TEMPORAL AND SPATIAL VARIATIONS OF TOTAL PHOSPHORUS IN THE BOTTOM SEDIMENTS OF CEDAR RIVER AND ITS TRIBUTARIES IN IOWA

Surface water eutrophication and nutrient fertilization is currently one of the most important environmental factors facing the state of Iowa and Mississippi River into the Gulf of Mexico. The agriculturally predominant Cedar River watershed has been estimated to contribute as much as one-fifth of the total nutrients into the Gulf of Mexico. Phosphorus is a significant contributing factor for eutrophication, as it is needed for biological processes and is used as a fertilizer on agricultural land. In this study, bottom sediments were taken weekly out of 6 major tributaries of the Cedar River to determine both temporal and spatial distribution of phosphorus adsorbed to the sediment. Samples were taken from the same location positioned at USGS water discharge meters. Average phosphorus concentrations for the five-month study range from a low of 109.63µg/g at Beaver Creek in New Hartford, IA, to 350µg/g at Black Hawk Creek in Hudson. Total phosphorus varied greatly during the sampling period, with the highest concentrations during the spring and late summer months. Beaver Creek at New Hartford had a range from 5.63µg/g in early August to 483µg/g in late August. A comparable increase was noted in all six of the sampling sites, correlating with a major flood event that occurred during the same time. The same relationship can be found in a major late June flooding. It is concluded from this study that Cedar River and its tributaries serve as an important transport route for phosphorus exiting agricultural lands in the watershed, with land use playing an important role in average total phosphorus concentration. This study will aid in ascribing the major streams contributing phosphorus to the Cedar River.