Stephen D. Sebestyen

I study how water, nutrients, and pollutants solutes flow through the landscape and affect streams, lakes, or wetlands.

As a research hydrologist with the USDA Forest Service in Grand Rapids, MN. I devote portions of my time to research at the Marcell Experimental Forest (MEF) and national-scale syntheses of data from multiple catchment studies. At the MEF, I co-lead research planning and research on hydrological and biogeochemical research. I have developed a research program that builds upon the 55-year legacy of research at this site. The MEF was established to study the ecology and hydrology of peatlands and uplands along the southern fringe of the boreal zone. I pursue research on the effects of nitrogen pollution on ecosystem functions, carbon cycling in peatlands, understanding effects of climate variability, interactions of dissolved organic matter with mercury and other trace metals, and quantifying effects of landscape disturbance on water and solutes yields. I am an investigator in the SPRUCE Experiment (Spruce and Peatland Response Under Climatic and Environmental change), a large-scale, experiment in which above- and below-ground temperatures are being manipulated in a black spruce-Sphagnum bog at the MEF.

While much of my research is based at the MEF, I continue to study lakes, streams, and wetlands elsewhere in Minnesota and on various catchment studies, whether in the USA or abroad. Some of these studies synthesize information from many sites and are intended to broaden understanding to national and global scales. My other research is focused on particular sites and particular environmental issues.  At the Sleepers River Research Watershed in northeastern Vermont, I explore how sources of stream nitrate and dissolved organic matter (DOM) vary over time and space. My research elsewhere in the northeastern USA includes studies of nitrate sources and DOM dynamics. Since the start of my graduate research, a portion of my work has been focused on how groundwater seepage influences biogeochemical cycles in lakes and wetlands. In several studies, I collaborate on research to quantify effects of groundwater seepage on lake trophic status.

I collaborate with a broad range of research scientists, graduate students, and undergraduate students. My position as a Forest Service scientist and being adjunct faculty at the University of Minnesota and Michigan Tech allow me to be highly involved with graduate and postdoctoral researchers.

• Quantify rates of terrestrial and aquatic biogeochemical transformations to definitively pinpoint the landscape processes that affect water chemistry.
• Determine how sources, transformations, and transport processes interact to control nutrient and pollutant concentrations within ecosystems.
• Quantify how short-term processes that occur at discrete locations and times (the hotspots and hot moments of biogeochemical processes) are important when considered at the ecosystem level.
• Synthesize understanding of hydrological and biogeochemical processes from various studies and locations to gain a general understanding of reference conditions and the effects of management decisions on water, air, and soil resources.

1. The flow of water transfers energy and matter from the atmosphere and land to lakes, streams, wetlands, and coastal zones. My scientific interests center on understanding how water and chemicals are transported and transformed in the environment. With an emphasis on catchment science, I study hydrological and biogeochemical cycles to identify ways to effectively maintain water quality and ecosystem productivity. I use multiple approaches (hydrologic, biologic, geochemical, biogeochemical, and isotopic) across range of temporal, spatial, climatic, and ecological settings to study such issues as atmospheric pollutant deposition, forest health, ecosystem acidification, nutrient enrichment of surface waters, and ecosystem responses to climate change.
2. The variation of stream nutrient concentrations over time and space reflects complex processes that affect ecosystem functions, but more fundamentally, relates to the availability of biologically-essential substances that fuel life cycles on land and in water.
3. In landscapes where human activities enrich nutrient availability and affect land use / land cover, my work highlights the need to consider how water and nutrient cycles affect surface water chemistry. Understanding linkages among the atmosphere, land, and water helps to inform scientists, land managers, and policy makers who seek to protect valuable natural resources.