In this Hindsight, Dicky Clymo, Emeritus Professor at Queen Mary University of London, writes about the first measurements of gas effluxes from a peat bog: the first drops of what has since become a storm.
I first went to Moor House (MH) National Nature Reserve 62 years ago (April 1955) as a first year undergraduate at UCL. W.H. Pearsall was instrumental in getting the Reserve declared a few years before, and encouraged us to go there to help with primary recording of vegetation, under the direction of Ken Park (Officer-in-Charge, drowned in the Tees a few years later). We were a party of half a dozen or so, collected by Ken at Alston Station and packed into a Land Rover. The seven miles of (mostly dirt) road to Moor House was rough, rose steadily (and sharply over the Whin Sill outcrop). Troutbeck foamed and looked like Guinness. It gave us a dramatic introduction to real ecology.
The house itself had not yet been ‘improved’. The only light after dark was from one of two Tilley lamps, and the bath spouted cold water from the hot tap when the boiler was on the blink, and steam when it was working properly. Verona Conway (VC) was the Director. When she was resident, she insisted on us ‘dressing for dinner’: nothing special, but changed out of fieldwork clothes – a useful requirement that enforced moderate civilisation. At one dinner time discussion turned to the ‘hummock and hollow’ hypothesis that in peat bogs hummocks were replace by hollows, and vice versa in repeated cycles. This idea had been devised by an eminent Swedish ecologist, and was thought to be supported by evidence from remains in the peat (you can see it in Tansley’s ‘The British Islands and their Vegetation’). Even as a green undergraduate, I could not understand the mechanism, and said so. VC herself believed the hypothesis at the time, but was willing to discuss it on its merits, not by wielding authority from on high. That was an important lesson learned.
That visit introduced me to peatlands, but it was 1962 before I visited Moor House again, this time to collect Sphagnum plants for experiments in London (at Westfield College where I had settled), and to establish field experiments on how best to try to measure Sphagnum growth. These experiments required monthly visits which were not always easy to manage.
Meanwhile the International Biological Programme (IBP, 1964-74) was in progress. It was an early example of ‘big science’ in biology, and sought to emulate the successful International Geophysical Year IGY). Its official purpose was to establish ‘The Biological Basis of Productivity and Human Welfare’, though this objective was vaguer than the IGY’s, and success was patchy. It did have four effects: it brought more money into ecology, it made serious attempts to get cooperative work across whole biomes, it stimulated co-operation among specialists, and it gave cover for scientists in ‘closed’ countries to travel abroad. Moor House was part of the Tundra Biome organisation: arguably the most successful of the biome projects. As part of the work Bill Heal asked me to make measurements of Sphagnum growth on the main sites on Bog Hill and Sike Hill. I set out to do that, but got permission to work on Burnt Hill too.
Jim Reddaway did most of the work in monthly visits. This was routine (‘boring’?) work so I looked round for something that Jim might find more interesting. During my visits I had begun to wonder how the peat accumulation process worked. Though the peat accumulated, gas bubbles were released from pools. Dalton had shown in 1802 that such bubbles contained a combustible gas we now call methane (there is a famous painting of him collecting the gas, part of the Manchester Murals). I wondered in particular what gases were released, and at what rates. The two obvious gases were CO2 and CH4, and a sample through the chemist’s mass spectrometer confirmed that they were the only detectable C‑containing gases. Martin Holdgate, Chief Scientific Adviser at the Department of the Environment, was by that time pointing out that increases in CO2 concentration in the air might have serious effects on air temperature, and then climate. Finding out the effluxes of gases from peat bogs, of which we knew there were large areas, was therefore timely.
The method was to insert permanent cylinders into the peat, and to place upturned buckets over them for sampling. The cylinders were of stainless steel, 27 cm diameter, 30 cm deep, with a 2 cm deep channel brazed around the top edge. (The diameter was determined by the polythene buckets we could get locally.) For sampling, the upended polythene bucket was put into the channel and the channel filled with water to seal the bucket to the cylinder. This basic construction is now the basis of most chamber samplers.
Samples were taken after a known time, typically 60 minutes, through a rubber tube in the top of the bucket (sealed during sampling with a glass rod) into a pre-evacuated 500 ml flask. Measurement of concentration was by Infrared Gas Analyser (IRGA). Ours was primitive. It needed at least 200 ml of sample for each gas, and the machine had to be set up separately for each gas, then stabilised for several hours before measurements. Gases were chivvied about using mercury in a simple gas rig. We had 12 permanent field samplers – 4 in each of hummock, lawn, and pool edge, and 10 sets of samples i.e.120 in all.
Here are the mean C values / g m-2 yr-1
|CO2 – C||50||31||54|
|CH4 – C||1||4||7|
|Total gas – C||51||35||61|
Each site (cylinder) had its individual character – usually higher than mean or lower, but each showed erratic higher values, particularly the pool edges (bubbles?). Efflux of CH4 increased from hummock to hollow; CO2 flux was more uniform.
Since this primitive start, tens of thousands of similar (but technically much better) chamber measurements have been made, and millions of micro-meteorological eddy covariance ones. Rather surprisingly these original Moor House values and generalisations are not inconsistent with the medians of later chamber measurements.
Later, Accelerator Mass Spectrometry (AMS) made it possible to assess the age of gases in volumes < 100 ml., which proved very interesting. But that is another story…
Read more Hindsights here!