Based on the results from this investigation, Saginaw Bay appears to be more heavily impacted by detached Cladophora than Grand Traverse/Little Traverse Bays. Mean E. coli concentrations in detached Cladophora were higher in Saginaw Bay (2,796 cfu/g dwt) than Grand Traverse Bay/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 Bay/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 farther 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 near-shore zone, where the detached Cladophora samples were taken. As noted in previous studies, Cladophora appears to hold trapped E. coli and does not release the entrained bacteria into 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 vi 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 beach 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.

Internal phosphorus loading in White Lake sediments ranged from 1.55 to 7.78 mg TP/m2/d in anaerobic conditions and from -0.18 to 0.14 mg/m2/d in aerobic conditions. The negative value suggests that the sediments in some areas of White Lake could act as a sink for TP during aerobic periods. These internal loading rates were generally similar to summer measurements made in Mona Lake in previous years but considerably lower than those measured under anaerobic conditions in Spring Lake in 2003.

Internal total loading contributed 1.24 tons of phosphorus based on our laboratory study, with about half coming from the eastern-most basin in White Lake. Compared to an estimated external total phosphorus load of 15.48 tons/yr (Mark Luttenton, GVSU, unpublished data), internal loading of TP accounts for ~7.4% of the total TP load entering White Lake. This percent is much lower than what has been measured in Spring and Mona Lakes, suggesting internal phosphorus loading is a less important process in White Lake than nutrients entering from groundwater or surface inflows. These data suggest that management strategies should be focused, at least initially, on reducing external phosphorus loads to White Lake.

Mona Lake Watershed Reference Map

Transportation Map

Political Units Map

HydrographyMap

Subbasins Map

Aerial Photography Mosaic – Mona Lake Watershed Map

Total Property Tax Base Map

Digital Elevation Model Map

Land Use/Cover Type Definitions

Land Use and Cover Map - 1978

Land Use and Cover Map - 1997

Land Use and Cover Change Analysis

Percent Impervious by Subbasin Map

Wetlands Map

Presettlement Landscape Map

Population Density Map

Trout Streams and Lakes Map

Water Sources of Mona Lake Map

Groundwater Stream Base Flow Map

Natural Runoff Potential Map

Sheet and Rill Erosion Potential Map

Total Phosphorus Concentration Map

Bacterial Contamination Map

The AWQI is designed to be used by agricultural technicians with limited experience in aquatic ecology; however, it does assume a reasonable background in soil characteristics. This index is intended for use during the active growing season (approximately mid-May through September). The purpose of the index is two-fold; to describe the level of vulnerability or potential environmental impact a particular farming operation may have to the stream environment, and to provide direction in developing farm management strategies that work to stabilize or improve water quality.

The following are condensed instructions that are designed to assist the farmer, field technician, or agricultural consultant that may be performing the assessment. A more technical version of the AWQI is available to individuals seeking additional background information or more detail involving individual metrics within the index.

Harbor Island (G20). Exceeds sediment PEL values for chromium, lead, nickel, and DDE in the top core section. Deeper core sections were extensively contaminated with heavy metals.

Spring Lake (G6). Exceeds sediment PEL values for chromium, lead, cadmium, nickel, and DDE.

Grand Haven (G12). Exceeds sediment PEL values for chromium and nickel. The sediments at this location exhibited a statistically significant level of toxicity to amphipods when compared to the control.

Phosphorus release rates were no different at alum concentrations of ≥ 15 mg alum/L compared to 24 mg/L. However, the higher alum concentration is likely to provide greater spatial coverage over the sediments in the lake, more protection from alum redistribution after sediment resuspension, and is still well below concentrations of environmental concern.

Resuspension events, which would cause the sediments to become mixed, substantially increase total phosphorus concentrations in the water column, even at high alum concentrations, although the total soluble phosphorus concentrations remain low in the water column provided alum is present.

Bioturbation has the potential to increase phosphorus release into the water column. However, several lines of evidence in our data suggest that this process does not play a significant role in Spring Lake sediments. Desktop analyses focusing on lake morphometry revealed that Spring Lake is very susceptible to internal loading but not very susceptible to resuspension events. In addition, calculations indicated that given the current concentration of P in the sediment, internal P loading can continue in Spring Lake for another 40 years, even if all new sources of phosphorus are eliminated.

Taken together, these results indicate that an alum application of 25 mg aluminum/L is likely to result in a substantial reduction in the phosphorus concentration in the water column of Spring Lake. The length of treatment effectiveness will depend on the degree to which 1) the alum remains in place on the sediment-water interface and 2) current and future external phosphorus loading to Spring Lake is reduced.

Uncertainties in our estimates are discussed, including spatial heterogeneity of sediment type, calculation of percent anoxia in Spring Lake, extrapolation of laboratory release rates to the whole lake, and external load estimates. We conclude that internal loading is a significant source of phosphorus to Spring Lake, and that alum is a potentially effective means of reducing this source. However, it is unknown how long an alum treatment would remain effective in this system. We recommend: 1) additional laboratory studies to obtain an estimate of how long an alum treatment would remain effective; 2) a pilot field study; and 3) continued efforts to reduce external loading to Spring Lake.

Macrophyte growth was extensive throughout most parts of the lake, but the plant composition was generally indicative of good water quality conditions. The clear water column and adequate concentrations of nutrients in the sediment provide excellent conditions for macrophyte growth in Little Black Lake. This may cause water quality problems in future years, however, as continual accumulation of organic matter may result in muck sediments and reduced oxygen levels. Phytoplankton abundance was low relative to other lakes in the region, and composition was indicative of good water quality. Little Black Lake has a healthy fish community, dominated by bluegill and pumpkinseed, with no invasive species being observed. The healthy fish community is likely a function of good habitat and good water quality.

Despite the current healthy conditions, there are some indications the lake is starting to experience ecological pressures. As a consequence, it is important that the City and lakefront homeowners become active stewards of the lake and its watershed to maintain the lake’s condition. A number of recommendations are provided in this report, including the development of a watershed management plan and the implementation of best management practices to limit nonpoint source loading to Little Black Lake.