To determine the influence of a multiple inversion aeration system upon the limnology of a small sinkhole lake, we monitored physical-chemical and biological parameters for 15 months prior to starting aeration and for 24 months thereafter. Aeration eliminated thermal stratification and dissolved oxygen concentrations of bottom waters increased significantly. Secchi disk transparency increased during aeration while turbidity, pH, alkalinity, total nitrogen, hydrogen sulfide and iron concentrations decreased significantly. Primary production and mean chlorophyll a did not change significantly during aeration but total phytoplankton cell volume decreased 2-fold. This decrease was caused by a marked reduction in blue-green algae which appears to be attributable to rapid mixing of the lake and to decreases in the pH. Cell volumes of green algae remained constant but numbers of taxa increased 70%. Densities of crustacean zooplankton were reduced markedly by aeration while densities of rotifers increased significantly during the first year but then returned to preaeration levels during the second year. Large-bodied cladocerans were replaced by small-bodied forms during aeration, and copepod populations became dominated by nauplii (97%). Densities of benthic macroinvertebrates declined 2-fold during aeration due to to a marked reduction (10-fold) in the Chaoboms population which correlated strongly with decreases in crustacean zooplankton abundance. The total number of taxa collected on individual sample dates increased throughout the two year aeration period (from 12 to 25) and chironomids became the predominant group (70%).The multiple inversion aeration system successfully eliminated many of the undesirable features of eutrophication (e.g., oxygen depletion, blue-green algal blooms, low benthic diversity), but it did not change the trophic state. Aeration of hypereutrophic lakes for multiple years may be necessary to maintain desired conditions.
A study of insect drift was conducted in a small, subtropical Florida stream from December 1971 to December 1972 to describe the seasonal and diel periodicity and to determine factors influencing behavioural drift. Paired samples of 2h duration beginning 15 min after sunset were taken biweekly, and hourly collections over a 24-h period were made quarterly. Benthic invertebrates were collected on each date from three habitats (riffle, pool and aquatic vegetation) and temperature, dissolved oxygen and current velocity were measured. Drift rates ranged from 100 ro 2125 organistiisjm^.h (003 to 0-49 organisms!m'^} (^"d were greatest in winter and early spring; minimal rates occurred in the summer months. The following six taxa, in order of relative abtmdance, comprised 87% of the drift: Baetis intercalaris, Cheumatopsyche sp., Stenonema exiguum, Chironomidae, Stenelmis fuscata and Simulium sp. Total drift showed no significant correlation with temperature, dissolved oxygen or mean benthic abundance and only slight correlation with cttrrent velocity (r=0'34). Stepwt'se, multiple regression analyses indicated that riffle density and mean size of drifting organisms were important factors influencing the drift rates of B. intercalaris (R=0-61) and S. exiguum (R = 0-82); mean size, riffle density and water temperature influenced the drift of Cheumatopsyche sp. (R = O-1S). The other taxa of drifting insects showed no significant correlation with the variables measured. Diel (24 h) studies of the major taxa showed marked differences in the periodicity, both within and between taxa, indicating the need for long-term sttidies with freqtient sample intervals in subtropical habitats. A new drift pattern for the family Chironomidae, alternans type, was observed for late instars of Folypedilum halterale.
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