Measuring gas emissions from animal waste lagoons with an inverse-dispersion technique

Abstract

Measuring gas emissions from treatment lagoons and storage ponds poses challenging conditions for existing micrometeorological techniques. This is due to non-ideal wind conditions, such as those induced by trees and crops surrounding the lagoons, and lagoons with dimensions too small to establish equilibrated microclimate conditions within the water boundary. This study evaluated the accuracy of an emerging backward Lagrangian stochastic (bLS) inverse-dispersion technique to measure lagoon emissions. It used a fabricated floating emission source with known emission rates from an irrigation pond that resembled typical treatment lagoon environments. The measured parameters were wind statistics and downwind path-integrated concentrations. Anemometers were located on the upwind, downwind, or side berm parallel to wind. Additionally, the berm surface was deliberately roughened during the summer by placing pine straw bales along the berms to simulate vegetation growth. Regardless of the surface roughness, when the surrounding vegetation (i.e. corn field) was short during spring and fall, using an anemometer located on the upwind berm produced the most accurate results (0.93±0.19). However, during the summer, the adjacent corn crop grew more than 2 m high. Consequently, the anemometer had to be moved to the side berm. This resulted in a decrease in accuracy to 0.81±0.18. Yet, even with less than idealized conditions, the bLS inverse-dispersion technique still produced reasonably accurate emission rates. This demonstrated the robustness of this easy-to-use bLS inverse-dispersion technique for complex agricultural emission measurements.