Macrobenthos was sampled during the summer of 1984 in a series of experimental fishponds with water alkalinity artificially adjusted to different levels (2.0, 3.8,6.9,8.4, and 35.8 mg/liter of CaC03 equivalents). Chironomid midges, nematodes, and tubificid oligochaetes accounted for 67% of all benthic organisms recovered. No significant trends were apparent as to abundance or type of benthic organisms encountered in each treatment. The most numerous midge in the samples was the detritivore/herbivore Einfeldia. The smaller predator midge Procladius was the second most abundant. Chironomus was most common in ponds with deep, rich bottom muds. Tanytarsus was more common in ponds where many aquatic macrophytes had developed. Taxa diversity indices ranged from 1.88 to 2.82 and were not significantly different among treatments. Fish biomass increased with alkalinity but no significant correlation was found with benthos numbers.
