The maximum number and diversity of macroinvertebrates from limestone-filled basket samplers were obtained by placing the samplers at a depth of 1 ft (0-3 m) below the water's surface for 8 weeks. The letigth ofthe exposure period had a greater effect on the number of organisms than depth of placement. The effects of longer exposure times (8 weeks, compared to 6 and 4 weeks) on Ihe number and diversity of organisms inhabiting baskets were more pronounced during cold weather. In rivers during the summer months, samples contain a variety of aquatic insects, which contributed as much as 95 % of the total number of individuals. The occurrence of some macroinvertebrate species was related to the depth of sampler placement, e.g. the caddisfly Cyrnellus fraternus was more abundant at depths exceeding 4ft {I•2 m); whereas the mayfly Stenonema interpunctatum was more abundant in samplers near the surface.The community diversity index (i) of collections on the same date varied by as much as two units depending on the depth of basket placement and length of exposure period, indicating that consistent practices in sampler installation and analysis are required for comparison of collections in water quality investigations.Baskets touching bottom accumulated greater amounts of sediments than surface satnplers and generally showed greater variability within pairs.In the Ohio River, three replicate baskets can be expected {F = 0 95) to provide an estimate ofthe true mean number of macroinvertebrates within ±20% ofthe sample mean and contain 71 % of the taxa in 10 replicates. However, estimates of sampling precision based on replicate series may vary considerably depending on time, place, number of replicates and natural history ofthe organisms.Baskets filled with 2-in. (5-1-cm) diameter porcelain spheres collect samples comparable in total abundance and diversity to baskets filled with 2-in. (5-1-cm) diameter limestone. However, the taxonomic groups occur in different proportions on the two types of substrates.Hardboard multiplates of l-ft^ (Ol-m^) surface area with -\-(0-32) or ^-in. (0-64-cm) spacings collect significantly greater numbers of individuals than porcelain multiplates with the same spacings. However, differences between samples from the same substrate type are not significant. Multiplates of the same surface area and plate spacing collect substantially the same number of taxa regardless of substrate type.Basket samplers (3-2 ft^ -0-3 m^ surface area) collect a greater abundance and diversity of organisms than the standard 1 ft^ = 0-1 m^ hardboard multiplates. The performance ofthe samplers in terms of abundance and diversity is equalized, however, by increasing the surface area of the multiplate to that of the basket. IntroductionField studies of effects of water quality on benthic macroinvertebrates are often handicapped by the problem of sampling similar, natural substrates suitable for colonization at all sampling stations. The problem is especially difficult in rivers, where fluctuations in hydrologic condition...

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This study shows that biological assessments of water quality status using biomass estimates of wet, dry, and ash-free dry weights and counts of individual organisms from a small, headwater stream in southwestern Ohio provide essentially similar results concerning the impact of a sewage treatment plant discharge. Of the indices of biotic status for the stream segment employed for data evaluation; Diversity Index (D), Community Diversity Index (d), Trophic Condition Index (TCI), and Empirical Biotic Index (EBI), the latter two provided evaluations most consistent with benchmark water chemistry and physics information concerning the trophic status of the stream. In addition, the percent composition of macro-invertebrate taxa by pollutional category; 'clean water', 'facultative', and 'pollution tolerant', as ascribed using TCI and EBI ranges for individual taxa collected in combination of Ekman grab, rock-filled basket sampler and drift net samples, proves adequate for interpretation of biotic status.

SUMMARY A new centric diatom, Microsiphona potamos gen. et sp. nov. (family Coscinodiscaceae), is described from the Little Miami River, Cincinnati, Ohio, where it occurred at cell densities ranging from 29 to 20,140/ml in surface grab samples during the period May 18–December 14, 1966, contributing an average of 11% and a maximum of 35% of the centric diatoms. This species has been observed in grab samples from rivers throughout the United States. The cells are 3–4 μ in diameter, 4–8 μ long, and contain 2 to several plate‐like chromatophores. They occur singly, or arc held together in short chains by the old girdle bands and by numerous apiculi that connect the opposing valves of adjacent daughter cells.