The potential use of filamentous bacterial growth on stream macroinvertebrates as an indicator of nutrient enrichment

Abstract

The influence of environmental stressors, such as nutrient enrichment and physical habitat degradation, can lead to a loss of biological integrity in streams. Nutrient enrichment in streams is a major concern in agriculturally dominated watersheds as fertilizers and animal waste runoff contaminate and pollute these systems through non-point source means. The impacts of nutrient enrichment on stream health requires further attention as well as the methods used to determine the source of contamination. One of the notable effects of nutrient addition in streams is the increased growth of aquatic, filamentous bacteria such as Sphaerotilus and Leptothrix. These bacteria have been known to colonize and grow on aquatic insects in nutrient enriched streams, and cases of high coverage on the insect have been found to be fatal. This study aims to analyze the differences in stream macroinvertebrate communities by looking at community composition, diversity, taxa richness, and biomass in nutrient enriched and non-enriched streams as well as evaluating the growth of filamentous bacteria on macroinvertebrates and its potential use as a bioindicator for nutrient pollution that is beyond extreme levels. Seasonal field measurements were taken of macroinvertebrate abundances, nutrient concentrations, and degree of bacterial growth on insects in six streams located in Western New York that were categorized as nutrient enriched or not based on nitrogen and phosphorus concentrations. Using non-metric multi-dimensional scaling (NMDS), analysis of similarities (ANOSIM), and similarity percentages (SIMPER), macroinvertebrate abundances in the enriched streams were compared to the non-enriched streams. The enriched and non-enriched streams were found to have significantly different macroinvertebrate communities, where the enriched streams had an abundance of pollution- tolerant organisms such as oligochaetes and leeches, while the nonenriched streams were mainly composed of pollution-sensitive insect species, and the non- Edwards 2 enriched streams were also significantly more diverse and had higher family richness. While the biological data indicate significant differences in stream integrity between the enriched and the non-enriched sites, bacterial growth and coverage did not follow similar expectations. There was no difference in the presence of bacteria between the enriched and non-enriched sites and the percentage of colonization was not greater in the enriched sites. Based on the data in this study, the use of filamentous bacteria growth on aquatic macroinvertebrates as a rapid bioindicator for nutrient enrichment in streams should be re-evaluated as nutrient levels in streams may not be the only contributing factor for bacterial growth to occur, and interpretation may not be broadly valid compared with traditional monitoring techniques