10.2 Natural Functions of Peatswamps
10.3 Environmental Impacts of Peat Reclamation
Previous chapters have indicated that peat has many uses. Only on a geological time scale can it be regarded as a renewable resource 1. Once extracted it can be used for many industrial purposes and is a raw material for the production of chemicals. However its most important uses are in agriculture and as an alternative source of energy.
1 Estimates of annual peat growth today vary between 0.5 and 1.0 mm and the subsidence rates of drained peat are of the order of 1.5-3.0 cm annually. Thus while the subsidence rate is 15 to 30 times the growth rate, peat cannot be defined as a renewable energy source.Technological developments make it increasingly more attractive to use peat and peat products as relatively cheap and clean fuel. It has a low sulphur and ash content whereas the carbon dioxide emitted to the atmosphere by combustion is about 10 percent lower than for coal (Table 34). Combustion is the conventional way to make energy from peat. However, new advances in thermochemical conversion (liquefaction) and biochemical conversion (anaerobic fermentation to methane) may make it possible to produce convenient fuels from peat, at a competitive cost, for heating or running internal combustion engines.
There is no question that, in the near future, peat will be increasingly used as a solid fuel on a large scale. This will be dependent on production and transport costs in relation to the prices of other fossil fuels such as oil, natural gas or coal. In the future peats will be increasingly used in the tropics for such purposes as soon as the reclamation methods have been developed. There is also the growing demand for arable land to feed the increasing population of many developing countries. Food cropping on the flat surfaces of reclaimed peatswamps is attractive in relation to the alternative steep hill sides where the risk of erosion seriously limits the cropping potential.
The need to produce more food, augmented by the demand for more energy, creates the stimulus to reclaim the vast peat areas in the tropics which are often the last untapped land resources. It is unwise to ignore these demands and it is pragmatic to accept that the peatswamps will be increasingly exploited in the future for agriculture, including pasture, forestry and extraction.
On the other hand environmentalists are warning against large scale exploitation and are attempting to preserve these unique ecosystems as much as possible. There is still time to ponder the question of what is the most sensible use of these natural resources. If peatlands are to be preserved, it is probably sensible for exploitation to go hand in hand with conservation.
The following sections will stimulate thought and debate. Their aim is to provide information on the land use alternatives and options, on the basis of which rational decisions on resource planning can be taken.
10.2.1 Regulating functions
10.2.2 Production function
10.2.3 Information function
10.2.4 Miscellaneous functions
A distinction is made between regulating functions, production functions, information functions and miscellaneous functions.
It is obvious that the peatswamps of the world play a significant role in the global cycles of carbon dioxide and water.
The carbon cycle
Peatlands developed during the last 10 000 years or so, constitute a large reservoir of carbon. The amount of carbon involved has been estimated by various sources, but the accuracy is dependent on the reliability of the assessment of global peat resources. Sjörs (1980) estimates the world content of carbon in peat to be in the order of 300 x 109 tons, whereas Moore and Bellamy (1974) arrived at a figure of 150 x 109. The latter was based on 230 million ha of world peat resources while present-day estimates are approximately 500 million ha; Sjörs values are therefore probably more realistic. Based on the fact that the atmosphere contains about 700 x 109 tons of carbon in the form of CO2, the deposition of carbon in peat has been an important, albeit very slow process. The accumulation rate is dependent on climate which showed much variation in post-glacial periods, the mid-postglacial period being least favourable. It is assumed by Sjörs (1980) that the world accumulation today of 90 x 106 tons yearly, based on climatic factors, is three times the average increment for the whole post-glacial period. Other authors give values of 210 x 106 tons per year, but their basic assumptions are probably incorrect. This Bulletin cannot cover this kind of discussion, nor be the arbiter but it should be noted that there are large discrepancies in the estimated values because of differences in basic assumptions. Sjörs indicates that the yearly world accumulation of carbon in the form of peat is very small in comparison with the estimated 100 x 109 tons annual ecosystemic world turnover of carbon. It is also much smaller than the annual combustion of fossil carbon (coal, oil, natural gas and, as yet, only small quantities of peat) amounting to about 5 x 109 tons, and also of less importance than the transfer of carbon dioxide from the air to the slightly undersaturated sea, estimated at about 2.5 x 109 tons of carbon per year. It is concluded by Sjörs (1980) that although peatlands are a considerable long-term reservoir for carbon, their role for the short-term turnover of CO2 is almost negligible. The global ecosystemic turnover of carbon would hardly be affected at all by destruction of the peatlands as accumulating ecosystems, other ecosystemic changes on earth being far more important.
Winkler and DeWitt (1985) in discussing environmental impacts of peat extraction in the United States, look at the possible disruption of the global balance in carbon dioxide cycling if all peat resources were burned in a relatively short period. Studies of this nature must be supported by factual and quantitative information. Sjörs adheres to the view that it would seem out of the question that more than a fraction of the global peat resources would ever be exploited by man, since so much is virtually inaccessible, and even more, is economically unexploitable due to excavation difficulties and transport costs. It would also be economically unrealistic to use most peatlands for agriculture or forestry due to cool climate, low nutrient content and unsuitable, physical characteristics. Therefore, although burning peat contributes to the contemporary global rise in atmospheric CO2, its contribution will remain subordinate to that of other fossil fuels. Further, a substantial increase in the CO2 content of the air by heavy burning of peat in situ is a theoretical possibility only.
Moore and Bellamy (1974) have said that it is speculative science fiction to say that burning the 500 x 109 tons of peat resource will increase the greenhouse effect and alter the global climate. Resource planning must be based on hard facts and not this kind of speculation.
Widespread drainage of peatlands for forestry, in temperate regions, decreases their comparatively high albedo, especially in winter. This effect would not be important in the tropics as peats are already forested in their natural state. However, a change to arable land after reclamation would have the opposite effect of increasing the albedo. This may have a local effect on climate but the climatic impact on a global scale is negligible.
The hydrological function
There is considerable evidence that peatswamps have an important regulating or controlling function on the hydrology of entire catchments. The main hydrological argument regarding the value of peatswamps is that peat acts as a reservoir, increasing the surface retention (storage capacity) of the landscape. Assessing their importance is difficult because of problems of quantifying the hydrological processes. In their natural conditions peatswamps act as a balancing reservoir smoothing the pattern of outflow during periods of heavy rainfall and drought (dry and wet monsoons). The reclamation of peat through drainage maintains the reservoir function and there will in fact be a greater controlling effect on run-off than in the undrained condition. The natural swamp is almost fully charged for most of the year otherwise conditions for peat growth would not exist. Drained peat can store more water initially and so control flash floods. However, drainage ultimately destroys the sponge effect of the peatswamp and the reservoir function is eventually lost. All these factors must be taken into account and carefully weighed if the catchment control argument is going to be used as a factor in land use planning.
Unmodified peat and peatland ecosystems can adsorb elements and compounds which have been released in toxic amounts into the environment. When peat is removed these adsorptive properties are lost and severe environmental degradation can result. Often heavy metals such as mercury, lead, cadmium, arsenic, zinc and selenium are tied up in peat deposits. Through the years the developing peat both adsorbs airborne and waterborne metals and then they are distributed in various ways throughout the peat. Peatswamps in this way act as natural filters in catchments. Studies in Finland and Sweden have indicated that high levels of the heavy metals mercury and lead in lakes are attributable to the drainage of peatlands upstream. Likewise toxic selenium levels were found in ditches from drained peatlands in the western United States (Winkler and DeWitt 1985).
The release of heavy metals upon drainage is of concern because they are toxic to many organisms. Toxicity is a matter of concentration and therefore the levels of heavy metals and their possible release through drainage and extraction should be studied in order to fully evaluate the environmental effects upon reclamation. For tropical countries such a precaution is especially necessary where proven deposits of heavy minerals occur in the country rock of catchment areas, or where the nature of the country rock gives reasons to suspect contamination with such metals. Burning peat containing concentrations of heavy metals also releases them into the environment.
In this connection the adsorption of organic pollutants such as PCBs and other polycyclic hydrocarbons used in agriculture and for controlling pests and diseases, must be mentioned. These materials when used upstream may concentrate in the peatswamps downstream. Concentrations may become toxic when such peats are burned as turf. Very little is known about the cycling, life span and hazardous effects of these elements, but the role of peatlands as natural reservoirs of toxic deposits should be borne in mind and duly investigated.
Peat holds concentrations of nutrients for varying lengths of time. These nutrients are released by peatland drainage and in North Carolina (USA) run-off from drained peatland had three times the nitrogen and 28 times the phosphorus concentrations found in run-off from undrained peatland (Winkler and DeWitt 1985). The sudden release of stored phosphorus from peat into surface waters can cause eutrophication of neighbouring lacustrine, riverine and estuarine systems.
However, since most peats in the tropics are oligotrophic with very low concentrations of nutrients, their drainage water is almost sterile and eutrophication of surface waters is unlikely to occur. It could however arise in the case of eutrophic peats, and in peats which are easily fertilized and used for intensive agriculture such as vegetable growing.
In coastal areas the buffering function of peatswamps between the salt- and fresh-water systems is particularly important. The natural edge between fresh-water and salt-water marshes for example between Mangrove and Nipah swamps, is changed upon drainage and subsequent disruption of the peatswamp hydrology. This drainage results in the conversion of run-off from a non-point-source from a natural peatland, to a point-source in drainage ditches, and contributes to the problems of already over-loaded estuarine ecosystems. Intrusion of salt-water into fresh-water wells in low-lying areas as well as fresh-water intrusion into delicately balanced salt-water estuary and deltaic ecosystems may occur. As a result of the latter, ecosystems essential to the survival of some forms of fisheries, such as shrimps, may be destroyed or irrepairably damaged.
There are many examples of these risks. The hydrological and related buffering function of peatswamps is dictated by their location and position in the landscape. It is important to realize the natural function of peatswamps before decisions are taken to destroy them.
It should be clear that where small interior valleys are concerned, the regulating functions operate within the watershed. Large coastal swamps, however, can also influence peripheral marine ecosystems and in general ecosystems beyond the confines of the water catchment, and impacts of reclamation can even be regional in scale.
Peatswamps in their natural state are generally poor producers of food. Oligotrophic peats harbour few plants supplying food for fauna because of the very low fertility level of the environment. Fauna is therefore scarce and that which exists is specialized to survive under conditions of low food supply. Certain specialized plant species are of commercial value, such as the raffia palm and papyrus of some African swamps, supplying important raw materials for the local population. Natural forest products may therefore be important sources of income. Valuable timber such as Ramin and Merbau occur profusely in the coastal oligotrophic peatswamps of South East Asia.
Although the products from natural peatswamps are generally of little importance their local value may be relatively significant.
Peatswamps are unique ecosystems harbouring many species of flora and fauna not found elsewhere. It is difficult to evaluate the importance of the preservation of ecosystems with all their in-built genetic possibilities stored in the specialized bio-forms. However, history teaches us to be careful and not to waste natures capital stored in the genetic resources, and since reclamation will no doubt destroy much of this part of natures inheritance it would be wise to count the losses before embarking on ventures which may in the end cost more than preservation. A pragmatic and realistic approach would be to set aside sufficient area for preservation purposes to be decided upon by authorities competent in this field.
Tropical peatswamps play an important and generally well-known role in the survival of migratory birds although this is not always acknowledged. The specific function which peatland plays is worth studying for tropical regions. From the general paucity in food one would surmise that the real oligotrophic peats of the coastal regions play a relatively minor role. Generally there are richer wetlands nearby which could be used, if needed. But as indicated there is little information to substantiate this.
Peatswamps finally have a social function in that they often form areas for recreation, in particular near large concentrations of population. Although this function is not yet much developed in tropical countries, it is nevertheless a function which in some localities is an important alternative use.
The study of the natural functions of peatswamps leads to an assessment of the environmental impacts caused by their reclamation. The following checklist which is not complete and does not cover all possible conditions may serve a useful purpose by indicating areas justifying attention:
- toxic metal release from peat,Added to these are impacts which are inherent to the removal of the swamp and the peat, namely:
- eutrophication of surface waters,
- increased run-off water (disturbance of hydrological balance),
- impacts on flooding and local fisheries,
- release of organic pollutants,
- changes of salt- and fresh-water systems,
- changes in groundwater supply,
- air pollution and fires.
- loss of genetic resources (flora and fauna),Most of these impacts have already been discussed above.
- loss of production functions,
- loss of the social function.
A third set of impacts, the evaluation of which is difficult, because of their ambiguity, is formed by environmental changes which are both positive and negative. As an example environmental health may be mentioned.
For centuries swamps have been drained and reclaimed because of their apparently poor living conditions. Incidence of malaria is often correlated with presence of swamps. This undoubtedly is true and draining the swamps may improve living conditions for the local people. It is, however, interesting to note that contrary to popular belief, peatswamps in their natural conditions are not necessarily a potent source of human disease. For example Beadle (1960) found that the two most important malaria carriers in Africa (Anopheles gambiae and A. funestus) do not breed in the interior of swamps though they are often found in open pools, footprints and other small hollows around the edges. An important factor which prevents some mosquitoes and not others from breeding in swamps, is the low concentration of oxygen in the peaty water. Larvae of A. gambiae have difficulty in surviving under anaerobic conditions. Shading is another factor that could deter egg laying. Peatswamps are therefore not always a potent source of malaria. Other swamps probably are. The problem of bilharzia (schistosomiasis) is rather different. Here, the snail Biomphalaria sudanica, which can carry Schistosoma mansoni, plays a major role as for example in Uganda. These snails have no difficulty in surviving under anaerobic conditions. They do not move very quickly nor spread far and the foci of infection are generally confined to small areas of water which people converge for washing and collecting water, or for fishing. Drainage of such swamps may result in the snails spreading over large areas and the impact of drainage on a variety of other diseases should be carefully assessed prior to reclamation.
Sanitary health also warrants study. The settlement of people in peatswamps carries problems of supplying drinking water, and disposal of sewage. The settlement of people from hilly areas, used to running water, in an environment of stagnant water is accompanied by adaptation problems concerning disposal of human faeces. This can cause epidemics of gastro-enteritis and related diseases and the death of many children unaccustomed to the new environment. Likewise adults may die because of other diseases for which no natural resistance was built up. Both aspects deserve attention and therefore environmental impact studies are often needed if a full assessment of the consequences of draining a peatswamp is required. In fact it should form part of a feasibility study carried out prior to implementation of peatswamp development. It is strongly recommended that a broad environmental assessment is made in an early stage of planning. Often costly feasibility studies can then be forestalled. It could form part of the initial survey discussed in section 6.3.
Such studies should be based on independent data. They should indicate present values and functions and their current (natural) sustainable potentials, together with the values and functions pertaining after large scale reclamation. Alternative uses and any mitigating measures should also be studied. Where development objectives are known and decided to meet demands it is realistic to search for and indicate other means by which these objectives could be met.
If the objective is to investigate the potential of a peatswamp for agriculture because of pressure for arable land there may be other land nearby more or equally suited which could be used instead. Likewise, a demand for sources of energy may be met by indicating means other than reclaiming peatswamps. In the final analysis the various options on use should be carefully weighed on their merits so that a rational decision on land-use planning can be made.
In conclusion, appropriate legislation is often lacking in many countries so that peatswamp development often proceeds without adequate initial investigation.