Stream water nutrient enrichment in a mixed-use watershed

Eutrophic conditions, in both saline and freshwater systems, result from nutrient export from upstream watersheds. The objective of this study was to quantify the surface runoff losses of nitrate-nitrogen (NO₃-N), total nitrogen (TN), dissolved reactive phosphorus (DRP), and total phosphorus (TP) resulting from prevailing practices on a managed golf course. Inflow and outflow discharge waters on a sub-area of Northland Country Club (NCC) located in Duluth, Minnesota were measured for both quantity and quality from April through November from 2003 to 2008. Nutrient losses were detectable throughout the year, had a seasonal trend, and routinely exceeded recommended levels to minimize eutrophication. The median outflow TN concentration (1.04 mg L⁻¹) was significantly greater (p < 0.05) than the median inflow (0.81 mg L⁻¹) concentration. Similarly, the median outflow TP concentration (0.03 mg L⁻¹) was significantly greater (p < 0.05) than the median inflow concentration (0.02 mg L⁻¹). Maximum recorded concentrations during the study period were 1.9 mg L⁻¹ NO₃-N, 3.93 mg L⁻¹ TN, 0.34 mg L⁻¹ DRP, and 1.11 mg L⁻¹ TP. Mean annual export coefficients at NCC were 0.7 kg ha⁻¹ NO₃-N (1.7% of applied), 4.43 kg ha⁻¹ TN (10.7% of applied), 0.14 kg ha⁻¹ DRP (2.6% of applied), and 0.25 kg ha⁻¹ TP (4.6% of applied). The findings of this study highlight the need for adopting conservation practices aimed at reducing offsite nutrient transport.