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Publication Abstract

Effect of Bottom Conditions on Eutrophy of Impoundments Roseboom, Donald P., Ralph L. Evans, Wun-Cheng Wang, Thomas A. Butts, and R. M. Twait, 1979  Illinois State Water Survey, Champaign, IL,  ISWS C-139    Full Text Available

Two man-made impoundments, Lakes Eureka and Canton in central Illinois, were studied to develop procedures for assessing behavior characteristics and thereby relative eutrophy of waters in man-made lakes, as opposed to traditional assessments of glacial lakes. Likenesses and differences for the two lakes in productivity, water chemistry, and sediment oxygen demand were identified.

Both lakes are used for public water supply and recreation. Both thermally stratify and maintain an anerobic zone in bottom strata for a 5-month period in summer; stratification is weak in the shallower Lake Eureka, but well defined in Lake Canton. The rate of anerobic zone formation is greater in Lake Eureka but the zone's extent from the bottom is less than in Lake Canton; overall, oxygen depletion conditions in Lake Canton are the most severe. The thermal stratification of the lakes is not a barrier to the extent the anerobic zone penetrates the overlying waters.

Both lakes support blue-green algae blooms. The density of algae at Lake Canton exceeds that at Lake Eureka; however, alkalinity reductions at the surface indicate algal productivity of Lake Eureka exceeds that of Lake Canton by 30 percent, and alkalinity increases in the bottom waters indicate microbial activity in bottom muds in Lake Eureka exceeds that in Lake Canton by 44 percent. Differences in alkalinity between the surface and bottom waters in both lakes were significant. Nonetheless, higher total and dissolved phosphorus contents in Lake Canton bottom waters give that lake a greater potential for productivity; overall, Lake Canton can expect more problems with nuisance algal blooms than Lake Eureka.

Significant quantities of iron and manganese (mainly Fe+ + and Mn++ forms) are released from the bottom muds of both lakes during summer stagnation. Migration of iron and manganese up the water column is limited to the vertical extent of the anerobic zone. Similarly, significant ammonia-nitrogen produced in the bottom waters is limited to vertical extent of the anaerobic zone; the oxygen demand potential of ammonia-nitrogen may be a major influence on the extent and duration of the anaerobic zone. Chlorine demand of bottom waters is greater than that in upper water layers in both lakes. Ferrous iron was the principal component of chlorine demand in Lake Eureka; sulfides imposed the principal demand at Lake Canton. Unexpected problems with gas production required developing new equipment for in-situ sediment oxygen demand (SOD) measurements, leaving time for only a few successful collections.

A method using SOD rates is given for predicting the rate of ascent of DO-depleted water in a water column during development of an anaerobic zone. Also given is a laboratory batch method using BOD bottles for determining relative rates of SOD in lake muds. SOD rates were less for Lake Eureka than for Lake Canton. The density and taxa of benthic macroinvertebrates were similar to those from anaerobic zones in other Illinois lakes. The relative eutrophy of the lakes determined mainly by bottom conditions indicates worse conditions in Lake Canton than in Lake Eureka; water depth may govern the extent and duration of the anaerobic zone. More precise and less time consuming measurement techniques are needed.

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