A model based upon simple assumptions about pond trophic dynamics was developed and used to examine the effects of various levels of plant control on sport fish populations. The model predicts a parabolic relationship between plant standing crops (mean concentrations) during the growing season in grams/m 3 and largemouth bass (Micropterus salmoides) production, implying the existence of an optimal target for macrophyte control efforts. Field data from experimental ponds were used to estimate model coefficients. As predicted by the model, invertebrate production and the production of insectivorous forage fishes were positively correlated with macrophyte population size, while piscivorous largemouth bass production was reduced at both high and low weed concentrations. Preliminary fits of the yield equation for largemouth bass gave an optimal macrophyte standing crop of 52 grams dry weight/m 3 for small ponds in central Illinois dominated by Potamogeton crispus and Najas flexilis.
Eleven species or functional types of heterotrophic bacteria were isolated during the study of a heterotrophic succession of an aquatic microcosm. Bacterial populations changed rapidly in numbers and in dominant types. The dominant primary producer, Chlorella, was dependent upon thiamin supplied by 5 of the 11 bacterial isolates. Bacteria were functional in four ways: as contributors of thiamin, CO2 and possibly sources of nitrogen to primary producers; as primary consumers of algal excretions; as secondary consumers of bacterial excretions and as decomposers. During succession net photosynthesis (Pn) surpassed night respiration (Rni) from day 5 through 45; as maturity approached the Pn/Rni ratio fluctuated around 1. Dissolved carbon was present at 240 mg C/liter at zero time and decreased owing to the heterotrophic activity of 1.5 x 109 bacterial cells/ml by day 8. Dissolved carbon was maintained at approximately 20.7 mg C/liter from day 8 through maturity. Particulate biomass increased steadily until day 50, after which there was no further increase. A bimodal pattern was apparent in bacterial numbers, Chlorella numbers, community metabolism, C14—U—glyoxylate uptake and bacterial species diversity in which peaks were recorded early and late in succession while a mid—succession decrease in activity occurred. The microcosm exhibited trends expected of larger, more open, developing ecosystems. The microcosm and methods used in the study are useful laboratory tools for examining various ecological principles.
As more people become infected with HIV, Health Care Workers (HCWs) have a greater likelihood of being exposed at work. HIV exposure threatens the life of the HCW and can elicit a stress reaction. Although HCWs have reactions similar to those of people who have been exposed to other traumatic events, the nature of this stressor and the length of time it lasts is unique. This article presents counseling interventions that address the needs of the individual HCW during this event. These counseling guidelines promote the HCW's discussion of the event and any relevant past unresolved traumatic experiences; evaluate and aid the worker and his or her support system; provide information on stress reactions and HIV; examine the HCW's practice methods; and helps to reintegrate the HCW back into the work environment.
Par Pond is a thermally enriched monomictic southeastern lake which receives heated effluent from a production nuclear reactor. Fish populations in the lake have lesions of epizooty from which Aeromonas spp. are readily isolated. Distribution and population densities of Aeromonas in the water column were measured along an oxygen and temperature gradient as well as seasonally. Greater population densities of Aeromonas occurred below the oxygen chemocline when the lake was stratified. Survival ofAeromonas hydrophila under in situ conditions in both epilimnetic and hypolimnetic waters was determined through the use of polycarbonate membrane diffusion chambers during two separate reactor operating conditions. Survival levels of pure cultures of A. hydrophila corresponded to the distribution patterns of the naturally occurring Aeromonas-like populations. The greater survival of A. hydrophila during full reactor operation suggests that the fish populations may be exposed to Aeromonas for a longer period of time than when the reactor is not operating.
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