Title: Greenhouse gas emissions from two prominent features of livestock management systems: Water pans and bomas in pastoral and agro-pastoral systems in Taita-Taveta County, Kenya
Author: Oswald Omuron
Supervising Institution: IHE Delft - Institute for Water Education
In Taita-Taveta County, Kenya, livestock keeping by pastoralists is among the predominant occupations. Pastoralists graze their animals throughout the day, water them in water pans and confine them in enclosures /livestock bomas at night for their safety. Evidence suggests that these two features of livestock management systems (water pans and bomas) are sources of greenhouse gas emissions.
Diffusive GHG fluxes were measured from these two prominent features of livestock management systems using a Los Gatos Research ultra-portable greenhouse gas analyser for CH₄ and N₂O measurements and a LI-COR gas analyser (LI-850) for CO₂ measurements, both of which were connected in parallel to a static chamber. Dissolved gases in the water pans were determined using gas chromatography after field sample collection using the headspace equilibration technique.
As expected, bomas produced higher CO₂ and N₂O than water pans, which produced higher CH₄, this can be attributed to the high accumulation of dung and urine in the bomas compared to this accumulation in the water pans as the livestock spend most of the time (approximately, 12 hours of every night) within the bomas and only visit the water pans for watering. The dung and urine are sources of organic N and C which through the biogeochemical transformations of N and C via ammonification, nitrification, denitrification and mineralisation processes lead to the observed high GHG emission in the bomas. However, CH₄ emission is prominent in the water pans suggesting anaerobic activity within the water pans. This is most likely to take place in the benthic areas of the water pans as all the water pans had relatively high amounts of DO. Both systems had variations in GHG emissions with distance from them. Water pan silt produced relatively high CO₂ and N₂O than the rest of the points along water pan transects. Recently exposed sediments (including silt) and dry water pans exposed due to water level fluctuation contributed to higher CO₂ gas fluxes than the water pans' water column. These suggest high mineralisation levels as buried organic matter both from the silt and dry water pans becomes available for microbial use. There were also high GHG emissions from water pans in a dry campaign 4 compared to the rest of the campaigns. Campaign 4 proceeds a rainy campaign 3 which is characterised by high surface runoff and thus high allochthonous input. This means that the observed high GHG emissions in campaign 4 can be explained by the allochthonous inputs in campaign 3 and the less GHG emissions in campaign 3 being probably due to the high-water amounts in the water pans creating a dilution effect. Since campaign 4 is a dry campaign, the allochthonous inputs from campaign 3 became concentrated as the water levels receded majorly through evaporation, consequently the observed high GHG fluxes. Next, CH₄ emissions in the water pans were high with little dissolved CH₄ gas suggesting ebullition which probably took place in the benthic zones of the water pans as the water column of the water pans had moderate DO levels. Lastly, there was no relationship between the perimeter to surface area ratio and the GHG emissions from the water pans which may be explained by the fact that only campaign 2 data was considered for this.
Keywords: Water pans. Livestock bomas. GHG emissions. Taita-Taveta County. Kenya