Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2004
Publication Date: September 1, 2004
Citation: Burkart, M.R., Simpkins, W.W., Morrow, A.J., Gannon, J.M. 2004. Occurrence of total dissolved phosphorus in unconsolidated aquifers and aquitards in Iowa. Journal of the American Water Resources Association. 40(5):827-834.
Interpretive Summary: Phosphorus (P) is the nutrient that controls aquatic plant production and ultimately the health of freshwater resources. Groundwater sources of P have not often been seen as important to understanding surface water ecosystems, even though groundwater is the dominant source of flow to streams and lakes in the Midwest. Well samples from a variety of groundwater materials in Iowa demonstrated that P is likely to be present in all shallow groundwater and that it is likely to continue discharging to surface waters for a long period of time. The presence of P in the variety of materials and settings studied for this paper demonstrates the need for more routine analysis of this nutrient as a part of groundwater monitoring and research programs. Such information will be important to producers, environmental agencies, and water users in order to manage the dominantly agricultural sources of P in Iowa and much of the Midwest.
Groundwater samples from wells were analyzed for total dissolved phosphorus (TDP) in four areas and five materials including loess and loess-derived alluvium in the Deep Loess Hills of western Iowa;outwash and fractured till beneath Clear Lake in north central Iowa; fractured till in central Iowa; and an alluvial aquifer in northwest Iowa. Land use in groundwater recharge zones in all four areas is dominated by crop or animal production that provide sources of phosphorus. Concentrations of TDP exceeding the minimum laboratory quantitation limit of 20 ug l**-1 as P were found in all areas and in all materials sampled. Samples from the outwash deposits associated with Clear Lake contained significantly larger concentrations than all other areas and materials with a mean of 212 ug l**-1. Fractured till produced the smallest range of concentrations. These results may be representative of similar agricultural systems throughout the Midwest, but may not constitute background or natural concentrations of P. Detailed analysis of sources and transport paths in each area will be needed to determine if the material characteristics, flow systems, or sources play greater roles in the occurrence of P. Phosphorus is likely to be present in all groundwater media, although its presence may often be dismissed as an analytical error. The presence of P in the variety of materials and settings studied for this paper demonstrates the need for more routine analysis of this nutrient as a part of groundwater monitoring and research programs. Such information will be critical to understanding trends as they develop in vulnerable areas.