Spatial Variation in Littoral Zone Benthic Algal Productivity in the Sierra Nevada, California

Abstract:

Observations of benthic algae have increased in recent years across mountain lakes in the western United States, similar to lakes across the globe. While there is quantitative knowledge on the effects of nutrient pollution and warming temperatures on increasing overall lake productivity, knowledge of what drives variation in benthic productivity between lakes is largely unknown. Littoral zone benthic incubation experiments were performed in alpine and subalpine lakes of Sequoia and Yosemite National Parks during the summers of 2018 and 2019 to estimate benthic gross primary productivity (GPP), capturing a drier, warmer year (2018) and a wetter, cooler year (2019). Benthic GPP varied by an order of magnitude between lakes (0.02 – 2.50 μg O2/cm2/hr), where 79% of lakes exhibited autotrophy and 21% exhibited heterotrophy. Despite different climatic conditions between years, GPP values correlated most strongly with specific basin characteristics such as slope, north or south facing aspect and percent barren landscape. Although average whole lake chlorophyll-a measurements were significantly higher in 2019, they did not correlate with higher benthic GPP values, suggesting that pelagic productivity may be disconnected from benthic productivity. The lack of variation between years and insignificance of temperature and precipitation on benthic GPP suggests that littoral zone benthic productivity might be less subject to short term perturbations in climatic factors and controlled more strongly by localized watershed morphology and nutrient fluxes.