Refinement of Wetland Bioassessment Methods in Wisconsin

Last Updated: September 27, 2000

Contact Information

Richard Lillie
Bureau of Integrated Science Services
Ecological Inventory & Monitoring Section
Wisconsin Department of Natural Resources
1350 Femrite Drive
Monona, WI 53716
Office: (608) 221-6338
Email: LILLIR@dnr.state.wi.us

Purpose(s) of Project

Title: Refinement and Expansion of the Wisconsin Wetland Biological Index for Assessment of Depressional, Palustrine Wetlands

• Test and refine a Biotic Index for Wisconsin's palustrine wetlands.

   

• Expand list of assemblages to include macroinvertebrates, zooplankton, diatoms, amphibians, plants, and small mammals.

   

• Establish a biological integrity rating system for classifying wetlands based on the response of selected biological attributes (metrics) of the above communities to surrogate measures of human disturbance.

Project History

This project represents the evaluation and expansion phase of an earlier study that resulted in the preliminary development of a Wisconsin Wetland Biological Index based on plant and macroinvertebrate metrics (please see final report to USEPA -Wetland Grant #CD985491-01-0). Data from the current study will be used to refine and further evaluate the preliminary indices and expand communities covered to include zooplankton, diatoms, amphibians, and small mammals. Field studies for this project were conducted during the spring and summer of 2000, with laboratory analysis and data synthesis in progress. Funding was provided by a grant from the U.S. Environmental Protection Agency – Region 5. A final report will be prepared and distributed after October 1, 2001.

Study Design

We sampled 75 palustrine depression wetlands in SE Wisconsin during early spring and summer of 2000. Study sites included a mixture of least-disturbed reference basins (18 prairie and 19 wooded kettles) and impacted wetlands (18 urban and 20 agriculture), representing a range in vegetative cover types and water chemistries. A severe drought, which began the previous year, caused most of the smaller wetlands with short hydroperiods (seasonal and temporary) to dry out, and consequently only long duration wetlands (semi-permanent and permanent) were sampled.

Assemblages Monitored

• Macroinvertebrates
• Aquatic Plants
• Zooplankton
• Diatoms
• Amphibians
• Small Mammals

Sampling Methods: Macroinvertebrates

We sampled macroinvertebrates early in the spring to minimize influences of immigration-emigration. On each wetland, we collected three standard D-frame net sweeps of approximately 1 meter length each. Sampling stations (less than 60 cm deep) were established at equally spaced points around the wetland perimeter that approximately trisected the basin (and assured coverage of the major plant communities present. The contents of the three net sweeps were concentrated (large coarse materials were rinsed, examined, and removed) into a one quart container, preserved in ethanol, and returned to the laboratory for processing. Seven field replicates were collected.

Laboratory Methods: Macroinvertebrates

Each macroinvertebrate sample was processed entirely, using a two-phase approach with sub-sampling employed only for extremely abundant organisms. The first stage consisted using a grid-marked tray with 24 cells. Cells were selected randomly, and organisms were picked and sorted at a coarse taxonomic level, usually to order or family level. The abundance of organisms present in the first two or three randomly selected cells was used to project the abundance of the most common taxa in the sample. Taxa, whose abundance was estimated to exceed 300 in the total sample, were then overlooked while processing the balance of the sample (the second phase of processing). All specimens were vouchered (preserved in 70% ethanol) for possible further evaluation.

Sampling Methods: Plants

We conducted simplified plant surveys during July 2000 using a combination of techniques. This included a subjective estimate of cover and an objective survey of percent cover and frequency of occurrence within six equidistantly spaced 20 by 50 cm rectangular quadrats positioned along each of three transects that trisected the wetland basin (total of 18 quadrats per wetland).

Laboratory Methods: Plants

No biomass or stem counts were performed. Voucher specimens were pressed and identified to species when possible, but most plant metrics are based on a coarser taxonomic level.

Sampling Methods: Zooplankton

[Note: zooplankton studies were conducted by Dr. Stanley Dodson, University of Wisconsin-Madison, Zoology Department, Madison, Wisconsin. E-mail: sidodson@facstaff.wis.edu]

We collected one zooplankton sample from a central basin location in each wetland during June 2000 using a 5-L plastic bucket. We filtered a known volume of water through a No. 10 (60 micron mesh) net to capture zooplankton within. Seven field replicates were collected. Samples were preserved in 70% ethanol until processed.

Laboratory Methods: Zooplankton

Each sample was scanned at moderate magnification for species of cladocera, copepods, ostracods, and aquatic insects. Slides and dissections were made where necessary – for example, to aid in the identification of copepod species. Total number of male and female Daphnia were counted in each sample. Over 200 slides were prepared, and identification of organisms is in progress. Organisms will be identified to species where possible.

Sampling Methods: Diatoms

[Diatom studies were conducted under the direction of Paul Garrison, WDNR, Bureau of Integrated Science Services, Environmental Contaminants Section, 1350 Femrite Drive, Monona, WI 53716. E-mail: garrip@dnr.state.wi.us]

Using a one-dram vial as a sample collection device, we collected and composited surficial (upper 0-1 cm) sediments from five sites in each wetland. Seven field replicates were collected. Samples were kept on ice or refrigerated until processed.

Laboratory Methods: Diatoms

Each diatom sample will be thoroughly mixed, and a small amount will be placed into a tall beaker. Hydrogen peroxide will be added and the sample will be allowed to steep for about 5 minutes. Potassium dichromate will be added (under a ventilated hood and handled with safety gloves) to facilitate reduction of organic matter. The sample will be washed at least four times with deionized water by centrifuging for 10 minutes. Two portions of the cleaned sample will be dried on separate No. 1 cover-slips and mounted with Naphraxâ, and labeled accordingly. Specimens from both cover slips will be identified and counted under oil immersion objective (1400X) until a total of 250 frustules are counted. Identification of difficult taxa will be made using a scanning electron microscope. Undetermined specimens representing a significant portion of a sample will be sent to Dr. Rex Lowe at Bowling Green University, Dr. Jan Stevenson at Louisville University, and/or Dr. Gene Stormer at the University of Michigan.

Sampling Methods: Amphibians

Because amphibians are extremely sensitive to weather and temperature, we assessed amphibian communities during two separate sampling periods. We conducted standardized frog-toad calling surveys (using WDNR protocols) during the first two phenologies (early spring and late spring) between the hours of 8-10:30 PM for 10-15 minutes when water temperatures were above 50° F during the first phenology or above 60° during the second phenology. We recorded all calling to permit verification of questionable identifications. In addition to calling, we added to the database any personal observations of amphibians made during any of the daylight visits and any specimens captured during the macroinvertebrate surveys.

Laboratory Methods: Amphibians

No laboratory methods used.

Sampling Methods: Small Mammals

[Small mammal studies were conducted by R. Bautz, WDNR, Bureau of Integrated Science Services, Ecological Inventory & Monitoring Section, 1350 Femrite Drive, Monona, WI 53716. E-mail: bautzr@dnr.state.wi.us]

We assessed small mammal communities by trapping during August-September, 2000. On each wetland, we set 46 baited traps (mixture of 40 museum special grade and 6 larger tomahawk traps) along transects (zig-zag scattered routes) in the riparian zone (variable dimensions, depending upon setting) for one night. A one-day/night trapping period was used to minimize disturbance by raccoons and other predators. Bait consisted of a mixture of peanut butter and rolled oats. Traps were cleaned and rebaited each morning. Specimens were placed in labeled freezer bags and returned to the laboratory for identification.

Laboratory Methods: Small Mammals

Identifications of rare taxa and species of special concern will be verified by local experts from the University of Wisconsin.

Other Data Collected

We also collected associated physical and chemical data on each wetland, and we are in the process of taking a series of aerial photographs to measure land use characteristics. The water chemistry measures included pH, alkalinity, conductivity, color, chloride, calcium, silica, nitrate-nitrite, organic-nitrogen, and total phosphorus. Chemical analyses were performed at the Wisconsin State Laboratory of Hygiene following standard EPA-approved procedures. Physical data collected included water depth, apparent color, temperature, and size. Riparian cover type within a 100-foot buffer area surrounding each wetland was subjectively estimated and recorded, as well as shade canopy cover.

Analytical Methods: Data Analysis & Development of Biotic Indices

Data will be entered into Excel spreadsheet and Access databases and examined for entry errors (univariate checks) and anomalies (e.g., bivariate plots) prior to analysis. Various community or species attributes (i.e., taxa or species richness, diversity, presence or absence of selected functional feeding guilds, trophic structure, percentages, etc.) will be evaluated and scored as potential metrics based on their responsiveness to measures of human disturbance. Community attributes will be examined using a combination of procedures (outlined below) to select promising metrics for index development. Attributes that exhibit strong positive or negative correlation with selected human response variables will be considered as prospective metrics. We will compare the sensitivity and correspondence among the selected community metrics, and develop a single multimetric index of ecosystem integrity that will best relate to overall wetland condition.

Because different forms of human disturbance elicit different responses among the various wetland biotic communities, it is difficult if not impossible to choose one measure that represents "the" single best measure of human disturbance. For example, the amphibian community may respond more directly to woodland impacts (distance to nearest woodland, patch size, corridor dimensions, etc.) than to nutrient or pesticide inputs, while zooplankton and diatom communities may be more responsive to percent row crops in the watershed. Consequently, we will select and evaluate as possible surrogates of human disturbance those land use cover attributes (impacted by humans) that we suspect, based on the scientific literature and research on life histories of the various component communities, are most likely to influence the respective communities. The multitude of possible interactions (i.e., masking influences) is enormous. Therefore, we have concentrated our efforts on agricultural row crops and the ameliorating influence of perimeter vegetative buffers. The group of urban-impacted wetlands will also be included in the analysis. In addition to examining possible linear relationships between the variables and counterpart biotic attributes, we will also search for evidence of thresholds. The presence/absence of indicator taxa among the three groups of row crop categories and two groups of buffer widths also will be examined.

Statistical procedures and approaches used in the analysis may vary among the communities assessed due to inherent differences in responses and the type of data collected. Canonical correspondence analysis will be used to explore unimodal distributions of the various biota along the various environmental gradients. We will use SYSTAT (SPSS 1997) and a combination of other available statistical software programs to perform statistical and graphical analyses. Metric development will be based on a series of visual comparisons of community attribute responses to measures of disturbance (combination of selected water chemistry and land use characteristics) using box plots and jittered dot density plots. Attributes that exhibit evidence of separation between reference and impacted wetlands will be selected as potential metrics (or incorporated into existing list of metrics). Attributes that exhibit inconsistent or overlapping responses between impacted and reference systems will be eliminated from further consideration.

Preliminary Findings

Work in Progress!

Lessons Learned

• Finding willing and cooperative private property landowners for access to potentially impacted wetlands is difficult!
• Determining what attribute or attributes (e.g., land use, chemical contaminant concentration, distance-to-nearest road, etc.) to use as surrogate measures of human disturbance is critical to the successful development of reliable multimetric biotic indices.
• Drought (or floods) can seriously hamper sampling plans and interfere with the best of plans!

Please contact R. Lillie at LILLIR@dnr.state.wi.us for additional details.