Collaborative Research: Understanding winter nitrogen cycling across gradients of winter severity and impacts on phytoplankton communities in an inland freshwater sea, Lake Erie

This project will investigate the cycling of the nutrient element nitrogen in Lake Erie. This study will be the first to comprehensively study the nitrogen cycle throughout the year, including in winter when the lake is covered with ice. Recent work in other lakes suggest that during winter, under-ice processes are important in determining the forms of nitrogen available to phytoplankton in spring and summer. A healthy spring bloom of phytoplankton called diatoms, in turn, is important to the lake food web and in mitigating against harmful algal blooms that can affect water quality. However, very little is known about winter nitrogen cycling in any of the Great Lakes, including Lake Erie, arguably one of the most important resources in the country in terms of drinking water supply, recreation, and fisheries. The project will support undergraduate students at both the University of Michigan and Bowling Green State University, and a graduate student at BGSU. The team will create a curriculum module on the Great Lakes and water quality for high school students. The goal of this work is to understand how winter nitrogen cycling impacts nutrient balance and phytoplankton community structure in large, temperate waterbodies, using Lake Erie as a case study. The researchers will generate the first quantitative measurements of nitrification, nitrogen uptake, and ammonia regeneration during winter in Lake Erie, to assess the effects of ice phenology on nitrification rates and how changes in nitrogen availability and speciation may affect seasonal phytoplankton communities. By combining nitrogen cycling rate measurements with community composition data, they will also investigate how different nitrogen substrates may favor certain phytoplankton groups (e.g., diatoms, dinoflagellates, cyanobacteria) across seasons. Over three years the team will 1) Measure ice onset, duration, and thickness throughout winter sampling; 2) track water column nitrogen substrate pools (nitrate, ammonia, organic nitrogen) and rates of uptake/transformation; 3) examine seasonal phytoplankton abundance and gene expression; and 4) conduct stable isotope probing experiments to measure cell-specific nitrogen incorporation in winter phytoplankton communities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.