Heinz Stefan’s interests include research and design to minimize the environmental impact of water handling facilities, and the connections between water quality, fish habitat, hydrology, and climate. His group is currently researching the effects of climate change on fish habitat in lakes, and the impact of urbanization and climate change on stream flows and stream temperatures. They have also conducted research on the transport and fate of salinity. Finally, the study of exchange processes of energy and mass at the air-water interface and at the sediment-water interface (hyporheic flows) rounds out their research interests.

The group’s methods have included the analysis of hydrologic and water quality records from streams and lakes in Minnesota. They have extracted mean annual flows, flood flows, high flows, dates of first spring runoff, spring peak runoff, summer low flow, and winter low flow. They also study trends in different time periods and correlations with single and multivariate climate parameters to determine and extrapolate potential future conditions. In addition, they analyze non-stationary processes by statistical methods. They apply oxythermal fish habitat parameters to water quality time series for 30-year time periods to capture the dynamics of stress. Finally, they develop deterministic, process-descriptive simulations of environmental transport and transformation processes and use them to either interpret historical records or make projections for future climate scenarios or changes in land use. 

The goal of their research on solute exchange at the sediment-water interface has been to relate transport rates in the sediment pore spaces to the characteristics of the surface water flow above the sediment-water interface. They are concerned with the effects of standing waves, progressive waves, and turbulence on advective and dispersive transport in the sediment layer, and they use multi-dimensional simulation and laboratory experimental data to relate the apparent vertical dispersion in the sediment to flow parameters in the surface water.

The group’s current research focus on transfer processes at the air-water interface is on the wind sheltering of small lakes by tree canopies and its effect on lake mixing, evaporation, and gas transfer. Experiments in a boundary layer wind tunnel, field measurements, and flow simulations are the main investigation tools.