Nitrogen and Phosphorus Biogeochemistry of Modern Lakes as Environmental Analogs for the Origin and Early Development of Life

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Presented By Sebastian Haas


The concentrations and stoichiometric balance of nitrogen (N) and phosphorus (P) nutrients play a central role in both past and present ecosystems with relevance for the origin and development of life. P occurs at micromolar concentrations in most modern environments but is required at near molar concentrations for the prebiotic formation of nucleic acids, which is a crucial step in leading origin-of-life hypotheses such as “RNA World”. Rare modern lake systems in which P accumulates to tens of millimolar concentrations may contribute to solving this conundrum and are analog settings to study the conditions under which P reaches high levels, providing possible insight into Hadean environments. Following the emergence and spread of life, the marine N:P ratio likely controlled the balance of biological N fixation and denitrification on geological time scales, thereby balancing biological carbon fixation over the eons. Modern meromictic (i.e., permanently stratified) lakes with anoxic bottom waters can be used as models to understand the redox-stratified Proterozoic Ocean because of their analogous biogeochemistry.

Here I present biogeochemical characterizations of modern lakes, that can respectively be seen as analogs to the Proterozoic Ocean and to small Hadean ponds from which the first life may have emerged. Powell Lake (British Columbia) is a 350-m deep meromictic lake with highly sulfidic, ammonic and methanic anoxic bottom water as well as very low phosphate concentrations. Despite its high N:P ratio, we found strong evidence for active biological N-fixation, which may yield insights that help to constrain nutrient limitation in the redox-stratified Mesoproterozoic Ocean. Goodenough and Last Chance lakes in British Columbia are shallow, carbonate-rich salt lakes that may contain the highest P concentrations of any known lake. My postdoctoral research at these lakes explores the influence of two factors that may allow for these unusually high P concentrations: i) exceptionally low rates of chemical P mineral precipitation, and ii) biological P assimilation limited by low N concentrations. I will be presenting results from chemical and microbiological sampling in these different lake systems and discuss their implications for the emergence and evolution of early life on Earth.