Measuring evaporation and seepage losses from lagoons used to contain animal waste

Seepage (S) from animal-waste lagoons was estimated using a water balance a pproach by measuring changes in waste level (i.e., depth) (Delta D) and eva poration (E) over brief periods (e.g., 6 days) when all other inflow and ou tflow were precluded. Data were collected at commercial swine and cattle fe edlots in southwestern Kansas. Precision waste level recorders, floating ev aporation pans, and meteorological models were used to measure each lagoon' s water balance. Different strategies for calculating evaporation and seepa ge were compared. Initial work at a 2.5-ha plastic-lined lagoon (S = 0, E a pproximate to 5.1 mm d(-1)) showed that evaporation over 6- to 11-day perio ds could be measured to within +/-0.5 mm d(-1) with floating evaporation pa ns using a pan coefficient of 0.81. A bulk-transfer evaporation model, whic h incorporated real-time measurements of lagoon surface temperature, predic ted evaporation to within 6% when using a transfer coefficient of 2.8 x 10( -3). Evaporation models that did not include surface temperature resulted i n significant errors (e.g, > 50%) under certain environmental conditions. T he water balance of a soil-lined, cattle-feedlot lagoon over an II-day peri od was: do = 2.1; E = 1.9, and S = 0.2, all in mm d(-1). Additional work ov er a 6-day period at a soil-lined, swine-waste lagoon resulted in a water b alance of: Delta D = 5.4; E = 4.5, and S = 0.9, all in mm d(-1). Data sugge st that seepage from lagoons can be determined to within +/-0.5 mm d(-1) by making precision water balance measurements over short periods (5 to 10 da ys), if evaporation is less than 6 mm d(-1).