Nonpoint source pollution from nitrate-nitrogen (nitrate) and phosphorus (P) contributes to nutrient enrichment in local streams and lakes and development of hypoxic (dead) zones in regional water bodies, including the Gulf of Mexico. IGS researchers are investigating water quality and nutrient patterns, processes, scales and trends throughout Iowa and the Upper Mississippi River Basin. Led by Dr. Keith Schilling, in collaboration with IGS geologists, IIHR partners and university scientists from University of Iowa, Iowa State University, several Iowa colleges (Grinnell, Coe, Kirkwood), commodity groups and non-government organizations like The Nature Conservancy, research is focused on assessing current conditions and finding new and innovative solutions to some of our water quality problems. Some examples of recent projects provide a glimpse of some of the water quality research that IGS is doing.
Classification of cropland in agro-hydrologic region watersheds in the Upper Mississippi and Ohio River basins (in: Schilling, K.E., C.F. Wolter and E. McLellan. 2014. Agro-hydrologic landscapes in the Upper Mississippi and Ohio river basins. Environmental Management, 55:646-656)
Watershed Water Quality Studies
Recent studies in Walnut Creek watershed have found spatial nitrate (NO3-N) and orthophosphorus (OP) concentrations in upland and floodplain groundwater differ depending on the landscape setting. Results are reported in Schilling, K.E., M.T. Streeter, T.M. Isenhart, W.J Beck, M.D. Tomer, K.J. Cole and J.L. Kovar. 2018. Distribution and mass of groundwater orthophosphorus in an agricultural watershed. Science of the Total Environment 65:1330-1340.
Total Phosphorus Surrogates
Groundwater discharge to a lake is an important, if often neglected, component to water and nutrient budgets. We conducted a study of 15.57 km2 West Lake Okoboji, Iowa, and developed a watershed-based groundwater loading model to evaluate groundwater recharge and quality under representative land cover types in a range of landscape positions. A groundwater load allocation model indicated 91% of the nitrate load was from cropped areas and 7% from residential areas. In contrast, P loads were more equally divided among cropped fields (43%), perennial grass (36%) and residential (19%) areas. Based on the mass of nitrate and P in the lake, groundwater accounts for 71% and 18% of the nutrient inputs, respectively.
Trends in surface water quality are being assessed in collaboration with Dr. Kung-Sik Chan and his students in the University of Iowa Department of Statistics and Actuarial Science. Results suggest that nitrate concentrations are increasing in some western Iowa watersheds while P concentrations are decreasing. This is consistent with the hydrology of nutrient transport in Iowa where improvements in soil conservation and reducing runoff are contributing to reductions in sediment-bound P but also serving to increase infiltration and soluble nitrate loss.
Other related water quality studies include: