Big Lake is a shallow (mean depth = 0.89 m in 1973) 256-ha backwater lake on the floodplain of the Mississippi River in NE Iowa. During the summers of 1973 and 1974 Sphaerium and Hexagenia made up 81% of the benthic macroinvertebrate abundance and 92% of the benthic biomass; both taxa had greatly reduced abundance and biomass within stands of emergent Sagittaria along the lake margin. During July 1974 the Sagittaria net productivity was about 19 g/m/sup 2//day. Cesium-137 levels were determined in sediment samples showing that between 1896 and 1973 about 76 cm of sediment had accumulated in Big Lake, and the recent sedimentation rate (1964-1974) was about 1.7 cm/year. The calculated annual reduction in lake volume of about 37,400 m/sup 3//year suggests that the physical and biological components of this productive aquatic habitat will be greatly modified during the next few decades.
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Eckblad et al. (1977) studied this question.