by Ed Tripp, University of Nottingham
Sampling and Sabotage
Nitrogen deposition comes in many forms. It can be diffuse, deposited in rain or from industry, or it can be more localised, from a single farm stocked with cattle or chickens for example. I have already investigated the former with bioassays and modelled nitrogen data. But the latter can be so localised, a matter of hundreds of meters, that it cannot be modelled. Therefore, it has to be measured in the field.
This localised nitrogen source usually comes in the form of ammonia and can be a significant input of nitrogen pollution to heathland, affecting vegetation composition and soil fertility. I can measure it relatively easily by placing a couple of ammonia samplers atop a 1.5 m wooden post. These samplers are capable of recording cumulative ammonia in the atmosphere for up to a month. So I can leave the samplers in the field, and replace them with new ones every month. To make sure that I include variation throughout the year, including manure spreading season for example, I record ammonia data for a 12 month period. Simple!
Or is it? Cows are curious things. They not only like to scratch up against conveniently placed posts (as do most livestock), but they also eat things readily, and quite happily munch on ammonia samplers!
Consequently, I had to make sure that my posts were out of the way of curious cattle. But there is another curious animal that is more difficult to avoid. People. Fingers stray into samplers, puncturing delicate membranes. Posts also go missing.
One post is even on a scout camp...not a safe place for anything! Little signs tell adults not to touch, but this doesn't work on kids. A sign saying "CHEMICALS! DO NOT TOUCH!!" however, seemed to do the trick.
The dataset will be complete by September 2011, sabotage notwithstanding. Let's hope there is a nice trend in there somewhere!