Physical and Environmental Controls of Urban Pond Hydrodynamics and Impacts on Dissolved Oxygen and Phosphorus

Small water bodies such as ponds and wetlands are highly abundant in urban landscapes. These systems are widely used to protect urban lakes and streams and as such, are often subject to intense inputs of runoff and pollutants, and are found across a vast range of age, land use, and topographic setting. Interactions between physical and biogeochemical processes are less studied in ponds and yet, as in lakes, oxygen dynamics and mixing processes have strong influences over nutrient cycles. We studied over 20 urban ponds in the Minneapolis-St. Paul metropolitan area (MN) to better understand the physical and biological factors that influence their water quality and phosphorus dynamics, and ultimately their function for stormwater management. Using continuous monitoring of drivers including water temperature, stormwater runoff, and wind speed, we studied patterns of sub-daily mixing across a gradient of pond size, depth and sheltering, and related to key water quality parameters like phosphorus concentration and dissolved oxygen. Causes of mixing and stratification were explored and found to relate to weather, wind sheltering, macrophyte coverage, and pond geometry. We found that anoxia was associated with higher phosphorus, enhanced by free-floating plant cover, and reduced by mixing frequency. Larger ponds with less surrounding canopy were mixed more frequently by wind or heat exchange, while smaller ponds with heavy vegetation cover were mixed more often by runoff. These results have implications for pond management, especially under warmer and wetter future climate.

Primary Presenter: Benjamin Janke, University of Minnesota (janke024@umn.edu)

Authors:

Jacques Finlay, University of Minnesota  (jfinlay@umn.edu)

Poornima Natarajan, University of Minnesota  (pnataraj@umn.edu)

William Herb, University of Minnesota  (herb0003@umn.edu)

John Gulliver, University of Minnesota  (gulli003@umn.edu)