Accounting for Field-Scale Dry Deposition in Backward Lagrangian Stochastic Dispersion Modelling of NH3 Emissions
A controlled ammonia (NH3) release experiment was performed at a grassland site. The aim was to quantify the effect of dry deposition between the source and the receptors (NH3 measurement locations) on emission rate estimates by means of inverse dispersion modelling. NH3 was released for three hours at a constant rate of Q = 6.29 mg s−1 from a grid of 36 orifices spread over an area of 250 m2. The increase in line-integrated NH3 concentration was measured with open-path optical miniDOAS devices at different locations downwind of the artificial source. Using a backward Lagrangian stochastic (bLS) dispersion model (bLSmodelR), the fraction of the modelled release rate to the emitted NH3 ( Q bLS / Q ) was calculated from the measurements of the individual instruments. Q bLS / Q was found to be systematically lower than 1, on average between 0.69 and 0.91, depending on the location of the receptor. We hypothesized that NH3 dry deposition to grass and soil surfaces was the main factor responsible for the observed depletion of NH3 between source and receptor. A dry deposition algorithm based on a deposition velocity approach was included in the bLS modelling. Model deposition velocities were evaluated from a ‘big-leaf’ canopy resistance analogy. Canopy resistances (generally termed R c ) that provided Q bLS / Q = 1 ranged from 75 to 290 s m−1, showing that surface removal of NH3 by dry deposition can plausibly explain the original underestimation of Q bLS / Q . The inclusion of a dry deposition process in dispersion modelling is crucial for emission estimates, which are based on concentration measurements of depositing tracers downwind of homogeneous area sources or heterogeneously-distributed hot spots, such as, e.g., urine patches on pastures in the case of NH3.
Ammonia emission measurements of an intensively grazed pasture
Abstract. The quantification of ammonia (NH3) emissions is still a
challenge and the corresponding emission factor for grazed pastures is
uncertain. This study presents NH3 emission measurements of two
pasture systems in western Switzerland over the entire grazing season 2016.
During the measurement campaign, each pasture system was grazed by 12 dairy
cows in an intensive rotational management. The cow herds on the two
pastures differed in the energy to protein balance of the diet. NH3
concentrations were measured upwind and downwind of a grazed subplot with
line-integrating open path instruments that were able to retrieve small
horizontal concentration differences
(< 0.2 µg NH3 m−3). The NH3
emission fluxes were calculated by applying a backward Lagrangian stochastic
(bLS) dispersion model to the difference of paired concentration measurements
and ranged from 0 to 2.5 µg N–NH3 m−2 s−1.
The fluxes increased steadily during a grazing interval from previous
non-significant values to reach maximum emissions at the end of the grazing
interval. Afterwards they decreased exponentially to near zero-values within
3–5 days. A default emission curve was calculated for each of the two
systems and adopted to each rotation in order to account for missing data
values and to estimate inflow disturbances due to grazing on upwind paddocks.
Dung and cow location were monitored to account for the non-negligible
inhomogeneity of cow excreta on the pasture. The average emission (± SD
of individual rotation values) per grazing hour was calculated as 0.64±0.11 g N–NH3 cow−1 h−1 for the herd with the N-balanced diet (system M) and 1.07±0.06 g N–NH3 cow−1 h−1 for the herd with the protein-rich grass-only diet (system G). Surveys of feed intake, body weight and milk
yield of the cow herds were used to estimate the nitrogen (N) excretion by
an animal N budget model. Based on that, mean relative emission factors of
6.4±2.0 % and 8.7±2.7 % of the applied urine N were found
for the systems M and G, respectively. The results can be used to validate
the Swiss national emission inventory and demonstrate the positive effect of
an N-balanced diet on pasture NH3 emissions.

Aging live Antarctic fur seals and southern elephant seals
This study describes a method for extracting post-canine or incisor teeth from live antarctic fur seals (Arctocephalus gazella) and southern elephant seals (Mirounga leonina) respectively and their use to determine age in a field situation. Dental elevators were used to loosen the teeth from the alveolus and periodental ligament. Most teeth were removed within l-2 min and a total of 214 and 81 teeth were collected by this method from antarctic fur seals and southern elephant seals respectively. No seal recaptured at intervals up to a year after a tooth was extracted showed signs of infection or distress related to removal of the tooth. Teeth were thin-sectioned for the purpose of aging. In both species cementum growth layer groups were a more satisfactory indicator of age than dentinal growth layer groups. Estimates of age from cementum growth layers were confirmed for Antarctic fur seals using seals which had been tagged as pups up to 16 yr before sampling.