The Long and Short Term Effects of Fire on Phytoplankton and Lake Chemistry in Yup'ik Territory (Yukon-Kuskokwim Delta, Alaska).

Increasing wildfire frequency and severity are impacting ecosystems and Indigenous lands across the Arctic. While research has been conducted to understand the effects of wildfire across terrestrial landscapes, wildfire impacts on Arctic aquatic ecosystems are not well understood. Changes in lake chlorophyll a concentrations , a key indicator of phytoplankton abundance, as a result of fire could have drastic effects on higher trophic levels, including economically important and subsistence fisheries. Our objectives were to better understand the short (4-7 years) and long (~50 years)-term impacts of wildfires on lake chemistry and physical properties and potential impacts on phytoplankton (using chlorophyll a) in lakes in the Yukon-Kuskokwim Delta.

Over the course of two weeks in July 2019 and 2022, we sampled surface water from 21 lakes, which included seven from an unburned area, seven from a 2015 burn, and seven from a 1972 burn. Water samples were analyzed for nitrate, ammonium, and phosphate concentrations and chlorophyll a. We also measured temperature, pH, and dissolved oxygen at the time of sampling. After four years following a fire (2019) chlorophyll a, dissolved oxygen, and phosphate were higher in lakes from the burned area than in the unburned. After seven years, trends were similar; chlorophyll a was lower in lakes from the unburned area than the 2015 burn. We did not detect a difference in chlorophyll a between lakes in the 1972 burn and the unburned area. These results suggest that tundra fires can have cascading effects on aquatic ecosystems that can last years following fires. This can have important implications for Yup'ik and Cup'ik communities who have lived with this land since time immemorial.