Great Lakes Coastal Wetland Bioassessments (Michigan BAWWG Case Study)

Last Updated: March 2000

Contact Information

Tom Burton*
Michigan State University
Department of Zoology
203 Natural Science
East Lansing, MI 48824-1115
Phone: (517) 353-4475
E-mail: Tom Burton (burtont@pilot.msu.edu)
*Also appointed in the Department of Fisheries and Wildlife

Donald G. Uzarski
Michigan State University
Department of Zoology
203 Natural Science
East Lansing, Michigan 48824-1115
Office: (517) 355-6474
E-mail: Donald G. Uzarski (uzarskid@pilot.msu.edu)

Bioassessment Procedures and Baseline Reference Data for Great Lakes Coastal Marshes and Inland Forested Wetlands in Michigan

Purpose(s) of Project

Subproject 1

• Collect baseline data on water quality and plant, invertebrate, and vertebrate communities from reference and impacted Great Lakes coastal wetlands for the Michigan Department of Environmental Quality.
• Develop a fish-and-invertebrate-based Index of Biotic Integrity (IBI) by plant zone, for Great Lakes coastal wetlands.

Subproject 2

• Collect baseline data on plant, invertebrate, and vertebrate communities with accompanying chemical/physical parameters from reference forested, depressional wetlands in southern Michigan for the Michigan Department of Environmental Quality.
• Develop an IBI for forested, depressional wetlands in southern Michigan based on invertebrates, plants, amphibians, fish (if present), and birds.

Project History

Subproject 1

We recently developed a preliminary IBI for Lake Huron (Burton et al. 1999) based on invertebrate data collected from coastal wetlands with funds provided by The Nature Conservancy, EPA, and the Michigan Department of Environmental Quality. While not yet completely tested across an array of reference and impacted coastal sites, these metrics seem to be robust and consistent enough to warrant further testing while extending them to other types of coastal wetlands associated with Lakes Michigan and Superior. During our IBI development and previous research, we have collected extensive data on invertebrates, plant, fish, and bird communities from Lake Huron coastal wetlands. Much of our work has been in collaboration with the Great Lakes Science Laboratory (BRD-USGS), Michigan Natural Features Inventory (MNFI), and the Ohio Biological Survey (OBS).

Our preliminary IBI was developed using macroinvertebrate data collected in 1997 from six Lake Huron coastal wetlands and was tested using data on macroinvertebrates collected from 11 Lake Huron Wetlands (six original and five additional) in 1998 at lake levels that were substantially lower than 1997. We continued to test the IBI using 12 sites (seven original and five additional) at even lower lake levels in 1999. These results appear promising.

We will be extending the IBI into Lake Michigan in 2000. We are optimistic that it will work for the northern Lake Michigan fringing wetland sites that are similar to our Lake Huron sites. These sites appear to be comparable in plant community composition and structure. We will also begin to collect data on the very different drowned-river-mouth wetlands along the eastern shore of Lake Michigan in 2000, and plan to develop a similar preliminary IBI for those systems.

We also plan to continue to collect data on fish communities of these wetlands and are convinced that a fish-based IBI is possible. Even if a stand-alone IBI based on fish proves to be difficult to develop, we are convinced that some fish-based metrics can be incorporated into an overall IBI and will be working with our data to develop such metrics.

Subproject 2

We have recently started our forested depressional wetland project. Invertebrates have been collected from seven forested depressional wetlands on four occasions using dip nets, activity traps, and black lights. These samples are currently being identified to the lowest taxonomic unit possible and results are being entered into a database. Accompanying chemical/physical samples taken from surface water and minipiezometers have also been recorded. Comparisons of the plant and invertebrate communities have been made using a subset of the sites.

 

Study Design

Subprojects 1 and 2

Wetlands that experience a wide range of anthropogenic disturbance, or stressors, are chosen from each hydrogeomorphic class or subclass of wetland. The extent of disturbance is determined using surrounding land use data. Initially, response variables are regressed, using both linear and nonlinear models, against land use variables if available. Those that exhibit high and significant R-squared values are deemed potential metrics.

Biotic data from wetlands are also graphically analyzed by constructing box plots including the 10th, 25th, 50th, 75th, and 90th percentiles. These are used to detect differences among wetlands with respect to individual metrics. The variance of each metric is used to predict the robustness and the resolution that can be obtained using a given metric. The resolution obtained from a given metric is established by the amount of interquartile overlap of box plots between impacted and unimpacted sites (Barbour et al. 1996). Sensitivity values of zero to three are assigned to each metric to provide an indication of metric quality. A metric receives a sensitivity value of three only if nearly all sites (greater than 95 percent) are ordinated with no major overlap according to anthropogenic disturbance. A metric will receive a sensitivity value of two if 80 to 95 percent of sites are ordinated according to disturbance. A metric will receive a value of one if less than 80 percent of the sites are ordinated according to anthropogenic disturbance and receive a value of zero if there is major overlap for 50 percent of the sites. Metrics with no overlap of the interquartile range are considered to have high resolution, while those with considerable overlap are considered to have low or no resolving power. Further, a metric that can distinguish between two sites with relatively similar exposure to anthropogenic disturbance is said to have high resolution.

We use medians in place of means in the IBI because medians are more resistant to the overwhelming effects of outliers. Our goal is to typify the wetland. If an area is sampled that is depleted or concentrated in the constituents of a metric, the area may be isolated from anthropogenic disturbance, receiving a dose of disturbance not typical of the entire wetland or vegetation zone, or may contain some "natural" chemical/physical component that is unique. Regardless of the cause, the area is not representative of the entire wetland. The influence of these outliers can be dampened by using the median, in place of mean, as a measure of central tendency.

Assemblages Monitored

• Macroinvertebrates
• Invertebrates
• Fish
• Birds
• Plants
• Amphibians and Reptiles

Sampling Methods: Macroinvertebrates

Subproject 1

Macroinvertebrate samples are collected with standard D-frame dip nets containing a 0.5-mm mesh. All major plant community zones are sampled at each site, including an emergent zone and a shallow, wet meadow zone. If certain depths contain more than one dominant plant community along the shoreline, each plant community type is sampled.

Dip net sampling entails sweeps through the water column at the surface, middle of the water column, and above the sediment surface to ensure that an array of microhabitats are included in the sample. Samples are placed in white enamel pans, and 150 invertebrates are collected by focusing on small areas of the pan and removing all of the specimens. Special consideration is made to ensure that smaller organisms are not missed, as there is a bias towards larger, more mobile individuals using this technique. Plant detritus is left in the pan and sorted through for a few additional minutes to ensure that sessile species are included in the sample. Three replicate samples are collected within each plant community zone in order to obtain a measure of variance associated with sampling.

Dip net samples are collected from late July through August. Samples taken from ice-out through mid-July generally contain less diversity and a greater proportion of early instars of aquatic insects, making identification very difficult. The July-August time period also corresponds to the time when plant communities, characteristic of these wetland systems, achieve maximum annual biomass.

Sampling Methods: Invertebrates

Subproject 2

Macroinvertebrate samples are collected with standard D-frame dip nets containing a 0.5-mm mesh. Three replicate samples are collected from pools spanning the entire wetland to obtain a measure of variance associated with sampling.

 

Dip net sampling entails sweeps through the water column at the surface, middle of the water column, and above the sediment surface. Samples are then placed in white enamel pans and 150 invertebrates are collected by focusing on small areas of the pan and removing all of the specimens. For small pools, taking three replicates of 150 specimens each, removes too much of the standing crop of invertebrates. In such cases, we only obtain 50 specimens or fewer per replicate and try to sample extra pools rather than taking all specimens from a single pool. Invertebrate sampling is conducted two to three weeks after snow melt, during annual high-water levels, and just before wetlands start to dry up. If more permanent pools exist in the wetland, additional samples are taken in midsummer and fall.

 

Sampling Methods: Fish

Subproject 1

Sampling consists of pulsed, direct-current backpack electroshocking surveys, small fish traps, and fyke traps placed in each vegetation zone for selected 24 hour or longer intervals. Numbers and arrangements of these traps will be worked out after site selection is complete, but a standard protocol will be developed and used for all wetlands. We will attempt to develop a comparable protocol to the one used by our partners in our previous studies to ensure that data are comparable.

 

Subproject 2

The temporary pools that dominate most depressional forested wetlands are unlikely to contain fish. Thus, fish sampling is only conducted for permanent pools in depressional wetlands when and if they occur. If such habitat occurs, sampling consists of pulsed DC backpack electroshocking surveys and use of small fish traps placed in each of the permanent pools for selected 24 hour or longer intervals during spring, summer and fall.

 

Sampling Methods: Birds

Subproject 2

Bird communities are surveyed using a modification of the variable circular-plot method proposed by Reynolds et al. (1980) using 25 m fixed-radius (0.2 ha) plots stratified according to elevation. Lowest elevations sampled will be the deepest areas of inundated pools during periods of standing water with highest elevations sampled extending 50 m from the edge of the wetland into the adjacent upland areas. The number of census plots increases with the area of the forested wetland (Blake and Karr 1987), but a minimum of four plots is sampled in each study site. If wetland size permits, up to three circular plots are sampled for each elevation included in the study design.

 

Sampling Methods: Plants

Subproject 2

The plant community is described for two transects per bird census plot for each of the elevations sampled per wetland. These transects extend the full 50 m diameter of the census plot at right angles to each other so that the transects intersect at the center of the plot. Diameter at breast height (dbh) is recorded for each living and dead tree and shrub stem within 1 m of the center of the two transects. Species that are less than 1 m high are included in these measurements. All downed logs greater than 10 cm in diameter are recorded for each of the transects if any part of it falls within 1 m of the center of the transect. The length of log in the transect and its state of decomposition are recorded using the decomposition classification system of Thomas (1979). Several other habitat measurements are recorded at the center of each of the bird census plots and at 10 and 20 m from the center of the plot on each of the transects (9 points total). Herbs and shrubs are sampled on a line transect basis.

Sampling Methods: Amphibians and Reptiles

Subproject 2

Amphibian populations are determined from call surveys during breeding seasons for frogs and toads using call stations set up along transects through the depressional wetlands. At least one call survey is completed every two weeks for each wetland during breeding season. After eggs hatch, amphibian larvae are sampled by dip net and/or dipper collections. Relative abundance of each tadpole species in each standing water habitat available in the depressional wetland is assessed by dip net sampling in each available habitat. Call and tadpole surveys are repeated from the beginning through the end of breeding season for all frogs and toads with fast developing larvae. For slower developing species such as green frogs and bullfrogs, sampling at least once per month for any permanent standing water habitats continues throughout the ice-free season.