General research interests: aquatic ecosystem ecology, biogeochemistry, hydrology, sediment-water interactions, anaerobic processes, influence of anthropogenic contaminants on ecosystem function, data science, open science

Current Project: The biogeochemical importance of flocculent organic sediment in shallow aquatic ecosystems

The sediment-water interface in shallow water bodies is thought to be a primary control on biogeochemical cycles, aquatic productivity, and nutrient movement to downstream waters. In humid, low relief regions like the Midwestern U.S., thick layers of flocculent organic sediments, or floc, persist in small water bodies like shallow lakes, wetlands, and even streams. Despite the very common occurrence of floc layers in a diversity of shallow waters, their biogeochemical importance has been little studied. My dissertation research, which is done in close collaboration with my advisor, Steve Hamilton, addresses the following overarching questions.

What are the environmental controls on floc quantity and quality?

Assessing the importance of floc layers in small water bodies first requires an understanding of their prevalence across the landscape. We surveyed* a wide variety of shallow waters in southwestern Michigan and are evaluating environmental controls on the prevalence and physicochemical characteristics of floc. It seems floc is more the rule than the exception in our region.

*Sampling floc is tricky business as this sediment type is easily disturbed. If you want advice about coring or pore water sampling techniques, feel free to contact me.

Why do thick accumulations of floc persist?

Investigating decomposition processes in organic-rich floc layers is necessary to understand how these thick accumulations are maintained over time and how they contribute to organic carbon storage in freshwaters. In collaboration with Scott Tiegs (Oakland Univ.) we are using cotton strips as a proxy for organic matter decomposition in floc layers in a variety of shallow water habitats.

What hydrologic processes drive solute exchanges between floc layers and overlying waters?

Relative to overlying waters, floc layers contain large pools of dissolved nutrients like phosphorus and nitrogen. Exchanges between these two compartments affect surface water quality. It’s reasonable to assume nutrients continuously move from the floc layer to more dilute overlying water via diffusion; however, we are curious whether there are times when advective exchanges (forced fluid flow) eclipse diffusion-dominated exchanges between floc layers and overlying waters. We are using heat exchange modeling to reveal the timing and types of hydrologic exchanges across the floc-water interface in shallow aquatic ecosystems. This work is done in collaboration with Mantha (Phani) Phanikumar (MSU), Martin Briggs (UGSG), and Jay Zarnetske (MSU).

Do floc layers remove excess inorganic nitrogen from overlying waters?

Surface waters in agricultural landscapes are typically impaired by elevated levels of nitrate. These levels of nitrate can contribute to unsightly and sometimes harmful algal blooms. We are investigating whether floc layers perform an ecosystem service by removing nitrate from overlying waters. Using in situ nitrate uptake assays, we are comparing nitrate uptake rates in various floc settings.

Past Project: Effects of chronic exposure to pharmaceutical compounds on stream ecosystem functions

Pharmaceuticals and personal care products (PPCPs) are frequently detected in freshwater ecosystems around the world. Scientists are just now beginning to understand the effect these emerging contaminants have on aquatic ecosystems. We developed one of the first methods to assess the chronic effect of PPCPs on ecosystem processes in streams - pharmaceutical diffusing substrates (PhaDS). Results of this initial work are published here (request PDF: Rosi-Marshall et. al. 2013 Ecological Applications). Collaborators: Emma Rosi (Cary Institute), Heather Bechtold (Lock Haven Univ.), Todd Royer (Indiana Univ.), & John Kelly (Loyola).

Past Project: Persistence of road salt in watersheds

Road salts are not immediately flushed out of our watersheds after winter applications. And many reports indicate they are accumulating in our surface waters. My NSF-REU project examined the potential for soils and groundwater to serve as a reservoir and source of dissolved ions associated with road salt (i.e., chloride) long after the winter deicing period. Results of this work are published here (request PDF: Kincaid & Findlay 2o09 Water, Air, & Soil Pollution). Collaborator: Stuart Findlay (Cary Institute).