Excess nutrient levels in surface water continues to be one of the leading causes of water degradation in the United States today. Excess nutrients usually are sourced from agricultural- practices in the form of non-point-source contamination. Both large- and small-scale farming practices can result in excess nutrients contaminating local water ways, mostly injected during and shortly after rain events. The most prevalent nutrients in these cases include dissolved and solid forms of nitrogen and phosphorus.
In Madison County, Kentucky, we investigate the nutrient export from Meadowbrook Farm, located within the Muddy Creek watershed, which flows into the Kentucky River and ultimately into the Mississippi river drainage basin. This small-scale farm, owned and operated by Eastern Kentucky University, raises typical crops and livestock. We quantify the nutrient export from the Farm in the form of dissolved nitrogen (ammonium, NH4+; nitrate, NO3-), dissolved phosphorus (orthophosphate, PO43-), and total phosphorus (ΣP).
We sampled water flowing over an instrumented weir, situated within the Farm’s Big Runoff Channel (BRC), during six different storm events in the 2018 field season. We determined nutrient concentrations during storms coupled with respective discharge measurements. Then, we used a cubic spline function embedded within Microsoft Excel that interpolated between data points to produce a continuous curve for each nutrient species and discharge. The area under these curves generates total water volume and nutrient export values for each storm event. The largest storm event (6-7 July) exported 4.1 kg of P-PO4; 11.3 kg of total phosphorus; 3.3 kg of N-NH4; and 1.7 kg of N-NO3 [5 kg N].
An approximate linear relationship between total storm water volume and P-PO4, ΣP, and N-NO3 is observed. However, these relationships are not robust enough to reliably estimate iv nutrient transport for any rainfall event from discharge data alone. The next step is to test if better relationships occur between nutrient export and rainfall intensity, rain event frequency, or other possible parameters. The overall aim is to estimate annual nutrient export with confidence in order to: (1) test the efficacy of mediation efforts to on the Farm; and (2) to compare annual nutrient export values to those of other studies
