Aquatic macroinvertebrate response to fire and substrate type in lakes of the Yukon-Kuskokwim Delta, Alaska

In recent years the Arctic has experienced increased temperatures and an altered fire regime, which has significant consequences for aquatic ecosystems. Aquatic invertebrates are often used as indicators of water quality and environmental change. With this project we investigated how fire affects the diversity and abundance of aquatic macroinvertebrate communities and how they can be used as a metric of arctic change. Despite the importance of aquatic invertebrates for community and ecosystem dynamics, there is little understanding of their distribution and abundance in lakes of the Yukon-Kuskokwim Delta, AK. We sampled a total of twelve lakes, six in areas burned in 2015 and six in unburned areas. Over the course of two weeks in July 2019, we collected invertebrates, benthic substrate and water from each lake. The invertebrates were preserved in the field, and identified in the lab to lowest taxonomic level possible. We calculated diversity using the Shannon-Wiener Index. Substrate samples were analyzed for chlorophyll a and organic matter content. There was little difference in overall diversity or abundance of invertebrates between the burned and unburned lakes; however, we did find differences in diversity and abundance in lakes with different substrate types. Lakes with fine sediment substrates had lower diversity than those with organic or mixed (fine sediment and organic material) substrates, while lakes with mixed substrates had the highest diversity. There was also a connection between substrate type, burn history, and community composition. Organisms in the Hydracarina group were most abundant in organic substrate and in unburned lakes, while those in the Corixidae family were most abundant in fine sediment substrate and in burned lakes. Additionally, all but one of the four organic substrate lakes were unburned, and all three lakes with fine sediment substrates were burned, which could indicate that fire is increasing the amount of fine sediments in lakes, which in turn may affect the macroinvertebrate communities in those lakes.