JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Abstract. The truncated lognormal distribution can be used to graduate certain species-abundance data, provided that estimates of the location and scale parameters are obtained. A computer program has been written which groups the data on a log2 scale and numerically solves the maximum likelihood equations for this type of distribution. Results show that the estimates obtained by this method compare well with those of Hald and Cohen. Examples are presented using the diatom data of Hohn and Hellerman, and it is shown that a better fit is obtained by using the entire data set instead of selectively disregarding the most abundant tail intervals. Other published techniques for this type of analysis are also discussed.

The lognormal distribution has figured prominently in the description of species-abundance relationships and in assessing effects of perturbation on aquatic ecosystems. Diatom communities, in particular, have been shown to conform relatively well to a normal law subsequent to grouping individuals on a logarithmic scale. Fitting of the distribution to sample data entails estimation of location and scale parameters. A more interesting and, indeed, ecologically important estimate that can be obtained is the total number of species in the community, S*. Unfortunately, estimates of S* are currently unsatisfactory since an estimator of the variance of S*, var (S*), is not available. Moreover, it is often the case that several different theoretical distributions are found to fit the same sample data equally well but provide discrepant estimates of S*. On this basis then, comparisons between different communities are impossible. In addition, a cautious attitude is warranted in certain applications of the Shannon-Wiener diversity index where knowledge of S* is required. The purpose of this paper is to report on the results of a computer simulation study which was designed to mimic the sampling and identification of diatom species from idealized, fully censused collections where the value of S* was known as was the proportional abundance of each species. Each simulation run consisted of sampling the idealized collections a total of 100 (independent) times; each sample being fit by a lognormal distribution and an estimate of S* calculated. It was thus possible to compute an estimate of var (S~*) and monitor its behavior as the sample sizes for various types of communities were increased. The results indicate that the precision of S~* depends on the relative size of the sample and that var (S~*) decreases asymptotically as the number of species sampled approaches S*. It is shown that, for some types of communities, species sample sizes on the order of S = 0.8 (S*) yield imprecise estimates of S*. The implications of these results have importance for the biologist who is faced with distinguishing between two or more similarly diverse communities on the basis on an index of evenness such as H/Hmax (in the case of Shannon-Wiener). Unless reliable knowledge of S* can be obtained, misleading conclusions regarding a community's diversity could result.

Biomonitoring systems designed to protect the integrity of aquatic ecosystems must satisfy two complementary requirements if they are to be used in a successful management program. First, they must generate reliable information with respect to the current biological status of the ecosystem; second, they must be capable of reducing the lag time in the feedback of this information. This paper describes a biomonitoring system, currently being developed, that employs coherent optical spatial filtering techniques to rapidly identify diatoms and process species-abundance information. Preliminary results indicate that the optical problems associated with such a system can be overcome satisfactorily, although investigations are continuing into the problem of interfacing a microscope directly to the optical system. We envision that this system can eventually be employed in a management program along with chemical and physical data to obtain full beneficial use of the ecosystem without damage.

Biomonitoring systems designed to protect the integrity of aquatic ecosystems must satisfy complementary requirements if they are to be used in a successful management program. First, they must generate reliable information with respect to the current biological status of the ecosystem ; and second, they must be capable of reducing the lag time in the feedback of this information . This paper describes a biomonitoring system, currently being developed, that employs coherent optical spatial filtering techniques to rapidly identify diatoms and process species-abundance information . Preliminary results indicate that the optical problems associated with such a system can be overcome satisfactorily, although investigations are continuing into the problem of interfacing a microscope directly to the optical system . We envision that this system can eventually be employed in a management program along with chemical and physical data to obtain full beneficial use of the ecosystem without damage .

Davis Creek is a southern Ohio, USA stream that receives a permitted discharge from the Belpre Elastomers Plant (BEP). A sediment quality triad investigation of Davis Creek was conducted over a 2-y period that included sediment and surface water chemistry measurements, toxicity tests of whole sediment, interstitial and surface water, and benthic and artificial substrate community assessments. The concentration of arsenic in surface and interstitial water was below United States Environmental Protection Agency ambient water quality criteria and was not toxic in laboratory tests (Ceriodaphnia dubia, Pimephales promelas). Similarly, sediments did not significantly affect survival and growth of Hyalella azteca and Chironomus tentans at most sampling locations despite sediments exceeding arsenic sediment screening values in nearly all samples collected. Differences in benthic community structure, determined by rapid bioassessment and Hester-Dendy sampling methods, were related primarily by variations in sediment moisture, particle size, and ammonia and not to arsenic concentrations. The Invertebrate Community Index (ICI) for Davis Creek was lower than values established for other warm-water ecoregional reference streams in Ohio. However, this ICI comparison may have been invalid because, unlike the reference streams, the Davis Creek watershed is small with intermittent headwater flow that limits macroinvertebrate recruitment and energy input. The sediment quality triad investigation indicated that Davis Creek was not significantly affected by arsenic associated with the BEP discharge despite having measured arsenic concentrations that exceeded sediment screening values.