Informe: Impacts of Smoke-Ash from the 2021 Wildfires to the Ecology of Lake Tahoe

CHANDRA, SUDEEP; SCORDO, FACUNDO; SUENAGA, ERIN; BLAZSCZAK, JOANNA; CARINA SEITZ; CARLSON, EMILIY M.; LORIA, KELLY; BRAHNEY, JANICE; SADRO, STEVEN; SCHLADOW, GEOFFREY S.; FORREST, ALEXANDER; LARRIEU, K. ; WATANABE, S; HEYVAERT, ALAN ; CRAIG E., CRAIG E.; OVERHOLT, ERIN

2021-08-01/2022-07-19

1-79

Ciencias atmosféricas e hidrológicas

Recursos hidricos

The smoke generated from the 2021 wildfires presents unique opportunities to understand how major disturbances outside of the basin influence short and long-term water quality dynamics in Lake Tahoe. Currently, the Tamarack, Caldor, and Dixie Fires burning outside of the Lake Tahoe basin have been impacting the air quality for weeks to months in the summer of 2021 and may continue into Fall (Figure 1). Understanding these disturbances is becoming particularly important for policymakers at regional scales as mega-wildfires become a more frequent occurrence with changing climate. In addition, investing in research during the 2021 fire season will help to explain the water quality dynamics and provide a mechanistic understanding of changes which can be included in the 2021 clarity evaluation when it is discussed by Tahoe Science Advisory Council in 2022. In the context of the Lake Tahoe TMDL and efforts to restore Lake Tahoe?s clarity, managers need to know the relative impact of processes beyond their control.There have been limited efforts to explore how indirect effects from wildfire smoke influence lake clarity in Lake Tahoe. While the smoke plumes from previous wildfires were limited in their duration and frequency of exposure, some insights can be gained on how they affected the lake. For example, Goldman et al. (1990) found that the Wheeler Fire in Southern California in 1985 increased algal production in July to its highest level reported at the time. The increase in algal production was attributed to changes in incident (surface) light and due to the stimulation of growth from nutrients, including micro and macronutrients, although these were not directly measured during the study. Williamson et al. (2016) found direct changes to light reaching the lake?s surface (incident ultraviolet to visible light ratio) in July to early August 2014 during the King Fire. These changes influenced the depth distribution of zooplankton, an important food resource for fish (Urmy et al. 2016). Most recently, a study at Castle Lake evaluated the effects of smoke from multiple fires in 2018 in a small mountain lake in Northern California (Scordo et al. 2021). In this study, wildfire smoke cooled the lake and decreased ultraviolet light in the upper waters that typically suppresses algal growth. The algal productivity increased by 109% in the upper part of the lake and the deep water algal production was near zero. Animals responded in different ways with slight changes to the composition of zooplankton and changes in the behavior of trout. These limited studies of wildfire smoke suggest there can be a number of complex yet direct changes to lake productivity in the offshore and changes in animal behavior. No published study to date evaluated changes to nearshore water quality in Lake Tahoe or elsewhere. Preliminary observations by Chandra (PI) the week of Sept 10, 2021, suggests a greening of the nearshore in South Lake Tahoe along Baldwin Beach, Bijou and South of Cave rock to Glenbrook. In addition, orange aquatic fungus is collecting on top of ash that is washing up on beaches.The project will explore direct connections of wildfire smoke and their interrelationships across different components of the lake ecosystem (Figure 2).1. Air quality, light regime, and air temperature (night and day) in the Tahoe basin;2. The particle size distribution and concentrations in Lake Tahoe?s water column affecting clarity;3. Algal growth and changes to vertical distribution and speciation in the open water (where long-term clarity measurements occur);4. Light changes in the atmosphere that depress or enhance nearshore algal production; and5. Spatial differences in the type and nutrient concentrations of particles around the Tahoe basin to assess the relationship to nearshore algal growth.