Peatlands, Climate Change

& Global Carbon Stores

Peaty Wetlands: Ecosystems of global importance

Wetlands cover a tiny percentage of the Earth (just 3%) and yet are arguably the most important ecosystem on the planet. And it's not just because they contain a range of unique plants and animals. These remarkable ecosystems also possess a valuable ability to 'treat' water pollution, and less desirably, to produce over 20% of our atmospheric methane. But in these days of climate change, perhaps their most important property of all, is their ability to trap and then lock away huge quantities of carbon dioxide. This remarkable property has allowed them to 'build up' an enormous carbon store - one that rivals the carbon content of the entire atmosphere! Rather worryingly, it looks like that carbon store may be becoming unstable......

About Wetlands in the British Isles

Wetlands generally occur on areas of land that are waterlogged due to high rainfall and/or poor drainage. They cover a substantial area (almost 10%) of the British Isles. They are essentially "unbalanced ecosystems", where the rate of plant growth exceeds the rate of decomposition. Plants assimilate (take up) carbon dioxide from the atmosphere, but hold onto that carbon after they have died. They do so because decomposition is extremely slow in peaty wetlands. The result is an accumulation of the partially decayed plant material that we call "peat". The process of accumulating plant carbon is often described as "carbon sequestration" and has resulted in our peatlands becoming a major global carbon sink). That sink could even be considered politically or economically important when considered in relation to the Kyoto Protocol.

Wetland Properties

The stability of wetland ecosystems is largely dependant on the persistence of waterlogged conditions. Wetlands lack oxygen due to the poor solubility of this gas in the overly-abundant water. Under such "anaerobic" conditions, the efficiency of microbial breakdown of organic materials is reduced. The carbon seems to be held in place by what could be described as an 'enzymic latch'.

There are a number of mechanisms by which our actions can undermine wetland stability. Most of these involve removing the very water that gives the wetlands their poor decomposition rates. The first involves deliberate direct intervention by increasing drainage. Two of the many examples of such exploitation include drainage for agriculture/afforestation, or peat-cutting for fuel. The consequences of such direct intervention have received a great deal of media attention in recent years, particularly from the point of view of loss of habitat for the many interesting species indigenous to peatlands. However, very little consideration has been given to the potential for indirect impacts of man's activities. These indirect impacts include the responses to rising carbon dioxide levels, and climatic effects related to the "Greenhouse-Effect".

The Greenhouse Effect & Wetlands

We are all familiar with the idea that the greenhouse effect could make our environment (including wetlands) warmer. Warmer conditions speed reactions - including decomposition reactions - and so this could help to release carbon that was previously safely stored away. But some researchers have suggested that the "Greenhouse Effect" could result in an increased number of high pressure areas (anticyclones) that we experience. This could lead to an increased number of droughts due to a weakening of the rain-bearing Westerlies that have largely governed the weather conditions experienced by the U.K. and Western Europe. The consequently reduced rainfall could seriously undermine peatland ecosystem stability by inducing a transition to a less waterlogged (more aerobic), state.

Possible global impacts on Wetlands

Among the consequences would be similar losses of peatland habitat to those occurring in response to man's direct intervention (drainage , above). In addition, however, these changes have the potential to impact upon the our environment beyond the bounds of the peatlands themselves. This could occur as a shift in the nature of the biogeochemical exports that leave the peatlands. Effects could occur through increases in two mechanisms; 1: Export of gases to the atmosphere (e.g. re-releasing carbon dioxide), and 2: Export of leachates into waterbodies such as lakes, rivers and the oceans (e.g. nutrients and dissolved carbon compounds). These solutes could even add to the greenhouse effect as the dissolved organic compounds are broken down to carbon dioxide, or adversely affect water quality with possible implications for human health.

Here in Bangor, we have been investigating the impacts of environmental change on these issues using a variety of laboratory and field experiments. In recent years, we have tended to specialise on studies of the role of enzymes in regulating those varied functions. This is because polymer breakdown is the rate-limiting step in decomposition, and thus extra-cellular enzymes clearly link microbes and their ecology to larger scale ecosystem processes. Knowing how microbes handle the nutrient and energy tradeoffs in exo-enzyme production can yield insight into ecosystem responses to environmental change - i.e. if nutrient levels increase due to drought-induced stimulation of mineralisation (or rising atmospheric inputs), do rates of peat breakdown decrease because soil microbes no longer require peat-bound nutrients? Or do they increase because microbes can invest more in N-rich enzymes? Can we predict the response of microbes to increased nutrient availability by determining whether nutrients or C limits them? Are shifts in the activities of the major classes of peatland enzymes accompanied by significant changes in the composition of the microbial community? Answering these questions will be crucial if we are to improve our understanding of how nutrient and C availability regulate the composition of the microbial community, decomposition, peat CO2 efflux, and nutrient cycling, at local, regional and even global scales.

How much carbon is there in our peatlands?

- How big is the problem?

Our recent studies have focussed on the potential for destabilisation of peat carbon stores. Various authors have estimated the peatland carbon that could be released:

Storage (Gt C)	Reservoir type	Author(s)
860 Gt (8.)	Peats, world-wide	Bohn (1976)
300 Gt (8.)	Peats	Sjors (1980)
202 Gt (8.)	Peats	Post et al. (1982)
500 Gt (8.)	Peats	Houghton et al. (1985)
249 Gt (8.)	Northern peatlands	Arm.& Men. (1986).
210 Gt (8.)	Boreal peatlands	Oeschel (1989)
461 Gt (9.)	Subarctic and boreal peat	Gorham (1992)
1576 Gt (10.)	Global soils (present-day)	Eswaran et al. (1993)
500 Gt (11.)	Global peats	Markov et al. (1988)

Units are in gigatonnes of carbon (1 Gt = 1 billion tonnes = 1 Petagram = 1 x 10¹⁵ g).

To put these values into context, the IPCC in 1990 noted that our entire atmosphere contains just 750 Gt of carbon, although this value is currently increasing at 3Gt per pear. (Full non-peat global datasets J.Anderson).

Wetland Enzymes

Enzymes are biological catalysts. They speed up chemical reactions, often very dramatically. For example, carbonic anhydrase hydrates 1,000,000 CO₂ molecules every second. Many biochemical reactions would not occur at environmental temperatures and pressures without enzymes. In short, enzymes allow the processes of life to occur.

Peatlands contain as much carbon as is present in the entire atmosphere (over 700Gt), and there are concerns that climate change could cause that carbon to be released back into the atmosphere as carbon dioxide. This would amplify the global-warming effect being caused by industrial carbon dioxide release.

Enzymes play a key role in breaking down "complex" organic materials and releasing the "simple" chemicals which are locked-up within them (biogeochemical cycling). If climate change does cause our vast stores of peat to begin to break down, then it will have been a stimulation of enzyme activities that will have allowed it.

Wetland Biogeochemistry at Bangor

We have been developing methods to allow us to identify the factors regulating peatland enzyme activities. If we can identify those factors, we may be able to find ways of ensuring that enzyme activities remain at their present low levels, and thus ensure that the dangers a global release of peatland carbon are avoided.

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Recent Publications

We have a range of publications in various journals, including the top scientific journal "Nature". The subjects covered include investigations of the effects of climate change on greenhouse gas release, water chemistry and the activities of wetland micro-organisms. They also include a number of new analytical methods which can be used to improve our understanding of the likely impacts of climate change on wetlands

Other Wetlands research Workers on the Web

There are many wetlands researchers on the WWW including: