Minnesota Pollution Control Agency Wetland Bioassessment Program

Last Updated: March 2000

Contact Information

Mark Gernes
Minnesota Pollution Control Agency (MPCA)
Environmental Outcomes Division
520 Lafayette Road
St. Paul, MN 55155
Phone: (651) 297-3363
Email: Mark Gernes (mark.gernes@pca.state.mn.us)

Judy Helgen
Minnesota Pollution Control Agency (MPCA)
Environmental Outcomes Division
520 Lafayette Road
St. Paul, MN 55155
Phone: (651) 296-7240
E-mail: Judy Helgen (judy.helgen@pca.state.mn.us)

Purpose(s) of Project

Develop the tools to assess wetland condition by studying vegetation and invertebrates in wetlands across a range of human disturbance. Develop two separate Indexes of Biological Integrity (IBI) for Minnesota depressional wetlands.

Project History

Minnesota has been developing their wetland biological assessment program since 1992. The first project was funded by the state legislature in 1992 to develop biological reference conditions for depressional wetlands in Central Minnesota. This initial research studied the quantity and quality of macroinvertebrates in both least-disturbed reference sites and known-disturbed depressional wetlands. A second project funded by U.S. EPA was undertaken in 1995 to develop multimetric biological integrity indexes for depressional wetlands in Central Minnesota. During the 1995 sampling season, MPCA collected data on macroinvertebrates and vegetation for a different set of depressional wetland sites than the 1992 study.

MPCA has analyzed data from both projects and has developed invertebrate and vegetation IBIs for depressional wetlands. Subsequently, MPCA published a report in 1999 that documents the various stages of sampling and analysis and also development of the Index of Biological Integrity. This document can be found on the Minnesota Pollution Control Agency website.

As of Spring 2000, MPCA has two ongoing biological assessment wetland projects, one on large depressional wetlands and the other on riparian wetlands. Field sampling for the two projects was completed in the summer of 1999 and the data for vegetation and macroinvertebrates was processed in the Winter of 1999-2000.

Study Design

In the first project, 32 least-disturbed sites and 3 known-disturbed sites were sampled for macroinvertebrates.

In the second research phase, 27 wetlands were sampled for macroinvertebrates and vegetation. The 27 wetlands represented the full range of human disturbance typical of wetlands in this part of Minnesota and were located in the North Central hardwood forest ecoregion of Minnesota. The sites included least-impaired reference sites (6 sites), to those highly impacted from human disturbances such as storm water (12 sites) and agricultural influences (9 sites). Five of the sites were on private property and 22 were located on public lands.

During the site selection phase of the project, MPCA contacted resource managers in the county and state and federal agencies within the proposed study area to solicit recommendations of suitable depressional wetlands. Resource managers were asked to recommend both significantly impacted and least-disturbed reference sites. MPCA selected reference sites that were removed from any human disturbance for typically at least 20 years, had natural hydrology, had not been farmed or impacted from storm water or direct agricultural runoff, were not restored or created, and had not been exposed to known sources of pollution. Additional information including site histories, aerial photographs, U.S. Geological Survey 7.5' quadrangle maps, and other sources were reviewed and issues of site access were determined for a large number of the wetlands.

In addition to invertebrate and vegetation sampling, the sites were sampled for water pH, conductance, turbidity, dissolved oxygen, temperature, calcium (hardness), chloride, total suspended solids, total phosphorus, and total nitrogen. Sediments were analyzed for 15 heavy metals using ICP methodologies, total organic content, textural classes, carbonates, chloride, total phosphorus, and total nitrogen.

Assemblages Monitored

• Macroinvertebrates
• Vegetation

Sampling Methods: General Considerations

Stratification of the habitat for each study site was done so as to minimize the biological variability within the different strata of the wetland. For the depressional wetland project, the following habitats were identified near-shore emergent zone and open-water submergent and floating zone.

Sampling Methods: Macroinvertebrates

Sampling was done during the seasonal index period of June to early July. This ensured that maximum species maturity and richness occurred before sampling. In previous field work, MPCA had determined that sampling in May was too early and some invertebrates are too immature for identification. Once collected, invertebrate samples were preserved and analyzed in the laboratory. Macroinvertebrates were sampled using both the dip net and the activity-trap method. Dip netting captured the greatest richness of invertebrates and the activity trap captured the active swimmers and night-active predators.

Dip Net

The D-frame aquatic dip net with 800 x 900 micron mesh net is used. Two dip net samples were taken within the emergent vegetation zones. A screen was used to hold the vegetation from the sample area. After sweeping the net strongly through the water column (four to five times) and also downwards to near the bottom, the contents of the dip net are emptied onto a hardware cloth screen fixed to a wooden frame. The frame is set over a pan containing sieved water to catch invertebrates as they drop down from the vegetation. For approximately 10 minutes, the vegetation is gently spread to ensure all invertebrates drop or crawl down to the water in the pan. After separation from the vegetation, the water is then poured through a 200 micron sieve to separate out the chironomid species. Preservation of the samples is done using an alcohol-water concentration. Using a squirt bottle with a strong alcohol solution, the sample is back-flushed into the sample jar and labeled for later lab picking and identification.

Activity Trap

The bottle-trap method works as a passive funnel trap that collects organisms as they swim into the funnel and pass through the neck into the bottle. Made from a clear two-liter round-bottomed plastic beverage bottle, the traps are nearly invisible underwater. The traps are supported on a 4.5' wooden dowel with a flexible half section thin wall PVC pipe that allows raising and lowering the bottle trap on the dowel.

Ten bottle traps were placed in the emergent vegetation zone and left overnight for two consecutive nights. Placement of the bottle traps was from the nearest shallow shore edge to the inner side of the deeper emergent vegetation zone in water no greater than one meter. In the shallowest water, the traps were placed on the bottom just under the surface of the water. Traps were placed horizontally about 15-20 cm under the surface. The bottle traps were back-filled with water leaving no air bubbles inside to reduce the amount of predation within the trap.

Analytical Methods: Macroinvertebrates

After the invertebrates were sorted, identified, and counted, the data was scored for 10 metrics. These 10 metrics comprise the overall IBI score for Minnesota depressional wetlands. The 10 metrics are published in the April 1999 MPCA report, which can be found on the Minnesota Pollution Control Agency website. Metrics were validated by plotting them against a ranking of the site disturbance based on professional judgment and also plotting them against selected chemical variables.

Of the 10 invertebrate metrics, Odonata genera (dragonfly), number of intolerant invertebrate taxa, and the ETSD metric (includes mayfly, caddisfly) showed the strongest responses to the estimated disturbance gradient and water chemistry factors.

Scoring criteria for 10 invertebrate metrics for depressional wetlands.

Metric Description	Range	Score
% Water boatmen of all bugs plus beetles from BT samples (Corixidae ratio)	< 33% 33 - 67% > 67%	5 3 1
% Leech Erpobdella in BT and DN samples of the total DN abundance	0 - 11% >11 - 22% > 22 - 33%	5 3 1
% Top three dominant taxa of total invertebrate abundance in DN samples	35 - 54% > 54 - 72% > 72 - 90%	5 3 1
Number of genera of Chironomidaelarvae	14 >20 7 – 13 0 - 6	5 3 1
ETSD, the number of genera of mayfly and caddisfly nymphs plus presence of fingernail clams and dragonfly nymphs	4 –6 2 - 3 0 – 1	5 3 1
Number of intolerant taxa: Leucorrhinia, Libellula, Tanytarsus, Procladius, Triaenodes, Oecetis	5 –7 3 – 4 0 – 2	5 3 1
Number of genera of leeches in BT and DN samples	4 – 5 2 – 3 0 – 1	5 3 1
Number of genera of dragonfly and damselfly nymphs	5 – 6 3 – 4 0 – 2	5 3 1
Number of snail taxa, identified to species where possible	5 – 7 3 – 4 0 – 2	5 3 1
Total number of taxa: Larval chironomids, caddisflies, mayflies, dragonflies, damsel flies, leeches, snails, and macrocrustaceans, plus presence of Chaobrus and fingernail claims	26 – 38 13 – 25 0 - 13	5 3 1

The chemical and biological data (also vegetation) were analyzed for statistically significant relationships for the metrics and IBIs. Common water-quality parameters such as phosphorus, nitrogen, chloride, and heavy metals were evaluated for their relationship to the biological communities. MPCA is currently working to develop additional metrics and further test the existing metrics.

Sampling Methods: Vegetation

Vegetation sampling techniques vary greatly for different wetland habitats and study designs. MPCA used the releve method for sampling vegetation in the depressional wetland study. The releve method was chosen for several reasons. The primary reason is that it is easily adapted to widely varying habitats and vegetation community structure, which is typical for depressional wetlands. This adaptability in sampling methodology is needed for wetlands that receive significant quantities of water during storm events. A second reason that MPCA selected releve sampling over more conventional line transect or quadrat sampling was that Minnesota DNR's Natural Heritage Program, the County Biological Survey, and Minnesota's academic researchers also use a similar releve method for collecting vegetation community data in Minnesota.

All vegetation sampling was done in July, which represents the peak maturity and the best time in Minnesota for determining community structure. In each wetland, a 10 x 10 meter plot was established at each site in representative sampling locations in the emergent and open water submergent zones. After establishing the releve plots with staked corners, the vegetation cover classes were determined for each plant species occurring in the plot. Voucher specimens were collected at least once during the project for each species/taxa encountered. All taxa unable to be reliably field identified to the species level was also collected.

Analytical Methods: Vegetation

Ten vegetation metrics were developed and validated, using methods similar to the invertebrates. Each promising attribute of the plant community was plotted against a suitable disturbance gradient. A disturbance gradient index was developed from professional judgment ratings of several disturbance factors including storm-water input, agricultural practices, quality of adjacent buffers, hydrologic alterations, and historical disturbances. Metric scoring criteria were then developed for the strongest responding metrics. Metrics were also plotted against selected chemical variables to demonstrate their response to traditional water chemistry concerns.

Scoring criteria for 10 vegetation metrics for depressional wetlands.

The 10 vegetation metrics showed significant responses to water (chloride) and sediment chemistry (copper). Tolerant vegetation taxa, sensitive taxa, and persistent litter taxa were found to be the strongest and most reliable vegetation metrics.

Sampling Methods: Water and Sediment

Sampling water and sediment chemistry were conducted by MPCA staff. Water analysis was done by the Minnesota Department of Health and sediment analysis was done under contract with the University of Minnesota Soils Analytical Laboratory. See April 1999 report for sampling methods for sediment and water chemistry.

Lessons Learned

• Vegetation IBIs show great promise for future applications in wetlands biological assessment as they are biologically rich and sensitive to a variety of human disturbances.
• The invertebrate community in wetlands respond differently than those used for stream IBIs. Stream IBIs are based on invertebrates which typically employ well-oxygenated riffle communities where pollution or disturbances promote an increase of taxa that tolerate lower oxygen conditions. In wetlands, many of the aquatic invertebrates are well adapted to the natural, diurnal fluctuations of oxygen and would be expected to be "pollution tolerant" but indeed may not be.
• Sampling method adaptability (vegetation) is needed in many wetlands that receive significant quantities of water during storm events. These wetlands frequently have poorly developed emergent fringe plant communities due to extreme water level fluctuations.