Surface-water hydrology and quality, and macroinvertebrate and smallmouth bass populations in four stream basins in southwestern Wisconsin, 1987-90

Data on streamflow, water quality, and macroinvertebrate and smallmouth bass (microptercus dolomieni) populations were collected from July 1987 through September 1990, in four streams in southwestern Wisconsin to determine the effect of surface-water hydrology and quality on populations of macroinvertebrates and smallmouth bass. The study was a joint project of the U.S. Geological Survey and the Wisconsin Department of Natural Resources.

Drought conditions greatly affected streamflows in southwestern Wisconsin throughout much of the period of study. Precipitation in all four basins in 1988 and 1989 was 9.91 to12.41 inches less than 1951-80 normal precipitation of 32.88 inches.

The lowest annual mean discharge was recorded in water year 1988 at all of the streamflow- gaging stations except at Rattlesnake Creek, where annual mean discharge was lowest in water year 1990. Overland-flow runoff during the reproductive period of smallmouth bass (mid-May to mid-July) was 0.02 inch in 1988 at the Sinsinawa River and Rattlesnake Creek. Overland-flow runoff in the Little Platte River and the Livingston Branch of the Pecatonica River also was low in 1988 (0.03 inch and 0.04 inch, respectively) during the reproductive period of smallmouth bass. The trend of low overland-flow runoff continued in 1989; in water year 1990, however, overland-flow runoff during the reproductive period of smallmouth bass was 1.38 inches at Livingston Branch of the Pecatonica River and 0.22 inch at Rattlesnake Creek.

Turbidity ranged from 1.5 nephelometric turbidity units at Rattlesnake Creek to 3,700 nephelometric turbidity units at the Sinsinawa River. Suspended-solid concentrations ranged from 2 milligrams per liter at Rattlesnake Creek to a maximum 24,300 milligrams per liter at the Livingston Branch of the Pecatonica River. The high turbidities and suspended-solid concentrations, which occurred during storms, did not last for long periods of time and are not thought to have been harmful to the biota of the rivers.

Un-ionized ammonia concentrations exceeded the State of Wisconsin, Department of Natural Resources' standard of 0.04 milligram per liter for warmwater streams at all four of the streams. The maximum concentration of un-ionized ammonia measured was 0.10 milligram per liter at Rattlesnake Creek and there was no discernible effects on smallmouth bass or macroinvertebrates.

Dissolved-oxygen concentrations at all four study streams occasionally decreased to below or near the concentration of 1 milligram per liter considered necessary to sustain life of smallmouth bass. Two fish kills were documented as the result of low dissolved-oxygen concentrations. All of these episodes of low dissolved-oxygen concentrations occurred during or just after rainstorms and subsequent increasing streamflows.

Samples of water-sediment mixture and bottom material were analyzed for pesticides commonly used in the basins. Samples from all of the stations had concentrations of herbicides that exceeded the analytical reporting limit. Water-sediment samples at the Sinsinawa River had the highest herbicide concentration. The concentration of metolachlor was the highest of the herbicides-- 110 micrograms per liter; concentrations of atrazine and cyanazine were next highest at 97 and 84 micrograms per liter, respectively.

All of the water-sediment mixture samples had insecticide concentrations below the analytical reporting limit, with the exception of carbofuran. One water-sediment mixture sample collected at the Little Platte River had a carbofuran concentration of 0.44 microgram per liter. No pesticides were detected in the bottom-material samples collected at the four study streams.

Richness of macroinvertebrate taxa did not differ substantially among the four streams during the study, but the abundances of several taxa differed significantly among streams. Livingston Branch of the Pecatonica River had comparatively few midges but many caddisflies, whereas Rattlesnake Creek had many non-insect taxa and relatively few caddisflies. The Little Platte River had consistently high numbers of caddisflies, mayflies, and riffle beetles.

Macroinvertebrate-community composition, as measured by Bray-Curtis dissimilarity coefficients, varied considerably over time within and among the streams. The macroinvertebrate community composition of the Little Platte River changed very little during the winter of 1987-88 as compared to the other streams, but the community composition of the Livingston Branch of the Pecatonica River changed substantially. The communities of Rattlesnake Creek and Livingston Branch of the Pecatonica River became more similar to the community of the Little Platte River from fall 1987 through fall 1988, whereas the community in the Sinsinawa River remained distinct.  

Water quality, as estimated by biotic-index values, generally was better in the Little Platte River than in the other streams from fall 1987 through fall 1988. However, water quality appeared to have deteriorated (biotic-index values increased) in the Little Platte River during the winter of 1988-89. Water quality in the Livingston Branch of the Pecatonica River also deteriorated during the same period.

The drought of 1988-89 and accompanying decrease in frequency of storms contributed to an uncharacteristically stable environment for macroinvertebrate development in most streams. Total taxa richness increased in three of the four streams. Total taxa richness did not increase in the Little Platte River, possibly because of moderate flooding that occurred prior to the spring 1989 sampling period or, more likely, because of changes in dissolved-oxygen concentrations. Although dissolved-oxygen concentrations were fairly similar in all streams, dissolved-oxygen concentrations were lower in 1989 in the Little Platte River than in other streams. The observed increase in biotic-index values in the Little Platte River during the spring of 1989 supports a decline in water quality.

Smallmouth bass reproduction was related to precipitation and streamflow during the critical mid-May to mid-July reproductive period. Reproductive success was good (38-297 Age 0 smallmouth bass per acre) in 1988 and 1989 and poor (0-3 Age 0 smallmouth bass per acre) in 1987 and 1990. This pattern corresponded with total precipitation of less than 7 inches in May and June in 1988 and 1989 and greater than 7 inches in 1989 and 1990.

In years when runoff exceeded 0.10 inch, only three or fewer Age 0 (smallmouth bass less than 1 year old) smallmouth bass per acre were caught in late summer to fall sampling surveys. In contrast, when overland runoff was less than 0.10 inch, 32 to 297 Age 0 smallmouth bass per acre were found in late summer or fall. The numbers of Age 0 smallmouth bass per acre were significantly different from each other at the 1 -percent probability level (p=0.0001). Smallmouth bass reproductive success indicated that smallmouth bass in these streams were extremely vulnerable to the amount of runoff during the early stage of their life.

Low concentrations of dissolved oxygen constituted the most detrimental water-quality problem affecting smallmouth bass populations. Dissolved-oxygen concentrations were occasionally less than 3 milligrams per liter, a dissolved-oxygen concentration that may be detrimental to early-life stages of smallmouth bass in the streams; however, smallmouth bass were apparently able to withstand these low dissolved-oxygen concentrations and seem to have survived in some situations when dissolved-oxygen concentration decreased to1 milligram per liter.