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Ecological Studies at the Woodworth Study Area

Chironomidae (Diptera) of the Woodworth Study Area, North Dakota

Dale Wrubleski*
U.S. Environmental Protection Agency
Mid-Continent Ecology Division
6201 Congdon Boulevard
Duluth, MN 55804

Introduction

The Chironomidae are a numerically dominant group of aquatic insects in prairie wetland habitats, and have also been reported to be important in food chain support (1). However, we know very little about chironomid species composition, relative abundances, or phenologies. Descriptions of prairie pothole chironomid communities have been provided by Driver (2) and Parker (3, 4) for sites in Saskatchewan. In North Dakota, only Nelson (5) has described the chironomid community of prairie potholes, but only information for the two dominant species is provided, along with a list of the 14 genera collected.

As part of a larger study examining the effects of sedimentation on chironomid production in prairie wetlands, emergence traps were placed in 10 study wetlands to help in determining species identification and life cycle patterns. This paper presents the emergence trap results for 1994, the second year of watershed manipulations.


Methods and Materials

This study took place in wetlands associated with the sedimentation study described by Gleason and Euliss (6). Ten of the twenty wetlands were selected for study, five wetlands with their watersheds in the Conservation Reserve Program (CRP) and five with tilled watersheds. For the purposes of this paper, watershed treatments will not be considered further.

Emergence traps used were a modified version of trap 1 described by Nelson (5) which sampled a surface area of 0.1m2. Three traps were set randomly within each wetland adjacent to previously established transects. Traps were initially set on 3 June and operated continuously until 8 September, 1994. As sites dried, due to declining water levels, traps were moved to deeper water. Wetland 2401 was dry by the end of July, and wetlands 13E2 and 0724 were dry by the end of August. Traps were emptied weekly, cleaned, and rotated around their support post to prevent continual collection over the same substrate.

Samples were preserved in 70% ethyl alcohol. Representative specimens of each species were mounted on glass slides in Euparol for identification. Voucher specimens will be deposited with the National Biological Service, Northern Prairie Science Center, Jamestown, North Dakota and the U.S. Environmental Protection Agency, Mid-Continent Ecology Laboratory, Duluth, Minnesota.


Results and Discussion

Peak chironomid emergence took place in May, before emergence sampling was initiated (Figure 1). Emergence declined through to the end of June and then remained at very low numbers through the rest of the summer. Nelson (5) also reported peak emergence in May from two semi-permanent wetlands at Cottonwood Lake, but he observed almost no emergence after the end of June.

Table 1 lists the 30 identified species of chironomids collected during 1994. Eventual identification of several undetermined specimens will probably increase this number slightly. Overall, this number is low compared to several other studies in prairie wetland habitats. For example, Driver (2) listed 48 species from 16 ponds sampled over a three-year period in central Saskatchewan. Parker (4) reported 43 species of Chironomidae collected over a three-year period from a single prairie pond, also in Saskatchewan. Wrubleski and Rosenberg (7) collected 84 species from the much larger Delta Marsh in Manitoba. The lower number of species found in the present study is probably more a reflection of sampling effort than real differences. Samples from the Woodworth wetlands are only from part of one year, whereas the other studies sampled over a number of years.

The number of chironomid species present within individual Woodworth wetlands averaged 16 (range 9-23). This number is close to the mean of 20 species that Driver (2) reported for semi-permanent wetlands in Saskatchewan. He observed that seasonal wetlands had a mean of only 5 species. Although initially selected as seasonal wetlands, high levels of precipitation in 1993 and 1994 raised water levels considerably, resulting in most wetlands becoming semi-permanent, except for the three ponds that did go dry in late summer. Consequently, the numbers of chironomid species present in the Woodworth wetlands is reflective of the increased water levels.

Increases in water levels affect the structure of the chironomid communities in prairie wetlands in several ways. First, species that would otherwise not be able to complete development in seasonal wetlands, because of the short period of flooding, are now capable of doing so due to the greater length of flooding. In addition, deep water over the winter period will modify overwintering conditions and the survival of chironomid larvae within bottom sediments. Water bodies that freeze completely during winter, termed "aestival", have lower numbers of chironomid species than when water levels are deeper (4, 8). The increased water levels also flooded considerable amounts of terrestrial vegetation, creating conditions favorable to increased chironomid habitat (9).

The chironomid community present in the Woodworth wetlands is very different from that found in two semi-permanent wetlands at Cottonwood Lake, just 10 miles away (5). The most abundant species collected from the Woodworth wetlands were: Corynoneura sp. 1, Chironomus pallidivittatus, Tanytarsus sp. 1, Psectrotanypus dyari and Chironomus atrella. Chironomus tentans and Glyptotendipes nr. paripes were dominant species at the Cottonwood Lake wetlands. Chironomus tentans was present in Woodworth wetlands, but in very low numbers. Also, four species of Chironomus were found at Woodworth, whereas only one was found at Cottonwood Lake. Three species of Glyptotendipes were found at Woodworth but only one species was found at Cottonwood Lake, and none of these species were shared by both areas. The disparities between these two areas is not unusual, as other studies have also reported very different chironomid communities between wetland areas (4, 10). These differences have been attributed to such features as pond permanency, water chemistry, and aquatic plant communities (2, 7).

Although the numbers of chironomid species present in prairie wetlands may be predictable, based on pond permanency for example (2), species composition and their relative abundances are not. Further studies are needed to understand how biotic and abiotic factors structure chironomid communities in prairie wetlands. This information is particularly important if we are to accurately assess anthropogenic impacts in these habitats.


References


1.     Wrubleski, D. A. (1987) Chironomidae (Diptera) of peatlands and marshes in Canada, pp. 
141-161.  In: Rosenberg, D. M. & H. V. Danks (eds.).  Aquatic insects of peatlands and 
marshes in Canada.  Mem. Entomol. Soc. Canada 140.

2.     Driver, E. A. (1977) Chironomid communities in small prairie ponds: some 
characteristics and controls.  Freshwat. Biol. 7,121-133.

3.     Parker, D. W. (1985) Biosystematics of Chironomidae (Diptera) inhabiting selected 
prairie ponds in Saskatchewan.  M.S. thesis, University of Saskatchewan, Saskatoon.

4.     Parker, D. W. (1992) Emergence phenologies and patterns of aquatic insects inhabiting a 
prairie pond.  Ph.D. thesis, University of Saskatchewan, Saskatoon.

5.     Nelson, R. D. (1989) Seasonal abundance and life cycles of chironomids (Diptera: 
Chironomidae) in four prairie wetlands.  Ph.D. thesis, North Dakota State University, Fargo.

6.     Gleason, R. A. and Euliss, N. H., Jr. (1996) Impact of agricultural land-use on prairie 
wetland ecosystems: experimental design and overview.  Proc. N.D. Acad. Sci. 50.

7.     Wrubleski, D. A. and Rosenberg, D. M. (1990) The Chironomidae (Diptera) of Bone Pile 
Pond, Delta Marsh, Manitoba, Canada.  Wetlands 10,243-275.

8.     Daborn, G. R. (1974) Biological features of an aestival pond in western Canada.  
Hydrobiologia 44,287-299.

9.     Wrubleski, D. A. (1991) Chironomidae (Diptera) community development following 
experimental manipulation of water levels and aquatic vegetation.  Ph.D. thesis, University of 
Alberta, Edmonton.

10.    Morrill, P. K. (1988) Disturbance of pond Chironomidae communities by deltamethrin 
insecticide.  M.S. thesis, University of Saskatchewan, Saskatoon.

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