Abstract
Lake browning, i.e., a gradual and long-term increase in the water colour, is a recognized and topical water quality problem that has received much less attention in water protection than eutrophication. Thus, new bioindicators that respond to environmental stress are needed to monitor lake browning. Recent study suggests that the chlorophyll content of macrophytes is a promising indicator for assessing lake browning, yet little is known about how quickly the changes in the total chlorophyll content of aquatic plants occur. For instance, it is not known whether the plants adjust their chlorophyll content to the daily changes in light availability or to the longer-term light environment in the lake. Therefore, the response time of macrophytes to changes in light availability needs to be clarified to assess their suitability for detecting changes in water quality. The objectives of this experimental study were to investigate the chlorophyll content of Egeria densa and their response time to changes in light availability. No significant change in total chlorophyll content was observed in E.densa , but our study showed a change in macrophyte chlorophyll a : b ratio within 5–7 days of light intensity alternation, suggesting the chlorophyll ratio can be a more promising indicator for the light conditions varying on the daily scale than the snapshot weather monitoring. Thus, our study corroborates the idea of using macrophytes as bioindicators of browning.