Effects of Channel Redredging on Wildlife and Wildlife Habitat of Buena Vista Marsh

[摘要] A two-year study was conducted on drainage ditchesin a 13 square mile study area of the Buena Vista Marsh,Portage County, Wisconsin, to determine what effectchannel maintenance by dredging has on the wildlife ofthe area and on the wildlife habitat. A 3-mile sectionof Ditch-3, dredged in 1967-68, was compared to anadjacent 2-mile control section which was last dredgedin 1921. The dredging widened the channel an averageof 7.9 feet, eliminated meanders and pools, and createda flat stream bottom of homogeneous structure. Siltaccumulation was absent in the control section but waspresent in depths from 1 to J feet in the dredgedsection after the spring run-off subsided. Sheet-watercovered a maximum of 4826 acres of the study areaduring the spring of 1973 and 832 acres in 1974, adecrease of 83 percent due to reduced amounts ofprecipitation. This was accompanied by a waterfowlbreeding population of 5.4 ducks per square mile in1973 and 2.6 per square mile in 1974, a reduction of52 percent. The nearest edge of the sheet-water waslocated an average of 87 feet from the dredged sectionof the ditch and an average of 274 feet on the controlsection. The dredging thus reduced the sheet-water onthe study area by 136 acres. Ground water levels were5.16 inches lower on the area adjacent to the dredgedsection when compared to a comparable area on thecontrol section. Fifty-one percent of the dabblingducks were found on sheet-water areas and 14 and 35percent on ditches and stock ponds, respectively, in1973. Waterfowl numbers decreased from 1455 in 1973to 316 in 1974, while usage in 1974 was 52, 11, and37 percent for sheet-water, ditches, and stock ponds,respectively. Diving ducks did not decrease innumbers and were found almost exclusively on thedeeper stock ponds. Nest predation was highest on theditch banks and the chief predator was the stripedskunk. The principal nesting species was the blue-wingedteal with an overall nesting success of 38percent and 20 percent on the ditch banks. Tealnests were located within 80 feet of water during incubation, but those nests adjacent to sheet-waterdid. not retain this proximity by hatching time becausethe sheet-water had disappeared. Ditches provided theonly available brood habitat. Waterfowl productionwas 7.48 broods per mile of ditch in 1973, and 0.62per mile in 1974. Twice as many broods utilized thecontrol section of the ditch as compared to thedredged section in 1973. Waterfowl hunting opportunities were limited to the opening hours of theseason. The majority of the blue-winged teal migratedprior to season;;s opening and those remaining werequite accessible. Bunting success in 1973 was 0.63birds per hunter. Accessibility to all ditches andlack of any refuge decreases the amount of waterfowlhunting opportunities. Vegetation was absent on theditch bank subsequent to the dredging operation andon the dredged section now consists of grasses, a fewforbs and scattered dogwood and aspen plants. Thecontrol section has a grass and forb ground cover withabundant shrub growth consisting of pin cherry, aspen,and dogwood. Trees of these species constitute 763stems per acre and range from 0.8 to 6.2 inches d.b.h..Non-game bird species were found to be fewer on thedredged section of Ditch-3 than on the control section. Total species counted on the dredged section in 1973was 8, while there were 18 species on the controlsection. Comparable figures for 1974 were 9 and 15for the dredged and control sections, respectively.The number of species was found to be a better indicatorof habitat quality than total number of birds present.Trapping of small mammals on the dredged section ofDitch-3 showed the meadow vole to be the most prevalentspecies during both years. The white-footed mouse was the most common mammal caught on the control section.The control section also had the greatest diversity ofspecies on the ditch bank. The striped skunk was themost common of the larger mammals caught on the ditchbanks. Others caught were raccoon, badger, andFranklin ground squirrel. White-tailed deer used theditches as watering sites and were present on themarsh with a density of 32 +/- 2 per square mile.

[发布机构] University of Wisconsin-Stevens Point