Differential Incorporation of Bacteria, Organic Matter, and Inorganic Ions Into Lake Ice During Ice Formation. Issue 3 (18th March 2019)

• Record Type: Journal Article
• Authors: Santibáñez, Pamela A.; Michaud, Alexander B.; Vick‐Majors, Trista J.; D'Andrilli, Juliana; Chiuchiolo, Amy; Hand, Kevin P.; Priscu, John C.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 3(2019)
• Page Start: 585
• Page End: 600
• Publication Date: 2019-03-18
• Subjects: Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2018JG004825
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: The segregation of bacteria, inorganic solutes, and total organic carbon between liquid water and ice during winter ice formation on lakes can significantly influence the concentration and survival of microorganisms in icy systems and their roles in biogeochemical processes. Our study quantifies the distributions of bacteria and solutes between liquid and solid water phases during progressive freezing. We simulated lake ice formation in mesocosm experiments using water from perennially (Antarctica) and seasonally (Alaska and Montana, United States) ice‐covered lakes. We then computed concentration factors and effective segregation coefficients, which are parameters describing the incorporation of bacteria and solutes into ice. Experimental results revealed that, contrary to major ions, bacteria were readily incorporated into ice and did not concentrate in the liquid phase. The organic matter incorporated into the ice was labile, amino acid‐like material, differing from the humic‐like compounds that remained in the liquid phase. Results from a control mesocosm experiment (dead bacterial cells) indicated that viability of bacterial cells did not influence the incorporation of free bacterial cells into ice, but did have a role in the formation and incorporation of bacterial aggregates. Together, these findings demonstrate that bacteria, unlike other solutes, were preferentially incorporated into lake ice during our freezing experiments, a process controlled mainly by the initial solute concentration of the liquid water source, regardless of cell viability. Plain Language Summary: Most of the freshwater lakes on Earth are found in regions where temperatures are below freezing for either all or part of the year. Here we studied the impact of freezing on the chemical and biological components of lake water. We simulated lake ice formation using water from perennially and seasonally ice‐covered lakes to describe and quantify the distributions of bacteria and solutes (chemical species) between the liquid and solid water phases during progressive freezing. The results of these simulations revealed that, contrary to solutes, bacteria are preferentially incorporated into the ice. Results from the control experiment, which used dead bacterial cells dispersed in lake water, indicated that the viability of the bacterial cells did not influence the incorporation of bacterial cells into ice; live and dead bacterial cells were incorporated into the ice equally. However, only live cells formed bacterial aggregates, which were also incorporated into the ice. The observed preferential incorporation of bacterial cells was mainly controlled by the initial solute concentration of the liquid water source. Our findings have implications not only for the habitability of cold environments on Earth and their impact on biogeochemical cycles on lakes but also for extraterrestrial environments (icy worlds: Europa, Enceladus). Key Points: Free bacterial cells and bacterial aggregates were found in natural lake ice covers Experiments on water from polar and temperate lakes showed bacterial cells were incorporated into ice cover, in contrast to dissolved ions Lake ice freezing fractionated organic matter of different qualities between the ice and liquid phases