Alternative approaches for monitoring aquatic ecosystems: a study on the effects of municipal sewage effluent on biota in the South Saskatchewan River

Abstract

Assessments of nutrient enrichment and contaminant toxicity from treated municipal sewage effluent were conducted on biota from the South Saskatchewan River through field monitoring and artificial stream experimentation. Field studies indicated that primary productivity was stimulated by nutrient enrichment, however, standing crop measurements were strongly influenced by increased abundance of invertebrates (i.e., chironomids). Periphyton quality was adversely effected by contaminants in the effluent, resulting in reduced lipid energy storage and physiological condition. Invertebrate community structure and composition at sampling stations were assessed through the use of diversity and similarity indices. Diversity indices were successful in identifying changes in community structure immediately downstream of the municipal effluent discharge, whereas the similarity index indicated a 51% difference in community composition between upstream and downstream sites. The evaluation of ecosystem processes based on invertebrate functional feeding groups were used to assess the influence of municipal sewage effluent on energy flow within the river. Energy storage within each group was measured by both biomass and areal lipid content. The identification of increased biomass and areal lipid content of gatherers and filter feeders immediately downstream of the effluent discharge suggests organic enrichment effects, whereas a reduction in scraper and predator biomass and lipid content indicated organic enrichment and toxicological effects. Measurements of invertebrate functional feeding groups provided descriptive, and ecologically meaningful information. When combined with the descriptive power of multivariate analyses, functional feeding group data was useful as a rapid bioassessment approach in the evaluation of effluent impacts on river ecosystems. Artificial stream studies were conducted to address questions on chronic effluent toxicity, and possible nutrient-toxicant interactions on growth and energy storage of the common stream scraper, Baetis tricaudatis. Larvae exposed to effluent had a 100% increase in thorax length over control animals, indicating growth stimulation of effluent exposed animals. Measurements of dry weight showed no effects of effluent on B. tricaudatis, however food effects were significantly different indicating that appropriate food levels were selected. Baetis tricaudatis exposed to 1% and 10% municipal effluent concentrations were found to have reduced lipid energy storage, indicating a reduction in physiological status. With increased food availability, the level of lipid energy storage increased to those of control animals, however, this was only apparent at the 1% effluent concentration, suggesting that at 10% effluent concentrations, food quantity can not alleviate effects. From a bioassessment perspective, this research provides important information on alternative methods for evaluating effluent impacts on river ecosystems. This research points out the importance of assessing energy flow and storage within stream biota to better understand the types of impacts that complex municipal sewage effluents have on riverine biota.