Concepts

 

If you have a concept or definition you think should be included on this page please let Simon know at Simon.Drew@stir.ac.uk.

acrotelm: (Dictionary of Ecology definition): The hydrologically active (and biologically accreting) upper layer of peat which is subject to a fluctuating water table, and is generally aerobic.

catotelm: The permanently saturated, anoxic, lower layer of peat where organic decomposition is significantly slowed. The acrotelm-catotelm model is discussed in further detail by Holden & Burt (2003).

carbon landscape: A relativley new concept which encourages the understanding of landscapes with respect to their ability to store, or process, carbon indifferent forms. Storage may be manifest as carbon captured in plant matter such as trees, shrubs, herbs and grasses etc, in organic matter present in soils, or dissolved in water bodies as organic and inorganic forms.

carbon loss: The loss of carbon in any form from a C-pool of interest. In the context of the CLAD project, C-losses in upland/peat-rich soils can occur via the formation of dissolved organic carbon (DOC) which is lost through hydrological pathways. However, C-losses in these environments can also occur through erosion of particulate organic soils, or remineralisation processes where bacteria use the organic matter and related breakdown products as an energy source and in doing so generate carbon dioxide and methane. Carbon losses can be enhanced indirectly by human activities which alter the hydrology of a site (e.g., by changing the water table through affecting drainage) or increase physical disturbance (e.g., removing large amounts of peat for commercial use or infrastructure development).

carbon sequestration: The term carbon sequestration is used relatively flexibly depending on the context. Ostensibly is it is used to denote circumstances where carbon is transferred to a location or form where it is no longer available for transfer to the atmospheric CO2 pool (where it may contribute to the greenhouse effect). The current wikipedia definition of carbon sequestration emphasises human influences in controlling such processes. However, carbon sequestration occurs in many natural situations including in upland environments during peat formation (a process of interest to CLAD).

carbon payback time: This is a measure of how long a CO2 mitigating process needs to run to compensate for CO2 emitted to the atmosphere during a pre-operational stage. Relevant to CLAD are payback times associated with windfarm developments, where payback time represents the time period of energy generation from wind that must take place to offset C-losses incurred during the installation period. One of the largest uncertainties here is considered to be loss of C to aquatic drainage systems.

DIC (dissolved inorganic carbon): DIC is made up of several types of inorganic carbon which are dissolved in a solution. These include carbon dioxide, carbonic acid, bicarbonate anion and carbonate anion.

DOC (dissolved organic carbon): DOC is a broad classification for organic molecules of varied origin and composition within soil porewaters and in aquatic systems. DOC is produced by different sources, but is generally the product of decomposing plants. When water drains through soils, DOC is transported to watercourses. DOC in marine and freshwater systems is one of the largest reservoirs of organic matter on Earth. In freshwater systems DOC constitutes the largest of the carbon pools. The "dissolved" fraction of organic carbon is an operational classification. Many researchers place the dissolved/colloidal cut off at 0.45 micrometers, but 0.22 micrometers is also typical.

EpCO2­: the excess partial pressure of free CO2 in an aquatic system. A value of 1 represents a system that is at equilibrium with the atmosphere equlibriated concentration; < 1 indicates an aquatic system under-saturated with respect to dissolved CO2 load and thus there may be drawdown of CO2; > 1 indicated a system that is over-saturated with respect to the CO2 equilibrated load and thus act as a source of CO2 to the atmosphere. Most river systems draining carbon landscapes are thought to be over-saturated with CO2  and thus represent a source of atmospheric CO2, linking the terrestrial with the atmospheric CO2 cycle. CO2 ­ in an aquatic system is part of the dissolved inorganic pool and can be imported in the form e.g. from soils, or be produced within the river system by respiration or organic matter and by plants.

patterned mire: A shrub and herb dominated peatland landform characterized by a series of peat ridges and hollows oriented parallel to the incline(usually approximately 2%, or 2-12 feet per mile) of the land and perpendicular to the flow of groundwater. The ridges vary in height, width, and spacing, but are usually less than one meter in heightl, resulting in a wave-like pattern that may be discernable only from aerial photographs. The hollows are saturated and dominated by sphagnum mosses, sedges, and rushes, while the ridges are dominated by sedges and shrubs.

peat (Dictionary of Earth Sciences definition): An organic soil or deposit; in Britain, a soil with an organic soil horizon at least 40 cm thick. Peat formation occurs when decomposition is slow owing to anaerobic conditions associated with waterlogging. Decomposition of cellulose and hemicellulose is particularly slow for Sphagnum plants, which are characteristic of such sites, and hence among the principal peat-forming plants. Fen and bog peats differ considerably. In fen peats the presence of calcium in the groundwater neutralizes acidity, often leading to the disappearance of plant structure, giving a black, structureless peat. Bog peats, formed in much more acidic waters, vary according to the main plants involved. Species identification of constituents (including animals as well as plants) remains possible after long periods. Recent bog-moss (Sphagnum) peat is light in colour, with the structure of the mosses perfectly preserved.

peat pipes: Some areas of peatlands can contain "pipes" which are naturally occurring tubes found below the surface of the peat. It has recently been shown that they occur in large numbers in many UK peatlands (Holden 2005). Pipe development may also be encouraged by the drainage of peat bogs and also by periods of summer drought. To date there have been no published studies examining carbon loss from pipes and they may be an important source of dissolved organic carbon and gaseous carbon. It is yet to be tested whether pipes are an important source of carbon for peatland drainage systems. A number of publications relating to peat pipes can be found on the publications page of Professor Joe Holden in the School of Geography, Leeds University.

POC (Particulate Organic Carbon): Carbon rich particles (greater than 0.22 or 0.45 micrometers in diameter- see DOC, above) suspended in the water column. POC is estimated by collection on pre-weighed fiberglass filters prior to combustion at 550oC, then determining weight loss. POC is an important material by which carbon is lost from erroding peatlands.