THE EFFECTS OF VARIABLE NUTRIENT STOICHIOMETRY ON BIOGEOCHEMICAL PROCESSES IN SHALLOW LAKE MESOCOSMS

Anthropogenic nutrient loading into freshwater systems can have significant impacts on ecosystem function. The application of fertilizer in agricultural settings can increase the relative amount of nitrogen (N) compared to phosphorus (P) entering freshwater systems during runoff events. How these potential stoichiometric imbalances influence microbial communities and associated biogeochemical processes remains poorly studied. We assessed the impact of stoichiometric extremes on the sediment-water interface during a fertilization experiment conducted in twelve experimental limnocorrals located in three ponds at the University of Mississippi Field Station in Abbeville, Mississippi. During the sampling seasons of 2019, 2020, and 2021, the limnocorrals were fertilized to target N:P (molar) ratios of 2.2, 16, 55, and 110. These open-bottomed mesocosms allowed for biogeochemical exchange with the sediments. In August of 2021, sediment cores were collected from each limnocorral as well as the surrounding ponds. Sediment cores were segmented and analyzed for total N, C, and P above the clay layer, as well as organic and inorganic C. Despite the differences in treatment dosing, preliminary results indicate that total N, C, and P in the sediments did not differ between treatments. Sediment DNA extractions will be used for whole genome metagenomics. Extracted DNA will also be used to quantify nifH gene abundance in the sediment to confirm previous sediment core flux data that suggests nitrogen fixation occurs in sediments from the 2.2 and 16 N:P treatments.

Primary Presenter: Alexa Hoke, Baylor University (alex_hoke1@baylor.edu)

Authors:

Alexa Hoke, Baylor University  (alex_hoke1@baylor.edu)

Isabelle Andersen, Baylor University  (isabelle_andersen1@baylor.edu)

Jason Taylor, USDA-ARS  (jason.taylor@usda.gov)

Katelyn McKindles, Baylor University  (katelyn_mckindles@baylor.edu)

Thad Scott, Baylor University  (thad_scott@baylor.edu)