Research

I am interested in how environmental factors, like oxygen availability, influence the preservation of organic matter. By analyzing organic matter at both bulk and fine-scale resolutions, I aim to uncover the mechanisms behind its preservation which are critical for understanding long-term carbon cycling and reconstructing past environments.

Oxygenation and alkalinity drive the lacustrine nitrogen isotope record throughout the past 3.2 billion years

(a) Enriched nitrogen isotopes are associated with alkaline lakes throughout the geologic record. (b) Marine nitrogen isotope record (c) Organic carbon isotope record of lakes. (d) Earliest origin dates of nitrogen cycling genes.

The oxygenation of Earth's atmosphere fundamentally changed the global carbon and nitrogen cycles. Due to their smaller volume and shallow waters compared to oceans, lakes could have been one of the first environments to experience the early impacts of increases in atmospheric oxygen. This work analyzes how water column redox conditions impact sediment nitrogen and organic carbon isotope signatures in over 150 global lakes. We apply our understanding of modern lake nitrogen isotope signals to interpret the lacustrine nitrogen isotope record and its connection to Earth's oxygenation and depositional environments. Unlike the marine record, the lacustrine nitrogen isotope record reveals distinct patterns related to alkalinity and the evolution of microbial metabolic pathways connected to the rise of oxygen.

Publication: https://doi.org/10.1111/gbi.70033

Organic matter preservation mechanisms in the hypoxic Middle Island Sinkhole, Lake Huron

Climate change is causing declining oxygen levels in freshwater lakes, impacting nutrient availability and threatening future water quality. Middle Island Sinkhole (MIS), located in Lake Huron, is a modern low oxygen lake environment with geochemical and microbial features potentially resembling future lakes impacted by climate change. I investigate carbon burial in MIS to contextualize organic matter preservation in future anoxic lakes. I use compound specific nitrogen isotopes of chlorophyll and amino acids.

Despite the presence of lush cyanobacterial benthic microbial mats at MIS, my work has revealed extensive contributions of water column phytoplankton to MIS sediments. Although Lake Huron oxygenated waters have the same source of organic matter to sediments, MIS hypoxic conditions better preserve source material.

News Article: https://www.thealpenanews.com/news/local-news/2024/06/sinkhole-science-in-the-sanctuary/

Cyanobacterial microbial mats at Middle Island Sinkhole, Lake Huron.

Sealing sediment cores upon collection with help from NOAA Thunderbay Marine Sanctuary divers.

Aboard R/V Storm for the deployment of a sediment trap, used to collect organic matter sinking down from surface waters to bottom sediments.

Changes in Lake Huron's nitrogen cycle throughout the Holocene

I am investigating shifts in the nitrogen cycle of Lake Huron and Middle Island Sinkhole throughout the Holocene to contextualize the impacts of anthropogenic climate change on biogeochemical cycles accounting for natural baselines. As a part of this NSF project, I participated in a ~2 week long research cruise to collect piston cores from sites within Lake Erie, Huron, and Superior. These piston cores were processed at the UMN Continental Scientific Drilling (CSD) Facility. I am measuring organic carbon and nitrogen isotopes from the cores. The cores are also being analyzed for trace metals by collaborators Dr. Anthony Chappaz and Dr. Dalton Hardisty.

Processing multicore samples aboard R/V Blue Heron.

Collection of a gravity core for Middle Island Sinkhole.

Imaging cores at the UMN CSD facility for high resolution image analysis.

Effectiveness of poisons/preservatives on freshwater organic matter

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A sediment trap in the bottom of Middle Island Sinkhole, Lake Huron collecting POM (white floating particles) from the water (video credit NOAA 2023).

Sediment traps collect sinking particulate organic matter (POM) and are often used with preservatives or poisons to prevent degradation during long deployments, especially in marine environments. However, the effectiveness of these substances in freshwater systems is understudied. In this project, I am testing how conventional preservatives and poisons affect freshwater POM collected from a pond by analyzing chlorophyll, stable carbon and nitrogen isotopes, and elemental concentrations. These findings will help researchers choose the most suitable preservation method for their analytical needs.

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