Responses of molecular indicators of exposure in mesocosms: common carp (Cyprinus carpio) exposed to the herbicides alachlor and atrazine.

Common carp (Cyprinus carpio) were treated in aquatic mesocosms with a single pulse of the herbicides atrazine or alachlor to study the bioavailability and biological activity of these herbicides using molecular indicators: Liver vitellogenin gene expression in male fish for estrogenic activity, liver cytochrome P4501A1 gene expression, and DNA damage in blood cells using the single-cell gel electrophoresis method. Both alachlor and atrazine showed dose-related increases in DNA strand breaks at environmentally relevant concentrations (<100 ppb). Gene expression indicators showed that neither herbicide had estrogenic activity in the carp, whereas atrazine at concentrations as low as 7 ppb induced cytochrome P4501A1. These results support the study of molecular indicators for exposure in surrogate ecosystems to gauge relevant environmental changes following herbicide treatments.

Ecosystem Modeling with Lisrel: A New Approach for Measuring Direct and Indirect Effects.

Evaluating the effects of toxicants in ecosystems is difficult despite numerous attempts to develop field and laboratory tests. The problem appears to be the lack of an analytical methodology capable of taking advantage of the available experimental designs. Therefore, we propose a technique for modeling ecosystems-linear structural modeling with LISREL. LISREL is a path analytic technique that is more flexible than classical path analysis. Modeling with LISREL involves placing ecosystem structure and function into a framework of concepts and indicator variables. Concepts are theoretical constructs that are placed into a cause-and-effect network to reflect true ecosystem structure. Concepts are @indicated" by indicator variables; these are the measured variables in the ecosystem. LISREL incorporates measurement error into the modeling process by establishing a portion of the variance of each indicator variable as measurement error. The framework of concepts and indicators in a cause-and-effect network becomes a hypothesis that is tested using LISREL. LISREL also provides a determination of the total, direct, and indirect effects of the variables on each other. A measure of ecosystem stability is provided as part of the modeling process.

FACTORS AFFECTING PHYTOPLANKTON DISTRIBUTION IN A DOUBLE-CELL SEWAGE LAGOON (1) (2).

The distribution of phyioplankton in a double-cell sewage lagoon at Hallam, Nebraska, was studied in relation to physical, chemical, and biological factors during the summer and fall of 1965. Sixteen species of algae were recorded in the first and more organically rich of the two physically similar ponds, with 28 species recorded in the second pond. Population sizes were always greater in the first pond due to reduced grazing during the summer and large quantities of ammonia-nitrogen during the fall. The dominant algal species in both ponds on nearly all sampling dates was Ankistrodesmus falcatus v. acicularis. Declines in this population occurred with high organic pollution and heavy grazing. Both ponds had severe reductions in algal numbers during late October due to heavy grazing by the rotifer Brachionus. The distribution of phytoplankton in the Hallam ponds is compared to that of other sewage ponds in the United States, and the general pattern which emerged is discussed.