Using fossil chironomids to investigate dissolved oxygen in New Brunswick lakes experiencing algal blooms

Abstract

Lake eutrophication often results from an increase in anthropogenic activities and poses a serious threat to the function and structure of lake ecosystems. In particular, algal blooms are increasing in frequency in low-nutrient lakes that would otherwise not be expected to experience signs of eutrophication. As algal-derived organic matter sinks in the water column, bacteria consumption uses a large amount of dissolved oxygen (DO). When DO levels become low in a lake’s hypolimnion, hypoxia can occur, threatening lake health. In this study, 20 low-nutrient New Brunswick lakes were examined for environmental changes using the paleolimnological approach of comparing the relative abundances of invertebrate taxa (chironomids) from “top and bottom” sediment intervals. Lakes were grouped into bloom and reference categories for comparison of measures of water quality and invertebrate bioindicators. Most water quality measures did not differ between categories. Assemblages indicated that there were ecological changes between top and bottom samples of several individual lakes as opposed to consistent differences in assemblage composition between bloom and reference categories. Findings indicate the importance of both direct and indirect monitoring of low-nutrient New Brunswick lakes.