The Ecological Functions of Peatlands
Ecological functions are the good and services that can be provided by natural systems that can be both beneficial to people, as well as nature. Some of the ecological functions of peatlands are explored below.
The Carbon Cycle and other Green House Gases
(For some supplemental information on the Carbon Cycle, please see this external page and come right back! )
Peatlands make up a significant part of the boreal forest biome and are considered to be one of Earth’s biggest terrestrial carbon sinks. This is due to the annual net accumulation of organic matter associated with boreal soils, permafrost deposits, wetlands and peatlands. This means peatlands represent a major storage of carbon, playing an integral part in the global carbon cycle. The main route in which carbon enters the peatland system is the through the process of plant photosynthesis, which use CO2 as part of its respiration. The CO2 will stay in the plant material until the organism dies and begins to decompose. One of the main features of peatlands is the decomposition of its organic material is prevented or delayed through a lack of oxygen, or its aerobic conditions.
In addition to acting a carbon sink, peatlands will release their carbon as well. Some carbon is returned to the environment through the decay of the peat. This decay can be caused by both natural and human changes to the peatlands water table, increasing decomposition through exposure to oxygen in the atmosphere. During the decompositions process, the carbon can transformed into a few different forms.
One such form is dissolved organic carbon (DOC), which can then leave peatlands through drainage waters. DOC can be viewed as an important aspect of the peatland carbon budget. The DOC found in peatland drainage and runoff comes in the form of organic acids such as fulvic and humic acid. Such acids can impact water quality, as they raise the pH of these runoff waters. It has been found that the concentration of DOC can be higher after dry peat conditions as these acids had more time to form through decomposition of plant material.
Decomposition can also lead to gas production. The production of such gases can occur in different regions of the peat that are defined by the level as well as fluctuations of the water table. Depending on whether the decomposition aerobic or anaerobic (has access to oxygen or not) will largely determine the types of gases being produced.
In addition to CO2, methane (CH4) gas is also produced in peatland environments. CH4 is another important green house gas. Peatlands happen to be the biggest “natural terrestrial source” of CH4 entering the atmosphere. This atmospheric CH4 is attributed to the anaerobic decomposition taking place in water-logged areas of the peatland. The gas is produced by processes facilitated by certain types of bacteria (methanogenic bacteria) in the oxygen deprived zones of the soil. CH4 production depends on environmental controls such as the water content, peat composition, temperature, nutrients and acidity. Peat composition will determine the type of the methanogenic bacteria present as well as the bulk density of the peat which can affect gas flow out to the atmosphere. Temperature displays a complicated relationship with the emission of CH4, as higher temperature can increase production but can result in lower water tables and thus oxygen rich conditions. This would instead lower CH4 emissions.
CO2 in peatlands is produced not only through decomposition of organic matter, but through anerobic decomposition as well. It is also emitted through plant respiration, especially in the root zone in the peat. The environmental factors affecting CO2 gas emission from peat are similar to that of CH4, and include temperature, peat type and water content. However, the level of the water table will have the opposite effect on CO2 emission as a higher water level will depress production.
Also important to the peatland carbon cycle are the rates of plant respiration and photosynthesis, as these factors combine to determine the net ecosystem exchange (NEE) of carbon. This means that if the NEE is positive, the peatland is storing carbon. However, if the NEE is negative, it is acting as a source of carbon. It has been determined through experimentation that the balance between positive and negative NEE is very narrow and can be influenced by environmental factors in either direction. The strongest of these factors appears to be moisture. Having enough water is a very limiting factor for the growth of certain peatland species of plants and when this level is below optimal, photosynthesis can decrease rapidly leading to a negative NEE value.
One green house gas produced by peatlands that generally receives little attention is nitrous oxide (N2O), a gas that is both consumed and produced by soil. It has been estimated from studies that significant amounts are not produced from natural peatlands, however estimates may vary. It has been determined production may be much higher in drained or otherwise damaged peatlands.
Catchment Hydrology and Water Quality
(For some extra information on hydrology and hydrologic cycle, feel free to check out this external page.)
Water exchanges between peatlands and the adjoining areas is one way these wetlands can influence their environments. Peatlands can receive water from both precipitation as well as through groundwater flow. Although at first it seems reasonable to think that peatlands may act as sponges that can soak up excess water during wet periods, and release water during dry periods, this is not the case. Peatlands can be up to 95% water, but only a small quantity of this stored water is exchanged with outside landscapes. Additionally, a wet sponge cannot hold more water. However, certain types of peatlands may impact the hydrology of surrounding environments. Sloping and valley fens allow water drainage from their systems due to the sloping ground. Low-lying flood plain and basin fens will accumulate and store run-off simply because they are the lowest land features in the landscape.
One way a peatland can affect the hydrology of a region is by affecting the speed at which water runs off the landscape after a storm. It has been found that wet peatlands can delay run-off for 3 to 6 hours longer compared to other soil types. After the peatland had been under dry conditions, this delay was extended to 22 hours. This increase in run-off delay can be attributed to a lower water table that increased the water storage capacity prior to the storm event.
Peatlands, in their natural state generally do not contribute a significant amount of suspended sediment to their run-off. This is good for the water quality of nearby lakes and rivers.
Peatlands can either become a storage or source of nutrients to their catchment area. This will depend on if there is any damage to the peatland, as well as the rate of peat accumulation. The accumulation of peat requires the growth of plants and plants require nutrients to develop. This means that the plants will take up these nutrients. Additionally, nutrients are often immobilized in partly decomposed organic matter that makes up peat. Studies in the Florida Everglades have also found uptakes of phosphorous that exceed predictions based on the expected activity of peatland organisms. However, these systems can become a source of nutrients to adjacent waters when they are disturbed by natural events such as forest fires and dry periods, or damage through human activities like drainage.
Peatlands Importance to Wildlife
The nature and distribution of peatlands mean they offer unique living conditions of value to many species of wildlife. Despite disturbances to these ecosystems, peatlands, especially in Northern regions, are regarded as some of the last truly natural landscapes in the world. This can be attributed to their general inhospitable to humans environment when in a natural state (wet, cool, acidic soils...). This makes peatlands very valuable in terms wildlife conservation. We will now look at two virtues of these ecosystems in terms of their importance to wildlife.
The first virtue of peatlands for wildlife conservation is the fact they are home to many rare organisms that are specific to these regions. Even when peatlands are not exactly necessary for the survival of the species, they are needed to maintain high enough numbers so populations may not crash. Additionally, peatlands themselves can be rare in certain parts of the world, with numbers shrinking especially from human activities, making conserving peatlands themselves a priority.
As previously mentioned, most intact peatlands are generally found in a natural or very near-natural state. This can be very significant as natural habitat is rare and at a premium for endangered and at risk species.
_ENVR 4000 Sustainable Water Management 2012