Seepage losses and nitrogen export from swine-waste lagoons: A water balance study

Seepage losses from animal-waste lagoons could affect ground water quality. Water balance methods were used to study seepage and N export from three s wine-waste lagoons in southwestern Kansas. Lagoons ranged in size from 0.8 to 2.2 ha and had an average waste depth of 5.6 m. Compacted soil liners we re 0.30 to 0.46 m thick and built with native soil or, in one case, a soil- bentonite mixture, Seepage was calculated from measurements of evaporation and changes in depth when the addition or removal of waste was precluded or quantified, Seepage rates were 1.1, 1.1, and 0.8 mm d(-1) from the three l agoons, with the lowest rate occurring at the site with a 0.46-m liner augm ented with bentonite. The in situ coefficient of permeability of the soil l iners ranged from 7.8 x 10(-8) and 1.5 x 10(-7) cm s(-1). In two lagoons bu ilt with silt loam liners (no bentonite), permeabilities on a whole lagoon basis were about five times less than those measured from soil cores collec ted before the addition of waste. Results imply that permeability was reduc ed by organic sludge on the bottom of the lagoons, The average ammonium-N c oncentration in the lagoons was 665 mg L-1, accounting for almost all of th e soluble N, Calculations indicate that the ammonium-N export rates were be tween 2187 and 2726 kg ha(-1) yr(-1), but more information is needed regard ing the fate of N deposited in the soil beneath lagoons.