Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 11/19/2008
Publication Date: 6/21/2009
Citation: Baffaut, C., Sadler, E.J., Lerch, R.N., Kitchen, N.R. 2009. Nutrient Sources and Transport from the Goodwater Creek Experimental Watershed. In: Proceedings of the ASABE Annual International Meeting, June 21-24, 2009, Reno, Nevada. Interpretive Summary: Nutrients discharged and transported by streams are implicated in algae growth in Mark Twain Lake and in the Gulf of Mexico. Algae growth in Mark Twain Lake causes taste and odor problems in drinking water; in the Gulf of Mexico excessive algae cause hypoxia problems once they die. For three of these nutrients, i.e., dissolved phosphorus, nitrates, and ammonium, concentrations have been measured in water samples collected in Goodwater Creek from 1991 to 1997 at the outlet of 3 nested watersheds (12.1, 31.5 and 73.0 km2 drainage area). Sampling has continued until present at the outlet of the larger watershed. Daily, monthly, and annual loadings of these nutrients were calculated at the three locations and statistically compared. Dissolved phosphorus and ammonium-nitrogen concentrations and loads at the upstream weir were significantly greater than those at the two other weirs, suggesting that wastewater discharge from city lagoons could have been a potential source of these nutrients. This explanation was tested with a hydrologic model, which indicated that additional sources of nitrogen were present in the headwaters of the watershed. The findings provide insight to what should be included in a complete analysis of the nutrient sources in the watershed and how stream processes affect nutrient transport. Water resources managers and policy makers will benefit from this research by understanding how nutrient loadings from different sources contribute to the stream nutrient load. Only then can they define strategies and goals to reduce nutrient loads.
Technical Abstract: The Goodwater Creek watershed has been monitored for flow since 1971 and for dissolved nutrients since 1991 for 3 nested watersheds (12.1, 31.5 and 73.0 km2 drainage area). This watershed includes row crop land (76%), grassland (14%), woodland (6%) and a small town at the upper end (4%). The objectives of this paper are to analyze nutrient loadings at the 3 gauging stations from 1991 to 2004. Daily, monthly and annual loadings and flow-weighted concentrations of ammonium-nitrogen, nitrate-nitrogen, dissolved phosphorus and atrazine were calculated and analyzed using the non parametric tests for differences, homogeneity, and trends. Atrazine was included in the analysis as one compound not implicated with point source discharges in the watershed. Dissolved phosphorus and ammonium-nitrogen concentrations and loads at the upstream weir were significantly greater than those at the two downstream weirs, which suggest wastewater was a potential source of these nutrients. Possible explanations for these differences were drawn from our knowledge of the watershed and tested with a SWAT model of the watershed. These findings provide insight to what should be included in a complete analysis of the nutrient sources in the watershed and how stream processes affect nutrient loadings.