Carbonate-rich alkaline lakes (“soda lakes”) often have very high phosphate but low inorganic nitrogen (N) concentrations. These unusual systems provide insights into mechanisms underlying biogeochemical nutrient cycling and are also interesting analogs for research on the origin of life, for which high concentrations of phosphorus (P) are required. Across a seasonal wet-dry cycle, we sampled the water columns and sediments of two neighboring (~100 m apart) shallow soda lakes in British Columbia, Canada. We measured 15N2 fixation rates, nutrient limitation, stable isotope signatures (δ15N, δ13C), as well as concentrations of various P, N and C phases. Last Chance Lake’s water column appears to be the most phosphate rich (up to 37 mM) on Earth and N is limiting its primary productivity, yet biological N2 fixation (BNF) rates were low to moderate (≤30 nM d-1). Goodenough Lake also has unusually low inorganic N:P ratios but is considerably less phosphate-rich (~0.1 mM) and contains cyanobacterial benthic mats fixing N2 at high rates (115.3 ±6.6 µM d-1), which may cause higher particulate N:P ratios and lower phosphate concentrations by creating P demand. Conversely, in Last Chance Lake, BNF limitation likely contributes to the remarkably conservative behavior of phosphate, and, together with geochemical mechanisms, explains why so much phosphate remains dissolved. We will present insights on the interactions of extremely high phosphate concentrations, low BNF rates, particulate C:N:P ratios, and primary production based on the natural experiment provided by these neighboring lakes.
Primary Presenter: Sebastian Haas, University of Washington (s.haas@dal.ca)
Authors:
NITROGEN FIXATION AND C:N:P RATIOS IN AN EXTREMELY PHOSPHATE-RICH SODA LAKE
Category
Scientific Sessions > SS040 Ecological Stoichiometry in a Dynamic World: Exploring the Ecology of Changing Environments Through Theory, Patterns, Processes and Experiments.
Description
Time: 09:45 AM
Date: 7/6/2023
Room: Auditorium Mallorca