AWRI Environmental Chemistry

Assessment of E. Coli and Microcystins in Cladophora Mats in the Nearshore Waters of Grand Traverse Bay, Little Traverse Bay, and Saginaw Bay.


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MDNRE Report:  Assessment of E. Coli and Microcystins in Cladophora Mats in the Nearshore Waters of Grand Traverse Bay, Little Traverse Bay, and Saginaw Bay.

Executive Summary

An assessment of the ability of Cladophora mats to sequester E. coli and microcystin LR and RR was conducted in the nearshore waters of Grand Traverse Bay (7 sites), Little Traverse Bay (2 sites), and Saginaw Bay (8 sites).  The sampling locations were at public beach access points where Cladophora mats previously have been observed.  The goals of this research were to determine the spatial and temporal variability of E. coli populations in Cladophora mats in these recreational waters and if cyanotoxins (microcystin LR and RR) are sequestered in the detached algae.  The collection of Cladophora samples was coordinated with local beach monitoring programs to facilitate the comparison with ambient water bacteria concentrations. This project provided important data for the assessment of public health impacts and the development of beach management programs to address the problems associated with Cladophora accumulations.

Based on the results from this investigation, Saginaw Bay appears to be more heavily impacted by detached Cladophora than Grand Traverse/Little Traverse Bay.  Mean E. coli concentrations in detached Cladophora were higher in Saginaw Bay (2,796 cfu/g dwt) than Grand Traverse/Little Traverse Bay (1,775cfu/g dwt); however, the difference was not statistically significant (Mann-Whitney ρ=0.40).  Cladophora deposits exhibited spatial and temporal variability in both systems.  At most beaches in Grand Traverse Bay, Cladophora deposits were limited to small pockets at 1 location.  Clinch Park had only one site with Cladophora on the last sampling event and two locations at the Traverse City State Park were free of detached algal accumulations. In contrast, Cladophora deposits in Saginaw Bay covered approximately 1 meter (m)of the shoreline at most beaches.  Two locations in Saginaw Bay also had no accumulations of Cladophora during the study period (White’s Beach and Pinconning Park). Differences in Cladophora accumulation between Saginaw Bay and Grand Traverse/Little Traverse Bay may be attributed to higher total phosphorus levels in Saginaw Bay.  Levels of E. coli in detached Cladophora in both systems were similar to concentrations previously reported in the Great Lakes (1,000 cfu/g dwt – 60,000 cfu/g dwt). In Saginaw Bay, the highest levels of E. coli in detached Cladophora were consistently found at beaches near the Saginaw River.  Even within individual sites, locations near tributaries and drains at Wenona Beach and South Linwood Beach were significantly higher than locations further away from a point source.  This relationship also was noted in Grand Traverse Bay where the location near Mitchell Creek at the Traverse City State Park had elevated E. coli concentrations in detached Cladophora compared to the other beach locations.  These results suggest that Cladophora can trap bacteria from point sources and also be stimulated by nutrient discharges.   Two locations, Pinconning Park and White’s Beach, had very limited Cladophora growth.  Both locations had Chara growing on the lake bottom.  Chara is known to exhibit allelopathic activity that can limit the growth of other aquatic plants.   No correlation was found between E. coli levels in the open water (designated beach monitoring locations) and the nearshore zone where the detached Cladophora samples were taken.  As noted in previous studies, Cladophora appears to hold trapped E. coli and not release the entrained bacteria to the offshore water.

This investigation was the first to document the accumulation of microcystins in the detached Cladophora of Saginaw Bay.  Total microcystins in detached Cladophora had a grand mean of 57 µg/g dwt for the study period.  Saginaw Bay has a history of Microcystis blooms in the late summer months that produce both microcystin LR and RR.  Since Microcystis has a high requirement for sunlight, cyanobacteria may become stressed when they are trapped in the detached algae mats.  While accidental ingestion by humans of microcystins trapped in Cladophora is unlikely, these compounds can act as skin irritants.  Walking through Cladophora accumulations to get to deeper water may provide sufficient exposure to cause irritation in sensitive individuals if microcystins are present.  Although the data suggest that swimming areas (1 m depth) are not impacted by the E. coli accumulations in detached Cladophora, entrained bacteria and cyanotoxins may pose a hazard to children playing in the nearshore water and sand.  Current regulations discourage beach grooming and altering the nearshore zone.  The presence of elevated bacteria and microcystin levels in the nearshore environment of Saginaw Bay suggests that the current policy should be reevaluated to balance potential impacts to public health with the ecosystem services provided by coastal wetlands.

MDNRE Report:  Assessment of E. Coli and Microcystins in Cladophora Mats in the Nearshore Waters of Grand Traverse Bay, Little Traverse Bay, and Saginaw Bay.


Project Description:

A nuisance in some areas of the Great Lakes, Cladophora is a filamentous green alga that forms thick mats that wash on shore and foul beaches. The proliferation of Cladophora along the shores of the Great Lakes is thought to be a result of invasive zebra and quagga muscles altering the nearshore cycling of nutrients. In order to assess the role of Cladophora mats in sequestering E. coli and the cyanobacteria toxin microcystin in the nearshore waters of Grand Traverse Bay, Little Traverse Bay and Saginaw Bay, the AWRI Environmental Chemistry Laboratory recently started work on a $59,860 grant from the Michigan Department of Environmental Quality (MDEQ). The Environmental Chemistry Laboratory has been involved with the beach monitoring program in Muskegon, Oceana, Mason and Manistee counties since 2001. Recently, our laboratory completed research projects funded by the National Oceanic and Atmospheric Administration and MDEQ that involved cyanobacteria (i.e., blue-green algae) and microcystin production. In June 2008, the Environmental Chemistry Laboratory initiated sample collection from 16 beaches within the Grand Traverse, Little Traverse and Saginaw Bays. These samples will be analyzed for E. coli and microcystins, which both pose human health risks when present in high concentrations. Building on the former studies, this grant allows for the examination of the role of Cladophora mats in the sequestration of E. coli and microcystins in important recreational areas in Michigan. AWRI is collaborating with the Great Lakes Water Studies Institute at Northwestern Michigan College in Traverse City, where a laboratory processes samples and analyzes Cladophora mats for E. coli. The Water Studies Institute also will coordinate outreach activities with support from Watershed Center Grand Traverse Bay and the Tip of the Mitt Watershed Council. In addition, sampling schedules have been coordinated in Saginaw and Grand Traverse Bays with the local health departments to provide nearshore and swimming depth results on the same days. Finally, AWRI will coordinate sampling schedules with Michigan State University and Watershed Center Grand Traverse Bay in order to track the source of E. coli in Saginaw and Grand Traverse Bays.

Page last modified February 26, 2013