PS 37-14 - The Spatial and Temporal Dynamics of Stream Bacterial and Fungal Abundance in Great Plains Non-Perennial Streams

Abstract: Non-perennial streams comprise approximately 50% of global stream length and 59% of the continental U.S. stream length, and increased duration of the dry phase in these waterways is a global response to climate change. Aquatic microorganisms are important drivers of carbon and nitrogen retention and immobilization, thus controlling both downstream water quality and integrated ecosystem metabolism. Surface flow connectivity to the local microbial habitat provides the organic energy and dissolved nutrients that support microbial growth, and in turn, nutrient immobilization. However, the sensitivity of microbial populations to stream drying and rewetting is not well understood. We predicted that greater hydrological connectivity would support higher bacterial and fungal populations, to some plateau level where the growth response was saturated. To understand spatial variation in connectivity across the study watershed (Kings Creek, Kansas, USA), 50 sensors for temperature, intermittency, and conductivity (STICs) were deployed in early June 2021. Each STIC sensor marked a sampling site where biofilm, leaf, sediment, and water microhabitats were collected for DNA extraction and quantitative PCR analysis to measure bacterial 16S rRNA gene and fungal ITS abundance. To evaluate temporal variation, the same microhabitats were sampled at intervals that reflected seasonal hydrological change at seven locations each at Kings Creek, Oka’Yahnali National Preserve, OK, and Youngmeyer Ranch, KS in 2022.

Spatial differences in non-perennial stream microbial populations did not all vary as expected: While biofilm populations tended to be higher at low-elevation, better connected locations (R2=0.15, P=0.007), and in flowing waters (P=0.006), as predicted, dry, disconnected sediments had higher bacterial populations than wet sediments (P=0.01). Temporal variation rivaled or exceeded spatial variation: Differences among sites were weaker than monthly variation. Microbial abundance was more strongly affected by sampling month (P< 0.05 for most sites and microhabitats) than by wet/dry status (P< 0.05 for biofilms at one site only), and fungal ITS abundance was less sensitive to month and wet/dry status than bacteria. Fungi may be more resilient to hydrological variation than bacteria due to their different cellular physiology, and/or bacteria may be more sensitive due to faster average growth rates. In continuing work, as we correlate flow data with gene abundance counts, we expect bacterial populations to be greater where water has resided the longest. With increasing climate change, it is critical we monitor microbial populations in non-perennial streams as they provide insight into downstream water quality, biogeochemical cycling rates, and help progress the field of microbial ecology.