fluxes with reported site-specific estimates.

Author: Muhammed N. Sahvelet, Ph.D. Student, Lyles School of Civil & Construction Engineering, Purdue University; Cary D. Troy, Professor, Lyles School of Civil & Construction Engineering, Purdue University

Fecal contamination in recreational waters represents a possible public health threat to humans using these impacted resources for swimming, fishing, boating, and the like. Identifying the source of contamination can help, first, to stratify the degree of risk, and second, to aid in mitigating the effects of the pollution or preventing it from initially entering the water. Microbial source tracking (MST) is employed to achieve the quantification of dominant sources of fecal contamination.

We report on the initial outcomes of an MST study of Dumont Lake, a small lake in west Michigan utilized by residents and visitors alike for recreation. Since its inclusion in Allegan County Health Department’s inland lake beach monitoring program in 2023, swim advisories have been issued for Dumont Lake each year due to high E. coli levels from previously unidentified sources. In the summer of 2025, a library-independent method was utilized alongside ongoing E. coli counts in order to identify origins of fecal contamination at this site. We have implemented a multiplex primer/probe approach recently released by GT Molecular (GT-Digital™ Microbial Source Tracking Human;E.coli;Cow;Gull;Dog Panel v1.0). Produced for use with the QIAGEN QIAcuity digital PCR system, the GT kit targets ribosomal DNA sequence from host animal specific bacterial strains from human, gull, dog, and cow origin, and a non-specific E. coli general fecal marker.

Composite samples (100 mL) were filtered by vacuum onto 0.45 micron membrane filters. The filters were processed by beat beating. DNA was isolated using QIAGEN Powerlyzer kit and eluted in the recommended 100 uL volume. 5 uL volumes were combined with the GT primer/probe reagent and dPCR master mix, transferred microfluidics plates, and subjected to PCR and quantitation in the QIAcuity instrument.

In these studies, very low probe target levels were found in the Dumont Lake samples. However, given that the sampling events we examined displayed correspondingly low detectable E. coli counts, this was not surprising. The occasional host-specific hits were mainly to the dog (BacCan) target; we note that the Dumont sampling location is an on-leash dog friendly public park. At the same time, we also ran DNA isolated in previous local watershed samples that the Hope GWRI lab had archived and were known to carry high E. coli counts. These samples, by comparison, showed high dPCR MST levels (mostly dog and human in origin). These preliminary studies suggest that the GT MST primer/probe set in combination with the QIAcuity dPCR instrument provides a cost- and time-efficient MST workflow. We intend to continue this project during the summer 2026 sampling season with the expectation that we will capture several high contamination events at Dumont Lake and analyze them for host sources accordingly.

Authors: Lauren Cribbs1, Emma Smith1, Tess Scheidel2, Aaron Best1, Michael Pikaart1; Hope College Departments of Biology and Chemistry and Global Water Research Institute (1) and Allegan County Health Department (2)