Geology & Environmental Science Dissertation Defense: Timothy Suder

Annual Variations in Carbon, Nitrogen, and Nitrate in Trophic Endmember Freshwater Lake Systems

Presented by Timothy Suder | PhD Candidate, Geology and Environmental Science, University of Pittsburgh

Talk Abstract:

With the increased prevalence of drought-like conditions in many areas of the world, freshwater has become a critically significant resource. Thus, not only is the presence of freshwater important, but the health of those aquatic ecosystems becomes increasingly consequential. One aspect of this is the impact of algae on lacustrine ecosystems. While algae is usually beneficial to the ecosystem in which it is present, as it is a major primary producer, it can become harmful to the same ecosystem if it grows out of control into what is known as a harmful algal bloom (HAB). These blooms can shade out other photosynthesizing organisms, deoxygenate the water, and, in the case where the HAB is made up predominantly of cyanobacteria, produce toxins that get released into the water column. HABs are largely the result of anthropogenic input of key nutrients, including nitrate and ammonia, and the shifts in climate resulting from anthropogenic climate change. With this, it becomes important to not only look at the modern algal communities, but to also understand historic changes in algal communities that allow a window into how algal populations have changed and are likely to change in a lacustrine system. There are currently many ways of characterizing algal communities experimentally, which are useful for looking at modern algal growth and community shifts. However, exploring past algal dynamics becomes challenging. This typically relies on metagenomics to study the fragments of RNA that are still present in the sediment record of a lake, where it is possible to recover intact RNA strands. To further advance the study of lacustrine algal dynamics we have been working to advance our understanding of an emerging proxy, the εpor proxy, which allows us to distinguish eukaryotic algae from cyanobacteria in aquatic settings dominated by those two domains. This work looks to assess the capabilities of this proxy on trophic endmembers of the Laurentian Great Lakes system, which will provide insight into both a continuous year of algal growth and the past ~200 years of algal dynamics. During the course of this study, a variety of sample types were collected for analysis using the εpor proxy. Moorings were deployed that collected sedimenting material and filtered water periodically, which allows us to look at a continuous year of both nutrient and algal dynamics on each lake. This provides an unprecedented look at the under-ice conditions of Lake Erie and helps to build out existing data for Lake Superior. We will look at this data to better understand how the lakes change during the end of a growing season, the colder, more challenging, season, and the beginning of a new growing season. This provides context for the application of the εpor proxy during the same time intervals, which will allow for a more complete understanding of the algal community reactions to fluctuations in nutrients and climate. We will also look at data following method development regarding the extraction of chlorins for isotopic analysis. All of this will lead neatly into the analysis of both lake systems using the εpor proxy, which will be covered in my defense.

Biography:

Timothy Suder is a PhD candidate working under Dr. Josef Werne.