Response of the cyanobacterium Aphanizomenon flos-aquae to vascular plant decomposition products

Abstract

Upper Klamath Lake in south central Oregon annually experiences intense blooms of cyanobacteria, primarily Aphanizomenon flos-aquae. Domination of the lake phytoplankton community by this single species regularly results in drastic changes to water quality. Photosynthetic activity of such extensive populations can result in pH over 10. Blooms typically expire in a short period of time, causing low oxygen conditions. Both situations are stressful to aquatic organisms and have been implicated in large scale fish die-offs, including 2 species that are federally protected. Understanding and controlling the intensity of such blooms should be an important consideration for lake management strategies. Based primarily on observation it has been thought that both barley straw and brown marsh waters have algistatic properties. However there are numerous studies that have demonstrated colored dissolved organic matter (CDOM) or humic substances, affect algal and cyanobacterial growth in a number of ways. During the 2005, 2006 and 2007 Upper Klamath Lake A. flos-aquae blooms a series of controlled laboratory assays and in situ limno-corral experiments were conducted to asses the effectiveness of barley straw, barley straw extracts, marsh water and dried wetland plants at suppressing A. flos-aquae growth. Initial results of these studies indicate that the application of barley straw or dried wetland plants were most effective at suppressing and even killing A. flos-aquae. Marsh water and barley straw extract showed mixed results. However further analysis revealed that the degree of suppression was directly related to the concentration of CDOM present and the level of light exposure. These finding are consistent with the hypothesis that light mediated hydrogen peroxide production is the mechanism responsible for suppression of cyanobacterial growth.