Lagoon Liquid Data. The NAEMS collected continuous monitoring data for pH, oxidation/reduction potential (ORP), and liquid temperature and intermittent data for the nitrogen, ammoniacal nitrogen and solids content of the liquid. The concentration of NH3 at the lagoon surface depends on the total concentration of ammoniacal nitrogen [i.e., NH3 plus ammonium ion (NH4+)] in the liquid. The balance between NH3 gas and highly-soluble NH4+ is a function of pH and temperature of the lagoon liquid. At a constant pH, the concentration of NH3 relative to NH4+ increases, thereby increasing NH3 emissions. At a constant temperature, the concentration of NH3 relative to NH4+ also increases, thereby increasing lagoon NH3 emissions potential (NAS, 2002). As noted in Section 5.1.1.1, previous studies [Xxxxx et al. (2001) and Xxxxxx et al. (1998)] have shown a positive relationship between liquid temperature and NH3 emissions from swine lagoons. Consequently, the EPA expected that increasing pH or lagoon liquid temperature or both would result in higher NH3 emissions. The ORP measures the activity of electrons in a liquid and indicates whether the liquid is an oxidizing or reducing environment. However, because the mineralization of organic nitrogen to NH3 occurs in both oxidizing and reducing environments, the ORP value only indicates if the potential exists for the reduction of NH3 emissions due to nitrification. Therefore, the EPA expected that NH3 emissions would decrease with positive ORP values indicating an aerobic and oxidizing environment. Although the pH, ORP and temperature of the lagoon liquid were expected to affect NH3 emissions from lagoons, the EPA did not include these data as candidate predictor variables due to the limited number of data values and because data were not provided for sites IA3A and WA5A. Because the organic and ammoniacal nitrogen present in the lagoon liquid are precursors to NH3 emissions, the EPA expected that NH3 emissions would be higher at lagoons with higher total nitrogen concentrations. Nitrogen compounds can be bound to lagoon solids thereby preventing the release of ammonia precursors into the bulk lagoon liquid; therefore, the EPA also considered using the solids content of lagoon liquid in EEM development. However, the EPA did not include data for the nitrogen or NH3 content of the lagoon liquid as candidate predictor variables due to the limited number of data values (see Table 5-4). At higher volumetric loading rates, the concentrations of tota...
