E. coli at Lake Superior Recreational Beaches

Increased usage of public beaches and heightened awareness of the need to monitor water for potential microbial contamination have led to passage of the U.S. Beaches Environmental Assessment and Coastal Health Act (BEACH Act) in 2000. This legislation calls for bacterial monitoring of recreational waters along the U.S. coastline, including the Great Lakes. The State of Wisconsin implemented this legislation in summer 2003, triggering extensive microbial monitoring of Lake Superior beaches. E. coli were measured at 27 beaches along Lake Superior, Wisconsin by defined substrate analysis. While E. coli concentrations were relatively low at these “cold water” beaches, monitoring did result in a few swimming advisories and beach closures (0.8% of total samples collected had E. coli concentrations that exceeded standards). Increasing water temperatures were not associated with increasing concentrations of bacterial contaminants. Location of sampling site and depth of water at the location where samples were taken did have an effect on detection of E. coli. Greater E. coli levels consistently were detected in shallower water and varied depending on the location of the sampling site horizontally across the beach. These findings support the notion that the concentration of E. coli in chest deep water may not be representative of E. coli concentrations in shallower water, closer to shore.     

Fecal indicator organism density in beach sands: Impact of sediment grain size,uniformity, and hydrologic factors on surface water loading

Fecal loading to beach sands and subsequent transport to surface water may result in the degradation of surface water quality. To better understand the relationship between Escherichia coli in sands, beach hydrology, and recreational water quality, we collected surface water, groundwater, and sand samples from three Lake Michigan beaches with varying substrates (fine sand to pebbles, July 2005–June 2006). Sediment cores collected within transects perpendicular to and at fixed distances from the shoreline (0 m, 10 m, 20 m) and surface water samples collected at a depth of 1 m were analyzed for E. coli. Grain size analysis was performed on duplicate core samples to assess the relationship between E. coli density and mean grain size and uniformity. Groundwater samples, collected from shallow drive-point piezometers within the test area, were also analyzed for E. coli. E. coli density in beach sands differed significantly with distance from shore with the highest density occurring at the berm crest (0 m). Mean grain size and uniformity accounted for variation in E. coli density with fine sand of uniform distribution having the highest content. E. coli density in surface water was correlated to E. coli density in beach sand samples at the berm crest. E. coli in groundwater was < 10 to 579 MPN/100 ml (2005); none was detected in 2006. Management interventions, including altered beach grooming practices and slope assessments, may be effective in reducing E. coli content at beaches comprised of fine sands of uniform grain size, hence reducing water quality advisories.     

Composite Analysis for Escherichia coli at Coastal Beaches

At some coastal beaches, concentrations of fecal-indicator bacteria can differ substantially between multiple points at the same beach at the same time. Because of this spatial variability, the recreational water quality at beaches is sometimes determined by stratifying a beach into several areas and collecting a sample from each area to analyze for the concentration of fecal-indicator bacteria. The average concentration of bacteria from those points is often used to compare to the recreational standard for advisory postings. Alternatively, if funds are limited, a single sample is collected to represent the beach. Compositing the samples collected from each section of the beach may yield equally accurate data as averaging concentrations from multiple points, at a reduced cost. In the study described herein, water samples were collected at multiple points from three Lake Erie beaches and analyzed for Escherichia coli on modified mTEC agar (EPA Method 1603). From the multiple-point samples, a composite sample (n =116) was formed at each beach by combining equal aliquots of well-mixed water from each point. Results from this study indicate that E. coli concentrations from the arithmetic average of multiple-point samples and from composited samples are not significantly different (t = 1.59, p = 0.1139) and yield similar measures of recreational water quality; additionally, composite samples could result in a significant cost savings.     

Microbial Concentrations in Sand and their Effect on Beach Water in Door County,Wisconsin

The seasonal variations and patterns of Escherichia coli in Wisconsin's coastal waters have been closely studied in recent years due to increased beach monitoring activities. Patterns of distribution of the indicator organism, E. coli, in the sand at these beaches are now being investigated as a source of E. coli to adjacent beach water. This project investigates the concentrations of E. coli in beach sand, and the relationship between these sand-microbe concentrations and concentrations of microbes in the corresponding beach water. Weekly sampling of upshore, swash, and submerged sand at six beaches provided numbers of the indicator bacteria in each beach's sand substrate for two consecutive summers. Overall concentrations of E. coli were highest in the swash sand of the beach, with the highest numbers seen in the summer months and lowest numbers in the winter months. Each location had very different concentrations of E. coli in the beach sand from 1,800 CFU/100 g to 21,670 CFU/100 g sand. Each location had a very different relationship between the indicator organism found in the beach sand and that found in the beach water. These data suggest that sand may be a reservoir for E. coli at some locations, and another source of contamination that should be considered in beach monitoring programs. However, elevated levels of E. coli in beach sand were not universal and varied greatly from location to location.     

Effect of hydrological and geophysical factors on formation of standing water and FIB reservoirs at a Lake Michigan beach

Water quality impairment of Great Lakes beaches is caused by fecal pollution from point and nonpoint sources. Erosion due to wind or wave action, invasive vegetation and chronically wet, flooded or standing water are conditions that can magnify water quality problems at beaches. We investigated the hydrological and geophysical characteristics of the Bradford Beach on Lake Michigan (Milwaukee, WI) and the linkage between standing water and persistent contamination by fecal indicator bacteria (FIB). Our study showed that there is a positive correlation between high concentrations of Escherichia coli (E. coli) in sand and high moisture content caused by standing water. The main factor associated with the formation of standing water was rainfall. There were also notable differences in standing water and/or wet sand conditions in the northern and southern parts of the beach. These differences could be accounted for by differences in ground water elevations and beach erosion and accretion patterns. Other important physical features of the beach were the presence of rain gardens and mean grain diameter (d₅₀). Rain gardens above the beach face that capture runoff contributed to transient increases in the water table, facilitating standing water formation. Standing water, stormwater runoff infiltrating through the sand and into groundwater as well as wave run up that delivered contaminated surface water to the back beach area were of health concern following heavy rainfall events. The outcomes of this study will likely be useful to beach managers investigating mechanisms/sources of fecal indicator bacteria loading and potential mitigative approaches.     

Escherichia coli (E. coli) distribution in the Lake Malawi nearshore zone

Residents along the shoreline of Lake Malawi depend on nearshore water for drinking, cooking, and bathing. Despite the importance of clean nearshore waters to public health, we are aware of no published studies of shoreline water quality in the lake. To address this gap, we explore seasonal and temporal trends of the fecal indicator bacteria Escherichia coli (E. coli) in nearshore water and sand. E. coli concentrations in sand ranged from 0 to 17,600 colony forming units (CFU)/100?ml, and in water concentrations ranged from 0 to 21,200?CFU/100?ml. Fifty-three percent of water samples exceeded the U.S. Environmental Protection Agency Recreational Water Quality Criteria of 126?CFU/100?ml, and 90% exceeded the World Health Organization drinking water standard of 0?CFU/100?ml. Distance from shore was the variable most predictive of E. coli concentration, with the level of beach use also playing a significant role. At 15?m from the shore, E. coli concentrations dropped to between 0.3% and 17% of shoreline values. Results suggest that the collection of water at distances >15?m from the beach could substantially decrease exposure to fecal bacteria. Further studies are needed to identify sources of fecal pollution and to determine the utility of E. coli as a predictor of the potential for waterborne disease.     

Modelling of nearshore microbial water quality at confluence of a local tributary in Lake St. Clair

Microbial water quality, measured as Escherichia coli (E. coli) concentration, at beaches along the southern shore of Lake St. Clair in Canada, often exceeds public safety guidelines. Belle River, located near a public beach and a drinking water intake, is one of the several smaller tributaries of the lake whose contribution to nearshore microbial water quality is currently unknown. A flexible mesh 3D coupled TUFLOW-FV and Aquatic Ecodynamic (AED2+) model was used to simulate the hydrodynamics and microbial water quality in Lake St. Clair. A higher resolution nested model was developed within the lake-wide TUFLOW-FV model for better spatial and temporal resolution in the local region surrounding Belle River. Regular and up to a factor of four difference in predicted E. coli concentrations were observed with the nested and lake-wide models at the public beach next to Belle River, whereas the difference was marginal at the drinking water intake about a kilometre away from the shore. While the E. coli loading to Lake St. Clair from Belle River is considered negligible, >90% of the predicted daily E. coli concentration at the beach and > 50 % at the water intake were attributed to Belle River from amongst all watershed sources to Lake St. Clair considered in the model. The model results also show that the construction of a new 150 m jetty in 2018, replacing the older 25 m jetty separating Belle River from the public beach, is expected to significantly reduce E. coli concentrations observed at the beach.     

Evaluation of Avian Waste and Bird Counts as Predicators of Escherichia coli Contamination at Door County,Wisconsin Beaches

Microbial source tracking (MST) has become a focus of some recreational beach monitoring programs. Suspected sources of contamination include human sewage, agricultural runoff, and feces from wildlife and domestic animals, depending on beach location. Waterfowl have been suggested as a primary source of fecal contamination at many beaches, but techniques to “prove” contaminating microbes are of avian origin are mostly unsubstantiated. Researchers often rely on bird counts to measure the impact of waterfowl on beach health. Since waterfowl populations at Door County, Wisconsin (USA) beaches are transitory, this study focused on enumeration of avian waste material along beach transects, rather than on once per day “snapshot” bird counts. Escherichia coli (E. coli) concentration in beach water was not correlated with avian waste counts at the ten beaches studied in 2004 or the 13 studied in 2005 (rural to semi-urban). Bird counts correlated with E. coli concentrations in beach water at 30% of the sample sites in 2004 and at only one site in 2005. During the 2004 swimming season avian waste counts correlated with bird counts at only one beach and there was no correlation in 2005. These results indicate that neither avian waste enumeration nor bird counts can successfully be used to predict microbial contamination of recreational water at selected Great Lakes beaches.     

Persistence and Potential Growth of the Fecal Indicator Bacteria,Escherichia coli,in Shoreline Sand at Lake Huron

Recent investigations found high abundances of the fecal indicator Escherichia coli in shoreline sand at freshwater beaches, but it is not known whether these high numbers are due to passive filtration/trapping of the bacteria, or to colonization and growth. This study was initiated to test the hypothesis that high abundance can be explained, at least in part, by the ability of E. coli to persist and grow in beach sand. A combination of laboratory and field studies was used to monitor the densities of environmental isolates of E. coli in beach sand. In controlled laboratory microcosm studies using autoclaved beach sand inoculated with E. coli strains previously isolated from ambient beach sand, E. coli densities increased from 2 CFU/g to more than 2 × 10⁵ CFU/g sand after 2 days of incubation at 19°C, and remained above 2 × 10⁵ CFU/g for at least 35 days. In field studies utilizing similarly inoculated beach sand in diffusion chambers incubated at a Lake Huron beach, E. coli also grew rapidly, reaching high densities (approximately 7.5 × 10⁵ CFU/g), and persisting in a cultivable state at high density for at least 48 days. In comparison, E. coli levels in ambient beach sand adjacent to the chambers always had densities <100 CFU/g. Lake Huron beach sand clearly provides nutrients, temperatures, and other conditions needed to support growth of E. coli. The growth of E. coli in sterile sand diffusion chambers to higher levels than occurs in ambient beach sand may indicate the presence in ambient sand of biological controls on bacterial growth, such as predation or competition.     

Escherichia coli toxin and attachment genes in sand at Great Lakes recreational beaches

The United States Environmental Protection Agency recommends density thresholds for the fecal indicator organism Escherichia coli in order to ensure the safety of recreational waters. A number of studies published over the past ten years indicate that E. coli is encountered frequently in sand at recreational beaches. While a majority of the sand-associated E. coli may be commensal or environmental strains, the potential for pathogenic strains of E. coli to be present exists. Therefore, the aim of this study was to assess the presence of attachment and virulence genes associated with enteropathogenic and enterohemorrhagic strains of E. coli (EPEC and EHEC) in populations of E. coli recovered from swash zone sand from seven recreational beaches along Lake Huron and Lake St. Clair in eastern Michigan, USA. Genes coding for attachment proteins in EPEC and EHEC were very prevalent in sand E. coli, but genes coding for toxin genes were uncommon. The paucity of genes associated with E. coli toxins suggests that the EPEC and EHEC pathotypes are not common in sand; however, the high prevalence of genes associated with attachment in E. coli pathotypes suggests that these genes are being retained within the beach sand E. coli population.     

Influence of Nearshore Water Dynamics and Pollution Sources on Beach Monitoring Outcomes at Two Adjacent Lake Michigan Beaches

Beach closings are a growing concern in coastal regions because of serious public health and economic ramifications. Two beach sites separated by 150 m of shoreline on Lake Michigan were monitored in the summer of 2003 and 2004 for E. coli densities to evaluate the potential outcome of relocating an existing beach to a site immediately to the south. Under identical weather conditions, there was a large disparity between the two sites for 25 of the 39 days tested, where E. coli levels at the existing beach were at least twice as high as those at the proposed beach. Following rainfall, E. coli levels at the existing beach increased up to 100-fold to levels as high as 4,500 CFU/100 mL, whereas only a 10-fold increase in levels was observed at the proposed beach site. Water exchange in the beach areas was predominantly from wind driven currents rather than dilution, and longshore current speed at the proposed beach was calculated to be twice that of the existing beach. Stormwater and combined sewer overflow (CSO) discharged from two closely spaced outfalls approximately 0.5 km north of the existing beach was found to have E. coli levels above the EPA recommended limit of 235 CFU/100 mL for recreational waters. However, this input did not appear to be a major influence on beach monitoring results. In some cases, E. coli levels at the beach did not exceed 235 E. coli/100 mL during a CSO. Defining the sources and spatial range of pollution inputs would allow beach monitoring results to be interpreted in a more meaningful context, which may lead to the formation of effective management strategies.     

Daily prediction of marine beach water quality in Hong Kong

Bacterial concentration (Escherichia coli) is generally adopted as a key indicator of beach water quality. Currently the beach management system in Hong Kong relies on past water quality data sampled at intervals between 3 and 14 days. Beach advisories are issued when the geometric mean E. coli level of the past five samples exceeds the beach water quality objective (WQO) of 180 counts/100 mL. When the E. coli level varies dynamically, the system is not able to track the daily bacterial variation. And yet worldwide there does not exist a generally accepted method to predict beach water quality in a marine environment, which is influenced by hydro-meteorological variables, catchment characteristics, as well as complicated tidal currents and wave effects.A comprehensive study of beach water quality prediction has been carried out for four representative beaches in Hong Kong: Big Wave Bay (BW), Deep Water Bay (DW), New Cafeteria (NC) and Silvermine Bay (SIL). Statistical analysis of the extensive regular monitoring data was carried out for two periods before and after the commissioning of the Harbour Area Treatment Scheme (HATS): (1990–1997) and (2002–2006) respectively. The data analysis shows that E. coli is strongly correlated with seven hydro-environmental variables: rainfall, solar radiation, wind speed, tide level, salinity, water temperature and past E. coli concentration. The relative importance of the parameters is beach-specific, and depends on the local geographical and hydrographical characteristics as well as location of nearby pollution sources.Multiple Linear Regression (MLR) and Artificial Neural Network (ANN) models are developed from the sparsely sampled regular monitoring data (2002–2006) to predict the next-day E. coli concentration using the key hydro-environmental variables as input parameters. The models are validated against daily monitoring data in the bathing seasons of 2007 and 2008. The models are able to track the dynamic changes in E. coli concentration and predict WQO compliance/exceedance with an overall accuracy of 70–96%. Both the MLR and ANN models are superior to the current beach advisories in capturing water quality variations, and in predicting WQO exceedances. For example, the models predict around 80% and 50% of the exceedances at BW and NC respectively in June–July 2007, as compared to 0% and 14% based purely on past data. Similarly, observed exceedances are predicted with success rates of 71%, 42%, and 53% at BW, NC, and SIL respectively during July–October 2008, as compared with 0%, 0%, and 6% using the current water quality assessment criterion. The MLR and ANN models have similar performances; ANN model tends to be better in predicting the high-end concentrations, with however a greater number of false positive predictions (false alarms).This work demonstrates the practical feasibility of predicting bacterial concentration based on the critical hydro-environmental variables, and paves the way for developing a real time water quality forecast and management system for Hong Kong.     

Impact of the Alga Cladophora on the Survival of E. coli, Salmonella, and Shigella in Laboratory Microcosm

E. coli is an indicator of recent fecal contamination of freshwater beaches around the Great Lakes region. Elevated concentrations indicate that a fecal contamination has occurred, and that the risk for contact with fecal pathogenic organisms is heightened. The green algae, Cladophora, harbors populations of E. coli and potentially allows for prolonged survival and even replication of the bacterium in the lake environment. If presence of Cladophora mats on beaches is associated with persistence of E. coli in beach water, then E. coli would be a useful indicator organism only if pathogens also were able to survive and persist in the algae. This study utilized lab microcosms to study the persistence of E. coli, and of the fecal pathogens, Salmonella and Shigella, in lake water with and without the presence of Cladophora. E. coli was able to persist for extended periods in the presence of Cladophora (attached to algal mats for 45 days). Salmonella and Shigella, however, were unable to persist for this time period while in the presence of Cladophora (Salmonella attached to Cladophora was detectable for 10 days and Shigella was detectable for only 2 days). These data imply that E. coli is able to survive in the presence of Cladophora for greater times than are the fecal pathogens and that E. coli may not be an appropriate indicator organism for beaches with accumulations of algal material.     

Sources and Sinks of Escherichia coli in Benthic and Pelagic Fish

Escherichia coli and fecal coliform bacteria were isolated from five benthic and four pelagic fish species to determine their role in the fecal contamination of recreational waters. All fish were collected during fall 2006 from Southworth Marsh in the Duluth-Superior Harbor, a public beach that is commonly posted to minimize water contact due to high E. coli levels. Although fecal coliform bacteria were isolated from each fish species, they were only isolated from 66% and 72% of the individual benthic and pelagic fish, respectively. While 42% of the fecal coliforms from benthic fish were E. coli, only 4% of these bacteria from pelagic fish were E. coli. Cluster analysis showed different fish species harbored identical strains of E. coli and some fish contained multiple E. coli strains. The potential source for 65% of the E. coli isolates obtained from fish were identified by using the HFERP DNA fingerprinting method and libraries of E. coli DNA fingerprints from warm-blooded animals and environmental isolates collected in the area. The E. coli strains whose source could be identified were most similar to strains isolated from sediments, Canada geese, mallard ducks, and wastewater. None of the fish E. coli had DNA fingerprints matching those from any water or beach sand isolates. Although our results demonstrate that benthic fish contain E. coli, it may be more appropriate to consider these fish as a vector of E. coli from other sources, rather than a new source of E. coli contamination in aquatic environments.     

Dynamics of fecal indicator bacteria,bacterial pathogen genes,and organic wastewater contaminants in the Little Calumet River–Portage Burns Waterway,Indiana

Little information exists on the co-occurrence of fecal indicator bacteria (FIB), bacterial pathogens, and organic wastewater-associated chemicals (OWCs) within Great Lakes tributaries. Fifteen watershed sites and one beach site adjacent to the Little Calumet River–Portage Burns Waterway (LCRPBW) on Lake Michigan were tested on four dates for pH, dissolved oxygen, specific conductance, chloride, color, ammonia- and nitrate-nitrogen, soluble phosphorus, sulfate, turbidity, and atrazine; for concentrations of FIB; and for genes indicating the presence of human-pathogenic enterococci (ENT) and of Shiga-toxin producing Escherichia coli (EC) from various animal sources. Nineteen samples were also tested for 60 OWCs. Half of the watershed samples met EC recreational water quality standards; none met ENT standards. Human-wastewater-associated OWC detections were correlated with human-influence indicators such as population/km², chloride concentrations, and the presence of WWTP effluents, but EC and ENT concentrations were not. Bacterial pathogen genes indicated rural human and several potential animal sources. OWCs of human or ecosystem health concern (musk fragrances AHTN and HHCB, alkylphenols, carbamazepine) and 3 bacterial pathogen genes were detected at the mouth of the LCRPBW, but no such OWCs and only 1 pathogen gene were detected at the beach. The LCRPBW has significant potential to deliver FIB, potential bacterial pathogens, and OWCs of human or ecosystem health concern to the nearshore of Lake Michigan, under conditions enhancing nearshore transport of the river plume. Nearshore mixing of lake and river water, and the lack of relationship between OWCs and FIB or pathogen genes, pose numerous challenges for watershed and nearshore assessment and remediation.     

Contaminant concentrations in bald eagles nesting on Lake Superior,the upper Mississippi River,and the St. Croix River

We measured concentrations of DDE, total PCBs, and mercury in bald eagle (Haliaeetus leucocephalus) nestlings at three locations in the upper Midwest: Lake Superior, the upper Mississippi River, and the St. Croix River, 2006–2008. We also analyzed trends in concentrations of these contaminants for eagles on the southern shore of Lake Superior, from 1989 to 2008, using the current and previously published data. Concentrations of DDE in nestling blood plasma samples were greatest on Lake Superior (geometric mean: 16.2 μg/kg, n = 29), whereas concentrations of total PCBs were highest in Mississippi River samples (88.6 μg/kg, n = 51). Mercury concentrations were highest along the upper St. Croix River (6.81 μg/g wet weight in feathers, n = 19). For Lake Superior, DDE concentrations declined significantly in nestling blood plasma samples from 1989 to 2008, an average of 3.0% annually. Similarly, total PCBs in Lake Superior eaglets decreased 4.0% annually from 1989 to 2008, and mercury concentrations in nestling feathers from Lake Superior nests also decreased significantly from 1991 to 2008, 2.4% per year. With the possible exception of mercury on the upper St. Croix River, mean concentrations in 2006–2008 of all three compounds were below levels associated with significant impairment of reproduction for all sites, and reproductive rates at all three sites averaged > 1.2 young per occupied territory, which is greater than the rate indicative of a healthy population.     

Microplastic contamination of sediments across and within three beaches in western Lake Superior

Microplastic pollution of the environment is ubiquitous, but the processes by which microplastics accumulate within beach sediments are not yet well understood. We isolate microplastic pollution from the sediments at three western Lake Superior beaches. Samples of both surface and subsurface sediments are considered. We find that the average microplastic contamination is 65 microplastic particles kg^?1 sediment across our sites with significant variability across beaches, but the microplastic composition is always dominated by polyester fibers. The variation across beaches does not seem to relate to the distance from suspected sources of microplastics to the lake. Within each beach, we find no significant variation of the mean microplastic concentration in the cross-shore direction or in the surface vs. subsurface sediments at the wrack line. We interpret this mean microplastic concentration in the sediment as a measure of the bulk microplastic concentration in the nearshore water at each beach. In subsurface sediments, we observe a significant difference in the variance of microplastic concentrations, and we attribute this variation to the intermittency of the extreme hydrodynamic conditions that deposit microplastics deeper into the sediment.     

Microbial source tracking to identify fecal sources contaminating the Toronto Harbour and Don River watershed in wet and dry weather

Identification of sources of fecal pollution in urban areas is critical for protecting public health, the environment, and guiding remediation. We collected 670 water samples at 46 sites in 2018 to study fecal pollution in the Toronto Harbour and Don River watershed. Water samples were analyzed for E. coli, wastewater chemicals, and microbial source tracking DNA markers using a digital PCR technique. Microbial DNA markers were useful for interpreting the sources of elevated E. coli concentrations in the study. The HF183 marker for human sewage was the most frequently detected DNA marker, occurring in 100% of samples taken from the Don River and associated outfalls. It was also frequently detected in the Inner Harbour and outfalls along the Toronto harbour front. It was detected less frequently and at lower levels in the outer harbour. Detection of a human mitochondrial DNA marker and wastewater chemical markers such as caffeine provided additional evidence of widespread sewage contamination. The gull DNA marker was widely detected, but at lower frequencies and levels than human source DNA markers. A wet weather response of increased E. coli and human DNA marker concentrations occurred at most sites. However, human DNA markers were also widely detected on dry weather sampling days, indicating sewage cross-connections in stormwater and dry weather CSO systems. The cumulative impact of cross-connected stormwater outfalls is likely an under-recognized source of sewage contamination. E. coli and HF183 DNA marker levels observed can serve as benchmarks for evaluating future water quality improvements from wastewater infrastructure investments.     

Beach sediment magnetism and sources: Lake Erie,Ontario, Canada

Measurements were made along the northwestern shore of Lake Erie, Canada to determine whether grain magnetic properties can be used to identify and distinguish sources of beach sediment. Although surface magnetic susceptibilities were highly variable, ranging from 56 to 9867 × 10⁻⁵ SI (Bartington MS2D), there was generally a gradual increase from the low beach (near the waterline) towards the high beach; there were also narrow, shore-parallel bands with high susceptibility at various points on the beach surface. Magnetic mineralogy on the beaches was dominated by low-Ti magnetite (570° < Tc < 580 °C), and the effective grain-size varied from pseudosingle domain in the low beach to multidomain on the high beach. Sandy bluff sediments in the eastern part of the study area had magnetic properties (e.g. S-ratios, hysteresis loops, thermomagnetic curves) that were similar to those on the beaches, whereas the magnetic properties of the extensive till bluffs and river basin sediments were quite different. The data suggested that, whereas the beaches in the western part of the study area are supplied with sediment from bluffs several tens of kilometres to the east, the source of the high magnetic concentrations on the eroding beaches of eastern Point Pelee remains to be determined.     

Microbial source tracking and evaluation of best management practices for restoring degraded beaches of Lake Michigan

Attempts to mitigate shoreline microbial contamination require a thorough understanding of pollutant sources, which often requires multiple years of data collection (e.g., point/nonpoint) and the interacting factors that influence water quality. Because restoration efforts can alter shoreline or beach morphology, revisiting source inputs is often necessary. Microbial source tracking (MST) using source-specific molecular markers, genomic community analyses, and physical modeling was used to identify contamination sources along three Lake Michigan beaches of the Laurentian Great Lakes with historically high fecal indicator bacteria (FIB, E. coli) concentrations. Genetic markers for human (Bacteroides HF183) and mixed gull species (Catellicoccus marimammalium) fecal sources were tested from water and sediment. Gene sequencing (16S rRNA) was used to identify similarities in bacterial communities in nearshore water, river inputs, sand, sediment, and groundwater. Synoptic surveys of water exchange were conducted to determine nearshore-offshore interactions of FIB. In addition to these MST studies, best management practices to mitigate FIB, including gull deterrence, slope grading, wetland establishment, and shoreline plantings, were reviewed for their effectiveness at reducing FIB concentrations over time. Using multiple tools for MST helped identify primary and secondary sources of FIB (gulls, stormwater inputs) and the physical processes that exacerbate FIB concentrations (onshore currents, limited circulation). Management actions were successful in the short-term at reducing FIB, but scope of success was temporally limited, with FIB concentrations often rebounding. Results highlight the usefulness of MST to inform best management practices and the need for a sustained adaptive approach that adjusts for changes in the coastal system.