Representation of Solid and Nutrient Concentrations in Irrigation Water from Tailwater-Recovery Systems by Surface Water Grab Samples

Abstract

Tailwater recovery (TWR) systems are being implemented on agricultural landscapes to create an additional source of irrigation water. Existing studies have sampled TWR systems using grab samples; however, the representation of solids and nutrient concentrations in these samples to water being irrigated from TWR systems has yet to be investigated. In order to test whether grab samples are representative of water pumped from TWR systems for irrigation use, this study compared concentrations of total suspended solids (TSS), total phosphorus (TP), total nitrogen (TN), total Kjeldahl nitrogen (TKN), nitrate-nitrite (NO3−NO2−), and ammonium (NH4+). Grab samples were collected simultaneously from the surface water and from the respective outflow of irrigation infrastructure in six TWR systems. Comparison of 14 irrigation events showed TSS, TP, TN, TKN, NO3−NO2−, and NH4+ did not differ (Pillai’s trace5,1=0.307, p>0.5) between surface water grab samples and irrigation water samples. No differences (p>0.05) were found for TN, TP, NH4+, and TKN across sites. This research suggests surface water grab samples from TWR systems represent the solid and nutrient concentrations being irrigated at that moment of time.