Wetlands

Author: Thomas Burton

 Methods

             During the spring of 2001, a total of 18 wetland and pond sites were sampled on the campus of Michigan State University.  Of these sites, 9 were classified as vernal pools or ponds and 9 were classified as wetlands (Table 1).  Sampling began in May and continued until the end of June.

At each site water samples were taken from each distinct vegetation/habitat type within the wetland or pond.  These samples were taken back to the lab to determine turbidity, alkalinity, pH, and the concentration of soluble reactive phosphate (SRP), ammonium, nitrate, sulfate, chloride, and silica.  From each vegetation zone the following parameters were measured in the field: water temperature, dissolved oxygen, depth, and specific conductance. 

In addition to the water samples, aquatic invertebrates were sampled at each vegetation/habitat type within a site.  Two methods were employed for sampling invertebrates: dip nets and activity traps.  Sweeps with a D-frame dipnet through the water column at three depths (surface, mid, bottom) collected invertebrates inhabiting the water column and the benthos, and those attached to aquatic vegetation.  The contents of the sweep were placed in an enamel pan and specimens are collected for 30 person-minutes.  At the end of this period, the number of collected specimens is determined and collecting continues to the next highest interval of 50 with 150 being the maximum number collected.  This process is repeated three times at each vegetation/habitat zone, providing three replicates.  In order to collect the more active invertebrates (e.g., dytiscid beetles, water boatmen, etc.) and vertebrates (e.g., tadpoles, fish) that may have been underestimated by dip net sampling, activity traps were placed at a subset of the sites.  Traps were placed at dusk and were collected in the morning.  Activity traps consisted of a plastic 2 L pop bottle with the bottom removed and replaced with the inverted top of another.  Traps were attached to wooden dowels and placed horizontally either immediately on top of the substrate or on vegetation mats growing on the substrate.  Specimens from both sampling techniques are field-preserved in 95% ethanol and then taken to the lab for processing.  The majority of the specimens were identified at least to the genus-level, and some groups (Trichoptera, Odonata, Gastropoda) were identified to species.  Some taxonomic groups, however, were not identified past family (e.g., Chironomidae, Tubificidae, Naididae, Sphaeriidae).  Identifications were made using the taxonomic keys found in Bright & O’Brien (1999), Burch (1980, 1982), Merritt & Cummins (1996), Peckarsky et al. (1990), Pennak (1989), Thorp & Covich (1991), and Wiggins (1978).

Results

            Examination of the water chemistry data reveals that a number of the study sites on campus appear to be impacted due to surface runoff.  Sites immediately adjacent to roads such as Hicks South, Hicks West, College Rd SE Pond, Farm Lane Pond, and Baker Woodlot (Corner & West Ponds) all have elevated concentrations of chloride (Table 2).  Nitrate concentrations were below detection limits (0.01) for the majority of the sites.  However, the Farm Lane Pond had very high concentrations presumably due to runoff from the Hancock Turf Grass Research Center study plots directly adjacent to this site.  Bennett wetland was another site that was apparently impacted with elevated levels of chloride and ammonium.  The two ponds south of Natural Resources were chemically distinct with very different specific conductance, pH, and sulfate concentrations (Table 3).  Sediment inputs were a problem at three of the sites as determined by turbidity measurements.  One site (Hicks West) receives direct runoff through a culvert from US 127 on its west edge and on its eastern edge it receives storm water runoff.  The Farm lane pond was just created last year and received large amounts of sediments during heavy precipitation due to the lack of vegetation surrounding this site.

            A total of 126 invertebrate taxa was collected via dip net sampling during the May-June inventory of campus wetlands and ponds, with the total broken down by major taxonomic groups as follows: Annelida 3, Mollusca 15, Crustacea 7, Insecta 98.  The disproportionately large number of insect taxa identified was partially due to the difference in taxonomic resolution among the groups as mentioned in the Methods section.  For instance, Annelida and Crustacea had a number of groups that were not identified past the family level. 

Sites that were impacted by their adjacent land use had a less diverse invertebrate community (Table 4).  Bennett wetland and Farm Lane pond, two of the most impacted sites, had very low diversity with Bennett dominated by chironomids (midges) and Farm Lane dominated by chironomids (midges) and corixids (water boatmen) (Table 5).  The Baker woodlot interior vernal pools (North and Northwest pools) and the Toomey woodlot pond also had a very low diversity, but chemically did not appear to be impacted by surface runoff.  The ephemeral nature and low productivity of these sites may result in a characteristically depauperate invertebrate community.

The identification and enumeration of activity trap samples in ongoing with only a small percentage of the samples completed at this time.  In addition to more invertebrate community data, we will also be able to obtain quantitative data on the diversity and abundance of amphibians at the study sites by identifying and enumerating larval amphibians collected in the traps.  This data will compliment the adult frog and toad call survey data that will be obtained this spring.

References 

Bright, E. and M. F. O’brien.  1999.  Odonata larvae of Michigan: keys for, and notes on, the dragon- and damselfly larvae found in the state of Michigan. (http://insects.ummz.lsa. umich.edu/MICHODO/MOS.html)

Burch, J.B.  1980.  North American freshwater snails.  Walkerana 1(3): 81-215.

Burch, J.B.  1982.  North American freshwater snails.  Walkerana 1(4): 216 - 366.

Burton, T.M., C.A. Stricker, D.G. Uzarski, and K.J. Divine.  2000.  Baseline characterization of water quality, invertebrate, fish, and amphibian communities of forested floodplains in southern Michigan. in “Improve Assessment and Monitoring of the Ecological Integrity of Wetlands in Michigan” (report submitted to Michigan DEQ).

McCafferty, W.P.  1981.  Aquatic entomology: The fisherman’s and ecologists’ illustrated guide to insects and their relatives.  Jones and Bartlett Publishers, Inc. 

Merritt, R.W. and K.W. Cummins.  1996.  An introduction to the aquatic insects of North America, third edition.  Kendall/Hunt Publishing Company. 

Peckarsky, B.L., P.R. Fraissinet, M.A. Penton, and D.J. Conklin Jr.  1990.  Freshwater macroinvertebrates of northeastern North America.  Comstock Publishing Associates. 

Pennak, R.W.  1989.  Fresh-water invertebrates of the United States: Protozoa to Mollusca, third edition. John Wiley and Sons, Inc. 

Thorp, J.H. and A.P. Covich.  1991.  Ecology and classification of North American freshwater Invertebrates.  Academic Press Inc.

Wiggins, G.B.  1977.  Larvae of the North American caddisfly genera (Trichoptera).  University of Toronto Press. 

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