Box 2140B, Northern Plains Biostress
Laboratory, South Dakota State University Brookings, SD 57007
The U.S. Fish and Wildlife Service (USFWS) has consistently worked to preserve wetlands for waterfowl habitat. However, since the mid-1970's other functions have received more attention. These functions include: improved water quality, flood control, recreational use, and fish and wildlife habitat production. Wetland management programs currently need to improve their understanding of these functions.
One program implemented by the USFWS is the Private Lands Program. This program helps create wetlands for private landowners. Presently, it is unknown whether created wetlands are as biologically diverse as natural wetlands. Our objective was to compare aquatic invertebrate diversity of created wetlands with natural semi-permanent wetlands in the Prairie Coteau, Missouri Coteau, and Northern Great Plains regions of South Dakota. Null hypotheses were:
Ho1: Biological diversity does not differ between
created and natural wetlands.
Ho2: Biological diversity does not differ among
physiographic regions.
Methods. Wetlands in the Prairie Coteau and Missouri Coteau of the Prairie
Pothole region were sampled in 1995. In 1996, the Southern Plateau of the Northern
Great Plains region was added. Within each region, six created and three natural
semi-permanent wetlands were studied. Created wetlands ranged from one to six
years of age. Wetland size ranged from 0.8 to 7.3 ha. Adjacent land-use was primarily
grazing; however, land surrounding a few wetlands was idled or hayed. Aquatic invertebrates were sampled in August 1995, May 1996, and July 1996 with aquatic activity traps constructed from 2 L plastic bottles. A total of fifteen traps were placed along three transects (5 traps each) in each wetland for a 24 hour period. Along each transect, three of the five traps were set horizontally at depths of 25, 50 and 100 cm; two traps were set vertically at the 50 and 100 cm depths. Samples were sieved through a dip net and preserved in 80% ethanol for later identification in the laboratory. All invertebrates were identified to order while all insects were identified to family. We calculated Shannon's Diversity Index, relative abundance and species richness for all wetlands.
A natural logarithmic transformation was used to normalize relative abundance data. Taxon richness could not be normalized through transformation so these data were ranked. For each index, differences between wetland types and among regions were tested with a factorial ANOVA. When three or more means were compared, the Least Squares Means Multiple Range Test was employed.
Results. Ho1 -
Ho2 -
Table 1. Factorial ANOVA results for three indices used to determine
diversity between wetland types and among regions.
Source d.f. F value p-value
Shannon's Index type 1 0.00 0.9588
region 2 5.71 0.0094*
type*region 2 0.82 0.4543
Relative Abundance type 1 2.99 0.0967
region 2 3.00 0.0686
type*region 2 0.41 0.6683
Taxon Richness type 1 71.49 0.0001*
region 2 283.52 0.0001*
type*region 2 1364.56 0.0001*
Discussion. Although relative abundance was not significantly different between created and natural wetlands at à=0.05, it was at à=0.10. An earlier study that compared created and natural wetlands in North Dakota found similar results (Keil & Crawford 1986). However, they found relative abundance differed between the two types of wetlands in 1983, but not in 1982.
Within each physiographic region, taxon richness differed between the two types of wetlands. In the Prairie Coteau region, taxon richness was greater in natural than created wetlands. Kreil and Crawford (1986) found the same. However, in the Missouri Coteau and Southern Plateau regions, taxon richness was greater in created wetlands than in natural wetlands. We attributed these differences to the occurrence of fish in wetlands in the Missouri Coteau and the morphometry of wetlands in the Southern Plateau. On the Missouri Coteau, fish occurred in all but one created wetland. The absence of fish predation in this wetland may be the reason why more taxa were found (Elmberg et al. 1992). In the Southern Plateau, natural wetlands are playas and tend to be shallow while created wetlands typically occupy intermittent drainages which are deeper. Deeper created wetlands may offer more habitat diversity and hydrologic stability than natural wetlands.
Among physiographic regions, Shannon's Diversity Index was greater for wetlands in the Missouri Coteau region than for wetlands in the Prairie Coteau or Southern Plateau regions. Wetlands sampled within the Missouri Coteau were more similar in size than wetlands sampled in other physiographic regions. Wetlands sampled in the Missouri Coteau region also were all used for grazing. Thus, similarity in wetland size and inputs of animal wastes could contribute to evenness and abundance, increasing the diversity index.
In conclusion, created wetlands were at least comparable in aquatic invertebrate diversity to natural wetlands in our study. This diversity of aquatic invertebrates serves to link primary production with fishes and waterfowl via food base. Therefore, this wetland function can be created. Creating wetlands for private landowners may counter wetland losses in the prairie pothole region. Other functions, however, need to be considered.
2. Elmberg, J., P. Nummi, H. Poysa, and K. Sjoberg. 1992. Do intruding predators and trap position affect the reliability of catches in activity traps? Hydrobiologia 239:187-193.