The effects of fire on phytoplankton of the Yukon-Kuskokwim Delta, Alaska

As a result of anthropogenic climate change, wildfires are occurring more frequently and with more severity throughout the world, including the Arctic. While research has been conducted to understand how these fires influence terrestrial landscapes, little is known about how aquatic communities may change. Changes in phytoplankton abundance and composition as a result of fire could have drastic effects on higher trophic levels, including economically important fisheries. Our objectives were to better understand the impacts of fire on phytoplankton communities in lakes in the Yukon-Kuskokwim Delta.

In the field, water samples were collected for analysis of nitrate, ammonium, and phosphate concentrations, dissolved oxygen, and chlorophyll a. Additionally, phytoplankton net tows were launched to collect samples for community composition. Over the course of two weeks, 12 lakes were sampled, 6 in an unburned area and 6 from an area that burned in 2015. We found that there were higher levels of chlorophyll a, dissolved oxygen, and phosphate in the 2015 burned lakes than in the unburned lakes four years following fire. These results demonstrate that tundra fires can impact aquatic phytoplankton activity, as demonstrated by an increase in chlorophyll a in burned lakes. In addition, aquatic nutrient data suggest that phytoplankton biomass in lakes of the Yukon Kuskokwim Delta may be more limited by phosphorus than nitrogen. While further research is necessary to understand how individual phytoplankton taxa themselves may be shifted as a result of the increase in nutrients, an increase in overall phytoplankton activity after fire may indicate an increase in resources for higher trophic levels in these Arctic lakes.