Water Quality Characterization of Irrigation and Storm Runoff for a Nursery

Commercial nurseries grow plants in containers on semi-permeable production areas. Fertilizer is added to the substrate or applied via irrigation to facilitate plant growth, the resulting runoff has increased levels of sediment, nitrogen and phosphorus compared to background. This runoff is often collected and recycled, but, if discharged, could negatively impact water bodies downstream. Several storm and irrigation runoff samples were collected from a mid-Atlantic nursery and analysed for pH, electrical conductivity (EC), total suspended solid (TSS), total nitrogen (TN), and total phosphorus (TP). Samples were collected downstream of 5.2 hectare production area, which consisted of 1.82 ha in gravel roads and 3.38 ha in 26 pads, draining to a central ditch. The nursery was modelled using the Storm Water Management Model (SWMM), an urban drainage model, since runoff hydrographs behave similar to urban areas (i.e., flashy). A preliminary hydrologic and water quality calibration was performed with the limited dataset to assess the potential of using SWMM to characterize runoff. During irrigation, there was a direct relationship between runoff and TSS peaks, i.e., TSS peaks follow peak runoff, with a defined lag. In contrast, there was an inverse relationship between runoff peaks and concentrations of TN and TP. During irrigation, simulated event mean concentrations (EMCs) of TP, TN and TSS were 0.42, 2.77 and 36.0 mg/L, respectively. SWMM was able to characterize the runoff well from the 5.2 ha area and can be potentially used to assess water quality treatment options if further calibrated data become available.