Spatial and temporal variation in physicochemical properties of dairy lagoons in south-central Idaho

Large quantities of wastewater are generated on dairies in south-central Idaho, which can be a source of valuable nutrients as well as contribute to air quality and climate change issues via ammonia (NH3) and greenhouse gas (GHG) emissions. The objective of this study was to examine the range of lagoon water properties among dairies in the region and to determine how they varied spatially and temporally. Twenty-seven lagoons were sampled twice in a nutrient survey to determine physicochemical characteristics, while six lagoons were sampled (3 to 27 times) over a longer period to determine how these characteristics changed with space and time. Lagoon properties measured consisted of total solids (TS), volatile solids (VS), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), total ammoniacal nitrogen (TAN), total phosphorus (P), total potassium (K), temperature, pH, dissolved oxygen (DO), and specific conductivity. Results indicate that all lagoon characteristics varied greatly between dairies and with sampling date. Seasonal trends indicated that N decreased from spring to fall, while specific conductivity, total P, total K, and in some instances TS and VS increased over the same period. There was an effect of housing type on these properties, with freestall dairies having higher concentrations of TS, VS, COD, TKN, TAN, and specific conductivity than dry-lot dairies. There was little effect of dairy size on the physicochemical characteristics measured. These results suggest that it is important to account for the nutrients applied with lagoon water in nutrient budgets in order to prevent over-application of N and K, which could lead to N leaching and forage quality issues. In addition, capturing the temporal variation in lagoon properties is important to accurately model seasonal variations in NH3 and GHG emissions.