Effects of artificial light on the drift of macroinvertebrates in urban Central Texas streams
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Since the majority of organisms operate on a circadian rhythm, light pollution in urban areas can possibly influence the aquatic community by affecting the drift of macroinvertebrates. The objective of this study is to examine if artificial night lights reduce drifting macroinvertebrates in the Edwards Plateau, by quantifying macroinvertebrate drift under ambient night light conditions and under extreme artificial lighting. This study was conducted in five streams (two large streams and three smaller streams) within urbanized areas of Central Texas. Drifting macroinvertebrates were sampled using drift nets under two treatments: ambient lighting (control) and extreme artificial lighting. Among all streams, both taxon diversity and richness of drifting insects was similar between treatments, but average abundance of drifting insects was 37% less in artificial lighting treatment than under the control treatment. Treatment effects were more evident in larger streams than smaller streams. Average abundance of drifting insects was 40% less in artificial lighting treatment with larger streams with notable decreases in Simuliidae (58% less than the control), Baetidae (51% less), and Coenagrionidae (50% less). Reduced drift by artificial light conditions found in this study suggests the potential of artificial lighting disrupting dynamics of macroinvertebrate drift. Results of this experiment support a growing body of knowledge on how urbanized systems will influence stream communities and provide evidence to support various management strategies to minimize the effects of artificial lights on aquatic communities.